Responses to pheromone compounds in Mamestra suasa (Lepidoptera: Noctuidae) olfactory neurones

Abstract

Responses of olfactory receptor neurones to pheromone compounds were studied in male Mamestra suasa moths by electroantennography and single cell recordings. In electroantennogram screenings, (Z)-11-hexadecenyl acetate (Z11-16:Ac), the major pheromone component, and (Z)-9-tetradecenyl acetate (Z9-14:Ac), a behavioural inhibitor of male orientation to an attractive pheromone blend were more effective than 28 other compounds. The firing of olfactory neurones was recorded extracellularly in individual sensilla trichodea. Most of the sensilla exhibited the activities of two receptor cells, more rarely three. Screenings and dose-response experiments revealed that neurones which produced large amplitude action potentials (A cells) were specifically tuned to Z11-16:Ac. Z9-14:Ac was the key-compound of B cells, which were also excited by (Z)-11-hexadecenol (Z11-16:OH), (Z)-9-hexadecenyl acetate (Z9-16:Ac) and (E)-9-tetradecenyl acetate (E9-14:Ac). The B cells could constitute a sensory channel for inhibition of male sex attraction. The presence of a cellular type sensitive to Z9-14:Ac and to other compounds absent in M. suasa pheromone but frequently found in other Hadeninae suggests that B cells enhance reproductive isolation. None of the 14 tested compounds were found to increase the impulse rate of C cells. We found only one sensillum specialized in the detection of Z11-16:Ald, a minor component of the pheromone and a potent co-attractant for the males in mixture with Z11-16:Ac. It is concluded that, in M. suasa, minor components could be processed through a minority of specialized neurones.