Differences in morphology and reproductive traits of Galerucella nymphaeaefrom four host plant species

The water lily beetle Galerucella nymphaeae L. (Coleoptera: Chrysomelidae) exploits different hosts, including Nuphar lutea Sm. and Nymphaea alba L. ( both Nymphaeaceae), as well as Polygonum amphibium L. and Rumex hydrolapath um Hudson (both Polygonaceae). The present study investigates whether withi n-species differences in morphological and reproductive traits are associat ed with differences in host species exploitation. A total of 1103 adult bee tles were collected from 11 localities in The Netherlands, one of which con tained all four hosts and three other localities contained hosts from both families (sympatric localities). Adults originating from Nuphar and Nymphae a were on average darker in colour and larger in size and had disproportion ally bigger mandibles than beetles originating from Polygonum and Rumex acr oss the 11 localities. Head capsules of first instar larvae from Nymphaeace ae hosts were between 17% and 28% larger than those of larvae from Polygona ceae hosts. Furthermore, beetles from Nuphar and Nymphaea laid larger sized eggs, but fewer eggs per clutch than beetles originating from Polygonum an d Rumex. Although host related variation was less pronounced at the sympatr ic localities than in the allopatric localities, differences in larval and adult size were still highly significant at the sympatric localities. It is not clear whether the observed differences are genetically based, as oppos ed to host induced. However, leaf toughness varied among species in a way s uggesting that leaf toughness may be partly responsible for host related di fferences in G. nymphaeae.