Host range expansion of a Polygonaceae-associated leaf beetle to an invasive aquatic plant Myriophyllum aquaticum (Haloragaceae)

Abstract

The expansion of available resources leads organisms to adapt to novel niches and create new biological interactions. Galerucella grisescens (Coleoptera: Chrysomelidae) is usually associated with Polygonaceae in Japan but a population feeding on an invasive plant species Myriophyllum aquaticum (Haloragaceae) was found in Chiba Prefecture, Honshu. To infer the process of host range expansion and possible rapid adaptations of G. grisescens to M. aquaticum, we studied larval host plant suitability and female oviposition site preference by G. grisescens in different strains. In laboratory rearing experiments, adult body weight and egg mass size of G. grisescens were smaller on M. aquaticum than on the native host Persicaria lapathifolia (Polygonaceae), suggesting that Polygonaceae are more suitable hosts for G. grisescens than M. aquaticum. On M. aquaticum, the larval survival rate was significantly higher in the Chiba strain collected from M. aquaticum than in the Saga strain originating from Polygonaceae. This raises the possibility that the Chiba strain rapidly adapted to M. aquaticum and improved survival rate on the plant. Oviposition site preference of G. grisescens females was slightly different between individuals reared on Polygonaceae and M. aquaticum. These results suggest that G. grisescens represents early stages of ecological adaptation to the introduced plant and it is a possible biological control agent against M. aquaticum.