EFFECTS OF PARASITISM BY TOMICOBIA TIBIALIS ASHMEAD (HYMENOPTERA: PTEROMALIDAE) ON REPRODUCTIVE PARAMETERS OF FEMALE PINE ENGRAVERS, IPS PINI (SAY)

The effects of Tomicobia tibialis Ashmead on the reproductive potential of adult Ips pini (Say) females were examined by comparing reproductive indices of parasitized and healthy females maintained in groups of three with healthy males. Parasitized females produced 50% fewer offspring than healthy females, and these offspring were distributed differently in the maternal gallery. Maternal gallery length and larval survival were not significantly different between the two groups, but a statistical power analysis (1 − β) shows this result to be equivocal. The potential to use T. tibialis as a biocontrol agent against I. pini is discussed.

PHEROMONES OF IPS PINI (COLEOPTERA: SCOLYTIDAE): VARIATION IN RESPONSE AMONG THREE POPULATIONS

Reciprocal field tests of attraction between populations of Ips pini (Say) from California, Idaho, and New York disclosed geographic variation in pheromone systems. These differences reside both in pheromone production and reception. However, it is unknown whether variation in the pheromone bouquets is qualitative, quantitative, or both.In New York, both sexes responded in higher numbers to their own pheromone than that produced by California or Idaho males. In California, beetles of both sexes discriminated against New York, but in Idaho only females made this distinction. In both California and Idaho, the local population showed a slight preference for the pheromone produced by Idaho males over that produced by California males.The predator Enoclerus lecontei (Wolc.) demonstrated a four-fold preference for attractants produced by males from New York over those produced by beetles from California and Idaho. The parasitoid Tomicobia tibialis Ashmead showed the opposite trend.There is no evidence that geographic variation in the pheromones produced by I. pini is sufficient to enforce breeding isolation between adjacent populations. However, these results dramatize the necessity of considering pheromonal variability in programs applying pheromones for the survey and control of widely distributed pests.

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.