Influence of Reproductive Ecology on Feasibility of Mass Trapping Diabrotica virgifera virgifera (Coleoptera: Chrysomelidae)

Abstract

(1) The degree of protandry, the average age at which females mated and the effects of size and adult nutrition on the reproductive performance of male western corn rootworms, Diabrotica virgifera virgifera, were evaluated to assess the potential of male removal as a management tactic for this pest. (2) Although some males emerged earlier, most males emerged at the same time as females. Dissections of teneral and young non-teneral females, as well as observations of newly emerged females in cornfields, showed that most females mate during the first 24 h after emergence. The synchrony between bimodal temporal distributions of mating and adult emergence, which reached peaks in the morning and the late afternoon/early evening, supported this conclusion. (3) When supplied an excess of virgin females in field cages, large males usually initiated mating at an earlier age and mated more often than small ones. However, neither longevity nor the mass of spermatophores were related to male size. Thus, small males, which sometimes mate twice daily, transfer a greater proportion of their resources at each mating. (4) Males which were provided young silks, ears of corn, leaves and tassles for the first week after emergence, after which they were only given leaves (i.e. poor food) died sooner and mated less often than similar sized males given continuous access to young silks, ears of corn, leaves and tassles (i.e. best food). The mass of spermatophores produced by males in the best food treatment was larger than those produced by males fed poor food. Spermatophore mass was positively correlated with age, especially during the first 10 days after emergence. (5) The reproductive potential of populations of D. virgifera virgifera males far exceeds the number of available virgin females in cornfields. Thus, intraspecific competition between males for mates should be considerable in this system. (6) The results of this study indicate that tactics relying exclusively on male removal do not have a large potential to manage D. virgifera virgifera populations.