Genetic Modification of Host Acceptance by a Seed Beetle, Callosobruchus Maculatus (Coleoptera: Bruchidae)

Abstract

Abstract Successful host shifts by herbivorous insects may require the modification of multiple larval and adult traits. The seed beetle Callosobruchus maculatus (F.) (Coleoptera: Bruchidae) rarely attacks lentil (Lens culinaris Medikus), which is distantly related to its typical hosts. In a previous study, larval survival in lentil seeds increased from <2 to >85% in fewer than 20 generations of laboratory selection. However, lentil is also a poor oviposition host; lifetime fecundity on lentil was initially less than a third of that on the ancestral host [ mung bean, Vigna radiata (L.) R. Wilczek ] and one fourth of females did not even recognize lentil as a potential host. This study examined the genetic lability of host acceptance. We performed both quasi-natural selection, in which replicate lines switched to lentil were compared with those remaining on mung bean, and artificial selection, in which lines were established using females from the base population that exhibited especially low or high acceptance of lentil during a short-term assay. After only five to eight generations of quasi-natural selection, lifetime fecundity on lentil was 2 to 3 times higher in the lentil lines than in the mung bean lines. Lentil-line females also accepted the novel host sooner after adult emergence. Similarly, a single generation of artificial selection was sufficient to increase oviposition on lentil in the acceptance line. Host acceptance was not genetically correlated with larval survival, which remained <2% in lines artificially selected for either high or low acceptance of lentil seeds. Although modification of oviposition behavior in this study was not nearly as striking as the increase in larval survival reported previously, the C. maculatus population possessed enough standing genetic variation in both larval physiology and adult behavior to permit rapid adaptation to a very poor host.