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.

FIR CONEWORM, DIORYCTRIA ABIETIVORELLA (GROTÉ) (LEPIDOPTERA: PYRALIDAE), PREFER CONES PREVIOUSLY EXPLOITED BY THE SPRUCE CONE MAGGOTS STROBILOMYIA NEANTHRACINA MICHELSEN AND STROBILOMYIA APPALACHENSIS MICHELSEN (DIPTERA: ANTHOMYIIDAE)

We tested the prediction that larvae of the fir coneworm, Dioryctria abietivorella (Groté), preferentially exploit cones previously damaged by cone maggots, Strobilomyia spp. In most years sampled, fir coneworm attacked a significantly greater proportion of maggot-damaged than healthy cones of both white spruce and black spruce. The ecological implications for pest management are briefly discussed.

FIRST- AND SECOND-YEAR EFFECTS OF ACECAP® IMPLANTS AGAINST CONE INSECTS OF BLACK SPRUCE

Acephate implanted in trunks of black spruce, Picea mariana (Mill.) B.S.P., trees in the fall, 3 weeks before female bud flush, and at female bud flush reduced insect damage to cones and increased seed yields for 1 year. Second-year effects of the implants reduced insect damage to cones, but without increased seed yields. In the 2nd year, cones from trees treated at bud flush had the least insect damage and the highest residues of acephate and its toxic metabolite, methamidophos. Damage to treated cones by the spruce cone maggot, Strobilomyia neanthracina Michelson, the dominant insect in untreated cones, was insignificant in the 1st year and was reduced in the 2nd year.