Interspecific Variation in Host-Finding Cues of Parasitoids of the Southern Pine Beetle (Coleoptera: Scolytidae)

Experiments were performed with host-associated olfactory attractants of the larval parasitoids of the southern pine beetle, Dendroctonus frontalis Zimmermann, to elucidate both their biological origin and their chemical composition. Sticky-screen traps were erected in an active D. frontalis infestation and baited with parts of D. frontalis-infested loblolly pines (Pinus taeda L.) or their extracts. The diversity of parasitoid species landing on trees infested with larval D. frontalis was substantially greater than that attracted to traps baited with wood and bark taken from similar, infested trees. Females of four parasitoid species, Spathius pallidus (Ashmead), Roptrocerus xylophagorum (Ratzeburg), Dinotiscus dendroctoni (Ashmead), and Eurytoma tomici Ashmead, were attracted to bark infested with D. frontalis larvae. Two of these species, R. xylophagorum and S. pallidus, were attracted to debarked wood from host-infested trees although this tissue was free of hosts and host frass. Spathius pallidus were more attracted to the excised bark (containing D. frontalis larvae and frass) than the debarked wood from D. frontalis-infested pine bolts, while R. xylophagorum were attracted in similar numbers to both materials. When traps were baited with steam/water-distilled extracts of D. frontalis-infested bark, R. xylophagorum strongly preferred extracts from bark containing early-instar larvae over extracts from bark infested with either younger (egg-stage) or older (late-instar larval and pupal) brood. In contrast, S. pallidus responded significantly only to extracts of late larval/pupal bark. Coupled gas chromatograph/mass spectrometer (GC-MS) analyses of the bark extracts revealed that the concentrations of numerous extract constituents correlated positively with trap catch of S. pallidus, but no such relationships were identified for R. xylophagorum. These data provide further evidence that members of the parasitoid complex associated with D. frontalis differ in their strategies for locating trees infested with susceptible hosts.

NOTES ON THE BIOLOGIES OF HYMENOPTEROUS PARASITES OF IPS SPP. BARK BEETLES IN VIRGINIA

Biological data are given for Coeloides pissodis (Ashmead), Dendrosoter sulcatus Muesebeck, Heterospilus sp., Spathius pallidus Ashmead, Eurytoma conica Provancher, Cecidostiba polygraphi Ashmead, Heydenia unica Cook and Davis, Roptrocerus xylophagorum (Ratzeburg), Rhopalicus pulchripennis (Crawford), Rhopalicus tutela (Walker), and Tomicobia tibialis Ashmead. Only Coeloides pissodis was always closely associated with its host. The other larval parasites were often found disassociated from any host, suggesting an ability to seek out hosts in Ips galleries and the potential to attack more than one host. Observations indicated that pupal parasitism may be significant. Comment on the potential of some parasites as control agents is included.