FIELD PERFORMANCE OF F-1-STERILE GYPSY-MOTH LARVAE (LEPIDOPTERA, LYMANTRIIDAE) ON LOBLOLLY-PINE AND SWEETGUM

The quality of sweetgum, Liquidambar styraciflua L., and loblolly pine , Pinus taeda L., as a foodsource for gypsy moth, Lymantria dispar (L. ), larvae was evaluated using caged F-1-sterile gypsy moths in a field study in southeastern Virginia. A Ist experiment compared host specie s at 3 sites. Because early instars do not feed on loblolly pine, 2nd and 3rd stadia larvae were caged only on sweetgum, and allocated to sw eetgum and loblolly pine at the onset of the 4th stadium. On sweetgum, survival of L2 and L3 gypsy moths was 32% across sites and was approx imate to 17% higher on the best site compared with the worst. Survival of L4 to pupae was not affected by site, but survival was significant ly higher on sweetgum than loblolly pine during this period. Host spec ies did not affect duration of the larval stage, pupal weight, duratio n of the pupal stage, or development time to adult of F-1-sterile gyps y moths; however, site had a significant effect on duration of the lar val period. A 2nd experiment using L4-L6 examined the effects of detac hing branches, on both host species, on the duration of the larval per iod, relative growth rate, and pupal weight. The main effects of host species, branch detachment, and frequency of larval handling (frequent versus infrequent) were not significant for any response variable. Th e interactions of branch detachment by host species and larval handlin g by host species were significant. On loblolly pine, larvae caged on detached branches developed more slowly than those on intact branches, but those larvae caged on intact branches and moved infrequently deve loped the slowest of any treatment. Larvae on sweetgum were unaffected by branch detachment or frequency of handling.