The effects of landscape complexity and local management on a generalist predator in Kenyan maize push-pull systems

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.