Defensive thrashing behavior of caterpillars incurs a fatal retaliation from predatory stinkbugs

Abstract

Thrashing behavior is generally assumed to be an effective means of defense of caterpillars to escape arthropod predators. Yet, scant attention has been paid to subsequent performances of escaped caterpillars. To address this knowledge gap, we conducted experiments with predatory stinkbug Arma chinensis nymphs or adults. As prey, we used armyworm Mythimna separata caterpillar and examined developmental consequences of the prey escaping the predator by thrashing. Surprisingly, we found that caterpillars which escaped from the stylet insertion of the stinkbug by thrashing underwent poor development and were less likely to survive to pupation. This effect did not vary with the life stage of the stinkbug or the duration of its stylet insertion. On the other hand, sham injuries caused by needle puncturing did not significantly affect the caterpillar’s survival. We also examined the overall activities of antioxidant enzymes, immune-related enzymes, and neuroregulatory bioamines as a known insect response to envenomation. We found that these biochemicals were more abundant in caterpillars exercising thrashing behavior. Based on these findings, we speculate that the increased defensive behavior by thrashing results in an increased venom injection by the predator, which is responsible for the observed increased mortality in those caterpillars that practice thrashing.