How labile are the egg‐laying preferences of seed beetles?

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Abstract.  1. Previous studies have produced conflicting results with respect to the genetic lability of host preference in the seed beetle Callosobruchus maculatus . 2. In this study, replicate lines of an Asian population were kept on an ancestral host (mung bean) or switched to a novel host (cowpea). After 40+ generations, lines were assayed for host preference (in choice tests) and host acceptance (under no‐choice conditions), and were compared to African lines chronically associated with cowpea. 3. Host preference diverged in the expected direction. When presented a mixture of cowpeas and mung beans, females from the cowpea lines laid a greater fraction of their eggs on cowpea than did females from the mung bean lines. Preference for cowpea was nearly as strong in the cowpea lines as it was in the cowpea‐adapted African lines. 4. In contrast, the experimental host shift did not affect long‐term host acceptance. African females laid more eggs if given cowpeas than if given mung beans, but realised fecundities in the cowpea and mung bean lines were similar on the two hosts. Females from all lines laid more eggs if they were reared on cowpea than on mung bean, but rearing host had no effect on either relative host acceptance or host preference. 5. Comparisons with earlier studies suggest that the lability of host preference varies among beetle populations, which precludes generalisation at the species level. Because lines were maintained under no‐choice conditions, modification of host preference probably occurred via a lower acceptance threshold for the novel host, without a concomitant change in the long‐term acceptance of the ancestral host.

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