none Dendroctonus frontalis; HYMENOPTERAN-PARASITES; Coeloides pissodis; Parasite olfactory responses to potential semiochemicals Coeloides pissodis; ANTENNAE-; Olfactory responses to potential semiochemicals; CHEMORECEPTION-; COLEOPTERAN-HOSTS; Dendroctonus frontalis; Antennal olfactory responses to potential semiochemicals. In studies using the electroantennogram (EAG) technique, bark beetle- and tree-produced semiochemicals were presented to Coeloides pissodis (Ashm.), a larval parasitoid of Dendroctonus frontalis Zimm. In a preliminary study, 20 test compounds and a standard mixture of oxygenated monoterpenes were presented individually as serial dilutions of 10 to 0.0001 mu-g/mu-l to the parasitoids. The largest dose-responses were observed for endo-brevicomin, E,Z-chalcogran, ipsenol, pino-/isopinocamphone (1:2),and E-7 methyl-1,6-dioxaspiro(4.5) decane (MAD). These compounds, along with the known attractants frontalin and alpha-pinene, were tested in the primary EAG study using a larger sample size. The individual compounds did not elicit responses greater than the standard mixture of oxygenated monoterpenes. Overall, no significant differences were observed in EAGs between males and females at all concentrations tested. However, females exhibited a lower threshold of response than males to alpha-pinene and ipsenol, whereas males exhibited a lower threshold of response than females to MAD and pino-/isopinocamphone (1:2). At 1 mu-g/mu-l, E,Z-chalcogran and MAD elicited significantly greater EAGs, relative to the standard, than the other test compounds. Differences among the compounds were less pronounced at 10 mu-g/mu-l. Most of the test compounds elicited similar responses which suggests that several of the compounds may be used together by C. pissodis in habitat and/or host community location.