Contrasting effects of landscape composition on crop yield mediated by specialist herbivores

Abstract

Landscape composition not only affects a variety of arthropod-mediated ecosystem services, but also disservices, such as herbivory by insect pests that may have negative effects on crop yield. Yet, little is known about how different habitats influence the dynamics of multiple herbivore species, and ultimately their collective impact on crop production. Using cabbage as a model system, we examined how landscape composition influenced the incidence of three specialist cruciferous pests (aphids, flea beetles, and leaf-feeding Lepidoptera), lepidopteran parasitoids, and crop yield across a gradient of landscape composition in New York, USA. We expected that landscapes with a higher proportion of cropland and lower habitat diversity would lead to an increase in pest pressure of the specialist herbivores and a reduction in crop yield. However, results indicated that neither greater cropland area nor lower landscape diversity influenced pest pressure or yield. Rather, pest pressure and yield were best explained by the presence of non-crop habitats (i.e., meadows) in the landscape. Specifically, cabbage was infested with fewer Lepidoptera in landscapes with a higher proportion of meadows likely resulting from increased parasitism. Conversely, cabbage was infested with more flea beetles and aphids as the proportion of meadows in the landscape increased, suggesting that these pests benefit from non-crop habitats. Furthermore, path analysis confirmed that these landscape-mediated effects on pest populations can have either positive or negative cascading effects on crop yield. Our findings illustrate how different pest species within the same cropping system show contrasting responses to landscape composition with respect to both the direction and spatial scale of the relationship. Such tradeoffs resulting from the complex interaction between multiple-pests, natural enemies, and landscape composition must be considered, if we are to manage landscapes for pest suppression benefits.

Laboratory and field tests of predation on the cereal leaf beetle, Oulema melanopus (Coleoptera: Chrysomelidae)

“…My result is in line with previous studies that reported a positive impact of woodland overwintering sites on the abundance of rape pollen beetle at multiple scales (Rusch et al, 2013b), and stem weevil (Zaller et al, 2008) and indicates the potential of semi-natural habitats to contribute to ecosystem disservices (i.e. increased pest problems) in some systems (Perez- Alvarez et al, 2018).…”

Modelling the effects of field spatial scale and natural enemy colonization behaviour on pest suppression in diversified agroecosystems

“…have been shown to alter population dynamics and interfere with prey suppression in agricultural settings (Snyder & Ives, 2001Banks et al, 2008;Rand et al, 2012). Furthermore, landscape complexity in agroecosystems may simultaneously increase natural enemy pressure while bolstering pest populations (Penn, 2018, Perez-Alvarez et al, 2018. Our results suggest that, within the larger ecological context, we can expect differences in aphid suppression stemming from variation in colonization type, keeping all other factorsincluding migration rates and local within-field movement behavior -constant.…”

“…Another common strategy for incorporating natural vegetation into agroecosystems, which is more amenable to use in larger-scale agriculture, is to retain weeds, woody plants, and other non-crop vegetation adjacent to or in the margins of crop production areas (Banks 2000, Banks and Stark 2004, Bianchi et al, 2006Gardiner et al, 2009;Fonseca et al, 2017). The adjacent vegetation may act as a source for predators and parasitoids; though increased biological control of crop pests is not always guaranteed (Jonsson et al 2008;Rusch et al, 2013, Bianchi et al, 2017Perez-Alvarez et al, 2018). This highlights the difficulty in establishing a general theory relating non-crop vegetation adjacent to crop fields to pest control.…”

Higher surfaces of a crop in the landscape increase outbreak risks the following growing season

“…Studies opposing the cropland to semi-natural habitats failed to define a general rule of thumb regarding the regulation of animal pest epidemics 10,17 . Complex trade-offs between the impact of such landscape elements on both the life cycle of animal pests and their natural enemies have been pointed out 8,18,19 . No clear agreement emerges either for the management of crop pathogens as empirical studies are scarce despite repeated calls for landscape level assessments 11,20. .…”