Abstrakt: |
SummaryThe parasitism of the encyrtid wasp Oobius rudnevi(Nowicki, 1928) on the eggs of the longhorn beetle Cerambyx(Cerambyx) milesBonelli, 1812, is recorded for first time through field and laboratory trials. Field trials with sentinel eggs of C. mileswere conducted in SW Spain oak forests in which O. rudneviwas known to occur, using as positive controls sentinel eggs of both Cerambyx(Cerambyx) cerdoLinnaeus, 1758, and Cerambyx(Cerambyx) welensii(Küster, 1845), the only two O. rudnevihosts known to date. Laboratory assays were conducted using non-choice tests and choice tests (C. milesvs. C. cerdo). Results showed that C. mileseggs were attacked and successfully parasitised by O. rudneviin the wild, uncorrected parasitism rates (PU) being similar to those of C. cerdoand C. welensii(2.2–5.2%), and net parasitism rates (PN) even significantly higher in C. miles(8.9%) than in C. welensii(3.3%). Interestingly, C. milessentinel eggs were parasitised in holm oak forests in which C. mileswas unknown to occur, suggesting that egg-derived volatile cues were important in host location. In the laboratory, non-choice tests showed no differences in PNamong C. miles, C. cerdoand C. welensii(80–88%), signifying that O. rudneviperformed alike in the three hosts. Choice tests showed that O. rudnevidid not exhibit host preference between C. miles(53%) and C. cerdo(47%). Similar tests proved that eggs of Cerambyx(Microcerambyx) scopoliiFuessly, 1775, and Prinobius myardiMulsant, 1842, were never selected as hosts by O. rudnevi. Our results and the chorological, ecological and phylogenetic available evidence suggest that O. rudnevibehaves as an oligophagous egg parasitoid, which could be associated to other Cerambyx(s. str.) species over the Western Palaearctic realm. |