EAG recordings revealed that from the six substances isolated so far from pheromone glands of Marnestra brassicae females, only (Z)-11-hexadecenyl acetate (Z11-16Ac), (Z)-9-hexadecenyl acetate (Z9-16Ac) and (Z)-11-heptadecenyl acetate (Z11-17Ac) are perceived by the males. This suggests that these substances may be female sex pheromone components.
The male olfactory sensilla also respond to (Z)-9-tetradecenyl acetate (Z9-14Ac) and (Z)-11-hexadecenol (Z11-160H), which are sex attractant constituents of various closely related species, but act as strong attractant inhibitors on M. brassicae males. This sensitivity to Z9-14Ac and Z11-160H is suggested to enhance the males' possibility to discriminate between conspecific and non-conspecific females.
Single sensillum recordings revealed that in 90% of the male antennal sensilla trichodea tested, three cell types (Types A, B, and C) were active. In the remaining 10% only B and C action potentials were seen. The Type C cells are exclusively responsive to the major pheromone component Z11-16Ac. The Type C cells are activated by the attractant inhibitors Z9-14Ac and Z11-160H, and to a small extent by Z11-16Ac. Responses to mixtures of these substances revealed that addition of Z9-14Ac and Z11-160H to Z11-16Ac changed the activity of the A cells only and did not affect the activities of the A and C cells. It is concluded that volatiles which exclusively or predominantly activate the Type B cells induce avoidance behaviour in the males, whereas substances activating the Type C cells evoke sexual behaviour and are attractive. This offers possibilities for relatively rapid electrophysiological determination of substances inducing sexual or avoidance behaviour. The function of the A cells is not yet clear. These cells respond to low concentrations of Z11-16Ac and Z11-160H, which may enhance the males' capacity to distinguish conspecific from non-conspecific females at a distance, when concentrations are low and the C and B cell activities are small.
It is suggested that cells sensitive to Z9-16Ac and Z11-17Ac are present in a limited number of sensilla only.