SINGLE CELL RESPONSES OF THE DOUGLAS-FIR BEETLE, DENDROCTONUS-PSEUDOTSUGAE HOPKINS (COLEOPTERA, SCOLYTIDAE), TO PHEROMONES AND HOST ODORS

Olfactory perception of pheromones and host odors [Pseudotsuga menziesii] by D. pseudotsugae males and females was investigated through single cell recordings. Responses of 71 cells (35 cells in males; 36 cells in females) were recorded to 1 .mu.g of 10 pheromones and 3 host terpenes. The olfactory cells were classified into 4 types based on sensitivity and specificity for the various odors: 3.2-MCHone (3-methyl-2-cylcohexenone) cells; 3,2-MCHol (3-methyl-2-cyclohexenol) cells; frontalin cells; and synergist cells. 3,2-MCHone and 3,2-MCHol cells in both males and females were the most sensitive and specific of all cells recorded with a threshold .apprx. 0.001-0.01 .mu.g on filter paper. Frontalin cells were less specialized than the 2 aforementioned cell types and had a somewhat higher threshold of .apprx. 0.01 .mu.g. A larger percentage of these 3 cell types were recorded in males than in females. The synergist cells had the highest threshold of all recorded cell types and were the least specific. Each of these cells was most responsive to either cis-verbenol, trans-verbenol, 1,2-MCHol, verbenone, .alpha.-pinene, or limonene; responses could be elicited by stimulation with other pheromones or host terpenes at higher dosages. Instances of inhibition of nerve impulse activity from spontaneously active cells were observed during 3,2-MCHol and 3,2-MCHone stimulation, suggesting multifunctional effects for these compounds. The results help explain the role of chemicals in host selection, aggregation, and colonization behavior of the beetle and further elucidate hypotheses put forth in an earlier electroantennogram study.