Evolution of host acceptance and its reversibility in a seed beetle

1. Adapting to a low-quality plant may require modification of an insect's digestive physiology, oviposition behaviour, or other host-use traits. If colonising a marginal host entails a cost, a decay in adaptation would be expected after selection is relaxed, i.e. if populations on a novel host are reverted to their high-quality ancestral host. 2. Replicate lines of the seed beetle Callosobruchus maculatus (F.) rapidly adapted to lentil seeds; larval survival rose from approximately 1 to ≥ 90%, and oviposition on lentil increased more than two-fold. This study compared egg-laying behaviour in lines that either remained on lentil or were reverted to the ancestral host, mung bean, for 22–62 generations. 3. Consistent with the trade-off hypothesis, females from two reverted sublines showed decreased oviposition on lentil (estimated as lifetime fecundity), but host acceptance in a third subline was unchanged. In a short-term assay, acceptance of lentil by newly emerged females was lower in ...