CHEMICAL COMMUNICATION IN HELIOTHINE MOTHS .5. ANTENNAL LOBE PROJECTION PATTERNS OF PHEROMONE-DETECTING OLFACTORY RECEPTOR NEURONS IN THE MALE HELIOTHIS-VIRESCENS (LEPIDOPTERA, NOCTUIDAE)

1. Projection patterns of olfactory receptor neurons, specifically tun ed to the two principal components of the female H. virescens sex pher omone blend, and to a third pheromone-like compound of possible antago nistic significance, were examined using a combined electrophysiologic al and morphological technique. 2. The macroglomerular complex consist s of four major glomerular subdivisions.3. In the sensillum type conta ining a receptor neuron detecting the main pheromone component, Z11-16 : AL, two cells were present. When the sensillum was stimulated with Z 11-16:AL, a single axon, stained by a method that selectively stains a ctive 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 seco nd 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 pro jecting into glomerulus a or two neurons projecting into glomerulus a were most often observed. 5. In the third sensillum type, one neuron s pecifically 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 involv ed in the detection of the pheromone blend do not display a clearcut m orphological separation into different glomeruli in the MGC. A separat ion between neurons detecting attracting and repelling odours was, how ever, present.