Shade trees decrease pest abundances on brassica crops in Kenya

Abstract

Agroforestry practices may mitigate the current loss of biodiversity and ecosystem services due to deforestation and agricultural intensification. To examine the effects of agroforestry on the ecosystem service of pest regulation, we assessed pest abundances and biological control potential in shaded and open kale (Brassica oleracea L. acephala) fields in Western Kenya. Specifically, we compared the abundance of pest aphids and caterpillars, ground-dwelling ants, spiders and predatory beetles, and examined aphid parasitism rates, predation rates on diamondback moth eggs, attack rates on surrogate caterpillars and bird predation on aphids. Shade trees effectively reduced abundances of aphids, caterpillars and increased abundances of spiders and predatory beetles, but neither affected ant abundances, or predation and parasitism rates. Our results suggest that presence of shade trees can decrease pest abundances, but that this is not only due to improved biological control by natural enemies but also due to microclimatic conditions affecting pest performance and bottom-up processes such as changes in plant quality and soil conditions. We encourage studies exploring simultaneously how top-down and bottom-up processes affect pest regulation in agroforestry settings.

Cool shade and not‐so‐cool shade: How habitat loss may accelerate thermal stress under current and future climate

“…In the desert, rocks and vegetation play additional ecological roles beyond that of thermal shelter. In various ecological systems, rocks increase prey abundance and diversity (Borkhataria et al, 2012;Guenat et al, 2017;Johnson, 2000), reduce competition, foodsearching movement, and increase foraging efficiency (Attum & Eason, 2006;Belliure et al, 1996;Kearney et al, 2021), reduce escape distances from predators (Amo et al, 2007;Huey, 1991;Monasterio et al, 2010;Newbold & MacMahon, 2014;Pietrek et al, 2009), and reduce water loss (Rozen-Rechels et al, 2019). In desert habitats where rocks are less abundant (like sandy deserts), bushes, trees, and burrows may provide most of the shade (Cain et al, 2008) and protection from predation (Pietrek et al, 2009) and competition (Zeng et al, 2016); such habitats may be at risk due to novel warmer and drier climates (Kim et al, 2018;Levy, Buckley, et al, 2016b), invasive species (Garcia & Clusella-Trullas, 2019), and habitat loss (Estavillo et al, 2013).…”

Integrated Management Approach to Citrus Fungal Diseases by Optimizing Cocoa-Based Agroforests Structural Characteristics

“…This type of interaction is likely to influence the presence of diseases. The action of shade trees on the understory microclimate decreases with decreasing distance between trees and pathogen transmission decreases as the distance between host individuals increases [51,52,[57][58][59].…”

“…Shade trees play various roles in tropical agroforests. They can improve adverse weather conditions by modulating temperature variations [51,52,57,59]. Shading has been recognized as one of the factors that can influence PLFSD dissemination [54,67,68].…”

Agroforestry: An Appropriate and Sustainable Response to a Changing Climate in Southern Africa?

“…AFS has often been touted as a land-use system that can contribute to natural pest control, the increase in structural diversity can augment the functional biodiversity of the site, thus benefiting the natural antagonists of crop pests [161,162]. Recent research and meta-analyses have shown that trees in agricultural lands were likely to be providing refuge to insectivorous vertebrates and ground dwelling natural predators [162,163] although this is most likely pest species-dependent while also being dependent on crop and tree species combinations [161]. Meanwhile, it is also reported that the presence of trees does not necessarily increase the resilience of AFS against antagonists alone, but in combination with microclimatic conditions that influence pest performance, crop growth and soil conditions [163].…”

“…Recent research and meta-analyses have shown that trees in agricultural lands were likely to be providing refuge to insectivorous vertebrates and ground dwelling natural predators [162,163] although this is most likely pest species-dependent while also being dependent on crop and tree species combinations [161]. Meanwhile, it is also reported that the presence of trees does not necessarily increase the resilience of AFS against antagonists alone, but in combination with microclimatic conditions that influence pest performance, crop growth and soil conditions [163]. Further research and empirical study is needed to increase the understanding of the relationships between tree cover, food webs and natural pest suppression [161,162] with the development and testing of crop-pest modelling tools in multiple AFS systems of varying complexity.…”