Parasitism and sex ratio of the Bedeguar gall wasp Diplolepis rosae (L.) (Hymenoptera: Cynipidae) in Sicily (Italy).

Abstract

The Diplolepis rosae gall community is analysed in Sicily (Italy), based on collections totalling 82 galls from 12 sites from which 1,026 adult insects were obtained. The gall wasp exits in March-June from galls induced the previous year. On average 5.6 D. rosae individuals per gall were obtained, corresponding to 44.8% of all the emerged insects. We obtained 4.3% of D. rosae males overall, the highest figure found till now for the cynipid overall in Europe, where male D. rosae are usually rarer, and the first record of them for the Mediterranean area. No inquilines were found, and, consequently, none of their specific parasitoids. However, Eurytoma rosae, generally considered as a specific parasitoid of the inquiline Periclistus brandtii, was obtained, together with the polyphagous Exeristes roborator. In all, seven parasitoid species came out from the galls: four of them, Orthopelma mediator, Torymus bedeguaris, Exeristes roborator, and Eupelmus urozonus, start to emerge together with D. rosae, while Glyphomerus stigma, Pteromalus bedeguaris, and E. rosae, have their maximum peaks later in the year. All the cited species, except for E. roborator, showed a second peak of emergence in September, when D. rosae is absent. Parasitization ranged from 12.5 to 100%, reaching more than 70% in 66.6% of the samples, but it was rather low (30.5%) when males were present, even though there was no overall correlation between parasitization and D. rosae sex ratio. Statistical analysis showed however that all the parasitoid species (except for males of T. bedeguaris and P. bedeguaris) are longer (which we take to signify larger) than D. rosae males, and neither the size nor the sex ratio of parasitoids differed statistically depending on the presence of male D. rosae. It would be interesting to compare parasitization percentages in other studies where good numbers of males of D. rosae were recorded.