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Abstract

Africa is burdened by food insecurity with nearly a billion people suffering from starvation, undernutrition, and malnutrition. Climate change prediction models forecast changes in rainfall patterns and rising temperature regimes, with impacts particularly on Southern and East Africa. These predictions are especially concerning for the production of major food crops, such as maize, sorghum, millet, and groundnut, because median temperature increases are associated with increased pest pressure and changes in migratory patterns. These factors will result in significantly more pest invasions and an increased need for innovative insect management practices. This review focuses on pest control strategies, highlighting important examples, their economic impact, and new alternative pest control strategies. African policymakers remain hesitant to move forward with establishing biosafety laws and commercializing GM crops, and it is often difficult to implement regulatory measures in smallholder agriculture to increase efficacy. This review summarizes current knowledge on insect pests based largely on the historical record of insect species that are already invasive, and that already greatly affect crop production in Africa, and unfortunately entering Europe and Asia in the future. The invasiveness of existing insect pests might increase further due to climatic changes that provide a better habitat and environmental conditions for growth and reproduction. In addition to classical insect control strategies, we discuss possible new strategies of insect control, highlighting biotechnological approaches that might limit or prevent climate change‐induced insect invasions.
Food Energy Secur. 2019;00:e191.
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https://doi.org/10.1002/fes3.191
wileyonlinelibrary.com/journal/fes3
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INTRODUCTION
Pests and pathogens can severely reduce food security by
affecting crop yield and the quality of agricultural produce
(Savary et al., 2019). The food-deficit regions in Africa with
their fast-growing populations, in combination with emerg-
ing or re-emerging pests and diseases, suffer the highest yield
losses. Africa is also in a highly vulnerable position with re-
gard to the negative impacts of climate change (IPCC, 2014;
Niang et al., 2014). The Food and Agriculture Organization
of the United Nations (FAO) has forecast that the current sit-
uation of food security is likely to deteriorate further over
the next 50years in Africa unless immediate action is taken
(FAO, 2018). The number of people suffering from hunger
as estimated by FAO in 2010 was 239million in sub-Saha-
ran Africa. This figure is predicted to increase in the near
future, and many climate change forecast scenarios are bleak
(Sasson, 2012; Serdeczny et al., 2016).
Climate change models forecast future global warming
trends with associated changes in rainfall patterns and in-
creases in average temperature and more frequent heatwaves
(Davies-Reddy & Vincent, 2017). Such models also predict
declines in the rainfall experienced in Southern Africa, while
increased precipitation is predicted for East Africa (Figure 1).
These predictions are especially worrisome for the pro-
duction of the major cereal and legume food crops, such
as maize, wheat, sorghum, millet, beans, and groundnut,
where losses of between 27% and 32% are predicted with a
Received: 4 June 2019
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Revised: 16 September 2019
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Accepted: 17 October 2019
DOI: 10.1002/fes3.191
REVIEW
Defining biotechnological solutions for insect control in sub-
Saharan Africa
Anna-MariaBotha1
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Karl J.Kunert2
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JoyceMaling’a3
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Christine H.Foyer4
This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original
work is properly cited.
© 2019 The Authors. Food and Energy Security published by John Wiley & Sons Ltd. and the Association of Applied Biologists.
1Department of Genetics, Stellenbosch
University, Stellenbosch, South Africa
2Department of Plant Sciences, FABI,
University of Pretoria, Pretoria, South
Africa
3Kenya Agriculture and Livestock
Organization (KALRO), Food Crops
Research Institute, Kitale, Kenya
4School of Biosciences, College of Life
and Environmental Sciences, University of
Birmingham, Edgbaston, Birmingham, UK
Correspondence
Anna-Maria Botha, Department of
Genetics, Stellenbosch University, Private
Bag X1, Matieland, Stellenbosch 7601,
South Africa.
Email: ambo@sun.ac.za
Abstract
Africa is burdened by food insecurity with nearly a billion people suffering from star-
vation, undernutrition, and malnutrition. Climate change prediction models forecast
changes in rainfall patterns and rising temperature regimes, with impacts particularly
on Southern and East Africa. These predictions are especially concerning for the
production of major food crops, such as maize, sorghum, millet, and groundnut, be-
cause median temperature increases are associated with increased pest pressure and
changes in migratory patterns. These factors will result in significantly more pest
invasions and an increased need for innovative insect management practices. This
review focuses on pest control strategies, highlighting important examples, their eco-
nomic impact, and new alternative pest control strategies. African policymakers re-
main hesitant to move forward with establishing biosafety laws and commercializing
GM crops, and it is often difficult to implement regulatory measures in smallholder
agriculture to increase efficacy.
KEYWORDS
biotechnology, climate change, CRISPR/Cas, Diuraphis noxia, fall armyworm, integrated pest
management, invasive pests, iRNA, resistance breeding, Russian wheat aphid, Spodoptera frugiperda
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warming of about 2ºC above pre-industrial levels by mid-cen-
tury (Schlenker & Lobell, 2010). Thornton, Jones, Ericksen,
and Challinor (2011) estimated even higher mean yield losses
(71%) particularly for beans under warming exceeding 4ºC.
In contrast, cassava is the only crop with a better production
forecast under these conditions as it appears to be more tol-
erant to higher temperature regimes and variable rainfall pat-
terns (Niang et al., 2014). Data from different models predict
future crop losses for both maize and soybean (Fodor et al.,
2017). However, when carbon dioxide (CO2) fertilization ef-
fects are taken into account, significant yield gains are pre-
dicted for soybean, together with a shift in global production
from the southern to the northern hemisphere (Foyer et al.,
2019).
Relatively little information is available in the literature
on plant responses to different combinations of biotic and
abiotic stress responses (Foyer, Rasool, Davey, & Hancock,
2016). Atmospheric carbon dioxide (CO2) levels arefor ex-
ample already well over 400ppm and are increasing annu-
ally. Growth under high atmospheric CO2 had little impact
on aphid performance on oilseed rape (Himanen et al., 2008).
However, the performance of the pea aphid (Acyrthosiphon
pisum) was decreased in free-air enrichment (FACE) studies
of performance on Vicia faba (Mondor, Tremblay, Awmack,
& Lindroth, 2005). Plants grown under elevated CO2 were
more suitable hosts for A.pisum than those grown at ambi-
ent CO2. However, when plants were grown at elevated tem-
perature (30°C), the effect of CO2 fertilization on amino acid
content was lost as was the enhanced susceptibility of plants
to aphid infestation (Ryalls, Moore, Riegler, Gherlenda, &
Johnson, 2015). These findings may be explained by recent
reports of the differential effects of high atmospheric CO2
and elevated temperatures on phytohormone signaling. Plants
grown with elevated atmospheric CO2 levels show activation
of salicylic acid (SA)-mediated defense pathways (Mhamdi
& Noctor, 2016; Noctor & Mhamdi, 2017). In contrast, in-
creasing evidence suggests that elevated temperatures selec-
tively dampen the SA response, while jasmonic acid (JA) and
abscisic acid signaling pathways are favored. Other observed
changes in the plant foliage grown under elevated CO2 lev-
els (550 and 700ppm) include altered the quality of peanut
foliage (i.e., significantly lower leaf nitrogen, higher carbon,
higher relative proportion of carbon to nitrogen, and higher
polyphenols content expressed in terms of tannic acid equiv-
alents). Similar effects have been reported previously in other
plant species and their interaction with pests (Bezemer &
Jones, 1998; Hunter, 2001). These measured changes directly
affected the tobacco caterpillar (Spodoptera litura) resulting
FIGURE 1 Progressively lower average rainfall has been recorded over the past five decades. Changes in measured rainfall (1960–2000)
(Taken from Davies-Reddy & Vincent, 2017)
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in higher consumption, lower digestive efficiency, slower
growth, and longer time to pupation (Rao, Manimanjari, et
al., 2012a; Rao, Rama Rao, et al., 2012b). Similarly, elevated
CO2 on maize resulted in a decrease in fitness of the Asian
corn borer (Xie et al., 2015). Rising CO2 levels also include
both indirect (i.e., changes in host plants) and direct (i.e.,
change in natural enemies) effects on insects (Guerenstein
& Hildebrand, 2008). Climate change effects like moderate
waterdeficit stress in combination with high temperatures
also negatively affected aphid survival even where night tem-
peratures were lower, and potentially could aid in the recov-
ery from direct heat stress (Beetge & Krüger, 2019).
While the relative importance of abiotic and biotic soil
components can differ between plants and their herbivores,
a study of the interactions between the aphid Schizaphis ruf-
ula and its host dune grass Ammophila arenaria revealed that
aphid population characteristics were dependent on the abi-
otic properties of the soils in different growing regions, irre-
spective of whether soil biota were present (Vandegehuchte,
de la Peña, & Bonte, 2010). Moreover, herbivore-induced
resistance is likely to be constrained in plants growing on
degraded soils because of JA-linked responses to prevailing
abiotic and biotic stresses (Held & Baldwin, 2005). Of the
abiotic properties of the soils, the availability of water and
essential nutrients such as nitrogen and phosphate, is the
most important in determining plant growth and productivity
(Comadira et al., 2015).
Increasing global temperatures will not only have nega-
tive impacts on food production by directly influencing plant
productivity, but they can also promote more frequent out-
breaks of pests and diseases due to enhanced insect growth
and development, as well as increased ease of colonizing
stressed plants (Mattson & Haack, 1987). Current crop losses
due to insect pests in African countries are estimated to av-
erage about 49% of the total crop yield each year (Centre
for Agriculture and Biosciences International, CABI, https
://www.cabi.org/proje cts/food-secur ity/tackl ing-pests-disea
ses/). These losses are expected to be even higher in some
crops in the future as a result of climate change. Therefore,
in the face of such predicted losses, novel strategies are ur-
gently required to control insects by either applying classi-
cal breeding approaches with improved markers for selection
or by the discovery and implementation of new approaches
that are designed to limit these losses. Furthermore, a recent
study has specifically modeled the losses in the production
of major cereal corps (i.e., maize, wheat and rice) and the
associated increased pest incidence in response to global
warming (Deutsch et al., 2018). In this model, global yield
estimates are projected to decrease by up to 25% per degree
increase in global mean surface warming (Dillon, Wang, &
Huey, 2010). These authors suggest that predicted losses are
the consequence of warming temperatures on increased in-
sect reproductive and metabolic rates, and hence greater food
requirements. The median increase in yield losses owing to
TABLE 1 Estimated annual production losses because of the invasion of new pests (modified from Pratt et al., 2017)
Invasive insect pest Crop
Eastern African coun-
try where IAS currently
recorded as present
Estimated current
annual production
losses to smallholders
(million US$)*
Estimated future annual production
losses to smallholders (million US$)
(5–10year scale)(per country and
in total)
Lower
estimate
Upper
estimate
Lower
estimate Upper estimate
Chilo partellus (spotted
stem borer)
Maize Ethiopia 61.3 73.2 47.9 56.6
Kenya 42.8 51.0 34.4 40.6
Malawi 104.3 139.1 82.5 106.1
Tanzania 30.0 42.4 26.5 37.1
Uganda 118.6 144.3 92.1 108.8
Liriomyza spp. (leaf-
mining flies)
Bean and pea
(dry/ green)
Kenya 54.0 64.5 61.5 71.7
Tanzania 49.8 59.3 57.1 66.6
Uganda 21.3 25.3 25.1 29.3
Tuta absoluta (tomato
leafminer)
Tomato Ethiopia 2.6 2.9 3.4 3.8
Kenya 45.9 52.4 59.8 66.5
Tanzania 20.4 23.2 26.5 29.5
Uganda 0.7 0.8 1.2 1.3
Cumulative losses 551.7 678.4 518 617.9
Cumulative losses
(5year scale)
2,590 3,089.5
*Adjusted to gross production pre-losses.
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pest pressure is expected to be in the ranges of 46%, 19%,
and 31% for wheat, rice, and maize, respectively for an in-
crease of 2°C in average global surface temperatures. This
would result in total estimated losses to 59, 92, and 62 metric
megatons per year (Dillon et al., 2010). In addition to the
increased metabolic requirements of insect pests, changes
in migratory patterns and dispersion ranges will be exacer-
bated with median temperature increases, possibly resulting
in significantly more pest invasions and introductions. For
example, in a recent analysis relating 1,300 invasive species
with the main crops in different countries and international
trade routes, sub-Saharan African countries were identified
as the most vulnerable to invasive species (Paini et al., 2016).
In addition, these countries generally have little or no diver-
sification of economic industries, and they are hence highly
dependent on agriculture (Organisation for Economic Co-
operation and Development/United Nations, 2011). Climate
change-associated changes in invasive species will therefore
greatly affect them.
The introduction or spread of relatively few invasive
species can have a devastating impact on important staple
crops such as maize, and other high-value cash crops includ-
ing tomatoes, peas, and green beans (Pratt, Constantine, &
Murphy,2017). This was highlighted in a recent study (Pratt
et al., 2017) on the economic impact that new invasive pests
would have on the mixed maize farming of smallholder farm-
ers in six eastern African countries (i.e., Ethiopia, Kenya,
Malawi, Rwanda, Tanzania, and Uganda) (Table 1). These
countries have large rural communities that are dependent
on smallholder farming for their livelihoods. The costs as-
sociated with invasive species equated to 1.8%–2.2% of total
agricultural GDP per annum for the eastern African region,
yet whose GDP is significantly dependent on agriculture con-
tributing between 24.5% and 43% (FAO, 2017). These losses
could be even higher in the long term, growing to $1.0–
1.2billion per year over the coming decade. Such findings
clearly highlight the urgent need for strategies for control and
coordinated responses to the imminent threat at the regional,
national, and international levels.
However predictive these models may be, the establish-
ment, spread, and biological success of invasive species will
definitely be altered by climatic change (Ziska, Blumenthal,
Runion, Hunt, & Diaz-Soltero, 2011). In fact, diseases have
completely blinded the International research community on
the emerging importance of insect pests in view of climate
change. To date, only limited investigations have been con-
ducted in Africa. Also, little information is available con-
cerning the precautionary measures that should be taken in
the event that future climate change causes an increased in-
cidence of insect invasion. Current literature largely focuses
on how climate change will affect weather patterns—mostly
rainfall and temperature, with little emphasis on how such
changes could influence or promote insect invasion, or the
resultant losses in crop productivity. Our aim in this review
is therefore to summarize current knowledge on insect pests
based largely on the historical record of insect species that
are already invasive in Africa, and that greatly affect crop
production in Africa, and unfortunately, entering Europe and
Asia in the future. The invasiveness of existing insect pests
might increase further due to climatic changes that provide a
better habitat and environmental conditions for growth and
reproduction. In addition to classical insect control strat-
egies, we discuss possible new strategies of insect control,
highlighting biotechnological approaches that might limit or
prevent climate change-induced insect invasions.
2
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INVASIVE INSECT PESTS IN
AFRICA
Invasive insect pests moving to new habitats in Africa will
pose a major threat to crop production and food security
(https ://theco nvers ation.com/afric as-most-notor ious-insec
ts-the-bugs-that-hit-agric ulture-the-harde st-83107 ). Since
insect pests are sensitive to climate change (Chakraborty &
Newton, 2011), invasive insects are likely to thrive in the
more suitable climatic niches of the future causing greater
harm, particularly in the absence of natural enemies or any
pre-emptive protective measures in these new habitats (Ziska
et al., 2011).
Insects are “ectotherm” organisms that rely on heat sources
in the environment to control metabolic rate (Heinrich,
1993). Climate change-induced increases in the air or host
plant temperatures in Africa will result in faster insect devel-
opment. In general, future temperature regimes will be more
optimal for insect growth even without effects on food sup-
ply and will exacerbate proliferation and decrease the time
to reproductive maturity. Moreover, insect mortality rates are
likely to decrease and more offspring will be produced per
unit of food intake (Mattson & Haack, 1987). Taken together,
these factors will result in dramatic increases in insect growth
and pest population size (Maffei, Mithofer, & Boland, 2007).
Insect pests will be more prevalent earlier in the crop growing
season due to higher temperatures or new habitats.
The ability to predict insect invasions into new habitats
is extremely challenging, particularly in the absence of re-
cords concerning the invasion history of selected regions.
Also, predicting the impact of an individual insect species
on a new habitat is difficult because of spatial and temporal
uncertainties. Insects can have a major impact in one loca-
tion but only a minor impact in another location. Such uncer-
tainties ultimately influence the assessment and predictions
of the economic impact that might result from invasion. A
further challenge is to acquire precise data on how higher
temperatures or changes in rainfall patterns contribute to in-
sect invasion. The extent of insect invasion may also depend
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on the extent of cultivation of host crops in new locations.
Currently, several insect pests such as the legume pod borer
are mainly endemic to Western Africa where it infects cow-
peas (Agunbiade et al., 2012). The pod borer is, however,
able to attack common beans and soybeans and beans, and
hence, it has the potential to become invasive in new areas
because of increased legume cultivation as well as climate
change. Predicted increases in land area dedicated to the pro-
duction of legumes particularly soybeans, in wider more fa-
vorable regions of sub-Saharan Africa, are needed to satisfy
the demands of a rapidly growing population with sufficient
cheap protein (Foyer et al., 2019).
2.1
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RUSSIAN WHEAT APHID
(DIURAPHIS NOXIA)
One of the best-documented and studied examples of an in-
vasive pest species in Southern Africa is the Russian wheat
aphid (RWA, Diuraphis noxia Kurdjumov) (Hemiptera:
Aphididae). This phloem-feeding aphid is able to survive in a
variety of habitats due to the ability to withstand a wide range
of temperatures. The insect lives inside the rolled leaves of ce-
real crops and grasses all year-round (https ://anima ldive rsity.
org/accou nts/Diura phis_noxia/ ). RWA was first reported as
an invasive species and a local insect pest in Southern Africa
as early as 1978. This insect was predominant in the sum-
mer rainfall area of the eastern Free State province of South
Africa, devastating wheat yields with reported losses up to
90% (Fouche et al., 1984; Walters, 1984; Walters et al., 1980).
Interestingly, this invasion coincided with prolonged periods
of low rainfall and increased temperatures. These conditions
are similar to those predicted to occur as a result of future
climate change in Africa and they might therefore contribute
to further invasiveness of the aphid (Figure 1). It was ini-
tially suggested that RWA serves as a virus vector because
of the symptoms and responses observed after feeding. This
typically includes leaf rolling, with white or yellow chlorotic
longitudinal streaks on infested leaves. However, this could
not be confirmed (Burger & Botha, 2018). Aphid-induced
yield losses are mainly due to chlorosis and decreases in the
content of photosynthetic pigments (Botha et al., 2006), lead-
ing to a lower photosynthetic capacity (Botha et al., 2011;
Fouche et al., 1984) as well as a decrease in effective leaf
area (Walters et al., 1980).
Concerted breeding efforts, to limit the spread of the
aphid in South Africa, resulted in the development of
RWA-resistant germplasm containing different sources of
resistance (i.e., Dn1, Dn2, Dn5, Du Toit, 1989). All these
resources originated from the Fertile Crescent region of
Middle Eastwhere RWA is endemic to. In 1992, the first
resistant cultivar, TugelaDN, was released (Van Niekerk,
2001), and by 2006, another 27 cultivars conferring
resistance to RWA had been identified and released (Tolmay,
Prinsloo, & Hatting, 2000). Biological control initiatives
were also launched, but rendered little success, as intro-
duced predator numbers were either too low or failed to
adapt to their new habitats (Hatting, Humber, Poprawski, &
Miller, 1999; Hatting, Poprawski, & Miller, 2000; Hatting,
Wraight, & Miller, 2004; Prinsloo, 1998, 2000; Prinsloo &
du Plessis, 2000).
Despite the successful implementation of integrated
pest management (IPM) strategies, which includes the
planting of resistant varieties, biocontrol agents and insec-
ticide spraying, this IPM only lasted for about 14 years.
By 2006, breakdown in resistance to RWA was reported in
the Free State province of South Africa (i.e., SA2, Tolmay,
Lindeque, & Prinsloo, 2007), with reports of two addi-
tional D. noxia biotypes (i.e., SA3 and SA4) soon to fol-
low (Jankielsohn, 2011, 2016). Biotypes are morphological
similar aphid populations that differ in their virulence to
their host. By 2006, the original SA1 biotype invaded the
winter rainfall areas in the Western Cape province, previ-
ously RWA free, by crossing a natural ecological barrier
(i.e., Great Karoo biome, arid region with limited vegeta-
tion) causing significant damage to wheat and barley yields
in this region (Botha, 2013). This migration coincided
with prolonged periods of lowered rainfall and increased
temperature trends as forecasted by climatic models for
Southern Africa (Figure 1).
In May 2016, this aphid was reported for the first time
in Australia (Plant Health Australia, 2017; Yazdani et al.,
2017). This invasion was already predicted in 1990, when
Hughes and Maywald (1990) using the CLIMEX model,
identified regions with climates highly suitable for settle-
ment by the species. Following the early reports, wide-
spread sampling confirmed the migration of the species
throughout the south-eastern regions, as well as into north-
ern Tasmania (Plant Health Australia, 2017; Yazdani et
al., 2017) confirming the validity of the early predictions.
More recently, a modified Hughes and Maywald (1990)
CLIMEX model (Table S1) that include irrigation areas
as favorable habitat was applied which expanded the pre-
viously identified favorable climatic regions in temperate
and Mediterranean areas in Australia and Europe; and in
more semi-arid areas in north-western China and Middle
Eastern countries, but also revealed new areas, not previ-
ously reported climatically suitable for the establishment
of D. noxia, such as parts of France, the UK and New
Zealand. (Figure S1).
The RWA was also introduced to Kenya in 1995, with
two RWA biotypes (i.e., Njoro and Timau) present in the
country (Ngenya, Malinga, Tabu, & Masinde, 2016). These
RWA biotypes differ from the biotypes in South Africa and
were found to be phylogenetically closest to the Middle East-
African RWA group, alongside biotypes RWA1 and RWA2
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occurring inthe United States and Mexico (Liu et al., 2010).
Comparable climatic conditions to those in the Southern
African wheat-producing regions promoted the settlement
and proliferation of this aphid, with some regions being
more suitable than others. In a study wherein Malinga et
al. (2007) compared the RWA biotypes in Kenya, the bio-
types from Njoro were shown to be fitter (i.e., experienced
higher survival, progeny and estimates of intrinsic rate of
natural increase) than the Timau biotypes. RWA severely
hampers wheat production (442,000 MT) in Kenya, to the ex-
tent that production does not meet annual domestic demand
(1,750,000 MT) (Njuguna, Macharia Mwangi, Kamundia,
Koros, & Ngotho, 2016). RWA thus causes yield losses of
up to 95% when not controlled (Macharia, Gethi, Ngari, &
Njuguna, 2012). As in many other wheat production areas,
RWA is mainly controlled by insecticide spraying (Macharia
et al., 2012), which not only poses a hazard to the environ-
ment, but is also costly, especially to rural smallholder farm-
ers. Hence, there is a need for alternative effective methods
of control, particularly in the face of climate change, which is
likely to spread this aphid into new habitats.
A key question concerns the cause of this breakdown in
aphid resistance. The answer is a combination of factors, such
as changing climatic conditions that favored the settlement
of RWA in new areas that were previously RWA free and
farmers relying on limited resistance varieties with a narrow
genetic base that were planted on a wide scale, with no or
limited refuge. Such practices were associated with heavy
insecticide dependence. Moreover, new RWA introductions
coincided with wheat grain imports. This practice led to ac-
cidental introductions of new insect pests, which rapidly be-
came invasive. This is a common phenomenon (Paini et al.,
2016). Wheat import data from 1988 to 2012 have been an-
alyzed (Burger, 2015). This study involved un-milled wheat,
either as seed or fresh material, as well as countries with a
record of RWA infection. Countries included in this investi-
gation were Argentina, Chile, Canada, Mexico, South Africa,
and the United States. In these countries, RWA was either
confirmed as an insect pest, or was believed to have acted as
a corridor for introduction. Also included in this investiga-
tion were major trading partners to South Africa for wheat
imports including the United States, Argentina, Canada, and
Germany (Figure 2). By making use of online world trade
databases, Burger (2015) thereby made the interesting obser-
vation that the reports of new RWA biotypes (i.e., SA2, SA3,
and SA4) in South Africa followed major wheat imports from
the United States (Figure 2). By also studying the genome of
the RWA endosymbiont (B. aphidicola), Burger (2015) also
reported sequence similarities with that of B.aphidicola from
RWA biotypes US2, US5, and US8, providing evidence in
support of the conclusion that the United States was the ori-
gin of South AfricanRWA biotypes, SA3 and SA4.
The breakdown in resistance also led to a new wave of
breeding efforts to identify alternative sources of RWA re-
sistance. Currently, RWA is controlled through integrated
management practices, consisting of cultural practices, plant-
ing of resistance varieties, and frequent insecticide spraying.
The latter strategy incurs the additional cost to South African
wheat farmers on average by US$12 per hectare, increasing
the annual financial burden of production costs to approx-
imately US$4 million to wheat farmers that already suffer
from low profit margins (De Lange, 2017). In general, all
these aspects have to be considered in future strategies to
limit damage by this aphid in relation to climate change sce-
narios, when this aphid will possibly invade new climatically
more favorable habitats. Therefore, future controls for the
aphid must seek to prevent further extensive spread to new
habitats and require much more effective strategies than are
presently available.
2.2
|
Fall armyworm (Spodoptera frugiperda)
The armyworm Spodoptera exempta is native to Africa
(Haggis, 1986). A different armyworm species that is closely
related to the native African armyworm is the fall armyworm
(Spodoptera frugiperda). This species is endemic to North
and South America and is a prime noctuid pest of maize.
This maize herbivore was introduced into Africa in 2016. It
is thought to be a haplotype from South Florida. The pres-
ence of this insect has been reported in over 30 African coun-
tries including Kenya (Sisay et al., 2018) and South Africa
(Erasmus, 2017) (Figure 3). As the fall armyworm has a wide
host range with almost 100 recorded plant species in 27 fami-
lies (Pogue, 2002), this accidental introduction in the African
continent will constitute a lasting threat to several important
crops. This is especially problematic within the African con-
text, because its preferred hosts are graminaceous plants,
including economically important staples such as maize,
sorghum, rice, wheat, sugar cane, and napier grass. Female
moths normally lay up to 200 eggs at the base of the plant
stalk, or protected in a leaf joint, and eggs hatch after 3days
making the dispersal capacity and the potential incurred dam-
age to crops due to feeding colossal as the worm eats the
plant's reproductive parts and even eats through the maize
cob itself (Prasanna, Huesing, Eddy, & Peschke, 2018).
Damage incurred by the fall armyworm on maize is esti-
mated to be in the range of USD$3billion annually, based on
data from Centre for Agriculture and Bioscience International
(CABI) (April, 2017). This accounts for more than 20 percent
of the total production for the region. Feeding damage, how-
ever, is not limited to these crops, but is also observed on
other major cash crops such as cowpea, groundnut, potato,
soybean, and cotton.
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Control of the fall armyworm is not easy because of its
broad distribution (Figure 3). Additionally, the insect only
to emerge at night necessitates the use of systemic insecti-
cides. Even though maize cultivars expressing the Cry1F
toxin against insect defoliators are widely commercialized in
the western hemisphere of South Africa, this is not the case
for tropical Africa. The deployment of transgenic Bt maize
and application of regular insecticide sprays is hampered by
economic, logistic, and socio-cultural and religious consider-
ations. Bt maize has been genetically modified (GM) to pro-
duce Bt protein, an insecticide that kills certain insect pests.
The gene has originally been isolated from a soil bacterium,
Bacillus thuringiensis (Bt), which has long been known to
possess an insecticide effect.
In general, most of sub-Saharan Africa lack the legal
framework to commercialize GM crops. Moreover, where
they have been approved as in Kenya, there exists a mora-
torium against environmental release and trade of GM foods
particularly maize. Notwithstanding, reports of fall army-
worm resistance to Cry1F (Storer et al., 2010) increase the
need to develop alternative control options such as endo-
phytic entomopathogenic fungi and insect biological control
agents. Reports from studies in Ethiopia on Cotesia icipe,
a dominant larval parasitoid, suggest that parasitism ranges
from 33.8% to 45.3%. The tachinid fly, Palexorista zonata,
resulted in 12.5% parasitism of plants in Kenya. However, the
most common parasitoids in Kenya and Tanzania are Charops
ater and Coccygidium luteum, with parasitism ranging from
FIGURE 2 Wheat imports to the
Republic of South Africa from 1988 to
2012. Reports of D. noxia biotypes that
coincided with significant wheat imports
indicated by arrows (Burger, 2015)
1990 1995 2005 2010
Wheat imports (M3 Tonnes)
0
200 × 106
400 × 106
600 × 106
800 × 106
European Union
France
Australia
Brazil
Germany
Argentina
Canada
2000
Year of wheat importation
Wheat imports (M3 Tonnes)
0
50 × 106
100 × 106
150 × 106
200 × 106
Ukraine
Russian Federation
Poland
India
United Kingdom
Denmark
Pakistan
Turkey
Belguim-Luxenbourg
Saudi Arabia
Romania
Malawi
Wheat imports (M3 Tonnes)
0
200 × 106
400 × 106
600 × 106
800 × 106USA SA3
SA4
SA2
8 of 21
|
BOTHA eT Al.
6% to 12%, and 4% to 8.3%, respectively (based on data from
CABI, April 2017).
Various countries have reported crop damage by the fall ar-
mywormthat varies from minimal to substantial (Table 2). For
example, Mozambique reported crop losses of up to 65% in
some regions (African Centre for Biodiversity, 2018). In addi-
tion, Uganda had an armyworm invasion in half of the country.
Other African countries reported low, or even insignificant, in-
festation (African Centre for Biodiversity, 2018). Without any
control measures, the worm has the potential to cause yield
losses in a range from 8.3 to 20.6m tonnes per annum in 12 of
Africa's maize-producing countries. This represents a range of
21%–53% of the annual maize production, averaged over a three-
year period in these countries (Day et al., 2017; Wild, 2017).
The recent application of control measures, together with
increased farmer awareness, and also improved rainfall has
served to limit the damage caused by the armyworm. The pre-
ferred habitat for the fall armyworm is in regions with little
forest cover, an average (500–700mm) rainfall, with a min-
imum annual temperature of 18–26°C (Nagoshi, Meagher,
& Hay-Roe, 2012). The worm cannot tolerate freezing
temperatures. Species distribution modeling indicates that
much of sub-Saharan Africa including Kenya which has
the pest all year-round (Sisay et al., 2018) and South Africa
(Erasmus, 2017), is highly suitable for this invasive insect
pest. Modeling predicts the possible extinction of the army-
worm due to future wetter climatic conditions in areas near
to the Equator (Ramirez-Cabarel, Kumar, & Shabani, 2017).
However, a further spread of the worm to other regions may
occur due to drier climatic conditions that creating a more
suitable habitat for the pest (Figure 1) (Davies-Reddy &
Vincent, 2017; Wild, 2017).
FIGURE 3 (a) Fall armyworm larvae,
and eggs (Spodoptera frugiperda), and its
distribution across the Africa continent (a);
(b) The African armyworm (S.exempta);
(c) The lesser armyworm (adapted from
FAO, 2018; Carzoli et al., 2018 https ://doi.
org/10.1016/j.gfs.2018.10.004S. exigua);
(d) The cotton leaf worm (S. littoralis); (e)
The False armyworm (Leucania loreyi);
(f) The African boll worm (Helicoverpa
armigera); and (g) The common cutworm
(Agrotis segetum) (Photographs: Courtesy of
Dr. Annemie Erasmus, ARCSummer Grain
Crops, Potchefstroom, SA)
(a)
(b) (c)
(e) (f)(d)
(g)
|
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BOTHA eT Al.
An important question concerns how future global warm-
ing may potentiate future invasions or depress the spread of
the fall armyworm in Africa. In this regard, more research is
required to increase the predicted periods of drought more
accurately, and also the periods of high sporadic rainfall that
may favor the spread of the insect. For example, the drought
linked to the El Niño weather system of 2014–16, followed
by the current high rainfall associated with the La Niña sys-
tem, created the “perfect conditions” for fall armyworm out-
breaks in Africa (Wild, 2017).
The fall armyworm, however, is not the only pest of maize
that is likely to become more invasive in Africa. The spot-
ted stem borer, Chilo partellus, and the maize stem borer,
Busseola fusca, which both feed inside the growing maize
plants in lowland and highland regions of East Africa, respec-
tively, cause severe damage to crops. These two pests cause as
much as $450million in grain losses to smallholder farmers
each year (CABI, April 2017). These two pests also have a
wide distribution (Figure S2) attacking other important crops
such as sorghum. However, the distribution of the two insect
pests varies with altitude (Glatz, Plessis,& Van den Berg, J.,
2017; Khadioli et al., 2014); whereas B.fusca prefers moun-
tain sides, C.partellus prefer a low altitude. In the future, this
spatial distribution may be altered due to climate change, with
increasing temperatures and more frequent periods of drought
and heavy rainfall. For example, an increase in atmospheric
temperatures at high altitude could improve the assimilation of
silicon by maize, which fends off B.fusca and benefits C.par-
tellus. This could lead to an extension of the distribution area
of C. partellus, which could expand its range into higher al-
titude areas, highland tropics, and moist transitional regions,
which have the highest maize agricultural potential and where
the species has yet not been recorded. The spread of these and
other insect pests has serious implication in terms of food se-
curity because these areas produce approximately 80% of the
total maize in East Africa (Calatayud et al., 2016).
2.3
|
Leafminer (Tuta absoluta)
Climate change is likely to cause an increase in the range of
the damaging leafminer species, particularly for Tuta abso-
luta. Modeling of CLIMEX data to predict future T.absoluta
distribution patterns of Africa revealed that the pest could in-
vade and become established in most areas of the African con-
tinent (Figure 4; Tonnang, Mohamed, Khamis, & Ekesi, 2015).
Introducing irrigation scenarios to optimize the CLIMEX
model (Sutherts, Maywald, & Kriticos, 2007), Tonnang et al.
(2015) were able to predict that T. absoluta not only presents
an important threat to West Africa, but most tropical regions
in Africa, as well as Asia, Australia, Northern Europe, New
Zealand, Russian Federation, and the United States (USA).
The model further suggests that the pest may upsurge mod-
erately in areas of Africa where the pest currently exists, or
it may expand its range into other regions of tropical Africa
with reasonable upsurge of damage potential. These possible
outcomes could be explained by the fact that the continent is
already warm, with the average temperature inthe majority
of localities near the threshold temperatures for optimal de-
velopment and survival of T.absoluta. (Tonnang et al., 2015).
The rapid successful invasion is due to the intensive cul-
tivation and cross border trade of tomato fruits, the primary
host of T.absoluta, but also the prevailing similar ecological
and climatic conditions to those of South American countries,
the native region of the pest (Tonnang et al., 2015). The insect
has so far invaded Tunisia (Desneux et al., 2010), north of
the Sahel (Desneux et al., 2010), western Africa, Sudan, and
Ethiopia as well as Kenya (Pfeiffer et al., 2013). Collectively,
this has already caused significant economic impact, with total
annual losses up to $149.1million for Liriomyza leaf-mining
flies and estimated losses of up to $79.4million for T.abso-
luta. However, these figures are likely to grow substantially
with the rapid spread of the latter pest (CABI, April 2017).
The reasons for this rapid spread are that horticultural crops
are often grown along with staples, such as maize, where they
are valuable nutritionally, and they also serve as cash crops
for smallholder growers. In northern Africa, this pest causes
80%–100% crop loss when proper management strategies are
not implemented (Giulianotti & Certis, 2010).
3
|
DETERMINANTS OF
INVASIVENESS
Invertebrates are especially sensitive to changing climatic
conditions, and their response to temperature, rainfall, relative
TABLE 2 Estimated yield and economic losses for maize and sorghum in Ghana and Kenya due to the fall armyworm (from Abrahams
et al.,2017)
Crop Country
Total Production without fall
armyworm (tons M)
Yield loss with fall army-
worm (tons M)
Estimated yield loss with
fall armyworm (USD $M)
Maize Ghana 1.8 0.500 136.1
Kenya 3.5 0.900 328.1
Sorghum Ghana 0.3 0.004 17.7
Kenya 0.2 0.030 14.4
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BOTHA eT Al.
humidity, and soil moisture is important predictors of success-
ful colonization (Chen, Xia, Fu, Wu, & Xue, 2014; Klapwijk,
Ayres, Battisti, & Larsson, 2012; Macfadyen, McDonnald, &
Hill,2018). As more information becames available, climate
models are becoming increasingly more valuable to assist
in the prediction of habitat suitability for invasive species.
Although these models prove valuable, the establishment of
a suitable model is not a straightforward process (Newbery,
Qi, & Fitt,2016; Macfadyen & Kriticos, 2012; Tonnang et al.,
2017; Ward & Masters, 2007) as several factors come into
play during the development, selection/choice, and applica-
tion of these models. Also, the ability of the developed model
to accurately predict future invasions is highly reliant on ac-
curate historical data and a good understanding of the fac-
tors that determine settlement of the targeted species. Many
of these can be species specific, while other factors relate to
the resource/niche availability (Ward & Masters, 2007; Wan
and Yan, 2016). Hence, the strong notion toward making use
of a whole system approach during the development of such
amodel as was recently reviewed (Tonnang et al., 2017).
Key factors determining the suitability of a new hab-
itat forinsects relate to traits like host range, phenological
plasticity, and lifecycle strategies (Ward & Masters, 2007).
While some insects have narrow host ranges and therefore
are specialist feeders, others have a broad host range includ-
ing many plant genera, hence generalists, making them likely
more successful during their invasions of new habitats. An
example of the latter, that are known for their successful colo-
nization of new habitats, are whiteflies (Bemisia tabaci) with
a host range of more than 600 species (Wan and Yan, 2016
and references within). Whiteflies are pests to crop plants on
several continents, including Africa.
Climate change like increased temperature will result in
accelerated development and increased voltinism for many
pest species (Ziter, Robinson, & Newman, 2012) and may
mean species become active earlier in the season (Harrington,
Fleming, & Woiwod,2001; Macfadyen et al., 2018). Close
synchrony of insects with their host plants to successfully
complete their lifecycles is hampering invasion to new areas.
Thus, phenotypically plastic invasive species that are not
dependent on close phenological coupling with host plants
(e.g., the highly variable egg load of the weevil, Rhinocyllus
conicus on Cirsium canescens plants) increase their success-
ful settlement in a new habitat (Ward & Masters, 2007 and
references within).
Another important factor determining the ability to in-
vade new habitats relates to reproduction. The top ten in-
vasive alien species, such as whiteflies (B. tabaci) (Goa,
Cong, & Wan, 2013) and vegetable leafminer (Liriomyza
sativae) (Zhang, Yu, & Zhou, 2000), share the following
traits; they all have high fecundity, short generation times,
and produce multiple generations per year, ensuring long-
term persistence at low population density after initial intro-
duction. The ability to reproduce through parthenogenesis
FIGURE 4 (a) Potential range shifts in the distribution of Tuta absoluta in Africa using the eco-climatic indices EI under climate change
scenario (a rise of 1.5°C Africa wide temperature and 10% increase of rainfall from March 2—September 30 and 10% decrease in the rest of the
year). The map was produced from the difference between the values of EI of the predicted future T. absoluta distribution (obtained when applying
climate change criteria) and the distribution of the pest originated from current climate (year 2000) in Africa. EI=0 demonstrates no range shift;
EI<0 signifies a reduction of climatic suitability; and EI>0 represents an increase in the likelihood of survival and permanent establishment
of the species. (b) Potential range of increase in number of generations per year of T. absoluta under the selected climate change scenario (from
Tonnang et al., 2015)
0 250 500 1,000 1,500 2,000
km
(a) (b)
|
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BOTHA eT Al.
provides an advantage as they can exploit new resources
without the hindrance of finding a mate and unpredicted
Allee effects (Liebhold et al., 2016). A good example of
the latter include Russian wheat aphid (Diuraphis noxia),
known for its invasiveness worldwide (Burger & Botha,
2018; Yazdani et al., 2017). Other traits of importance
determining successful invasion include adaptability to
changing climates (thermal tolerance—adaptation to low/
high temperatures), insecticide resistance, and immune
priming (i.e., immune memory to previous pathogen expo-
sure; Wan and Yan, 2016 and references within).
4
|
ECOSYSTEM INVASIBILITY
AND INTEGRATED PEST
MANAGEMENT
Several theories about ecosystem invisibility exist, including
crop system complexity, land use patterns, and geographic
and climate barriers (Wan & Yang, 2016 and references
within). Reduction of habitat heterogeneity and increased in
mono-agricultural ecosystems due to farming (maize, wheat,
and rice) provides suitable habitats for most invasive crop
pests (Knops et al., 1999).
Commercial monoculture farming systems are highly
dependent on external inputs (synthetized fertilizers, chem-
ical pesticides, and growth regulators) with simplified eco-
systems (Kremen, Iles, & Bacon, 2012; Malézieux, 2012).
In contrast, agricultural systems that promote functional
biodiversity and support ecological processes allow for
benefits from many ecosystem services, such as nutrient
cycling, soil structuration, and pest control (Afrin et al.,
2017; Altieri & Rosset, 1996; Zhang, Werf, Zhang, Li, &
Spiertz, 2007).
Disrupting monoculture agriculture systems through
intercropping, using at least two crops species at the
same time on the same land (Kahn, 2010; Konar, Singh,
& Paul, 2010), enhances pest control (Baidoo, Mochiah,
& Apusiga, 2012; Baliddawa, 1985; Rao, Manimanjari, et
al., 2012a; Rao, Rama Rao, et al., 2012b; Sharaby, Abdel-
Rahman, & Sabry, 2015; Sulvai, Chaúque, & Macuvele,
2016). Intercropping with several crop species assists in
pest management because it is unlikely that different crops
will be infested by the same pest species (Baidoo et al.,
2012).
Field studies have demonstrated that intercropping pro-
tects the target crop through several mechanisms, including
the release of organic chemicals by non-host crops grown
in intercropping which adversely affect the pest insects
(Sulvai et al., 2016). The released organic chemicals may
act as repellents to insect pests, but also attracts biocontrol
agents (natural enemies) of insect pests (Dassou & Tixier,
2016; Letourneau et al., 2011; Song et al., 2013). Mixed crop
agriculture has also been shown to sometimes act as barri-
ers that hinder movements of insect pests, providing some
protection to susceptible plants (Parker, Rodriguez-Saona,
Hamilton, & Snyder, 2013).
Intercropping is commonly used in small-scale farming
systems for pest control as it diversifies crops in a given
agro-ecosystem to reduce the population of insects and
consequently their attack (Degri, Mailafiya, & Mshelia,
2014; Pimental, Hepperly, Hanson, Douds, & Seidel, 2005;
Vaiyapuri, Amanullah, Rajendran, & Sathyamoorthi, 2010).
Studies in Kenya (Kinama, Habineza, & Jean Pierre, 2018
and references therein) and Egypt (Abdel-Wahab, Abdel-
Wahab, & Abdel-Wahab, 2019) demonstrated that cereal–le-
gume intercropping has benefits beyond just pest and disease
control, as they also measured increased yield, better biolog-
ical nitrogen fixation, and better weed control. Consequently,
they reported significant economic benefits for these farmers.
5
|
BIOTECHNOLOGY, A TOOL
TO LIMIT INVASIVE INSECT PEST
DAMAGE
The initial commercialization of Bacillus thuringiensis (Bt)
maize in 1996 was hailed as the ultimate solution for pest
control and it was widely adopted. Since then, studies showed
that the adoption of Bt maize and cotton has reduced the use
of insecticides by 85%. The use of Bt crops also protected
neighboring crops such as peppers and beans (Gitig, 2018).
Management of the fall armyworm, for example, already
includes the application of GM plants expressing one or more
insecticidal proteins derived from Bacillus thuringiensis (Bt)
(Ingber, Mason, & Flexner, 2018) (Table 2). In sub-Saha-
ran Africa, the Bt technology has also been recommended
to limit invasion of the fall armyworm (ISAAA, 2018).
Although maize cultivars expressing the Bt Cry1F toxin are
already worldwide applied for control of the fall armyworm,
including South Africa, it is not widely used in other African
countries with recent invasions. These countries are currently
engaged in research and testing of GM crops to limit further
spread of this pest (ISAAA, 2017).
Even though planting Bt maize would be useful in these
countries and limit the spread of the fall armyworm, this tech-
nology is not a lasting solution because of the breakdown of
resistance to Bt proteins, as has been observed in Cry1F and
Vip3AA20 (Haung et al., 2014). Resistance may also develop
against Vip3AA20, the latest Bt toxin that is effective in the
field. Such findings suggest that Vip3AA20 will not be effec-
tive for much longer. Therefore, more research is needed to
determine which fall armyworm strains are already present in
Africa, and whether these strains already carry the Bt resis-
tance alleles. This knowledge is essential if future Bt varieties
are to remain effective in dealing with the insect pest.
12 of 21
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BOTHA eT Al.
Maize plants expressing the Bt toxin are also widely ap-
plied for control of the insect pests B.fusca and C.partellus
(Mugo et al., 2011; Tefera et al., 2016). However, similar re-
sistance problems as found for the fall armyworm have been
found when applying the Bt technology for the control of
B.fusca. A shift in levels of susceptibility of B.fusca to Bt
maize was specifically found with a very low larval survival
on Bt-maize leaf tissue before the release of Bt maize many
years ago to current much higher larval survival (Strydom,
Erasmus, Plessis, & Berg, 2019). Such reports of Bt resis-
tance have already led to also consider alternative control
options such as application of endophytic entomopathogenic
fungi and application of exotic parasitoids like Cotesia flavi-
pes, already released in 1993 in Kenya, for biological control
of the introduced stemborer Chilo partellus (Overholt et al.,
1994).
In addition to protecting maize, the Bt technology has also
been applied to the control of the tomato leafminer (Tuta ab-
soluta). When the cry1Ac gene was introduced into tomato
plants, Bt-expressing tomato lines were better protected
against the leafminer (Selale, Dağlı, Mutlu, Doğanlar, &
Frary, 2017). The recently introduced South American tomato
leafminer (also known as the South American pinworm), Tuta
absoluta, and three species of Liriomyza leaf-mining flies
are the most important and most widely distributed pests on
horticultural crops in Africa. Current control measures rely
mostly on chemical spraying, although implementation and
pest management practices such as surveillance and the intro-
duction of appropriate phytosanitary activities to manage the
spread of T.absoluta in Africa have also been widely imple-
mented (Tonnang et al., 2015).
Although the Bt technology offers advantages as a mea-
sure to limit future invasion by insect pests, the deployment
of transgenic Bt maize and application of regular insecticide
is hampered in Africa by the GMO resistance problem and by
economic, logistic, and socio-cultural and religious consider-
ations. Not onlyis the cost of Bt-maize seed an additional bur-
den, as smallholder farmers rarely have the financial means to
annually purchase expensive seed (Fischer, Van den, Berg, &
Mutengwa, 2015), but most of sub-Saharan Africa still lacks
the legal framework to commercialize GMO crops. Where
GMO crops have been approved, as in Kenya, a moratorium
against the environmental release and trade of GMO foods,
particularly maize, still exists. These problems have impeded
the utilization of GM crops in Africa, for example during the
2002 food crisis when Malawi, Mozambique, Zambia, and
Zimbabwe initially refused US food aid shipments despite
widespread food shortages (Zerbe, 2004). The concerns of
these countries are based on the percieved potential health
impact of GM foods on recipients, the impact of GM food on
domestic agricultural biodiversity and impact of GM food on
their ability to export agricultural commodities in the future
(Zerbe, 2004).
Additional factors contributing to the poor implementa-
tion of GMO varieties into smallholder agriculture include
(a) a lack of education and technology transfer, (b) conflicts
of interest (commercial investment) (Fischer et al., 2015),
and (c) the lack of political will and good governance (Zerbe,
2004). It is important to note that most African countries are
aligned to their former colonial “masters.” These are mainly
European, whose philosophy still plays a leading role in mat-
ters of education, science, technology, and trade. It is there-
fore not surprising that most African countries have adopted
the precautionary approach to GMOs that is similar to that of
the European Union (Elliot & Madan, 2016). GM crops face
strong opposition in most countries of the European Union
and Japan (Smyth, 2017). Heated debates still continue in
Africa, regarding whether GM crops will help alleviate food
insecurity or whether the adoption of this technology could
result in negative impacts (Falck-Zepeda, Gruere, & Sithole-
Niag,2012). Consequently, African policymakers are hes-
itant to move forward with establishing biosafety laws and
commercializing GM crops, largely due to risk perceptions
and fears spread by anti-biotech lobbying groups (Paarlberg,
2010).
Poor transfer of information on Bt maize (genetically
modified, GM) underpins the lack of the successful adoption
of the GM maize by smallholders in many Southern African
countries. One should have in mind that, although risks as-
sociated with GM crops are very likely low or non-existent,
adoption of a GM technology will not succeed if simply im-
posed on a farmer (Carzoli et al., 2018). Education on the
benefits (such as it provides resistance to stem borers) and
prevention of resistance breakdown (i.e., refuge practice—
need to plant a refuge cropof non-Bt maize next to Bt crop) is
required to successfully adopt Bt maize. Smallholder farmers
must also be better informed that the crop protection only
lasts while hybrid seed is being planted. In this regard, as seed
is mostly distributed by commercial seed companies, govern-
mental regulations for the distribution of Bt maize obstruct
smallholders from fully benefitting. Education and training
on proper insect resistance management following approval
of GM maize crops; especially training on proper implemen-
tation of refuge is a further a problem for better adoption of
the Bt technology (FAO, 2018; Fatoretto, Michel, Silva Filho,
& Silva, 2017). The reality of a refuge cropmeans that fall
armyworm will destroy the maize in this portion of the field,
equaling little or no harvestable yield. However, implement-
ing and monitoring non-Bt refuges will likely be a challenge
in the smallholder farm context as already found in India and
China (Tabashnik et al., 2013). Mixing non-Bt seeds into Bt
seed bags (“refuge in a bag”) may be therefore a more suit-
able option, at least when seeds are purchased in the formal
seed market.
As Bt insecticides and Bt transgenic crops have been
widely used internationally for pest control (Bravo,
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BOTHA eT Al.
TABLE 3 Major insect pests, reported insecticide resistance, methods of control, and new applications (such as iRNA, CRISPR/Cas9) with the objective of insect management
Species Methods of control
New applications: Genes, delivery, and
function Affected food crops Distribution in AfricaaReference to technology
Diuraphis noxia (Russian
wheat aphid)
Cultural control;
chemical control;
biocontrol; host
plant resistance;
mRNA delivery/
knockouts
RNA delivery knockouts
Gene target: cpRR1 (developmental func-
tion, cuticle)
Wheat, barley, oats, triticale,
rye
South Africa, Zimbabwe,
Kenya, Ethiopia, Morocco,
Algeria, Egypt, Libya
Botha et al. (2018)
Spodoptera litura (taro
caterpillar)
Cultural control;
chemical control;
biocontrol; host
plant resistance;
mRNA delivery/
knockouts
RNA delivery knockouts
Gene targets: Slabd-A; SlitPBP3 (female
sex pheromones)
Over 40 families, contain-
ing at least 87 species of
economic importance (in-
cluding groundnut, a wide
selection of vegetables and
beans)
Ghana and Reunion Bi, Xu, Tan, and Huang (2016)
Zhu et al. (2016)
Spodoptera littoralis (cot-
ton leafworm)
Cultural control;
chemical control;
biocontrol; host
plant resistance;
mRNA delivery/
knockouts
RNA delivery knockouts
Gene target: SlitOrco
Over 40 families, contain-
ing at least 87 species of
economic importance (in-
cluding groundnut, a wide
selection of vegetables and
beans)
Widespread across the African
continent
Koutroumpa et al. (2016)
Helicoverpa armigera
(cotton bollworm)
Cultural control;
chemical control;
biocontrol; GM
technology—Bt
varieties; host plant
resistance; mRNA
delivery/knockouts
RNA delivery knockouts
Gene target: HaCad (demonstrated that
the HaCad gene is related to Bt toxin
Cry1Ac resistance)
OR16 (control of mating)
Cotton, pigeonpea, chickpea,
tomato, sorghum and
cowpea; other hosts include
groundnut, okra, peas, field
beans (Lablab spp.), soya-
beans, lucerne, Phaseolus
spp., other Leguminosae,
tobacco, potatoes, maize,
flax, a number of fruits
(Prunus, Citrus), forest
trees, and a range of veg-
etable crops.
Widespread across the African
continent
Wang et al. (2016)
Chang et al. (2017)
Plutella xylostella (dia-
mondback moth)
Cultural control;
chemical control;
biocontrol; host
plant resistance;
mRNA deliv-
ery/knockouts;
knockout plasmid,
CRISPR/Cas9
CRISPR/Cas9
Gene targets: Pxabd-A, PxCHS1
Pea; horseradish, most
Brassica spp.; watercress;
radish; lettuce, rocket;
cabbage;
Widespread across the African
continent
Huang et al. (2016)
Douris et al. (2016)
ahttps ://www.cabi.org/isc/datas heet/.
14 of 21
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BOTHA eT Al.
Likitvivatanavong, Gill, & Soberón, 2011), more reports
on the development of resistance to Bt toxins are surfacing
(Elliot & Madan, 2016). Hence, the need to seek alternatives
is becoming more urgent. If the transfer of BT transgenic
crops is not accompanied by effective regulatory require-
ments, then efficacy may be decreased. For example, in the
United States, BT crops were introduced with surrounding
non-GMO Crop refugia as a regulatory requirement to trap
insects. Even with this measure in place, Bt breakdown lead-
ing to crop susceptibility has occurred. While such regulatory
requirements are good practice, they will need to be mod-
ified for implementation by small-scale holders in Africa,
who mostly lack the land to practice such measures on a
large scale. Unfortunately, they are often supported by weak,
poorly motivated extension services.
Furthermore, any predicted consequences of climate
change in these countries, such as more intense drought con-
ditions, might possibly severely affect the efficacy of the Bt
toxin for insect control (Martins et al., 2008). The problems
Bt technology currently faces in Africa raises the question
whether new gene silencing technologies, such as RNA in-
terference (RNAi) and CRISPR/Cas9, should be developed
as alternatives or additions to limit a possible future spread of
invasive insect pests. Also, will these technologies be feasible
and acceptable technologies to strengthen particularly food
security for poor African farming communities?
Without doubt, RNAi technology with small interfering
or silencing RNA (siRNA), when expressed in a plant to tar-
get an insect gene, could be useful to specifically protect a
crop against invasive insect pests. Usually an instantaneous
process, unless the dsRNA is supplied continuously, appli-
cation of the CRISPR/Cas9 technology generates changes at
the genomic level that are stable and heritable, and the mu-
tant gene can be transmitted to the next generation (Perkins
et al., 2016). This would clearly have benefits in providing
more sustainable pest resistance as targets are specific and,
in most, examples either developmental or structural in na-
ture (Sun, Guo, Liu, & Zhang, 2017 and references therein;
Botha, Swiegers, & Burger, 2018). Despite the promise this
technology offers, only a limited number of pests that dam-
age food crops haveso farbeen targeted. Examples include
H.armigera (Chang et al., 2017; Sun et al., 2017; Wang et al.,
2016 and references therein), Diuraphis noxia in our group
(Botha et al., 2018), Spodoptera litura, Spodoptera littoralis,
and Plutella xylostella, however all of these are still in the
experimental phase (Table 3).
Using CRISPR/Cas9, Wang et al. (2016) provided di-
rect evidence that HaCad is a key receptor for Cry1Ac and
is related to Cry1Ac resistance, opening up new avenues to
prolong the use of Bt toxins. CRISPR/Cas9 was also used
in a new pest control strategy with H. armigera to destroy
pest mating through antagonist-mediated optimization of
mating time that ensures maximum fecundity (Chang et al.,
2017). In D.noxia, a significant reduction (±50%) in intrin-
sic reproduction rate (as measured in nymph production)
has been measured targeting Dncprr1-8, a gene containing
a conserved R&R region (Rebers and Riddiford Consensus)
(Rebers & Willis, 2001) and an important cuticular protein
(Botha et al., 2018). The same gene is now tested for its po-
tential use to protect leafy crops against other phloem-feeding
hemipterans.
Studies have demonstrated that climate change will greatly
influence the interactions between plants, phloem-feeding
pests like aphids and whiteflies (the latter already a signif-
icant problem in Africa), and their natural enemies. Since
whiteflies also differ in their adaptability, better adapted spe-
cies will likely experience increased distribution and abun-
dance provided their tolerance limits are not exceeded, while
species with lower tolerance and adaptation limits will suffer
reduced fitness, which will have overall effects on their dis-
tribution and abundance in space and time. Changes in cli-
matic suitability modifying the distribution and abundance
of whiteflies, and environmental suitability for plant viruses,
will likely also affect epidemics of viral diseases (Aregbesola,
Legg, Sigsgaard, Lund, & Rapisarda, 2019). However, when
RNAi technology will be regarded as a technology to limit
whitefly spread, it would be essential to express such siRNA/
dsRNA in the phloem under a tissue-specific promoter to tar-
get these phloem-feeding insects. RNA interference (RNAi)-
mediated gene silencing has been indeed explored with some
success for the control of the sap-sucking whitefly, a major
pest in Africa. In addition to cereals, the whitefly causes
damage to root and tuber crops, including cassava and sweet
potato, and transmits hundreds of plant viruses including the
Cassava Mosaic and Cassava Brown Streak viruses (Mugerwa
et al., 2018). Knockdown of whitefly genes involved in neu-
ronal transmission and transcriptional activation of develop-
mental genes reduced the whitefly population size and also
decreased any virus spread (Malik et al., 2016).
6
|
IMPORTANCE OF
COMMUNICATION
By 2017, about 17 million farmers across 24 countries
planted biotechnology-derived crops across 189.8 million
hectares (ISAAA, 2017), signifying the importance and
impact that biotechnology hasc had on global agriculture.
However, planting these crops also sparked debate on di-
verse issues that range from scientific, political, economic,
ethical, and cultural viewpoints. Also, to ensure an enabling
environment where farmers gain the full benefit these crops
offer, a scientific-balanced (i.e., evidence based information
on advantages/disadvantages/possible risks) view should be
communicated effectively to increase public understanding
(Traynor, Adonis, & Gil, 2007). Navarro and Hautea (2011)
|
15 of 21
BOTHA eT Al.
provided additional reasons for proper communication to
the public, which include the benefits of having an informed
public, improved policy, and better regulatory decisions, as
well as increased public confidence.
Communication, however, is not only important for public
acceptance of biotechnology crops, but also for maintaining
effective networks wherein new pest invasions can be re-
ported, as well as to convey the benefits of planting refuges
for the sustainability of the resistance in these crops. The
Southern African Development Community (SADC) Multi-
Country Agricultural Productivity Programme (MAPP) is
an example of such network in Africa (https ://www.sadc.int/
theme s/agric ulture-food-secur ity/). SADC is a collective of
16 African countries, with the objective to increase agricul-
tural productivity by at least 6% per year. The SADC-MAPP
focuses on agricultural research and seeks to strengthen tech-
nology development, technology dissemination, and linkages
among agricultural institutions in the SADC region, includ-
ing communication of new pests and diseases that pose risks
to food security in the region.
Minimizing the risk of invasions is an important aspect of
integrated pest management and ensuring food security. The
risk of new pest invasions can be minimized through policies
(i.e., National and Regional Guidelines), monitoring technol-
ogy (i.e., DNA bar coding, etc.), databases, and early-warning
systems (e.g., CABI’s Horizon Scanning Tool, CABI, 2018,
https ://www.scidev.net/sub-sahar an-afric a/agric ultur e/opini
on/insect-pests-invas ions-in-africa.html), as well as a collec-
tive eradication and spread blocking (Wan & Yang, 2016).
7
|
CONCLUSION
The continent of Africa has been identified to be extremely
vulnerable to the negative impacts of climate change. Climate
change models forecast global warming, with associated
changes in rainfall patterns and increases in heatwaves. These
factors alone are predicted to have a negative impact on the
yields of most major crops, such as wheat, rice, and maize
(Deutsch et al., 2018). This effect may in many cases be ex-
acerbated by insect pests that already consume between 5%
and 20% of major grain crops. Studies concerning the effects
of temperature on the population growth and metabolic rates
of insects suggest that future yield losses caused by insects
will increase by 10%–25% per degree increase in temperature
(Deutsch et al., 2018). Such predictions provide a benchmark
for future regional and Africa-specific studies on the effect of
climate change on crop/insect interactions.
New invasive pests and changes in pest migratory patterns
are but a few of the upcoming challenges to African agricul-
ture that collectively add additional burdens to resource-poor
farming communities. Key questions concern how further
invasions of insect pests can be prevented or contained,
particularly when caused by a changing climate. Controlling
pests, such as the fall armyworm will certainly be challenging
because of the significant ability of the insect to adapt to a
broad range of habitats. For example, addressing the feeding
habit of the caterpillar within the leaf whorl during the day
and emergence only at night requires the application of sys-
temic insecticides. Smallholder farmers would have to spray
insecticides like pyrethrins and organophosphates. Since the
armyworm has already developed resistance to these insecti-
cides, it is particularly difficult to control the insect at an ad-
vanced larval developmental stage. Thus, alternative control
methods are essential which may include physically picking
the caterpillars off the plants, intercropping with plants not
in favor to the insect, application of bio-pesticides, plant-
ing early in the season before any insect pest populations
can build up or applying genetically modified plants such as
plants engineered with the Bt toxin (Niassy & Subramanian,
2018; Yu, 1991). It is thus imperative that key pests and the
crops that are susceptible to attack are identified, in order to
support prioritized decision-making and support tools, for
example policies and sanitary measures, to control the intro-
duction and spread of new pests. It may also assist research-
ers, governments, and developmental agencies to prioritize
their focus areas for research investment and action which
may assist in enhanced food security for Africans.
CONFLICT OF INTEREST
None declared.
ORCID
Anna-Maria Botha https://orcid.
org/0000-0002-9868-1566
Karl J. Kunert https://orcid.org/0000-0002-7740-3508
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SUPPORTING INFORMATION
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How to cite this article: Botha A-M, Kunert KJ,
Maling’a J, Foyer CH. Defining biotechnological
solutions for insect control in sub-Saharan Africa.
Food Energy Secur. 2019;00:e191. https ://doi.
org/10.1002/fes3.191
... Moreover, 258 documents were excluded after scrutiny of full-texts. These also include 52 reviews, systematic reviews and meta-analyses (Abegunde et al., 2019;Agrawal et al., 2014;Belhabib et al., 2016;Biazin et al., 2012;Botha et al., 2020;Brown et al., 2011;Cairns et al., 2012;Carr et al., 2020;Chuku & Okoye, 2009;Corbeels et al., 2019;Druyan, 2011;Epule et al., 2014;Forabosco et al., 2017;Gautier et al., 2016;Gil et al., 2017;Hansen et al., 2011;Hassen et al., 2017;Islam et al., 2016;Katikiro & Macusi, 2012;Kim et al., 2016;Koubi, 2019;Lahive et al., 2019;Lal, 2019;Loboguerrero et al., 2019;Makate, 2019;Mbow et al., 2014;Mngumi, 2020;Muchuru & Nhamo, 2019;Müller, 2013;Muller et al., 2011;Mundia et al., 2019;Mutuo et al., 2005;Nkiaka et al., 2019;Nkrumah, 2019;Partey et al., 2018;Powlson et al., 2016;Pushpalatha & Gangadharan, 2020; Roudier et al., 2011;Sarr, 2012;Shcherbak et al., 2014;Sileshi et al., 2019;Snapp et al., 2019;Sultan & Gaetani, 2016;Terdoo & Feola, 2016;Totin et al., 2018;Vaughan et al., 2019;Webber et al., 2014;Wilcox et al., 2019;Williams et al., 2018;Zougmoré et al., 2018). Consequently, 117 documents were selected and underwent bibliometric and topical analyses ( Table 2). ...
... Climate change is also expected to affect the incidence of pests and diseases (Botha et al., 2020;Jarvis et al., 2012;Sileshi et al., 2019;Wilcox et al., 2019) with increasing damages on crops and animals. Botha et al. (2020) suggest that "[…] median temperature increases are associated with increased pest pressure and changes in migratory patterns. ...
... Climate change is also expected to affect the incidence of pests and diseases (Botha et al., 2020;Jarvis et al., 2012;Sileshi et al., 2019;Wilcox et al., 2019) with increasing damages on crops and animals. Botha et al. (2020) suggest that "[…] median temperature increases are associated with increased pest pressure and changes in migratory patterns. These factors will result in significantly more pest invasions and an increased need for innovative insect management practices". ...
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The impacts of climate change (CC) are expected to be higher in developing countries (e.g. Sub-Saharan Africa). However, these impacts will depend on agriculture development and resilience. Therefore, this paper provides a comprehensive analysis of the multifaceted relationships between CC and agriculture in Burkina Faso (BF). A search performed in March 2020 on the Web of Science yielded 1,820 documents and 217 of them were included in the systematic review. The paper provides an overview on both bibliometrics (e.g. journals, authors, institutions) and topics addressed in the literature viz. agriculture subsectors, climate trends in BF, agriculture and CC mitigation (e.g. agriculture-related emissions, soil carbon sequestration), impacts of CC on agriculture (e.g. natural resources, crop suitability, yields, food security) as well as adaptation strategies. BF is experiencing CC as evidenced by warming and an increase in the occurrence of climate extremes. The literature focuses on crops, while animal husbandry and, especially, fisheries are often overlooked. Moreover, most of the documents deal with CC adaptation by the Burkinabe farmers, pastoralists and rural populations. Analysed adaptation options include conservation agriculture and climate-smart agriculture, irrigation, crop diversification, intensification, livelihoods diversification and migration. However, the focus is mainly on agricultural and individual responses, while livelihoods strategies such as diversification and migration are less frequently addressed. Further research is needed on the dual relation between agriculture and CC to contribute to the achievement of the Sustainable Development Goals. Research results are crucial to inform policies aimed at CC mitigation and/or adaptation in rural BF.
... Nearly one billion people are food insecure in Sub-Saharan Africa today (Botha et al., 2020). Predictions indicate that in the absence of effective mitigation measures, reliable access to sufficient, affordable and nutritious food is likely to deteriorate further in the next 50 years. ...
... Despite regions of Sub-Saharan Africa suffering greater crop losses due to pests, availability of genetic engineering and other modern plant breeding technologies (i. e., targeted mutagenesis) are less available (Botha et al., 2020), likely due to the lagging pace in technology, inadequate research funding schemes as well as hesitance of policymakers to establish biosafety laws (Agbowuro et al., 2021;Botha et al., 2020). By contrast, induced mutagenesis is a cost effective, widely accepted tool used for generating genetic variation to abiotic (i.e., drought tolerance) and biotic (i.e., pest resistance) stresses (Singh et al., 2006). ...
... Despite regions of Sub-Saharan Africa suffering greater crop losses due to pests, availability of genetic engineering and other modern plant breeding technologies (i. e., targeted mutagenesis) are less available (Botha et al., 2020), likely due to the lagging pace in technology, inadequate research funding schemes as well as hesitance of policymakers to establish biosafety laws (Agbowuro et al., 2021;Botha et al., 2020). By contrast, induced mutagenesis is a cost effective, widely accepted tool used for generating genetic variation to abiotic (i.e., drought tolerance) and biotic (i.e., pest resistance) stresses (Singh et al., 2006). ...
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Aphids (Hemiptera: Aphididae) are important agricultural pests in sub-Saharan Africa. These pests are primarily controlled by the use of synthetic insecticides, which has consequently led to the emergence of insecticide-resistant aphid populations as well as negative impacts on non-target organisms. Resistant crop varieties offer a sustainable approach to manage aphids. Despite regions of sub-Saharan Africa suffering greater crop losses due to pests, there is only limited availability of genetic engineering and other modern plant breeding technologies. Here we consider whether induced mutagenesis can contribute to the sustainable management of aphid pests or whether the lack of research in this area reflects the limitations of this approach.
... In Pakistan, pesticides worth more than 10 billion rupees are imported, out of which about 70-80% are sprayed against cotton pests (Bashir et al., 2020). It is the foremost need to use the new insecticides which not only control the target insect pest (Galdino et al., 2021) but also protect the beneficial insects like ladybird beetle, spider, Chrsoperllaspp, Trichogrammaspp and human being (Botha et al., 2020;Egler et al., 2012). Pesticides cause foodborne illness in human through intoxication of various food items (Ishaq et al., 2021). ...
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Development of insecticides resistance mainly hinge with managements techniques for the control of Jassid, Amrasca biguttutla biguttutla. Five insecticides were applied against field collected and laboratory rared jassid populations during the years of 2017 to 2019 to profile their resistance level against field population of jassid through leaf dip method. Very low resistance level was found in jassid against confidor whereas high level of resistance was observed by pyriproxyfen against other test insecticides. Gradual resistance was observed against diafenthiuron. It is concluded that for the management of Jassid repetition of same insecticide should be avoided. The use of confidor may be reduced to overcome resistance against Jassid.
... In Pakistan, pesticides worth more than 10 billion rupees are imported, out of which about 70-80% are sprayed against cotton pests (Bashir et al., 2020). It is the foremost need to use the new insecticides which not only control the target insect pest (Galdino et al., 2021) but also protect the beneficial insects like ladybird beetle, spider, Chrsoperllaspp, Trichogrammaspp and human being (Botha et al., 2020;Egler et al., 2012). Pesticides cause foodborne illness in human through intoxication of various food items (Ishaq et al., 2021). ...
... In Pakistan, pesticides worth more than 10 billion rupees are imported, out of which about 70-80% are sprayed against cotton pests (Bashir et al., 2020). It is the foremost need to use the new insecticides which not only control the target insect pest (Galdino et al., 2021) but also protect the beneficial insects like ladybird beetle, spider, Chrsoperllaspp, Trichogrammaspp and human being (Botha et al., 2020;Egler et al., 2012). Pesticides cause foodborne illness in human through intoxication of various food items (Ishaq et al., 2021). ...
Article
Development of insecticides resistance mainly hinge with managements techniques for the control of Jassid, Amrasca biguttutla biguttutla. Five insecticides were applied against field collected and laboratory rared jassid populations during the years of 2017 to 2019 to profile their resistance level against field population of jassid through leaf dip method. Very low resistance level was found in jassid against confidor whereas high level of resistance was observed by pyriproxyfen against other test insecticides. Gradual resistance was observed against diafenthiuron. It is concluded that for the management of Jassid repetition of same insecticide should be avoided. The use of confidor may be reduced to overcome resistance against Jassid.
... 1,2 IAS have become major threats to global agriculture because of their rapid spread across the globe facilitated by increased trade and transport. 3,4 As an example, the increasing spread of pests into Africa has caused critical crop losses estimated to be several billions US dollars per annum. 5,6 The southern armyworm (SAW) Spodoptera eridania (Stoll) (Lepidoptera: Noctuidae) is one of these invaders. ...
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Full-text available
BACKGROUND The southern armyworm (SAW) Spodoptera eridania (Stoll) (Lepidoptera: Noctuidae) is native to tropical Americas where the pest can feed on more than hundred plant species. SAW was recently detected in West and Central Africa, feeding on various crops including cassava, cotton, amaranth and tomato. The current work was carried out to predict the potential spatial distribution of SAW and four of its co‐evolved parasitoids at a global scale using the maximum entropy (Maxent) algorithm. RESULTS SAW may not be a huge problem outside its native range (the Americas) for the time being, but may compromise crop yields in specific hotspots in coming years. The analysis of its potential distribution anticipates that the pest might easily migrate east and south from Cameroon and Gabon. CONCLUSION The models used generally demonstrate that all the parasitoids considered are good candidates for the biological control of SAW globally, except they will not be able to establish in specific climates. The current paper discusses the potential role of biological control using parasitoids as a crucial component of a durable climate‐smart integrated management of SAW to support decision making in Africa, and in other regions of bioclimatic suitability. This article is protected by copyright. All rights reserved.
... The change in precipitation activities where minor rainy seasons appears to exceed major rainy season in precipitation and humidity is largely due to heightened seasonal variability as a result of climate change. Botha et al. [25] argue that climate change prediction models forecast changes in rainfall patterns and rising temperature regimes, negatively impacting soil chemical characteristics and food security. Jansson and Hofmockel [26] found that warmer temperatures during some seasons are predicted to result in increased microbial mineralization of stable soil organic matter and a corresponding increased CO2 flux. ...
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Depending on soil, climate and crop characteristics exposed subsoils can be amended with gypsum for agricultural activities when topsoil is inadequate as a result of natural and geophysical activities. To determine how exposed subsoil amendment with gypsum interact with weather patterns to influence soil chemical properties, cucumber growth, fruit characteristics and heavy metal concentration, a two-seasonal experiment was conducted in the major and minor rainy season of 2020 in the Ahafo-Kenyasi Mining Area in Ghana. The experiment was laid out as a 6x2 factorial arranged in randomized complete block design, consisting of 6 gypsum application rates (20 ton/ha, 40 ton/ha, 60 ton/ha, 80 ton/ha, 0 ton/ha (subsoil control) and 0 ton/ha (topsoil control)) in two rainy seasons and replicated three times. The results show that gypsum application and rainy seasons interact to significantly influence soil chemical properties, cucumber growth and fruit characteristics. Increasing gypsum application resulted in decreased organic carbon, increased calcium, increased available P, increased exchangeable magnesium (Mg), increased pH during both major and minor rainy seasons. Vine length, number of leaves, number of fruits per plant and fruit weight of cucumber were increased with increasing gypsum application during the minor rainy season. In spite of exceeding permissible limits in soils and crops, arsenic (As), cadmium (Cd) and mercury (Hg) showed similar concentrations (below 2 mg/kg) in cucumber during the minor and major rainy seasons across gypsum treatments. Lead (Pb) concentration in cucumber was significantly higher in the major season across treatments. There was no difference in lead (Pb) concentration for treated vs untreated, and no increase across the amendment range. Further studies on how heavy metals in soil and plants interact with phytochemicals in ecosystems and living tissues are recommended.
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The food security challenge is one of the most topical issues of the 21st Century. Sub-Saharan Africa (SSA) is the least food-secure region, and solutions are constantly being sought to alleviate the problem. The region’s exponentially growing population is in dire need of affordable and nutritious food. The “Gene Revolution” (genetic engineering) presents opportunities in which food security can be ensured in SSA. Genetic modification (GM) has potential to solve myriad problems currently being experienced in SSA agriculture, hence improving yields and reducing the costs of production. Most of the SSA countries have a precautionary stance towards GM crops; thus, only a handful of countries have approved the commercialized production of transgenic crops. The lack of understanding and sound knowledge about the GM system is reflected in the formulation of policies and regulatory frameworks for biosafety and their implementation. There is need to conscientize the policymakers and the public about the general principles of genetic engineering for better decision making. Considering the multiple beneficial aspects demonstrated by transgenic crops it will not be prudent to ignore them. The versatility of GM technology makes it adaptable to the food crisis in SSA.
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The recent invasion of Africa by fall armyworm, Spodoptera frugiperda, a lepidopteran pest of maize and other crops, has heightened concerns about food security for millions of smallholder farmers. Maize genetically engineered to produce insecticidal proteins from the bacterium Bacillus thuringiensis (Bt) is a potentially useful tool for controlling fall armyworm and other lepidopteran pests of maize in Africa. In the Americas, however, fall armyworm rapidly evolved practical resistance to maize producing one Bt toxin (Cry1Ab or Cry1Fa). Also, aside from South Africa, Bt maize has not been approved for cultivation in Africa, where stakeholders in each nation will make decisions about its deployment. In the context of Africa, we address maize production and use; fall armyworm distribution, host range, and impact; fall armyworm control tactics other than Bt maize; and strategies to make Bt maize more sustainable and accessible to smallholders. We recommend mandated refuges of non-Bt maize or other non-Bt host plants of at least 50% of total maize hectares for single-toxin Bt maize and 20% for Bt maize producing two or more distinct toxins that are each highly effective against fall armyworm. The smallholder practices of planting more than one maize cultivar and intercropping maize with other fall armyworm host plants could facilitate compliance. We also propose creating and providing smallholder farmers access to Bt maize that produces four distinct Bt toxins encoded by linked genes in a single transgene cassette. Using this novel Bt maize as one component of integrated pest management could sustainably improve control of lepidopteran pests including fall armyworm.
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