Chemical communication in heliothine moths

Abstract

1. Projection patterns of olfactory receptor neurons, specifically tuned to the two principal components of the female H. virescens sex pheromone blend, and to a third pheromone-like compound of possible antagonistic significance, were examined using a combined electrophysiological and morphological technique. 2. The macroglomerular complex consists of four major glomerular subdivisions. 3. In the sensillum type containing a receptor neuron detecting the main pheromone component, Z11-16: AL, two cells were present. When the sensillum was stimulated with Z11-16:AL, a single axon, stained by a method that selectively stains active neurons, was seen projecting into the large a glomerulus. The b glomerulus was innervated by a second neuron in a few double stainings. 4. In a second sensillum type, one receptor neuron tuned to the second major pheromone component, Z9-14:AL, was found. In these sensilla, one or two receptor neurons of unknown specificity were also observed. When the sensillum was stimulated with Z9-14: AL, a single neuron projecting into glomerulus a or two neurons projecting into glomerulus a were most often observed. 5. In the third sensillum type, one neuron specifically tuned to Z11-16:AC projected to glomerulus c, and a second cell of unknown specificity projected to the same area. 6. The axonal arborizations of different physiological receptor neuron types involved in the detection of the pheromone blend do not display a clearcut morphological separation into different glomeruli in the MGC. A separation between neurons detecting attracting and repelling odours was, however, present.