Species composition, structure and impact of larval parasitoids of poplar twig borer, Gypsonoma aceriana (Dup.) (Lepidoptera, Tortricidae), on poplar ornamental trees in Sofia

Studies on the species composition and structure of parasitoid complex of poplar twig borer, Gypsonoma aceriana (Dup.), on poplar ornamental trees in Sofia and their role in reducing the number of this pest have been conducted during the period 1990-1997. Six larval parasitoids - Bracon variator Nees, Orgilus obscurator (Nees), Microdus tumidulus Nees, Apanteles erevanicus Tob. (Braconidae), Pristomerus rufiabdominalis Ucida and Pristomerus vulnerator (Panz.) (Ichneumonidae) were identified. Most numerous were M. tumidulus (41.0%), A. erevanicus (30.6%) and P. rufiabdominalis (19.1%). A erevanicus and M. tumidulus were dominating during the different years. The parasitoids of G. aceriana were solitary, as B, variator is an ektoparasite, and the rest - endoparasites. They attack young host larvae and emerge at the end of the pupal stage. The life cycle of parasitoids, that have double generation, are well synchronised with the pest development. This was expressed in the high levels of parasitism, which in some cases reached 61.5%, and as a whole for the different generations they were 5.9-44.4%. A. erevanicus and M. tumidulus were the most important in reducing the number of the pest.