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 emerged 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. __________________________________________________________________________________________________________________________________________________________ Diplolepis rosae (Linnaeus, 1758) is a palaearctic species, introduced in the nearctic region (Shorthouse and Ritchie 1984). It is widespread in peninsular Italy (Pagliano 1995), from where it has been known since at least 1600 (Tuscany: Pagliano et al. 1997), and in Sicily (De Stefani Perez 1887, as Rhodites rosae L.). Its multilocular galls have been recorded on 18 species of Rosa in Italy (De Stefani Perez 1887, 1902, 1905, Pellizzari Scaltriti 1988, Pagliano et al. 1997), and on 32 species in Europe and the Mediterranean basin (Houard 1908, Nieves-Aldrey 2001), though the gall wasp seems to prefer those species that are taxonomically allied in the Section Caninae (Randolph 2005), and particularly R. canina L. (Schroder 1967). Although D. rosae reproduces itself by amphitokous parthenogenesis (Beauvisage 1883, Callan 1940), males are reproductively inactive (Stille and Davring 1980) and of spasmodic occurrence probably due to female infection with Wolbachia bacteria, which is also common in other Diplolepis species (Plantard et al. 1998, 1999). Larvae grow inside the galls and overwinter in diapause as prepupae; they pupate the following spring and emerge soon after (Schroder 1967). Diplolepis rosae galls host a large insect community that has been extensively studied in many countries (Randolph 2005, and references therein). Considering only Hymenoptera parasitoids, Noyes (2003) lists 29 species of Chalcidoidea, and numbers increase when parasitoids belonging to other superfamilies are included (Fulmek 1968). However, several of the names listed by Fulmek (1968) are invalid or misidentifications or probably erroneously associated with D. J. HYM. RES. Vol. 15(2), 2006, pp. 277–285