EVIDENCE FOR THE OCCURRENCE OF SIBLING SPECIES IN EUBAZUS SPP (HYMENOPTERA, BRACONIDAE), PARASITOIDS OF PISSODES SPP WEEVILS (COLEOPTERA, CURCULIONIDAE)

Comparative studies were made on three presumed sibling species of the genus Eubazus, parasitoids of European Pissodes spp. weevils, to clar ify their taxonomy and define diagnostic characters. Several populatio ns of E. semirugosus (Nees), E. robustus (Ratzeburg) and Eubazus sp. w ere compared with respect to their morphology (mainly through morphome tric analyses), fecundity, isoenzyme patterns and host preference. Cro sses were made to assess the genetic and behavioural compatibility of the populations. In addition, the North American E. crassigaster (Prov ancher), a parasitoid of Pissodes strobi (Peck), was compared to E. se mirugosus, a species selected for introduction against P. strobi in Ca nada. The ratio of the length of the ovipositor sheath to the fore win g length was the most discriminating morphometric variable, but discri minant analyses including several measurements were needed to complete ly separate European species. A canonical discriminant function provid ed a total separation between males of E. crassigaster and E. semirugo sus, but not between females. Eubazus crassigaster and E. semirugosus were totally separated by the banding pattern of the enzyme phosphoglu conate dehydrogenase whereas hexokinase and esterase provided a diagno stic separation between Eubazus sp. and E. robustus. Eubazus sp. diffe red from all the other species by having a greater number of ovarioles and, consequently, a higher potential fecundity. Ln a two-choice ovip osition test, E. semirugosus and Eubazus sp. showed a significant pref erence for their natural host, P. castaneus De Geer and P. piceae (Ill iger), respectively. A similar test made with their progenies reared u nder standard conditions showed that the difference in host preference was genetically fixed. Males and females of different species did not mate readily, in contrast to individuals from the same species. All a ttempts to interbreed E. robustus and Eubazus sp. failed, but a few cr osses between E. semirugosus and the two other European species produc ed fertile offspring. These observations strongly suggest that the com plex of Eubazus spp. parasitoids attacking Pissodes spp. in Europe is composed of at least three sibling species, two of which appear to hav e specialized on distinct host species that occupy exclusive microhabi tats.