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The use of weeds as insectary plants is an emerging management tactic by agroecologists to sustain beneficial insect species. Fallow lands have always been used by insects, and are an important part of their diet in fragmented ecosystems. Weeds provide nectar and floral resources to beneficial insects, and provide resources to keep those insects within a field in between flowering events. Using weeds as a tool in agricultural production reliant on pollination allows farmers to increase yield, end herbicide use, and increase biodiversity of both plants and insects. Native weeds expand the range of native insects from natural areas into agroecosystems, supporting insects that buffer against lapses in pollination by agricultural honey bees. Weeds also support parasitoid and predatory insects by providing nectar and pollen to adults, as well as alternative prey. This review examines the plant-insect ecological interactions supported by weeds left within a farm, and their potential role in supporting pollinators and parasitoids.
Corresponding author, email: (Blaire M. Kleiman).
Journal of Research in Weed Science Volume 3 Issue 3 (2020), pp 382-390
Journal of Research in Weed
Journal homepage:
Review Article
Weeds, Pollinators, and Parasitoids-Using Weeds for Insect
Manipulation in Agriculture
Blaire M. Kleiman a,*, Andrea Salas Primoli b, Suzanne Koptur b, Krishnaswamy Jayachandran a
a Department of Earth and Environment, Florida International University, 11200 SW 8th St, Miami, FL, 33199. USA.
b Department of Biological Sciences, Florida International University, 11200 SW 8th St, Miami, FL, 33199, USA.
Received: 3 January 2020
Revised: 16 January 2020
Accepted: 15 Febuary 2020
Available online: 17 Febuary 2020
DOI: 10.26655/JRWEEDSCI.2020.3.9
The use of weeds as insectary plants is an emerging management tactic by
agroecologists to sustain beneficial insect species. Fallow lands have always
been used by insects, and are an important part of their diet in fragmented
ecosystems. Weeds provide nectar and floral resources to beneficial insects, and
provide resources to keep those insects within a field in between flowering
events. Using weeds as a tool in agricultural production reliant on pollination
allows farmers to increase yield, end herbicide use, and increase biodiversity of
both plants and insects. Native weeds expand the range of native insects from
natural areas into agroecosystems, supporting insects that buffer against lapses
in pollination by agricultural honey bees. Weeds also support parasitoid and
predatory insects by providing nectar and pollen to adults, as well as alternative
prey. This review examines the plant-insect ecological interactions supported
by weeds left within a farm, and their potential role in supporting pollinators
and parasitoids.
Cultivated crops are often subject to pest pressure, a major focus of agricultural entomological
research for the last century. There is a growing interest in environmentally sound pest control,
using beneficial insects rather than pesticides, and this approach holds much promise for increasing
food production and growing healthy crops without harmful chemicals in foods and the
environment. The presence of non-crop plants may be very useful in this approach, and weeds can
provide resources that attract and maintain populations of parasitoids, predators, and pollinators.
The role of weeds in agriculture as a tool for insect management is an emerging topic of inquiry in
agroecology, with multifaceted theories and varied results.
Kleiman et al. 383
In this review, we examine the possibility that weeds (defined as wild, unwanted plants) can be
used in agriculture to increase floral resources for both pollinators and parasitoid insects.
Parasitoids benefit the crop by reducing pest insects, and pollinators increase pollination and crop
yield. Just as insects disappear with the disappearance of their weeds, they can also reappear when
their weeds return (Pickett and Bugg, 1998). The principles of Integrated Pest Management (IPM)
in manipulating weeds to increase predators and parasitoids for plant protection can also
simultaneously benefit pollination services. we focus here on studies of parasitoids and pollinators,
types of insects overshadowed by the focus on predators in the current literature on weed-insect
interactions. we will also review the variety of issues and further areas of study in the new field of
weed-insect interactions in agriculture.
There are various hypotheses that can help in understanding the interactions of weeds and
insects, and why on a case by case instance, results vary from pest reduction to exacerbating pest
populations. The “Resource Concentration Hypothesis” states the relative attractiveness of a habitat
to a particular insect is based on the concentration of resource host plants or prey species. Weeds
can dilute the concentration of the predominant crop plant, and therefore the attractiveness of the
crop to its pests. This hypothesis is based on the concept of “Apparency”- hosts that are more
apparent are more likely to be attacked (Castagneyrol et al. 2013). Crop host plants more apparent
to herbivores are more likely to be fed upon, and therefore weeds can alter crop “apparency”, and
act as a sort of camouflage against pests.
The “Enemies Hypothesis” states that having more diverse plant habitats supports a greater
diversity of prey insects, and thus more stable populations of natural enemies. Monocultures of
crop plants are easily detected and exploited by their herbivores, which are more easily diverted
and confused in a varied environment (Andow, 1991). The “Diversity Stability Hypothesis” states
that increasing species diversity in an ecosystem results in increased stability. Pest outbreaks are
less likely to occur in highly diverse ecosystems due to increased diversity and numbers of enemies.
Weeds increase biodiversity, which increases the diversity of natural enemy insects available to
prey on crop pests. Increasing diversity, therefore, is a pest management method, one increasingly
studied in crop management. Parasitic wasps of pests, for example, have increased fecundity due to
nectar obtained from weeds, and are supported by immature arthropods living on the weeds
(Pavuk and Stinner, 2017). These beneficial insects naturally suppress pest populations, and may
enhance agricultural output and quality.
These theories support the premise to study the utility of weeds, and warrant future research to
investigate their potential benefit in various crop systems. Previous work has shown increased
Weeds, Pollinators, and Parasitoids-Using Weeds 384
success of beneficial parasitoid insects in the presence of weeds, as beneficial insects use nectar or
pollen during their adult life stage to increase life span and fecundity (Norris and Kogan, 2000).
Similarly, pollinators can have their populations greatly bolstered in the presence of weeds, and
have been shown to have a unique relationship with them (Kremen et al. 2002).
Parasitoid Insects
Parasitoid insects, the majority of which are wasps, are used as biological control of pests as they
lay their eggs inside of a host to feed on and ultimately kill. Establishment of parasitoids in farms is
enhanced by the presence of weeds that provide nectar to adult female wasps (Altieri and Nicholls,
2018), and pest outbreaks are generally less common in the presence of weeds due to increased
mortality by natural enemies. Tolerable weed levels enhance these beneficial insects, without
reducing crop yield.
Some studies have shown the success of parasitoids with more floral resources. Parasitism rates
of armored scales by Encarsia citrina increased over time in the presence of floral resources,
through incremental growth of parasitoid populations and immigration in response to increased
floral resources (Rebek et al. 2006). Similarly, while both hosts and parasitoids feed on shared
floral resources, when exposed to common flowering plants, parasitoids benefited eight times more
than their leaf-mining hosts (Kehrli and Bacher, 2008). In maize fields, parasitism by Trichogramma
chilonis of Helicoverpa armigera eggs was positively correlated to the proportion of non-crop
habitat diversity and other host crops (Liu et al. 2016). Increasing agricultural intensity and loss of
biologically diverse habitat would have great reductions in the presence and parasitism of T.
Weeds adapted to local environments were found to provide similar resources to common
insectary plants, like alyssum, to significantly increase whitefly parasitoids longevity, egg load, and
fecundity (Araj et al. 2019). Native weeds, therefore, have the potential to act as insectary plants
when growing companion plants isn’t possible, or can add to the variety of diets for parasitoids.
Weeds, then, can greatly bolster the establishment and success of parasitoids.
Weeds can provide alternative prey, that are not crop pests, to parasitoids as well. A study on the
parasitoid of grape leafhoppers, Anagrus, showed that they overwinter on adjacent habitat to
vineyards (Provost and Pedneault, 2016). The vegetation within and around the vineyard provided
alternate prey for the parasitoid that isn’t a crop pest, and kept this parasitoid in the field between
seasons. Similarly, European corn borer infestations were decreased in the presence of weeds.
Parasitoids of this pest were supported by moth species living on the weeds in corn fields (Pavuk
Kleiman et al. 385
and Stinner, 2017). Weeds both provide food for beneficial insects as well as provide oviposition
(egg laying) sites. There are better egg survival rates when oviposited on weeds than the crop. In
the absence of prey for the larvae of predatory lady beetles, Coleomegilla maculata oviposits on
weeds rather than the crop, and as a result the eggs had better survival through less predation and
parasitism (Cottrell and Yeargan, 1998). Weeds, therefore, can be a reservoir of alternative prey,
and by living on weeds, parasitoids also protect crop yields by reducing pests.
Pollinators are an important, and sensitive, group of insects that can rebound greatly in the
presence of floral resources, or alternatively be diminished when they are lacking. There is a
pollinator decline crisis in areas of intensive farming, with fewer and fewer pollinators, and
increasing agricultural reliance on them. The use of herbicides to reduce weeds limits the
availability of nectar provided by plants for pollinators (Altieri and Nicholls, 2018). Agroecosystems
have thwarted the opportunity for co-evolution of insects and plants, with massive synchronous
blooms of a single species, and vegetational simplification of large expanses of land. This lack of
wild plant floral resources within a farm or adjacent to it before and after the crop blooms can
cause a decline in pollinators, due to a lack of support when the crop isn’t in bloom. Pollinators can
use weeds as alternative resources before, during, and after the bloom of a crop, and increase crop
yields if given these resources (Carol and David, 1997). Decline in pollinators is interlinked with
weed and habitat decline, through increased applications of pesticides and fertilizers (Nicholls and
Altieri, 2013), and the expansion of monocultures.
Native bees are important, yet often overlooked, insects in agriculture. The contribution in the
United States of wild pollinators is between $49-310 million, with no cost to farmers for this
ecosystem service. Farms near natural habitats containing native bees see them provide full
pollination services, without the use of managed honey bees (Kremen et al. 2002). Resident
pollinators are healthiest with 15 or more flowering species providing a season-long food supply
(Willmer, 2011), and refuges with weeds can provide this floral diversity, while helping alleviate
the pollinator decline crisis. Use of adjacent habitats can ameliorate large losses of habitat for
pollinators, but if the farm is too large (>5 ha), native pollinators cannot spill over and penetrate
into farms (Nicholls and Altieri, 2013). That is why creating strips or pockets of flowering weeds
within farms, especially monocultures, can benefit native pollinators (Pickett and Bugg, 1998).
Most farms operate in isolated areas, so that restoring vegetation helps provide floral resources
and nesting habitat to native pollinators. Increasing diversity of native bees can buffer against low
populations of European honey bees (Kremen et al. 2002). During seasonal fluctuations of crops
Weeds, Pollinators, and Parasitoids-Using Weeds 386
and pollinator needs, native pollinators can provide a substantial portion of crop pollination,
provided the farm in near natural habitat. In farms near natural areas, native bee communities were
found to provide full pollination services, even for watermelon, a crop with heavy pollination
requirements (Kremen et al. 2002). Ecosystem service arguments align with conserving
biodiversity arguments, and increasing diversity with weeds can begin this increased diversity
within farms.
Weeds are resilient, hardy plant species. Agricultural intensification leads to decreased
landscape biodiversity for plants and insects, making weeds a significant part of the remaining
floral diversity. Weeds are generally ambophilous, both insect-and wind-pollinated, which
promotes genetic diversity and adaptation to environmental disturbances. This generation of gene
flow and environmental plasticity allows successful persistence of weeds in arable landscapes.
Increased habitat diversity and patches of unmanaged habitat reduces extinction rates of weeds,
through increased genetic variability and species richness (Rollin et al. 2016). There is an
evolutionary trend in agroecosystems of de-specialization of plant-pollinator networks, lowering
the risk of pollinator absence due to disturbance. Mutualistic pollination networks are key
ecological processes, and their stability depends on many links between species. The frequency of
rare weeds in farmlands is an indicator of the stability of a community, as their presence is in part
due to pollinators, which are the slowest to recover after high levels of agricultural intensity (Rollin
et al. 2016).
Mass flowering of crops alters floral availability temporarily, changing pollinator preferences
and the stability of wild networks. The use of local weeds in farmed land safeguards pollinator
diversity and the specialized links between pollinators and specific weeds. It also buffers against
possible lapses in pollination by the European honeybee, a troubled species (Paudel et al. 2015), by
ensuring native bee health and range in farmland. This link between plants and insects, and the
presence of native weeds, can serve as indicators of the biodiversity of arable lands.
Using weeds as an insect management tool is a relatively new area of study, and there is still
much debate as well as unanswered questions to be evaluated further. The issue of hyperparasitism
underscores biological control programs, illuminated through the resource concentration
hypothesis. Increased concentrations of crops (host plants) in weed-free plots leads to a greater
density of pests. This may send signals and attract parasitoids and hyperparasitoids into weed-free
plots, where their host resource (the pest arthropods) is more concentrated. This effect could
perhaps negate the benefits of weeds, should weed-free plots have increased parasitism of crop
Kleiman et al. 387
pests. Without the presence of a hyperparasitoid, Aphidius ervi, a biological control agent of aphids,
eliminated their populations in a controlled test. However, A. ervi itself was eliminated by a
hyperparasitoid, Asaphes suspensus, within seven generations (Schooler et al. 2011). This
phenomenon, however, contrasts with what actually happens in field surveys, in which the
hyperparasitoid doesn’t entirely eliminate the primary parasitoid, due to disturbances. Small
primary parasitoid populations, however, are particularly susceptible to hyperparasitism (Schooler
et al. 2011).
Another vein of debate that needs further research is the idea that weeds providing nectar to
beneficial insects also can provide resources to crop damaging pests, and may even attract
beneficial insects away from the crop. Similarly, the movement between weeds and different crops
by individual beneficial insect species is rarely quantified, but assumed to occur (Norris and Kogan,
2000). Increased fecundity of pests has been observed when weeds were present, due to nectar
obtained by the adults, which leads to the question on the utility of leaving weeds as a source of
nectar for beneficial insects (Shields et al. 2019). Additionally, weeds need to provide alternative
prey sources (arthropods) that are not crop pests, seen successfully done in the study of leafhopper
parasitoids of vineyards (Provost and Pedneault, 2016). A similar study found some genera of aphid
pests on weeds attack crop plants, while the majority of other aphid species did not. They did,
however, represent a good source of food for aphid eating predators and parasitoids, and can act as
alternative prey when crop aphid populations are low (Pickett and Bugg, 1998). Alternatively,
controlling or eradicating weeds to manage pests causes the issue that the weeds may also be
supporting beneficial insects; therefore, monitoring of insect pests hosted by weeds can allow
managers to anticipate problems. This approach, to understand movements of pests between
weeds and crops, has not yet been solidified, and may prove a useful management technique.
The economic value of field margins and weeds as refuge for pollinators to agricultural
productivity is relatively unknown, and few farmers manage this vegetation to enhance beneficial
insects. Therefore, managing flowering weeds at tolerable levels to provide alternative resources
for pollinators within farms is an overlooked habitat management tactic. Native pollinators can
provide free pollination services, and further studies on their requirements and success can help
provide solutions to the pollinator decline crisis. There are some economic questions left
unanswered in this burgeoning field that need to be addressed before farmers can successfully use
weeds to manage insects. Information is needed on how increased numbers of beneficial insects
affect certain pests, and the economic data of overall impacts on crop yields when trying to
manipulate types of insects. The critical period of interference between specific weeds and crops is
Weeds, Pollinators, and Parasitoids-Using Weeds 388
likely to differ with crops and regions, and is still unknown; it is important to determine when the
benefits of added pollination to crops may outweigh crop interference of weeds for certain species.
Farmers need to know when there are enough weeds to support pollinators and predators, but not
pull nutrients and interfere with their crop’s production.
The effects of granivorous beetles like carabid beetles on weed seed banks is similarly unknown
(Collins et al. 2002). Carabid, or ground beetles are primarily used as insect predators, but they can
also have negative impacts on weed populations. They consume the weed seedbank in the soil,
decreasing the number of subsequent weeds. Beetles, however, are effective predators that can
easily move over long distances, meaning weed strips cannot be seen as a crucial pest reservoir
(Pickett and Bugg, 1998). This should also be evaluated when assessing carabids use in insect pest
Overall, the use of weeds in increasing beneficial insects has shown promise (Araj et al. 2019; Provost
and Pedneault 2016; Kremen et al. 2002; Pickett and Bugg 1998). The varying hypotheses dictating the
potential for increasing these insects number through increasing plant diversity, and the success of
some studies in proving that, show that this merits further study. While this approach may not always
prove a success, studies need to be done for specific crop species, regions where they are grown, and
varying combinations of weed species, to learn how these variables affect insect ecological dynamics.
These, in turn, must be quantified economically, through increased pollination and less pest damage, to
gain insight on the feasibility of implementing this across various crop monocultures. This review shows
that studies are limited by the lack of big picture insights as to the behavior of insects, and how
anthropogenic influences can shift certain types of species dramatically. By increasing parasitoids and
pollinators, inevitable interactions between these and other species can occur, and should be studied in
agricultural regions, as natural systems vary greatly. Overall, our insights are still limited, and the best
management practices moving forward are to quantify the economic ramifications of shifts in insect
populations accompanying the increased habitat complexity provided by weeds.
The primary author acknowledges her support from USDA-NIFA-HSI, grant number 2015-
38422-24075. Thanks to Dr. Cara Rockwell for her support, and Dr. Michael S. Ross and Dr. Jennifer
Rehage for their constructive comments.
Conflicts of Interest
Authors declare no conflict of interest.
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... Other investigations have highlighted that alien plant species and subsequent novel ecosystems can create contemporary roles that maintain native biodiversity in a world depleted of many native keystone species (Carlos et al. 2014). Alien plant species have been shown to maintain native pollinators, supply nectar, food and shelter for native animals and their indiscriminate removal can adversely affect wildlife (Carlos et al. 2014;Chandrasena 2014;Bretagnolle and Gaba 2015;Kleiman et al. 2020). Thus, the wholesale eradication of alien plant species with the aim to reintroduce indigenous vegetation can result in local extinction of native species with flow on effects through trophic levels (van Riel et al. 2000;Zavaleta et al. 2001;Rodríguez 2006;Hunter and Hunter 2017). ...
Aeolian sand dunes on the Broughton Island are heavily disturbed by nesting birds and invaded by Opuntia stricta (Prickly Pear). Biological control agents do not establish well on exposed coastal systems and thus herbicide treatment is currently the main control, but it is expensive in terms of resource allocation. Invasive species are generally considered by many to be controlled at all cost but in many situations, they are benign or even beneficial. We test if O. stricta causes significant change to the vegetation on aeolian sands on Broughton Island. 40100 m 2 plots were placed randomly over areas of differing cover of O. stricta. Within these plots additional six subplots of 4 m 2 were placed. All flora species were scored for cover. Univariate and multivariate analyses were performed testing the effects of O. stricta on floristic composition and species density and turnover. Regression models showed a non-significant (r 2 ¼ 0.95; P ¼ 0.0557) negative effect of O. stricta cover on species density at the 100 m 2 plot size and at the 4 m 2 scale (r 2 ¼ 0.013; P ¼ 0.0858). Global comparison of species density between plots with and without O. stricta at the 4 m 2 scale was non-significant. Homogenisation occurred (lowered beta diversity) across plots with O. stricta presence at the 4 m 2 scale. More species had their average cover reduced by O. stricta presence than those that were benefited. The scale at which the investigation was undertaken (4 or 100 m 2 ; species density and beta diversity) affected the magnitude and significance of O. stricta on the results obtained. The scale at which investigations are made was found to be of importance. Overall, although negative changes were noted in flora species diversity and homogenisation was apparent the negative impact may not be sufficient to justify the costs and resources needed to control the species which is unlikely to be eradicated from the site.
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Agricultural intensification has been implicated in global biodiversity declines. In the European Union, agri‐environmental schemes are designed to address this. For pollinating insects, funding has been provided to sow wildflower mixes. However, previous research indicates that a suite of agricultural weeds are also of great importance to pollinators. Here, we compare the biodiversity associated with the species which are considered harmful to agricultural production and legally deemed as ‘injurious’ by the United Kingdom 1959 Weeds Act (common ragwort Jacobaea vulgaris, creeping thistle Cirsium arvense, spear thistle C. vulgare, curled dock Rumex crispus and broadleaved dock R. obtusifolius), with plant species recommended for pollinator‐targeted agri‐environmental options. In our field study, the abundance and diversity of pollinators visiting the weed species averaged twice that of the recommended plants and included the main insect orders (Coleoptera, Diptera, Hymenoptera and Lepidoptera). This relationship was also seen in a meta‐analysis of literature data, which indicates that fourfold more flower‐visitor species and fivefold more conservation‐listed species are associated with the weeds. Additionally, the literature shows that twice the number of herbivorous insect species are associated with these plants. We suggest that several factors are responsible for this pattern. Injurious weed species are widely distributed, their flower morphology allows access to a wide variety of pollinator species, and they produce, on average, four times more nectar sugar than the recommended plant species. Freedom of information requests to public bodies such as local councils, Natural England and Highways England indicate that c. £10 million per year is spent controlling injurious weeds. Meanwhile, the cost of the four pollinator‐targeted agri‐environmental options in the United Kingdom exceeds £40 m annually. Synthesis and applications. Our results clearly show that weeds have an underappreciated value to biodiversity. Unfortunately, current UK agricultural policy encourages neither land sparing for nor land sharing with weeds. The UK government is, however, currently committed to overhauling agricultural payments to encourage more wildlife‐ and climate‐friendly practices. Thus, the challenge of reconciling the conflicts between agricultural production and these native and biodiverse species should be a renewed priority to land managers, researchers and policymakers. Our results clearly show that weeds have an underappreciated value to biodiversity. Unfortunately, current UK agricultural policy encourages neither land sparing for nor land sharing with weeds. The UK government is, however, currently committed to overhauling agricultural payments to encourage more wildlife‐ and climate‐friendly practices. Thus, the challenge of reconciling the conflicts between agricultural production and these native and biodiverse species should be a renewed priority to land managers, researchers and policymakers.
Agricultural production is increasingly viewed as more than a source of food, feed, fiber and fuel, but also as a system of interdependent biotic and abiotic components that interact to produce ecosystem services and disservices. Weeds and insects are commonly viewed as non-desirable components of agroecosystems that should be managed. However, weeds can also provide benefits to cropping systems, such as providing resources and habitat to pollinators and other beneficial arthropods. This review on weed–insect interactions in annual cropping systems focuses on functional interactions within the context of regulating and supporting ecosystem services and disservices. Regulating services are those that act as regulators of the environment, such as weed–insect interactions that contribute to the regulating services of pollination and biological control, but also contribute to the disservices of crop and cover crop seed predation, and maintenance of insect pests and insect-transmitted phytopathogens. Supporting services include habitat and biodiversity that are necessary for the production and maintenance of the other types of ecosystem services. Here we review the impacts of weed–insect interactions as a component of biodiversity. We conclude by identifying some knowledge gaps that hinder our understanding of trade-offs when seeking to improve net positive ecosystem services in annual cropping systems.
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We deployed >50,000 Helicoverpa armigera eggs in maize fields to assess the rate of parasitism by Trichogramma chilonis across 33 sites during a three-year span (2012–2014) in northern China. Subsequently, we used a partial least squares (PLS) regression approach to assess the relationship of landscape diversity with composition and parasitism potential. The parasitism rate of H. armigera eggs by T. chilonis ranged from 0–25.8%, with a mean value of 5.6%. Landscape diversity greatly enhanced parasitism at all four different spatial scales (0.5, 1.0, 1.5 and 2.0 km radius). Both the proportion of arable area and the total planting area of two major crops (cotton and maize) had a negative correlation to the parasitism rate at each scale, whereas parasitism was positively correlated to the proportion of host crops of H. armigera other than cotton and maize at the 0.5 to 2.0 km radius scales as well as to that of non-crop habitat at the 0.5 and 1.0 km radius scales. The study indicated that maintaining landscape diversity provided an important biocontrol service by limiting H. armigera through the egg parasitoid T. chilonis, whereas rapid agricultural intensification would greatly reduce the presence and parasitism of T. chilonis in China.
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European honey bees (Apis mellifera L.) are important pollinators of many fruits, nuts, vegetables and field crops. Honey bees also pollinate different wild flowering plants and help to maintain the ecosystems. Currently, these pollinators are facing a number of threats including habitat destruction, pesticides, mites, parasites and loss of genetic diversity. Because of the decline in their number, there is a great loss of ecological services which impacts the world's economy. This review of honey bee and pollination issues highlights the need of protection and conservation of these important pollinators. Research is required to quantify the synergistic effects of potential drivers for current colony loss and to identify the ecotypes and native species of honey bees which are more resistant to pests, pathogens and pesticides.
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Thirty-five percent of global production from crops including at least 800 cultivated plants depend on animal pollination. The transformation of agriculture in the past half-century has triggered a decline in bees and other insect pollinators. In North America, losses of bee colonies have accelerated since 2004, leaving the continent with fewer managed pollinators than at any time in the past 50 years. A number of factors linked to industrial modes of agriculture affect bee colonies and other pollinators around the world, ranging from habitat degradation due to monocultures with consequent declines in flowering plants and the use of damaging insecticides. Incentives should be offered to farmers to restore pollinator-friendly habitats, including flower provisioning within or around crop fields and elimination of use of insecticides by adopting agroecological production methods. Conventional farmers should be extremely cautious in the choice, timing, and application of insecticides and other chemicals. Here, we review the literature providing mounting evidence that the restoration of plant biodiversity within and around crop fields can improve habitat for domestic and wild bees as well as other insects and thus enhance pollination services in agroecosystems. Main findings are the following: (1) certain weed species within crop fields that provide food resources and refuge should be maintained at tolerable levels within crop fields to aid in the survival of viable populations of pollinators. (2) Careful manipulation strategies need to be defined in order to avoid weed competition with crops and interference with certain cultural practices. Economic thresholds of weed populations, as well as factors affecting crop–weed balance within a crop season, need to be defined for specific cropping systems. (3) More research is warranted to advance knowledge on identifying beneficial weed species and ways to sponsor them to attract pollinators while not reducing yields through interference. (4) In areas of intensive farming, field margins, field edges and paths, headlands, fence-lines, rights of way, and nearby uncultivated patches of land are important refuges for many pollinators. (5) Maintenance and restoration of hedgerows and other vegetation features at field borders is therefore essential for harboring pollinators. (6) Appropriate management of non-cropped areas to encourage wild pollinators may prove to be a cost-effective means of maximizing crop yield.
Weed floral resources are often overlooked in biological control manipulations, yet common species in this group can contribute to enhanced biological control efficacy. Weed floral resources may not be examined as frequently as certain insectary species (buckwheat). Furthermore, they may require less maintenance and are adapted to grow in the planted area. Here, we investigated the effects of weed and other non-crop floral resources on Eretmocerus mundus, a parasitoid of the whitefly, Bemisia tabaci, in the laboratory. The two common weeds evaluated were shepherd’s purse (Capsella bursa-pastoris) and white rocket (Diplotaxis erucoides). These were compared with buckwheat (Fagopyrum esculentum) and alyssum (Lobularia maritima). Adults of the above parasitoid were exposed to flowers of the selected plants and survived six times longer with buckwheat than those in the control (water only) and 2.8, 3.1 and four times longer with shepherd’s purse, rocket and alyssum, respectively. All plant species significantly increased parasitoid longevity, egg load and fecundity compared to the control. Buckwheat had the greatest effect on these parameters. Parasitism rate of the pest increased by up to 72.1%. This work illustrates that the selected non-buckwheat species could have value where buckwheat germination rate and phenology may be limiting such as in arid climates, for which this work was targeted.
Meeting the growing global demand for agricultural products requires the development and use of ecologically-based strategies that will allow sustainable intensification based on ecosystem services. An important component of this approach is conservation biological control. This approach encompasses a variety of management practices that protect natural enemy populations in the agro-ecosystem and enhance their fitness and ultimate impact on pests. It represents an alternative to dependence on pesticides which is associated with environmental damage and risks to human health. The interventions used to achieve conservation biological control are commonly based on managing vegetation patterns at the local scale (e.g. flowering strips that promote parasitoids by supplying nectar) or at wider scale (e.g., woodland to serve as donor habitat for natural enemies). Importantly, such vegetation management also offers scope to provide agriculture with additional ecosystem services as diverse as pollination and carbon sequestration. Despite these attractive features and the success of a small number of conservation biological control strategies, it remains underutilized. We identify as barriers to adoption the relative complexity of conservation biological control and challenges with economic evaluation, as well as perceptions and communication. Climate change is a challenge that will demand the development of flexible strategies that can respond to changes in pest distributions and/or food web structure.
Pollination and Floral Ecologyis the most comprehensive single-volume reference to all aspects of pollination biology--and the first fully up-to-date resource of its kind to appear in decades. This beautifully illustrated book describes how flowers use colors, shapes, and scents to advertise themselves; how they offer pollen and nectar as rewards; and how they share complex interactions with beetles, birds, bats, bees, and other creatures. The ecology of these interactions is covered in depth, including the timing and patterning of flowering, competition among flowering plants to attract certain visitors and deter others, and the many ways plants and animals can cheat each other.Pollination and Floral Ecologypays special attention to the prevalence of specialization and generalization in animal-flower interactions, and examines how a lack of distinction between casual visitors and true pollinators can produce misleading conclusions about flower evolution and animal-flower mutualism. This one-of-a-kind reference also gives insights into the vital pollination services that animals provide to crops and native flora, and sets these issues in the context of today's global pollination crisis.Provides the most up-to-date resource on pollination and floral ecologyDescribes flower advertising features and rewards, foraging and learning by flower-visiting animals, behaviors of generalist and specialist pollinators--and moreExamines the ecology and evolution of animal-flower interactions, from the molecular to macroevolutionary scaleFeatures hundreds of color and black-and-white illustrations.
Herbivore regulation is one of the services provided by plant diversity in terrestrial ecosystems. It has been suggested that tree diversity decreases insect herbivory in forests, but recent studies have reported opposite patterns, indicating that tree diversity can trigger associational resistance or susceptibility. The mechanisms underlying the tree diversity–resistance relationship thus remain a matter of debate.We assessed insect herbivory on pedunculate oak saplings (Quercus robur) in a large‐scale experiment in which we manipulated tree diversity and identity by mixing oaks, birch and pine species.Tree diversity at the plot scale had no effect on damage due to leaf chewers, but abundance of leaf miners decreased with increasing tree diversity. The magnitude of this associational resistance increased with host dilution, consistent with the ‘resource concentration hypothesis’.At a smaller scale, we estimated tree apparency as the difference in total height between focal oak saplings and their nearest neighbouring trees. Levels of oak infestation with leaf miners decreased significantly with decreasing tree apparency. As the probability of having taller neighbours increased with tree diversity, notably due to the increase in the proportion of faster growing nonhost trees, such as birches and pines, tree apparency may be seen as a ‘hidden’, sampling effect of tree diversity.Synthesis. These findings suggest that greater host dilution and lower tree apparency contribute to associational resistance in young trees. They also highlight the importance of taking plant size into account as a covariate, to avoid misleading interpretations about the biodiversity–resistance relationship.