Biology and management of economically important lepidopteran cereal stem borers in Africa.
ABSTRACT Cereals (maize, sorghum, millet, rice) are extremely important crops grown in Africa for human consumption. Of the various insect pests attacking cereal crops in Africa, lepidopteran stem borers are by far the most injurious. All 21 economically important stem borers of cultivated grasses in Africa are indigenous except Chilo partellus, which invaded the continent from India, and C. sacchariphagus, which has recently been found in sugarcane in Mozambique. C. partellus is competitively displacing indigenous stem borers in East and southern Africa. A parasitoid, Cotesia flavipes, was introduced from Pakistan for biological control of C. partellus and caused a 32-55% decrease in stem borer densities. This article is an attempt to summarize the status of knowledge about economically important cereal stem borers in Africa with emphasis on their distribution, pest status and yield losses, diapause, natural enemies, cultural control, host plant resistance, and biological control. Special attention is given to Busseola fusca and C. partellus, the most important pests of maize and grain sorghum.
- SourceAvailable from: Michael A Birkett[Show abstract] [Hide abstract]
ABSTRACT: Food insecurity is a chronic problem in Africa and is likely to worsen with climate change and population growth. It is largely due to poor yields of the cereal crops caused by factors including stemborer pests, striga weeds and degraded soils. A platform technology, 'push-pull', based on locally available companion plants, effectively addresses these constraints resulting in substantial grain yield increases. It involves intercropping cereal crops with a forage legume, desmodium, and planting Napier grass as a border crop. Desmodium repels stemborer moths (push), and attracts their natural enemies, while Napier grass attracts them (pull). Desmodium is very effective in suppressing striga weed while improving soil fertility through nitrogen fixation and improved organic matter content. Both companion plants provide high-value animal fodder, facilitating milk production and diversifying farmers' income sources. To extend these benefits to drier areas and ensure long-term sustainability of the technology in view of climate change, drought-tolerant trap and intercrop plants are being identified. Studies show that the locally commercial brachiaria cv mulato (trap crop) and greenleaf desmodium (intercrop) can tolerate long droughts. New on-farm field trials show that using these two companion crops in adapted push-pull technology provides effective control of stemborers and striga weeds, resulting in significant grain yield increases. Effective multi-level partnerships have been established with national agricultural research and extension systems, non-governmental organizations and other stakeholders to enhance dissemination of the technology with a goal of reaching one million farm households in the region by 2020. These will be supported by an efficient desmodium seed production and distribution system in eastern Africa, relevant policies and stakeholder training and capacity development.Philosophical Transactions of The Royal Society B Biological Sciences 01/2014; 369(1639):20120284. · 6.23 Impact Factor
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ABSTRACT: Volatile organic compounds derived from non-host plants, Ocimum basilicum, Rosmarinus officinalis, Corymbia citriodora, and Ruta graveolens, can be used to mask host plant odors, and are repellent to the tea geometrid, Ectropis obliqua. Volatile compounds were collected by headspace absorption, and the components were identified and quantified by using gas chromatography/mass spectrometry. The responses of antennae of female E. obliqua to the compounds were evaluated with gas chromatography/electroantennography detection. Qualitative and quantitative differences were found among the four odor profiles. Consistent electroantennographic activity was obtained for eight of the volatiles from the four plants: β-myrcene, α-terpinene, γ-terpinene, linalool, cis-verbenol, camphor, α-terpineol, and verbenone. In a Y-tube bioassay, six chemicals, β-myrcene, γ-terpinene, (R)-(-)-linalool, (S)-(-)-cis-verbenol, (R)-(+)-camphor, and (S)-(-)-verbenone, were the main compounds responsible for repelling E. obliqua. An eight-component mixture including all of the bioactive compounds (in a ratio of 13:2:13:8:1:24:6:17) from R. officinalis was significantly more effective at repelling the moths than any single compound or a mixture of equal amounts of the eight compounds. Field results demonstrated that intercropping tea plants with R. officinalis effectively suppressed E. obliqua infestations in a tea plantation. Our findings suggests that odor blends of R. officinalis play a role in disturbing host orientation behavior, and in repelling E. obliqua adults, and that R. officinalis should be considered when developing "push-pull" strategies aimed at optimizing the control of E. obliqua with semiochemicals.Journal of Chemical Ecology 09/2013; · 2.46 Impact Factor
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ABSTRACT: Current population genetic models fail to cope with genetic differentiation for species with large, contiguous and heterogeneous distribution. We show that in such a case, genetic differentiation can be predicted at equilibrium by circuit theory, where conductance corresponds to abundance in species distribution models (SDM). Circuit-SDM approach was used for the phylogeographic study of the lepidopteran cereal stemborer Busseola fusca Füller (Noctuidae) across sub-Saharan Africa. Species abundance was surveyed across its distribution range. SDM models were optimized and selected by cross validation. Relationship between observed matrices of genetic differentiation between individuals, and matrices of resistance distance was assessed through Mantel tests and redundancy discriminant analyses (RDA). A total of 628 individuals from 130 localities in 17 countries were genotyped at 7 microsatellite loci. Six population clusters were found based on a Bayesian analysis. The eastern margin of Dahomey Gap between East and West Africa was the main factor of genetic differentiation. The SDM projections at present, last interglacial and last glacial maximum periods were used for estimation of circuit resistance between locations of genotyped individuals. For all periods of time, when using either all individuals or only East-African individuals, partial Mantel r and RDA analyses conditioning on geographic distance were found significant. Under future projections (year 2080), partial r and RDA significance were different. From this study, it is concluded that analytical solutions provided by circuit theory are useful for the evolutionary management of populations and for phylogeographic analysis when coalescence times are not accessible by approximate Bayesian simulations.Molecular Ecology 03/2014; · 6.28 Impact Factor
Annu. Rev. Entomol. 2002. 47:701–31
Copyright c ? 2002 by Annual Reviews. All rights reserved
BIOLOGY AND MANAGEMENT OF ECONOMICALLY
IMPORTANT LEPIDOPTERAN CEREAL STEM
BORERS IN AFRICA
1ARC-Plant Protection Research Institute, Private Bag X134, Pretoria 0001,
South Africa; e-mail: email@example.com
2International Centre of Insect Physiology and Ecology, P.O. Box 30772,
Nairobi, Kenya; e-mail: firstname.lastname@example.org; email@example.com
3CABI Bioscience UK Centre, Entomology Department, Imperial College at
Silwood Park, Ascot, Berkshire SL5 7PY United Kingdom; e-mail: firstname.lastname@example.org
maize, diapause, competition, pheromones, cultural control, biological
grown in Africa for human consumption. Of the various insect pests attacking cereal
crops in Africa, lepidopteran stem borers are by far the most injurious. All 21 eco-
nomically important stem borers of cultivated grasses in Africa are indigenous except
has recently been found in sugarcane in Mozambique. C. partellus is competitively
displacing indigenous stem borers in East and southern Africa. A parasitoid, Cotesia
a 32–55% decrease in stem borer densities. This article is an attempt to summarize
the status of knowledge about economically important cereal stem borers in Africa
with emphasis on their distribution, pest status and yield losses, diapause, natural ene-
mies, cultural control, host plant resistance, and biological control. Special attention is
given to Busseola fusca and C. partellus, the most important pests of maize and grain
Cereals (maize, sorghum, millet, rice) are extremely important crops
INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 702
STEM BORERS AND THEIR DISTRIBUTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . 702
DIAPAUSE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 704
DISPLACEMENT OF NATIVE STEM
BORERS BY C. PARTELLUS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 706
INDIGENOUS NATURAL ENEMIES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 707
Parasitoids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 707
Predators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 707
Nematodes and Pathogens . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 707
KFIR ET AL.
PEST STATUS AND YIELD LOSSES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 708
MANAGEMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 709
Utilization of Synthetic Sex Pheromones . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 709
Cultural Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 710
Intercropping and Habitat Management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 711
Management of Crop Residues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 712
Manipulation of Sowing Dates and Densities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 714
Fertilizer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 715
Host Plant Resistance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 715
Breeding for Resistance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 716
Biological Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 716
is also an important cash crop grown in some areas. The crops are grown primarily
far the most injurious (224). Because of their economic importance, stem borers
have been the subjects of many studies, which resulted in an enormous amount
of literature. This review summarizes the status of knowledge about cereal stem
borers in Africa.
STEM BORERS AND THEIR DISTRIBUTION
Maes (105) listed 21 economically important lepidopteran stem borers of culti-
21 species, 7 are primarily pests of rice, and one mainly attacks pearl millet in the
Sahelian region. Among the noctuids, Busseola fusca and six Sesamia spp. are
considered economically important. Two pyralids are serious pests: the rice borer,
Maliarpha separatella, and Eldana saccharina, a pest of sugarcane and maize.
The largest group (12 species) of injurious stem borers are crambids, with the ma-
jority (7 species) belonging to the genus Chilo Zincken. Within specific crops and
geographic regions, fewer species are considered to be important pests (Table 1).
In South Africa, B. fusca and Chilo partellus are the only important stem
borers of maize and sorghum (94), while in sugarcane in the same region, only
E. saccharina is considered to be a serious pest (47). In East Africa, C. partellus,
Chilo orichalcociliellus, E. saccharina, B. fusca, and Sesamia calamistis are men-
tioned as important and widely distributed stem borers of maize and sorghum
(168). Major stem borers of maize and sorghum in West Africa include B. fusca,
most important cereal crop, Coniesta ignefusalis is the dominant stem borer (73).
AFRICAN STEM BORERS
distributions, and major cultivated host plants
Important stemborer species in Africa and the Indian Ocean Islands, their
FamilySpecies DistributionHost plantsReference
eastern and southern
coastal eastern, Malawi,
West and Central
Indian Ocean Islands;
maize, sorghum, rice
Information on rice stem borers is primarily from West Africa and the Indian
Ocean Islands, as these are areas where rice is an important food crop. Chilo
zacconius, M. separatella, and S. calamistis are considered the most economically
important stem borers of rice in West Africa (13,37). M. separatella is the only
rice borer that has a widespread distribution in sub-Saharan Africa, and it also
occurs in the Comoro Islands and Madagascar (37). Other rice stem borers of
and Sesamia nonagriodes botanephaga (37,38). Additionally, Chilo aleniellus is
reported to be a rice stem borer in Ivory Coast (189,190).
Two of the economically important cereal stem borers in Africa are introduced
species: C. partellus and C. sacchariphagus. C. partellus is an Asian species
(29) that invaded Africa sometime before 1930 when it was first recorded in
Malawi (186), but it was not reported again until some 20 years later in Tanzania
(53). The distribution of C. partellus now includes Ethiopia, Sudan, Somalia,
Kenya, Tanzania, Uganda, Mozambique, South Africa, Swaziland, Lesotho,
Zimbabwe, Zambia, Malawi, and Botswana (41,71,79,127). Using GIS tools,
Overholt et al. (145) predicted the eventual distribution of C. partellus in Africa
based on the climate at locations where it was known to occur and then extrap-
olating to other locations with similar climates. The prediction included several
countries in southwestern and West Africa where C. partellus is not yet known to
KFIR ET AL.
The other invasive species, C. sacchariphagus, is a serious pest of sugarcane
in the Indian Ocean Islands. C. sacchariphagus may have been accidentally in-
troduced into the islands either from Sri Lanka or Java with the introduction of
sugarcane around 1850 (222). There are recent confirmed reports of C. saccha-
riphagus attacking sugarcane in Mozambique (209).
others are found throughout sub-Saharan Africa. C. orichalcociliellus, a pest of
maize and sorghum, occurs in coastal East Africa, Malawi, and Madagascar at
altitudes below 600 m (51,108,127). C. aleniellus has been reported as a pest of
rice in West and Central Africa and more recently as an important pest of maize
in Ivory Coast (120). C. ignefusalis is the dominant stem borer of millet in the
Sahelian zone of West Africa (69).
grasses and sedges (23,45,61,78). In southern Africa, E. saccharina is a major
pest of sugarcane but rarely causes damage in maize (177). In contrast, E. sac-
charina is considered to be a pest of maize, sugarcane, and rice in West Africa
B. fusca and Sesamia spp. occur throughout subsaharan Africa (79). Of the
Sesamia spp., S. calamistis is the most widely distributed and economically im-
portant species, but several others, including S. cretica, which occurs in Somalia,
Sudan, and Ethiopia, and S. nonagrioides botanephaga, which is found in both
East and West Africa, are also important. As with E. saccharina, the pest status
of B. fusca varies by region. In East and southern Africa it is a pest at higher alti-
tudes (>600 m) (127,178), but in West Africa, B. fusca occurs from sea level to
>2000 m (187) but is primarily a pest in the dry savanna zone (68).
Many cereal stem borers have a resting period toward the end of the cropping
eral months in the dry season (130,161,163). However,S. calamistis was reported
not to enter diapause in Uganda (78) or in Nigeria (68). In West Africa, B. fusca
enters diapause during the dry season, and it takes up to six months to complete
development. With the initiation of the rains, the larvae pupate within the stems,
and 10–12 days later adult moths emerge (68). Similar observations were made
on C. ignefusalis, which has a facultative diapause in dry millet stems (226).
cold dry season (April–September), in the lower parts of the dry stalks, where they
are well protected from natural enemies and adverse climatic conditions (83–85).
B. fusca diapauses throughout its distribution in Africa, whereas C. partellus does
not diapause in the warm low-lying regions of the South African Provinces of
Kwazulu-Natal (203) and Mpumalanga (R. Kfir, unpublished data), Swaziland
AFRICAN STEM BORERS
(218), and southern Mozambique (27). In regions where there is an abundance of
host plants and the climate is warm, C. partellus normally develops continuously
all-year round. In other regions with long dry periods in winter or in summer, the
borer enters into a resting period. C. partellus was reported to diapause in the dry
season in India (187) and on several islands off the coast of Africa (39,51). How-
ever, populations without a resting period were reported from the Coast Province
lus found in the dry season on the Kenya Coast and at lower elevations in South
Africa. In the coastal area of Kenya, in periods between cropping seasons, some
stem borers diapause in maize stubble, whereas others remain actively feeding in
wild grasses, such as Napier grass, in the proximity of cultivated areas (124).
An increase in carbohydrates and decrease in protein and water of the food
plant are the main factors inducing diapause in B. fusca (193). Dry condition of
the host plant (127) and the general deterioration of the nutritive environment
(51,160) induced diapause in larvae of C. partellus even when climatic conditions
were favorable for development (161). Diapause could be artificially induced in
nondiapause larvae introduced into aged maize stems.
During diapause, larvae of B. fusca and C. partellus progressively decreased in
weight and had up to seven additional stationary molts. The longer time the larvae
remained in diapause, the lighter in weight the emerging adults were, with fewer
eggs and oocytes in their ovaries. After eight months in diapause, emerging adults
that emerged from nondiapausing larvae (86).
of time they were kept in the laboratory at 21◦C and 60% relative humidity. Lar-
vae of C. partellus collected in April–June emerged in November, whereas those
collected in July emerged in October and those collected in August emerged in
September. Regardless of the collection date, C. partellus started to emerge from
Kfir (85) concluded that B. fusca had an obligatory diapause and C. partellus a
facultative diapause. In the field, C. partellus starts to emerge from diapause in
the second part of August, and it continues until the first week of November, a
period of 12 weeks. In contrast, B. fusca pupates only during October–November
(83,85,95). This difference in the pattern of emergence from diapause by the two
lapping generations of C. partellus (85,205) occurring every year in South Africa.
Conditions of continuous moisture during the long rainy season in Kenya play
a significant role in the termination of diapause by B. fusca (135,137). Rain-
fall alone did not appear to be the main factor (192). Contact with water was a
more significant factor in diapause termination than water uptake (136). Applica-
tion of water or rainfall played an important role in promoting pupation during
postdiapause dormancy of B. fusca in Ethiopia (59) and Ivory Coast (119). De-
lay in wetting larvae after diapause and access to water early in diapause had a
KFIR ET AL.
deleterious effect on the larvae. The main factor enabling diapausing B. fusca
larvae to survive adverse conditions appears to be efficient water conservation
A combination of temperature and photoperiod played an important role in
termination of diapause in B. fusca in South Africa, and water was important
as a stimulus for morphogenesis following diapause (89). Long days accelerated
termination of diapause in C. partellus, but under 16-h daylight, termination of
diapause was faster than when under constant illumination. In contrast, tempera-
ture, relative humidity, and day length did not affect diapause of C. partellus and
C. orichalcociliellus in Kenya (161). C. partellus collected in South Africa at
25◦38?S, 27◦47?E (90) is more affected by day length than the Kenyan population
located near the equator. Kfir (89,90) suggested that the right combination of day
length and temperature could be used for breaking diapause to provide large num-
bers of insects for artificial infestations for plant-resistance trials. This requires
only simple facilities and can save the large expense of keeping a continuous
culture in the laboratory on artificial diet.
DISPLACEMENT OF NATIVE STEM
BORERS BY C. PARTELLUS
The invasive stem borer, C. partellus, has proved to be a highly competitive col-
onizer in many of the areas it has invaded in eastern and southern Africa, often
becoming the most injurious stem borer (93,163) and displacing native species
(92,141). In coastal Kenya, there is evidence that C. partellus has partially dis-
placed the indigenous stem borer, C. orichalcociliellus (130–132, 141). However,
C. orichalcociliellus continues to be found at a relatively high frequency (10–
30% of the borer complex), which suggests that the displacement of C. orichal-
cociliellus will not proceed to extirpation (228). Recent investigations have found
that C. orichalcociliellus completed development in two native grasses, in which
C. partellus could not develop (131), which may be one factor that allows their
ment of native stem borers in two other areas in Africa. In the Eastern Province
of Kenya, C. partellus was present in the early 1980s but was less abundant than
B. fusca (163). However, in the same area in the period 1996–1998, B. fusca was
rare and C. partellus was dominant (183). Similarly, in the eastern Highveld re-
gion of South Africa, C. partellus partially displaced B. fusca over a period of
seven years (92). The displacement was most evident in grain sorghum where the
proportion of C. partellus in the total stem borer population increased from about
3% in 1986 to 91% in 1992.
Several factors have been investigated that may be responsible for the competi-
a generation in less time than C. orichalcociliellus (101,131), which may result
AFRICAN STEM BORERS
in a higher population growth rate. Moreover, C. partellus terminates diapause
more rapidly than C. orichalcociliellus (130) or B. fusca (92), which may allow C.
partellus to colonize host plants before the two native species at the beginning of
growing seasons. Kfir (92) speculated that B. fusca avoids plants already infested
by C. partellus, using odors associated with host plant feeding. Ofomata (129)
showed that when equal numbers of C. partellus and C. orichalcociliellus infest
the same maize, sorghum, or wild-sorghum plant, more C. partellus successfully
more neonate C. partellus larvae dispersed from the plant where they hatched, and
they dispersed greater distances than C. orichalcociliellus, which may allow C.
partellus to colonize more plants than the native borer (129).
INDIGENOUS NATURAL ENEMIES
The indigenous parasitoids associated with African cereal stem borers have been
treated in Polaszek (150). All stem borer parasitoids belong to either the
Hymenoptera or Diptera. Their effectiveness in keeping stem borer populations
below acceptable thresholds has been doubted by several authors (93,142). How-
ever, no studies are yet available that examine the effect of the absence of par-
asitoids on stem borer populations. Recent investigations (R. Kfir, manuscript
submitted) into the effects of removal or partial removal of parasitoids from stem
There have been a number of studies of the effectiveness of indigenous predators
on several borer species in the past decade (30,31,93,103,162). Virtually all
studies have concluded that indigenous predators are not able to keep stem borer
populations below economic injury levels (31,162).
Nematodes and Pathogens
have been summarized recently (149). These authors also provided summaries for
the study and identification of these agents. In doing so, they also concluded that
Knowledge concerning viruses associated with African cereal stem borers has
been reviewed (128). Iridoviruses, granulosis viruses, cytoplasmic viruses, and
nuclear polyhedrosis viruses are known to attack and kill borer larvae in Africa,
but no detailed studies have been conducted.
KFIR ET AL.
PEST STATUS AND YIELD LOSSES
Feeding and stem tunneling by borer larvae on plants results in crop losses as a
consequence of destruction of the growing point, early leaf senescence, interfer-
ence with translocation of metabolites, and nutrients that result in malformation
of the grain, stem breakage, plant stunting, lodging, and direct damage to ears
(18,33,36,94). Infestations by stem borers increase the incidence and severity of
stalk rots (33).
In South Africa, estimated yield losses from B. fusca damage ranges between
10% and total loss (24,106,109,206). Yield loss in maize by B. fusca was signif-
icantly correlated with leaf damage, but a higher correlation was observed with
stem-boring damage (24). The estimated yield losses due to C. partellus in maize
and sorghum exceed 50% (153). A positive correlation between infestation level
populations using artificial infestation on sorghum indicated that C. partellus was
more injurious than B. fusca (200,201). More damage by C. partellus was ob-
served on long-season, grain-sorghum cultivars because of exposure over a longer
period in the susceptible preflowering stages (199).
In Lesotho, seasonal variation in yield loss due to B. fusca damage on maize
ranged between 0.4% and 36.6% (55). In Mozambique, larvae of third-generation
C. partellus, the most important stem borer, were reported to infest 87% of cobs of
late-planted maize and to severely damage 70% of grain (27). Infestations of up to
100% of plants, with considerable yield losses, have been recorded in the Maputo
and Gaza Provinces (125), the Limpopo Valley (27), and in southern Mozambique
In Zimbabwe, C. partellus caused yield loss of 50–60% in sorghum (178).
In maize, borer infestations range from 30% to 70% in fields of resource–poor
farmers but are less than 30% in commercial farms where insecticides are used
(177). In Tanzania (215) and Kenya (216), loss of about 12% maize grain for
every 10% plants infested by B. fusca were reported. In Kenya, 18% yield losses
were attributed to C. partellus and C. orichalcociliellus in maize (217) and 88%
in sorghum owing to C. partellus (165).
Maximum stalk damage in maize and up to 80% grain yield loss in sorghum
by C. partellus were observed in Kenya on 20-day-old crops, whereas similar
In Tanzania, Jepson (81) reported 40–100% sorghum plants infested by B. fusca,
whereas in Ethiopia movement of B. fusca larvae into the base of the sorghum
head resulted in undersized heads and grain loss of 15% (112).
AFRICAN STEM BORERS
of Sesamia sp. larvae and the extent of damage to maize stems, and a negative re-
lationship between damage to maize stems and maize yield were shown (64). The
calculated yield loss caused by Sesamia sp. to maize in the rain forest coastal, de-
rived, and Guinea ecological zones were 27%, 15%, 18%, and 14%, respectively
(64). In Burundi, insecticides and exclusion-cage trials indicated maize yield re-
ductions of 12–15% by E. saccharina and 30–50% by B. fusca (121). In Burkina
Faso and Niger, yield loss in sorghum by C. partellus and in millet by C. igne-
fusalis was estimated by using carbofuran to protect the crops and by infesting the
crops at different growth stages. The highest grain yield was obtained when the
crop was protected between 15 and 30 days after emergence; artificial infestation
at 15 days after emergence resulted in the greatest damage. The infestation in un-
protected sorghum plots was 60–62% (188). Stem borer control in sorghum in the
southern Guinea savanna of Nigeria, where S. calamistis predominates, improved
yields by 16–19% (1), whereas in the northern Guinea savanna, where B. fusca
and unsprayed sorghum in 22 farmers’ fields were studied in Nigeria, and a mean
yield loss of 21% was determined (11). Yield loss in sorghum depends on the time
of infestation (12). Sorghum infested by B. fusca before the booting stage suffered
greater yield losses (110). Proportion of internodes bored in the lower part of the
stalk had a more consistent negative correlation with grain yield than did propor-
tion of stem tunneled (110). A recent study in Cameroon found that stem borers,
and caused an 11% loss of plants owing to deadheart (43).
Utilization of Synthetic Sex Pheromones
Pheromone-baited traps are useful devices for monitoring moth population levels
of stem borers. Trap catches of male moths can provide useful information for
the timing of insecticide applications (154,208,210). Campion & Nesbitt (42)
reviewed the progress in the identification and the utilization of sex pheromones
for stem borer monitoring and concluded that mass trapping is unlikely to provide
satisfactory control but that mating disruption is more likely to be effective. Syn-
Chilo auricilius and C. zacconius have shown satisfactory attractiveness to male
moths in the field (25). Sex pheromones for B. fusca, C. partellus, S. calamistis,
(95,96) revealed that the first flight resulting from moths emerging from hiber-
nating borers peaked about the middle of November. The second flight, usually
larger, peaked in the second half of February; a third flight, which occurred in
KFIR ET AL.
Mpumalanga Province, peaked around the middle of April. No catches of moths
were recorded during winter (June–September). Larval peaks of B. fusca in the
field lagged about 4–6 weeks behind the corresponding moth flight peaks (95,96).
Omni-directional traps were superior to delta traps for quantitative and qualitative
estimation of B. fusca moth populations (95,96,207).
tions in the field are required before trapping C. partellus can be used to determine
economic threshold levels.
A slow-release pheromone formulation gave high levels of communication
disruption in B. fusca when applied at 40 g a.i. ha−1as 250 or 500 point sources
ha−1(49). This effect was observed to persist for at least 18 weeks and from
release rate studies was predicted to last for 6 months. In field trials in Kenya,
some reduction in damage levels was observed, indicating that mating disruption
had occurred (49).
Various methods of cultural control of stem borers in Africa have been reviewed
(102,113,164,166,196). It is the most relevant and economic method of stem
borer control available for resource-poor farmers in Africa. Other control options
cultivars are not widely available, and biological control of stem borers is only
partially successful. Cultural control is among the oldest traditional practices and
normally cannot be used as a tactical means of control (52). Cultural control is
considered the first line of defense against pests and includes techniques such as
dates, and tillage methods (196). The latter three agronomic practices can directly
affect crop yield (52). Many cultural control practices are labor intensive, but they
have little adverse effects on the environment and are readily available without
extra investment in equipment.
However, an understanding of stem borers’ behavior and the relationships with
their respective crops are important for the development of efficient management
strategies. The differences in the behavior of E. saccharina in South and eastern
Africa provide an example of the importance of understanding pest behavior in
making control decisions. In South Africa, larvae of E. saccharina mainly infest
lower parts of sugarcane stalks. It is recommended that farmers cut stalks low
and leave the tops, which are then cut off and left in the field. In East Africa, on
the other hand, recommendations are to not leave tops of plants in fields because
E. saccharina larvae largely occur in upper-plant parts, and these residues would
house the carryover population (196).
most African farmers have not adopted them (126). Cultural control is severely
constrained by the lack of management capabilities of farmers, especially in areas
where farming communities lack the support of an adequate extension service
AFRICAN STEM BORERS
Intercropping and Habitat Management
Intercropping or mixed cropping has been widely practiced for centuries by small-
scale farmers in Africa to reduce risk of crop failure, attain higher yields, and
improve soil fertility (155,196). Although some of these practices also lead to
suppression of cereal stem borer populations, no studies have shown that farmers
grow specific intercrops to exploit this effect. Many field studies have been con-
ducted in Africa during the past two decades in an effort to identify the best crop
combinations for reducing stem borer populations on cereal crops.
Studies in Kenya have concentrated both on the practice of intercropping cow-
be adopted by small-scale farmers in eastern Africa (16,138,148,162). Most con-
cluded that intercropping reduced the incidence of stem borers. In West Africa,
maize, millet, and sorghum intercropping were studied (3,57,82). Maize/cassava-
intercropping systems in Nigeria reduced by half larval numbers of E. saccharina,
B. fusca, and S. calamistis populations (82). Many of these intercropping studies
did not seek to determine the underlying mechanisms behind the effect of inter-
cropping on stem borer population levels. Intercropping maize with cowpea was
an effective way of reducing damage caused by C. partellus larvae migrating from
neighboring plants (146,148). This finding was confirmed by the reports that 30%
of C. partellus oviposition in maize/sorghum/cowpea-intercropping systems was
on cowpea, and the number of larvae reaching host plants from cowpea decreased
with distance (15,16).
A recent study from Kenya has reported the effectiveness of intercropping
maize with the nonhost molasses grass, Melinis minutiflora (98,99). In field tri-
als, molasses grass showed no colonization by stem borers, and when used as an
intercrop with maize, it significantly reduced stem borer infestation of the main
crop. A significant increase in parasitism of stem borers by the larval parasitoid
Cotesia sesamiae was also observed. Volatile agents produced by the molasses
grass repelled stem borers but attracted foraging C. sesamiae. Female C. sesamiae
were attracted to (E)-4, 8-dimethyl-1,3,7-nonatriene, one of the volatile compo-
nents released by intact molasses grass. Nonatriene has been implicated as an
SOS signal for recruiting predators and parasitoids and is also produced by stem
borer–damaged maize plants. Intact plants with an inherent ability to release such
as an effective cover crop, the molasses grass provides good fodder for livestock.
The grass is now being tested in on-farm trials in Kenya to control stem borers on
Another useful diversionary tactic for stem borer control is planting an outer
encircling row of some highly preferred host to act as a trap plant. Napier grass,
Pennisetum purpureum, and Sudan grass, Sorghum vulgare sudanense, common
fodder plants in Africa, were reported from Kenya to provide natural control to
stem borers by acting as trap plants (99,100). Although the stem borers oviposit
heavily on the attractive Napier grass, only few larvae complete their life cycles
(76). Napier grass has its own defense mechanism against crop borers. When the
KFIR ET AL.
larvae enter the stem, the plant produces a gummy substance that causes the death
of the pest (76). In on-farm trials in Kenya, planting Napier grass around maize
fields significantly increases crop yields by reducing the stem borer population in
maize. Sudan grass, also a fodder grass, provided natural control of stem borers
by acting as a trap plant and as a reservoir for its natural enemies (99). In field
trials conducted in Kenya, planting Sudan grass around maize fields decreased
grass around maize field also increased efficiency of natural enemies.
For the control of stem borers in resource-poor, maize farming systems in
eastern Africa, novel habitat-management strategies have been developed using
“push-pull” or stimulo-deterrent diversionary tactics (100). These strategies in-
a push-pull strategy, are Napier grass, Sudan grass, molasses grass, and silverleaf
desmodium, Desmodium uncinatum. Napier grass and Sudan grass are used as
trap plants, whereas molasses grass and silverleaf desmodium repel ovipositing
stem borers. Molasses grass, when intercropped with maize, not only reduced in-
festation of the maize by stem borers but also increased stem borer parasitism by
a natural enemy, C. sesamiae (98). All four plants are of economic importance to
farmers in eastern Africa as livestock fodder.
The economic gain from the use of intercrops depends on the balance between
a lowered cost of control of stem borers and the increased cost of maintaining an
intercropped field, along with any decrease in yield of the main crop from greater
balance between income and costs. Economic data assessing the financial returns
as well as the biological effects are therefore most useful in making decisions on
the use of intercrops and trap plants for stem borer control.
Management of Crop Residues
Crop residues are important for carrying over stem borer larval populations from
one growing season to the next. In Nigeria, larvae of B. fusca, E. saccharina,
and S. calamistis were found in crop residues below the soil surface, and higher
incidences of these borers were observed in no-tillage plots (82). In Kenya,
C. orichalcociliellus, C. partellus, E. saccharina, and S. calamistis were observed
to mulch the next crop (115). Under these conditions, borers from the old stalks
constantly infested the newly planted crops.
An effective control option would be to reduce the first generation of adult
population by destroying the larvae in old stalks (78,84,97,192). Ploughing in
order to bury maize stubble was an effective control measure used early in the
twentieth century in South Africa to control B. fusca (106). In Zimbabwe, it was
AFRICAN STEM BORERS
observed that B. fusca moths emerging through 5 cm of soil were crippled and
that deeper burial of the stalks under 10–15 cm of soil ensured that no adult moths
226,000 larvae overwinter per hectare (84). Slashing maize and sorghum stubble
destroyed 70% of C. partellus and B. fusca populations, and additional plough-
ing and disking destroyed a further 24% of the pest population in sorghum and
19% in maize (84,97). Tillage may reduce borer populations through mechanical
damage either by burying them deeply into the soil or by breaking the stems and
system is not widely practiced in South Africa because of the advent of minimum
tillage and the importance of winter grazing of maize to beef farmers (88,95).
In rural Africa, farmers often use dry stems of maize, sorghum, and millet for
building houses and fences, as fuel, bedding for livestock, boundaries of terraces
on slopes, and as stakes (68,156,161). Farmers normally stack dry stalks in the
field where they are kept until commencement of rains before being taken to vil-
lages, thus creating a reservoir for infestation in the following season (196). To
solve this problem, early cutting of stalks and horizontal placement on the soil
surface has been recommended. This was observed to cause mortality of 97% of
stem borers in maize and 100% in sorghum in Ethiopia (58) and to reduce the
residual population of borers in millet from 16% in uncut stems to 3% (227). The
high level of mortalities of C. partellus, C. orichalcociliellus, and S. calamistis in
horizontally placed stalks was ascribed to the effects of sun and heat, more specif-
ically, the reaching of the thermal threshold for survival (147). On the other hand,
in Nigeria, the control of S. calamistis, B. fusca, C. ignefusalis, and E. saccha-
rina on maize by removing stalks and stubble after harvest did not reduce stem
borer populations significantly apparently because of migration of adults into the
immediately after harvest has been recommended (8,68,80,192). In Tanzania,
almost complete eradication of C. partellus on maize and sorghum was achieved
by burning (53). About 95% of farmers in Nigeria kept sorghum stalks and did
not follow the recommended practice of burning them after harvest (4). As a
compromise, partial burning was recommended while the leaves are dry but the
stalks are not (4,8). Heat generated from the burning leaves kills up to 95% of
larvae and at the same time cures the stalks, making them stronger as building
materials and more resistant to termite attack (4,12). Crop residues are the only
organic matter added into soils in many small-scale African farms. Burning crop
residues can create problems in farms where the organic content of soils is low
and soil erosion from wind and rain is severe (196).
KFIR ET AL.
Manipulation of Sowing Dates and Densities
Growing crops when the pest is least abundant ensures that the most susceptible
the February–May period, when infestation is normally low. There is no available
information on the effectiveness of these measures, and the last implementation
of this legislation was in 1937–1938 (72).
Several workers have reported more damage by stem borers to late-planted maize
(62,64), Nigeria (5,44,68), and Zaire (77). Thus, in some areas of West Africa
This affects the borer populations in the rain forest zone where alternative wild
host plants in the dry season are scarce (34). This strategy is also desirable in the
semi-arid tropics, where rainfall is variable and unpredictable; late sowing is not
desirable because the yield of late sown crops is low, even if free from stem borers
In the Highveld region of South Africa, the second-generation population B.
fusca is larger and can cause more damage than the first generation (211). The
best strategy to reduce damage would be to plant early in the growing season.
Similar observations were made in Lesotho (55), Zimbabwe (179), and Ethiopia
where second-generation larvae caused crop losses of 22.5–100% compared with
0–22.6% by first generation (60).
In the lower elevations of South Africa, it is recommended that sorghum
be planted after mid-October to avoid infestation from the first moth peak of
season was more infested by B. fusca than maize sown later. In Malawi, planting
date influenced infestation levels of B. fusca and C. partellus on sorghum; how-
ever, the choice of optimum sowing date depends on the sorghum cultivar (111).
In contrast, in the Sahelian region, manipulating the planting dates of millet is not
a good method to reduce infestation by C. ignefusalis (227).
Sowing density may affect the crop and its pest population, as well as the
behavior of the pest in searching for food or an oviposition site (102). Young
C. partellus migrate from their hatching site to the funnel leaves or to other plants
within the vicinity. During this migration, up to 100% mortality may occur (108).
The lowest incidence of deadheart caused by B. fusca occurred at the lowest
plant density in sorghum in South Africa (198) and maize in Nigeria (134). A
reduction in row width increased the number of larvae able to reach adjacent plant
rows through migration, and this in turn resulted in more damaged plants (211).
B. fusca larvae migrate up to 2.4 m (68) and at a 0.9 m interrow spacing, which is
common in commercial agriculture; they migrated over 4 rows from the hatching
AFRICAN STEM BORERS
E. saccharina damage (118). Studies on C. partellus in maize planted at different
densities (56) and on C. ignefusalis in millet (57) showed no significant difference
in oviposition or borer incidence.
In subsistence farming systems in Africa where farmers normally intercrop
cereals with other crops and lack of water is a major constraint, manipulation of
sowing dates and management of plant densities is not always practical as farmers
often plant after first rains (196). Farmers’ choice of sowing dates is affected by
many constraints, and it is unlikely that a change in sowing date alone will result
in higher sustainable yields (126).
increased with the application of fertilizer (191), and in South Africa sorghum
plants without fertilizers were less preferred for oviposition by C. partellus (197),
in the survival of S. calamistis larvae and acceleration in larval development with
in the number of generations per year (171).
Nitrogen fertilization enhances borer development as well as the plant’s toler-
ance to borer attack. Yield losses decreased linearly from 20% with no fertilizer
to 11% with 120 kg of nitrogen per hectare (172). Ajayi (10) observed that time of
that the manipulation of time of nitrogen application may achieve a compromise
between using low levels of nitrogen for low stem borer infestation and using high
levels for better yields.
Host Plant Resistance
Host plant resistance as an approach to pest management in gramineous crops
confers many advantages (34). Resistant crop varieties provide an inherent con-
trol that involves no environmental problems, and they are generally compatible
with other insect-control methods. The cultivation of resistant crop plants is not
subject to the vagaries of weather as are chemical-control measures, and in certain
circumstances it is the only effective means of control. Resistant varieties control
even a low pest density, whereas insecticide use is justifiable only when the den-
sity reaches the economic injury level. Efforts are underway in Africa to identify
sources of stem borer resistance in cereal crops, but high levels of resistance have
not been found.