Host Preference of F_1 Hybrids between Two Host Specific Phytophagous Ladybird Beetles (Epilachna spp., Epilachninae, Coccinellidae)

We reared Epilachna niponica, E. yasutomii and their F_1 hybrids throughout the larval stage on thistle (Cirsium kamtschaticum, the host plant of E. niponica), blue cohosh (Caulophyllum robustum, the host plant of E. yasutomii) or Japanese nightshade (Solanum japonense, a plant preferred by both species in the laboratory). When allowed to choose between the three plants, the majority (80-100%) of E. niponica and E. yasutomii fed on their own host plants and the Japanese nightshade, but none accepted the host plants of the other species. About one third of the individuals of either species accepted the host plants of the other species when no choice was offered. On the other hand, hybrids mostly preferred nightshade, followed by blue cohosh. Although they least preferred thistle, a considerable proportion (ca. 15-65%) ate this plant even when they were allowed to select between all three. When given no choice, all but one individual of the hybrids accepted all the three plants. The effect of pre-imaginal conditioning on adult host preference was weak, if it existed at all. However, the possibility of hybridization in natural conditions and its effect on the reproductive isolation between E. niponica and E. yasutomii remains unclear.