Parasitoids of grass-feeding chalcid wasps: a comparison of German and British communities

We compared the parasitoid communities associated with grass-feeding herbiv ores in Germany and Britain to examine geographical consistency in communit y composition and to test ecological characteristics of the plants and host insects that may explain variability in parasitoid community structure. Th e parasitoid communities of 16 chalcid wasps feeding on ten grass species w ere sampled between 1986 and 1989 at 4-11 sites per grass species in southw est Germany. The data were compared to published data from Great Britain, c omprising 18 chalcid hosts on ten grass species sampled between 1980 and 19 92 at 24 sites in Wales and England. Results showed that many conclusions d rawn from patterns in Britain did not hold for Germany, emphasizing the nee d to repeat analyses in different geographical regions. The parasitoid comm unities of the Tetramesa hosts included on average 8.1 parasitoid species i n Germany, while the British hosts supported only 4.1 parasitoids. The numb er of monophagous parasitoid species was similar in both areas (2.4 vs 3.2) , but German host populations supported many more polyphagous species (5.1 vs 0.9). This difference reinforces the earlier conclusion that parasitoid communities in Britain are highly undersaturated. Increased numbers of para sitoid species in Germany did not result in increased parasitism rates, so the closer species packing was paralleled by reduced impact of each species . In Germany, percent parasitism (range: 5-74%) was closely correlated with log host density, explaining 90% of the variance, while in Great Britain, percent parasitism was less variable (range: 36-76%) and was not related to host density or other host or host plant characteristics. Gallers and non- gallers supported equal numbers of parasitoids in both Germany and Britain, offering support for neither the enemy hypothesis of the adaptive nature o f plant galls nor for the finding that galls are often more susceptible to enemy attack than their non-galling relatives. Furthermore, gregarious Tetr amesa hosts were not attacked by more parasitoid species than solitary host s.