Local variation in the thistle species Cirsium grayanum affects its utilization by the herbivorous ladybird beetle Henosepilachna niponica

Abstract

AbstractHost plants are the most critical environmental factor for phytophagous arthropods. Adaptation to a novel host will alter the distributional range of an herbivore to include the area the novel host covers, and might promote divergence between populations utilizing the old and new hosts. On the Oshima Peninsula, Hokkaido Island, northern Japan, the ladybird beetle Henosepilachna niponica (Lewis) (Coleoptera: Coccinellidae) usually occurs exclusively on the thistle Cirsium alpicola Nakai (Asteraceae), which is distributed in the southernmost part of the island, although some other Cirsium species often grow in sympatry. At least at one site (Assabu), however, H. niponica depends on another thistle, Cirsium grayanum (Maxim.) Nakai, the most abundant and widely distributed thistle species on the Oshima Peninsula. We examined adult feeding acceptance and preference, and larval performance, in two populations of H. niponica that utilize different species of thistles (the Assabu population occurs on C. grayanum; the Shiriuchi population, on C. alpicola) by testing three kinds of thistles (C. grayanum from Assabu, C. grayanum from Shiriuchi, and C. alpicola from Shiriuchi). Results strongly suggested that among the three plants tested, C. grayanum from Assabu was the most suitable host for H. niponica. We concluded that local differences in C. grayanum mainly explain why it is not used at Shiriuchi, but that there are also local differences in host use among the beetle populations, suggesting some degree of local adaptation. This suggests that different selective regimes associated with different host plants might promote divergence among beetle populations. We conclude that H. niponica is at present unlikely to expand its range to the whole range of C. grayanum.