Sex-Based Differences in Antipredator Behavior in the Spotted Cucumber Beetle (Coleoptera: Chrysomelidae)

Abstract

Adult females of many arthropods require high food intake for producing eggs, whereas males feed less and spend more time searching for mates. If males and females differentially prioritize activities, they may experience a different ratio of costs to benefits of antipredator behaviors. We investigated sexual differences in the behavioral responses of spotted cucumber beetles, Diabrotica undecimpunctata howardi Barber, to the spider Rabidosa rabida Walckenaer in laboratory arenas in which the beetle could detect the spider, but the spider was prevented from preying upon the beetle. In structurally simple arenas with a single plant, the presence of a spider caused female beetles to spend less time on the plant, and to feed less when on the plant. In contrast, male beetles did not alter their behavior in response to the spider. A second experiment used larger arenas, in which the beetle could choose between a side containing a plant with a spider at its base, and the other side with no spider. Female cucumber beetles spent less time on the side with the spider, whereas males did not consistently change their behavior in response to the spider. The weaker antipredator response of males leads to a greater predation risk, as revealed by a third experiment in which predation was allowed. In this experiment males were 16 times more likely than females to be killed by R. rabida, demonstrating that the lower responsiveness of male beetles to predators increases the risk of being preyed upon.