FIELD RESPONSE OF SOUTHERN PINE-BEETLE PARASITOIDS TO SOME NATURAL ATTRACTANTS

Studies were performed to isolate and identify semiochemicals that med iate location of host-infested trees by parasitoids of the southern pi ne beetle (SPB), Dendroctonus frontalis. Bark or bolts removed from pi nes infested with SPB broods attracted significant numbers of the hyme nopterous parasitoids Spathius pallidus and Roptrocerus xylophagorum t o sticky traps placed in an active SPB infestation. Traps baited with the water distillate of SPB brood-infested bark also attracted both sp ecies of parasitoids. In contrast, a synthetic bait composed of 18 com pounds identified from the headspace volatiles of attractive bark fail ed to trap parasitoids. The oxygenated and hydrocarbon components of t he bark distillate were partitioned by silica gel liquid chromatograph y, and the resulting two fractions were tested in the field. Parasitoi d attraction was greatest when both fractions were released from traps simultaneously. The hydrocarbon fraction, which failed to attract par asitoids, enhanced the weak attractiveness of the oxygenated fraction. Hence, it appears that no single compound is responsible for mediatin g SPB parasitoid host-tree location and that both oxygenated and hydro carbon semiochemicals are involved in this process.