Does Rapid Adaptation to a Poor-Quality Host by Callosobruchus maculatus (F.) Cause Cross-Adaptation to Other Legume Hosts?

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Journal of Stored Products Research



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Initial assays indicated that lentil is a very poor host for an Asian population of the seed beetle Callosobruchus maculatus (F.). Larval survival was near zero, and females laid few or no eggs on lentil seeds. However, mass selection in the laboratory consistently produced a rapid increase in survival (from <2% to >80% in <20 generations) as well as a moderate increase in host acceptance. We investigated whether adaptation to lentil simultaneously causes cross-adaptation to other grain legumes, particularly those closely related to lentil. After 30 generations of selection, survival in lentil exceeded 90% in the lentil line, but remained near zero in a line maintained on the ancestral host, mung bean. Despite this extreme divergence in performance in lentil, the lines did not differ in their survival on eight other legume hosts, including two hosts (pea and fava bean) that belong to the same tribe (Vicieae) as lentil. Similarly, females from the lentil line laid more than three times as many eggs on lentil as females from the mung bean line did, but the lines exhibited only minor differences in their acceptance of eight alternative hosts. Lentil-line females did not show greater acceptance of artificial seeds (glass balls), as might be expected if increased egg-laying on lentil was simply due to a reduction in the overall threshold for oviposition. We conclude that the changes in larval physiology and adult behavior that permitted rapid colonization of a marginal host were largely specific to that host, and not likely to promote a further expansion of the beetle's host range.

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