Sex-based differences in antipredator behavior in the spotted cucumber beetle (Coleoptera : Chrysomelidae)

Adult females of many arthropods require high food intake for producing egg s, whereas males feed less and spend more time searching for mates. If male s and females differentially prioritize activities, they may experience a d ifferent ratio of costs to benefits of antipredator behaviors. We investiga ted sexual differences in the behavioral responses of spotted cucumber beet les, Diabrotica undecimpunctata howardi Barber, to the spider Rabidosa rabi da Walckenaer in laboratory arenas in which the beetle could detect the spi der, but the spider was prevented from preying upon the beetle. In structur ally simple arenas with a single plant, the presence of a spider caused fem ale beetles to spend less time on die plant, and to feed less when on the p lant. In contrast, male beetles did not alter their behavior in response to the spider. A second experiment used larger arenas, in which the beetle co uld 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 b ehavior in response to the spider. The weaker antipredator response of male s leads to a greater predation risk, as revealed by a third experiment in w hich predation was allowed. In this experiment males were 16 times more lik ely than females to be killed by R rabida, demonstrating that the lower res ponsiveness of male beetles to predators increases the risk of being preyed upon.