Oviposition, life cycle, and parasitoids of the spruce cone maggot, Strobilomyia anthracina (Diptera: Anthomyiidae), in the Alps

The life cycle of Strobilomyia anthracina (Czerny) which exploits Norway spruce seed cones was investigated in 1992 and 1993 in the Alps at c. 1800 m at Torgnon (Valle d'Aosta, Italy) and Lac de Tseuzier (Valais, Switzerland) by sampling cones at fortnightly intervals. Oviposition occurred primarily singly in the basal third of cones at the beginning of June when cone scales were open for pollination. Infestation rates were higher when cone crops were poor. Most larvae left the cones in August to pupate in the litter beneath trees, usually at a depth of 1-4 cm. Prolonged diapause of pupae coincided with failed or poor cone crops. Parasitism was investigated at these two and 27 additional sites in the Swiss, French and Italian Alps. Among several hundred host eggs only one was parasitized by Trichogramma sp. (Trichogrammatidae). Among the larval-pupal endoparasitoids, the figitid Sarothrus areolatus Hartig was more common than an ichneumonid, Atractodes sp., but parasitism by both was commonly below 10%. Parasitism by an ichneumonid larval ectoparasitoid, Scambus sp., also rarely exceeded 10%. Puparia of S. anthracina that were buried in the litter to detect pupal parasitoids revealed the gregarious pteromalid Tritneptis sp. near lophyrorum (Rushka). This is the first record of a pupal parasitoid of Strobilomyia species. Information on the biology of the three larval parasitoids is presented. The potential for biological control of North American Strobilomyia neanthracina Michelsen and S. appalachensis Michelsen by importation of natural enemies of S. anthracina appears limited.