NEMATODE PARASITISM IN A NORTHERN EUROPEAN DROSOPHILID COMMUNITY

Many factors may influence the structure of invertebrate communities. Among these is the presence of parasites which attack some or all memb ers of a guild and potentially promote coexistence of competitor speci es. We assessed the prevalence of nematode (Allantonematidae) parasiti sm in Dutch woodland drosophilids (Diptera). Nematodes were found in 6 of the 18 drosophilid species sampled (percentage parasitism in paren theses): Drosophila phalerata (16%), D. kuntzei (5.1%), D. immigrans ( 0.5%), D. testacea (1.2%) and D. transversa (2.8%) were all parasitize d by Howardula aoronymphium and D. subobscura (3%) was parasitized by Parazitylenchus diplogenus. This is the first report of nematode paras itism of D. immigrans and D. transversa. There were no important seaso nal trends in percentage parasitism. We explored the consequences of n ematode parasitism for individual drosophilids. Nematodes did not exer t an important influence on the wing length (adult body size) of the d rosophilids we sampled, but egg loads (fecundities) of female D. phale rata, D. subobscura and D. kuntzei were reduced by nematode parasitism . Parasitism rates were positively correlated with relative host abund ance, in Dutch and other communities, suggesting that species diversit y is promoted by a disproportionately high parasitism of more common h ost species.