Invertebrate community structure predicts natural pest control resilience to insecticide exposure

1. Biological pest control has become one of the central principles of ecological intensification in agriculture. However, invertebrate natural enemies within agricultural ecosystems are exposed to a myriad of different pesticides at both lethal and sub-lethal doses, that may limit their capacity to carry out pest control. An important question is how underlying diversity in invertebrate predator species,
linked to their unique susceptibility to insecticides, can act to increase the resilience of natural pest control.

2. We explore this issue by assessing the effects of sub-lethal insecticide exposure on the predation rates of 12 generalist predators feeding on the aphid Sitobion
avenae (Aphididae). Predation rates within a 24-hr period were assessed (predation assessment) for each species after receiving one of the following treatments:
(a) no prior deltamethrin exposure before the predation assessment (control); (b) deltamethrin exposure immediately before the predation assessment (resistance) and
(c) deltamethrin exposure 5 days before the predation assessment (recovery). Extrapolating from these species-specific measures of resistance and recovery, we predicted the resilience of community level predation to insecticide exposure for predator communities associated with 256 arable fields in the UK.

3. There was large variation in sub-lethal effects of the insecticide between even closely related species. This ranged from species showing no change in predation rates following sub-lethal insecticide exposure (high resistance), species showing only immediate depressed feeding rates after 24
hr (high recovery) or those with depressed feeding rates after 5 days (low resistance and recovery).

4. The community level analysis showed that resistance and recovery of natural
pest control was predicted by both community phylogenetic diversity (positively)
and weighted mean body mass (negatively). However, the removal of numerically
dominant species from the analysis modified these effects.

5. Synthesis and applications: Our results highlight the role of community diversity in maintaining the resilience of natural pest control following insecticide use.
Importantly, less diverse assemblages dominated by predator species that show low resilience to insecticide exposure, may show a greater depression in pest control than diverse assemblages under insecticide based farmland management.