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Title: Contest-Behavior of Maize Weevil Larvae when Competing within Seeds

Author
item GUEDES, NELSA MARIA - Universidade Federal De Vicosa
item GUEDES, RAUL N. - Universidade Federal De Vicosa
item Campbell, James - Jim
item Throne, James

Submitted to: Journal of Animal Behavior
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/1/2009
Publication Date: 1/20/2010
Citation: Guedes, N.P., Guedes, R.C., Campbell, J.F., Throne, J.E. 2010. Contest-Behavior of Maize Weevil Larvae when Competing within Seeds. Journal of Animal Behavior. 79: 281-289. doi:10.1016/j.anbehav.2009.10.022.

Interpretive Summary: Maize weevils are cosmopolitan pests of stored grains. We investigated the behavioral mechanisms underlying fitness of an insecticide-resistant and a susceptible strain of maize weevils. No differences in the behavioral process were found, with both strains having an optimal egg density of two. That is, usually no more than two individuals will survive in a single maize kernel because of cannibalism. Understanding the biology of pest insects will help us design better pest management programs.

Technical Abstract: Food limitation induces severe competition for obligate seed-feeding insect larvae that are unable to leave the seed selected by their mother. The number of eggs laid per seed and the number of larvae hatched from the eggs determine whether larval behavior within the seed will be of the scramble or contest type. In maize weevils only few adults emerge per seed, which may arise from scramble competition if the optimum egg density is low compared to the number of eggs laid per seed, or from contest competition due to direct interference among the larvae. The behavioral process and the ecological outcome of competition were assessed in two strains of the maize weevil. Neither strain exhibited reduction in body mass with increased competition, and they had similar optimal egg density (two eggs/seed, corresponding to the peak of total larval fitness). This scramble outcome is recognized by the humped curves of total larval fitness. Nonetheless, the small optimum egg density suggests that body mass is unlikely to be reduced in the emerging adults compromising the conclusion of a contest-type behavioral process based on this trait. X-ray imaging of seeds was used to resolve the issue and showed direct interference among the larvae. This provides evidence of contest-like competition within seeds even though egg density was low. Hence, one should be cautious in inferring the underlying type of competitive behavior from variables, such as body mass and initial egg density per seed. Direct observation of behavior is required to make such an inference.