No abstract

The tibial contact chemosensilla of Schistocerca americana contain several neurons, one of which responds to nicotine hydrogen tartrate and certain other compounds. The activity of this cell is sometimes briefly interrupted by the firing of a second cell in the same sensillum which usually only fires a few times in the first 500 ms of a stimulation. The evidence suggests that the nicotine-sensitive cell is directly inhibited by the activity of the second cell. Not all cells in the sensillum produce the same effect.

Electrophysiological recordings from antennal olfactory receptor cells were obtained fromIps grandicollis. Recordings were made from olfactory receptor cells from nine regions of the antennae in response to stimulation with the semiochemicalsα-pinene, frontalin,endo-brevicomin, verbenone,trans-verbenol,cis-verbenol, ipsdienol, and ipsenol. In many cases, up to two cells were recorded concurrently from the same location. When compared to males, females had a greater percentage of cells responsive to the primary pheromones ofDendroctonus frontalis, frontalin andtrans-verbenol, and ofIps spp., ipsdienol and ipsenol. Among females, more cells responded totrans-verbenol and theIps-produced volatiles than to host or otherD. frontalis-produced compounds. Olfactory cells of males responded mostly tocis-verbenol, followed byα-pinene, verbenone,trans-verbenol, andendo-brevicomin. Of those cells responsive primarily to one compound, the greatest percentage were responsive totrans-verbenol in females and to verbenone in males. The response of the antennal olfactory receptor cells to semiochemicals used by male and femaleI. grandicollis is consistent with the presence of these compounds during the host colonization period for each sex. Our results, which show a lack of specificity in most pheromone and host odor receptor cells, is in contrast with previously published accounts of olfactory receptor cell specificity in otherIps species.

In studies using the electroantenno ram (EAG) technique, bark beetle-and tree roduced semiochemicals were presented to Coeloicfes pissodis (Ashm.), a larval parasitoid of Denzoctonus frontalzs Zimm. In a preliminar study, 20 test corn ounds and a standard mixture of oxygenated monoterpenes were presented ind%idually as serial diLtions of 10 to 0.0001 pg/pl 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 pino4sopinocamphone (1:2). At 1 pg/pl, 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 pg/pl. 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.