Larval parasitism of a forest pest, the common pine sawfly Diprion pini (L.) (Hym., Diprionidae), during an endemic density phase

Species composition and impact of larval parasitoids during an endemic dens ity phase of a pine forest pest, the common pine sawfly Diprion pini (L.), were investigated by exposure of laboratory-reared larvae of the sawfly to parasitoid attack in natural habitats. Colony-associated host larvae of dif ferent instars were exposed continuously from early June until end of Septe mber of the years 1994 and 1995 in two pine stands with a different history of pine sawfly outbreaks. Host larvae were exchanged after a defined time interval and those collected up were examined in the laboratory for parasit ism. Parasitoid assemblages were shown to be very species poor at both pine stands. The dominant species were the ichneumonid Olesicampe macellator an d the tachinid Drino gilva, which reached attack rates on the collected hos t larvae of 60 and 94%, respectively, during peak activity. The patterns of temporal attack, of multi-parasitism, and of superparasitism of these domi nant species were studied. In an additional experiment, the response of the se species to different host-patch sizes (number of host larvae per colony) were investigated. No aggregative response to higher host-patch densities could be detected. The role and function of these larval parasitoids in the population dynamics of D. pini are discussed.