Location: Integrated Cropping Systems ResearchTitle: Male reproductive competition and components of female fitness in relation to body size in Northern Corn Rootworm (Coleoptera: Chrysomelidae) Author
|French, Bryan - Wade|
Submitted to: Annals of the Entomological Society of America
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/9/2013
Publication Date: 1/1/2014
Citation: French, B.W., Hammack, L. 2014. Male reproductive competition and components of female fitness in relation to body size in Northern Corn Rootworm (Coleoptera: Chrysomelidae). Annals of the Entomological Society of America. 107(1): 279-287; DOI: http://dxdoi.org/10.1603/AN13153. Interpretive Summary: In insects, body size for both females and males is often related to successful reproduction, and successful reproduction is directly related to crop damage and pest control costs. For insects, larger females generally lay more eggs over their lifetime and are often preferred by males as mates. Likewise, larger males generally have a reproductive advantage over smaller males when competing to mate with females. Because resistance in corn rootworms to Bt corn is spreading across the U.S. Corn Belt and damaging large areas of corn, it is important to understand the reproductive biology of these corn pests. We looked at the reproductive biology of northern corn rootworm, a pest of corn, and found that large males dominated small males and were more than twice as likely as small males to mate regardless of the size of the females. The results indicate that the resistance to Bt maize in relation to reduced male size in corn rootworms could place resistant males at a competitive disadvantage for mating with females. In contrast, resistance to Bt maize could enhance male size and offer resistant males a competitive advantage over susceptible males thereby speeding the rate of resistance. Changing the size of male corn rootworms in response to evolving Bt resistance could affect the rate to which resistance occurs and eventually the level of damage to corn plants. Incorporating nonrandom mating into insect resistance management models could lead to more accurate predictions of resistance evolution in corn rootworms. Understanding the repercussions of the effects on body size and reproduction could alter or reassure insect resistant management plans.
Technical Abstract: In insects, larger males generally have a reproductive advantage over smaller males when competing for mating partners. We examined male reproductive competition together with pre-copulation and copulation durations, female longevity, and fecundity in northern corn rootworm in relation to the body size of males and females that were combined for mating. Longevity and fecundity were determined for individually caged, mated females. Of the females in 108 combinations of two males and one female, 35 chose not to mate. Of the females in the 73 combinations that resulted in copulation, 38 were small and 35 were large. The proportions of large and small males that mated did not vary significantly with female size, but large males were more than twice as likely as small males to mate. The pre-copulation duration did not vary with either male or female size, and no interaction occurred between male and female size for either the pre-copulation or copulation duration. However, both male and female size affected the duration of copulation, with small males copulating longer than large males and large females copulating longer than small females. No female longevity or egg number differences occurred among the body-size categories of the mating pairs. The results indicate that the concurrent evolution of resistance to Bt maize and reduced male size could place resistant males at a competitive disadvantage for female ova. Alternatively, the concurrent evolution of resistance to Bt maize and enhanced male size could offer resistant males a competitive advantage over susceptible males. Incorporating models of sexual selection, which include nonrandom mating, could lead to more accurate predictions of resistance evolution in corn rootworms.