Compatibility of biological control and pesticides mediated by arthropod movement behavior and field spatial scale

Integrated pest management programs frequently rely on a combination of pesticide use with cultural controls such as diversifying agroecosystems to control pest populations. Selective pesticides can impose both lethal and sublethal effects on natural enemies. However, understanding the compatibility of pesticide use with biological control strategies is critical for pest management success. The population dynamics of natural enemies subjected to the effects of pesticides, especially those that experience sublethal effects, is critical to this understanding. Although lethal effects of pesticides on natural enemies are well-studied, sublethal effects of pesticide exposure such as the impact on natural enemy movement is less well understood – especially across different habitat spatial scales. We present a simulation model using coupled partial differential equations to explore the sublethal effects of pesticide use, via reduced predator movement, on pest suppression across a gradient of farm spatial scales. Using a beetle-aphid model system, we find that in small fields, increased abundance of natural enemies can reduce the need for pesticide sprays. However, in mid-sized fields, we find that impaired predator mobility caused by pesticide sprays has a negative impact on biological control by the natural predator community. We also demonstrate how timing of predator introduction to a field can complement timing of pesticide sprays. We discuss the implications of these results for biological control planning and implementation.