Aggregation and male attraction to feeding virgin females in Macrodactylus subspinosus (F.) (Coleoptera: Scarabaeidae: Melolonthinae)

Abstract

In several field assays, Macrodactylus subspinosus (F.) adults were significantly more attracted to feeding adult conspecifics than to any other treatment; males were more attracted to feeding virgin females than feeding field-collected (i.e., mated) females. Alternative treatments among the experiments included plant material, artificially damaged plant material, screened artificially damaged plant material + adults, virgin females, mating adults, field-collected males, and field-collected females. Repeated-measures experiments in laboratory bioassays indicated that wild grape leaf disks damaged and treated with beetle regurgitant were no more attractive than unaltered or artificially damaged disks; however, the treatments that had been fed upon first attracted significantly more beetles than those that had been fed upon subsequently. Beetles were never observed "calling", and scanning electron microscopy did not reveal cuticle pores as in some scarabs. We conclude that the act of feeding causes the immediate release of plant volatiles that act with normal levels of plant volatile release to increase adult attraction. Furthermore, virgin females enhance male attraction over mated females by causing the release of either female-based or plant-based volatiles.