Insecticide-resistant cotton bollworms encountering wolf spiders: Predation risks and behavioral effects

Insecticide-resistant cotton bollworms (Helicoverpa) survive on genetically modified cotton, and after the larva forages on cotton plants, it descends to pupate underground before emerging as a moth. During this ground-dwelling stage, Helicoverpa is at risk of attack by diverse predators, including a common inhabitant of cotton agroecosystems, the wolf spider Tasmanicosa leuckartii. Predation of Helicoverpa by wolf spiders reduces densities of Helicoverpa that emerge into the next generation carrying insecticide-resistant genes. The aim of this study is to assess which spider traits predict whether it attacks a larva or emerging moth, and it examines wolf spider influence on the behavior and development of Helicoverpa. In laboratory trials, most larvae (66%) and moths (77%) were attacked but we found no evidence that attack was predicted by prey size, spider sex or spider stage. Helicoverpa tended to descend from the plants to pupate sooner when spiders were present but, despite the reduced time available for larvae to feed, more mass was lost from cotton bolls when spiders were present. In glasshouse trials, the presence of a spider reduced by 66% on average the proportion of emerging moths, and it influences Helicoverpa microhabitat choice, since fewer caterpillars are found on the top soil. These results suggest that Tasmanicosa leuckartii is an effective predator at any life stage, and its presence can also trigger a trophic trait-mediated effect that can affect Helicoverpa development, foraging behavior, and plant biomass.