Trans-sexually grafted antennae alter pheromone-directed behaviour in a moth

When tobacco hornworm moths (Manduca sexta) are tested in a wind tunnel with a source of female pheromones upwind, males but not normal females show pheromone-modulated anemotaxis and a characteristic mate-seeking behavioural sequence^1-7. These behaviours are produced by stimulation of sensory neurones found only in male antennae^8-10. These neurones project axons only to dendrites of pheromone-specific interneurones^11,12 in the macroglomerular complex, a region of neuropil in the antennal lobe characteristic of males but not present in normal females^13-15. Some interneurones in the antennal lobes of female moths that have received grafts of male antennae (gynandromorphs) respond postsynaptically to stimulation with bombykal, a major component of the pheromone¹⁶. They branch into a region resembling the macroglomerular complex¹⁶, like their counterparts in normal males. We show here that gynandromorphic females respond to pheromonal stimulation with anemotaxis. We also find that normal females display a similar sequence in response to the odour of their egg-laying site, the tobacco plant. It is likely that a common motor path is used either by pheromone-specific interneurones in the antennal lobes of males or by tobacco-specific interneurones in females. We assume that the interneurones in gynandromorphic females that branch into the macroglomerular complex induced by a grafted male antenna can activate this pathway.