ELECTROANTENNOGRAM RESPONSES OF DOUGLAS-FIR SEED CHALCIDS TO PLANT VOLATILES

Douglas fir seed chalcids females oviposit specifically into Douglas c ones which they locate using olfactory and visual cues. We have tested whether this specialization was correlated with a specialized sensiti vity towards cone volatiles. Field collected adults were presented a s eries of pure volatile chemicals. Electroantennogram responses (EAG) w ere recorded to generally occurring terpenoids and straight chain alco hols and aldehydes found in flowers and plant leaves. Monoterpenes ide ntified in Douglas cone headspaces (alpha-pinene, beta-pinene, 3-thuje ne, alpha- and beta-phellandrene, gamma-terpinene and myrcene elicited lower EAG responses than fatty acid derivatives corresponding to gree n odours. The EAG response profile of females differed significantly f rom that of males; Females were very sensitive to hexanol-1, heptanal, (Z)-3 hexenol-1, terpineol and terpinen-4-ol. Male responses were sig nificantly higher to humid air, nerolidol, thujan-4-ol, hexanal, carva crol, piperitone and farnesol. Several compounds (Z- verbenol, carvone , jasminol, geraniol, nerol and eugenol) elicited long lasting electro physiological responses lover 5 s) in both sexes. (C) 1998 Elsevier Sc ience Ltd. All rights reserved.