Abstract
The change from predominantly natural to agricultural landscapes has been shown to reduce pollination and biological control services and also affect the functional traits of the insects ...that provide such services. Research shows that increasing agricultural area at the landscape scale can have variable effects on functional traits such as body size in predators. Moreover, local factors such as farm management strategies have also been shown to affect functional traits in insects. Studies of local or landscape effects on functional traits are often contradictory in temperate regions, and absent from tropical regions. In Kenya, local pest management technologies, e.g. push–pull systems have been shown to increase biological control, but data is lacking on how local management could affect body size of natural enemies. We investigated how the proportion of natural areas in the landscape and local management (push–pull) affected the body size of rove beetles (Staphylinidae) in Kenyan maize fields. Elytral and pronotal measurements were used to quantify body size, and a mixed-effects model was used to test the effect of landscape complexity and local management on the body size, richness, and abundance of rove beetles. We found no effect of landscape composition or local management on body size, richness, or abundance of rove beetles. We hypothesize that the lack of landscape effects could be caused by less plasticity in functional traits in tropical versus temperate zones. Our results demonstrate that changes in land use and local management do not always lead to changes in the diversity and functional traits of predator communities.
Plants can alter nutritional availability, structure, and chemistry of the soil they grow in. These soil changes can positively or negatively influence the growth and metabolism of other plants that ...co-occur or grow later in the conditioned soil. Plant-soil feedbacks could affect community interactions and dynamics but also be applied in sustainable agriculture to promote plant growth and resistance to pests. In this study, we use a maize companion cropping system, commonly known as “push-pull,” as a model to investigate soil-mediated effects of functional biodiversity, on maize plant growth, and resistance against insect herbivores. We grew maize in soils collected from push-pull (polyculture) and non-push-pull (monoculture) fields. We evaluated maize performance by measuring plant growth, as well as resistance traits (herbivore oviposition and larval feeding, production of defense-related volatile, and non-volatile secondary defense metabolites). Maize plants grown in soil conditioned by push-pull companion cropping had a higher growth rate compared to those grown in soil from non-push-pull monoculture fields. In addition, soil from push-pull fields induced a constitutively higher and qualitatively different emission of volatile organic compounds than soil from non-push-pull fields. Moreover, secondary defense metabolites such as 2,4-dihydroxy-7-methoxy-2H-1,4-benzoxazin-3(4H)-one (DIMBOA), were produced in larger quantities in plants grown in soil from push-pull fields compared to those from monoculture fields. These soil-mediated alterations in plant secondary metabolism were associated with reduced herbivory by larvae of the stemboring pest Chilo partelllus. This study provides novel evidence that plant-soil feedbacks can affect plant metabolism, growth, and resistance to pests. The observed soil-mediated effects on maize plant secondary metabolism can be viewed as emergent properties of plant community composition as well as a potent mechanism of associational resistance. In addition, these soil-conditioning effects provide a novel pest control mechanism of push-pull companion cropping.
Assessing effects of climate change on agricultural systems and the potential for ecological intensification to increase food security in developing countries is essential to guide management, ...policy-making and future research. ‘Push-pull’ technology (PPT) is a poly-cropping design developed in eastern Africa that utilizes plant chemicals to mediate plant–insect interactions. PPT application yields significant increases in crop productivity, by reducing pest load and damage caused by arthropods and parasitic weeds, while also bolstering soil fertility. As climate change effects may be species- and/or context-specific, there is need to elucidate how, in interaction with biotic factors, projected climate conditions are likely to influence future functioning of PPT. Here, we first reviewed how changes in temperature, precipitation and atmospheric CO2 concentration can influence PPT components (i.e., land use, soils, crops, weeds, diseases, pests and their natural enemies) across sub-Saharan Africa (SSA). We then imposed these anticipated responses on a landscape-scale qualitative mathematical model of maize production under PPT in eastern Africa, to predict cumulative, structure-mediated impacts of climate change on maize yield. Our review suggests variable impacts of climate change on PPT components in SSA by the end of the 21st century, including reduced soil fertility, increased weed and arthropod pest pressure and increased prevalence of crop diseases, but also increased biological control by pests’ natural enemies. Extrapolating empirical evidence of climate effects to predict responses to projected climate conditions is mainly limited by a lack of mechanistic understanding regarding single and interactive effects of climate variables on PPT components. Model predictions of maize yield responses to anticipated impacts of climate change in eastern Africa suggest predominantly negative future trends. Nevertheless, maize yields can be sustained or increased by favourable changes in system components with less certain future behaviour, including higher PPT adoption, preservation of field edge density and agricultural diversification beyond cereal crops.
•Push-pull technology (PPT) improves cereal yield based on agroecological principles•We review future climate change impacts on PPT components across sub-Saharan Africa•Anticipated PPT component responses are imposed on a holistic model of maize yield•Predictions are negative, but reversible through PPT & agricultural diversification
Farmers looking to maximize ecosystem services often use diversification practices on their fields to increase abundance and diversity of insect natural enemies. These practices affect functional ...traits of natural enemies such as body size that can play an important role in their effectiveness as biological control agents. However, landscape features out of the control of farmers might also affect functional traits of natural enemies and their herbivores, including land use surrounding farms. There have been few studies elucidating how landscape complexity and local diversity interact to affect functional traits, and ultimately ecosystem services such as predation on herbivore pests. We examined combined effects of landscape complexity and a local management practice (push‐pull) on lady beetle size, and its consequences for egg predation of lepidopteran pests in Kenyan smallholder maize farms. Cheilomenes sulphurea (Olivier) (Coleoptera: Coccinellidae), a potential predator of the invasive fall armyworm, Spodoptera frugiperda J.E. Smith (Lepidoptera: Noctuidae), was collected in push‐pull and control fields along a landscape gradient. We measured beetle size and conducted feeding assays with fall armyworm eggs. We found that female beetles had larger bodies in landscapes with greater complexity. Predation rates not only increased as a response to beetle size but also in response to landscape complexity, suggesting it is not just size that determines predation. Surprisingly, we did not find any effect of the local management practice or its interaction on functional traits or predation rates. Our study suggests that landscape complexity could benefit pest control through two mechanisms: (1) increase in predator body size, leading to higher predation rates; and (2) changes in predator behavior as a function of landscape characteristics – increasing egg predation. Further studies on these mechanisms would allow deeper understanding of landscape simplification's effect on ecosystem services, as mediated by morphological and behavioral traits, and help us harness these traits to increase biological control.
We examined effects of landscape complexity and local management practice (push‐pull) on predator size Cheilomenes sulphurea (Coleoptera: Coccinellidae), and its consequences for egg predation of Spodoptera frugiperda (Lepidoptera: Noctuidae), in Kenyan smallholder maize farms. Female beetles were larger in more complex landscapes. Predation rates increased in response to beetle size and landscape complexity. Our study suggests landscape complexity may benefit pest control through (1) increased predator size (i.e., greater predation), and (2) changes in predator behavior as a function of landscape characteristics.
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