Chemical communication in heliothine moths - IV. Receptor neuron responses to pheromone compounds and formate analogues in the male tobacco budworm moth Heliothis virescens

Single receptor cell recordings from the sensilla trichodea type 1 of the Heliothis virescens male antennae have revealed: 1) Three distinct types of receptor neurons, two previously identified types tuned to the principal pheromone components, (Z)-11-hexadecenal (Z11-16:AL) (79% of neurons recorded) and (Z)-9-tetradecenal (Z9-14: AL) (12%), and a third type (9%) that is tuned to (Z)-11-hexadecenyl acetate (Z11-16: AC). The acetate suppresses male attraction to conspecific females. 2) The Z11-16:AL receptor neurons respond with about equal frequency to the formate analogue, (Z)-9-tetradecenyl formate (Z9-14:FO) at comparable concentrations. The Z9-14:AL receptor neurons, however, show only weak responses to the corresponding formate (Z)-7-dodecenyl formate (Z7-12:FO). These results correlate well with results from field studies, showing that Z9-14:FO can substitute behaviourally for Z11-16:AL, whereas Z7-12:FO cannot substitute for Z9-14:AL. 3) The Z11-16:AC receptor neurons also respond to Z7-12:FO at higher concentrations. Therefore, Z7-12:FO would not be able to simulate the effect of Z9-14:AL, even at high concentration, because Z7-12:FO would mediate suppression of pheromone attraction through the Z11-16:AC neurons. 4) A difference in the interaction between the pheromone aldehydes and their membrane receptors is shown by the different effects of the two formate analogues. Furthermore, shortening and lengthening of the two moieties of the Z11-16:AL chain does not reduce the stimulatory effect to the same extent.