Competitive Interactions Between Larvae from Divergent Strains of the Cowpea Weevil (Coleoptera: Bruchidae)

Document Type

Article

Journal/Book Title/Conference

Environmental Entomology

Volume

20

Publication Date

1-1-1991

First Page

1438

Last Page

1443

Abstract

Previous studies demonstrated that larvae from an Indian strain (S) of the seed beetle Callosobruchus maculatus (F.) are much more competitive than larvae from a Nigerian strain (I) during both intra- and interstrain competition in a small host seed (mung bean). The competitive superiority of the S strain was Similarly evident when two larvae cooccurred in a larger host species (adzuki bean) that represented a novel host for both strains. If one or both larvae within a seed belonged to the S strain, survival to adult emergence was 50% lower than it was in the absence of competition. In contrast, survival decreased by only 15% when two I-strain larvae shared a seed. In head-to-head encounters between strains, most seeds produced a single survivor, and nearly 75% of adults from such seeds belonged to the S strain. Reciprocal crosses suggested an additive genetic component to these differences in competitive ability; the reduction in survival following competition was intermediate among F 1 progeny. In contrast, the genetic basis of strain differences in adult weight was largely nonadditive, with hybrid progeny displaying a strong dominance deviation toward the heavier S strain. Differences in competitive ability were therefore independent of differences in body size between strains. Variation in competitive ability may ultimately be a consequence of variation in the sizes of host seeds typically encountered by beetle populations.

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