Life history characteristics of Elachertus cacoeciae (Hymenoptera: Eulophidae), an ectoparasitoid of spruce budworm larvae, Choristoneura fumiferana (Lepidoptera: Tortricidae)

We carried out a 2-year study to elucidate the biology of the gregarious, idiobiont ectoparasitoid Elachertus cacoeciae (Howard) by placing (implanting) laboratory-reared spruce budworm larvae [Choristoneura fumiferana (Clemens)] on current-year balsam fir (Abies balsamea L.) shoots in the field, simulating low (endemic) densities of the budworm. Spring female E. cacoeciae attacked fourth-, fifth-, and sixth-instar budworm larvae, beginning near the predicted peak of the fourth instar and ending about 10-12 days after the predicted peak of the pupal stage of the wild budworm population. The mean (+/-SE) brood size of spring females was 2.9 +/- 0.3 E. cacoeciae pupae per host. The proportion of females increased during the season, with many broods consisting of 100% females late in the season. In 1994 and 1995, the mean proportion of females was 0.74 +/- 0.05 and 0.79 +/- 0.05, respectively. In the laboratory, development time from eggs to adults was approximately 20 days at 20.6 degrees C. Adult males provided with honey water lived 43.6 +/- 3.2 days, whereas females provided with hosts and honey water lived 90.1 +/- 6.6 days. Spring females had a pre-oviposition period of 11.5 +/- 1.3 days, resulting in a gen eration time (egg to egg) of similar to 31 days. The oviposition period lasted 76.3 +/- 7.7 days during which time spring females parasitized 19.2 +/- 1.9 hosts, and produced a clutch size of 4.9 +/- 0.4 eggs per host, for a lifetime fecundity of 96.8 +/- 14.7 eggs. The post-oviposition period was 18.5 +/- 3.7 days. Throughout their lifetime, spring females host fed only (host feeding without oviposition) on an additional 9.3 +/- 1.9 hosts. Approximately 2% of pupae developing from spring females overwintered, whereas approximately 95% of pupae developing from summer females overwintered. Laboratory results for summer females suggest that they may be adapted to parasitizing alternate host(s) rather than spruce budworm.