Effects of landscape complexity and habitat management on stemborer colonization, parasitism and damage to maize

Lepidopteran stemborers are a serious constraint to efficient production of maize in sub-Saharan Africa. One of the most effective ways of managing these pests is through a habitat management system called push–pull. Landscape complexity has been shown to enhance biological control of insect pests, and therefore may influence effectiveness of habitat management systems designed to control pests. We studied the relative importance of the push–pull cropping system as a local effect and proportional cover of grassland as a landscape effect on (i) stemborer population density and damage to maize, and (ii) parasitism and mortality of stemborer life stages in western Kenya. We found a significant interactive effect between cropping system and grassland cover on abundance of stemborer larvae and pupa, and a near significant interactive effect of these variables on rates of egg parasitism. Cropping system had the largest effect on larval and pupal abundance in more complex landscapes, whereas it affected egg parasitism most strongly in the simplest landscapes. Grasslands appeared to primarily function as a source for the pests, rather than for natural enemies. However, sites from landscapes with a larger range of grassland cover need to be studied to fully explore the combined effects of cropping system and landscape complexity on pest control in this system. The push–pull cropping system significantly suppressed stemborer colonization of the maize and enhanced activity of stemborer parasitoids, with significant reductions in crop damage and increase in grain yield.