Distinct protocerebral neuropils associated with attractive and aversive female-produced odorants in the male moth brain

Reproductive behavior of sympatric heliothine species depends on a few female-produced compounds including both intra- and inter-specific signals serving as attractants and repellents, respectively. In the male moth, Helicoverpa armigera, three male specific glomeruli receive input about three female-produced compounds: the primary pheromone, serving as an attractant, and two minor constituents, serving a dual function, i.e. attraction versus inhibition of attraction. From the antennal-lobe glomeruli, the signals are carried to higher brain centers via three parallel tracts: the medial, lateral, and mediolateral antennal-lobe tract (mALT, lALT, mlALT). Based on intracellular recording/staining of individual MGC output neurons (29 medial-tract neurons, 10 lateral-neurons, and 3 mediolateral-tract neurons), we found distinct properties typifying the neurons confined to each tract. Notably, output neurons passing along the two main tracts, the medial and the lateral, had distinct morphological and physiological characteristics. The medial-tract neurons, originating from all MGC-units, had wide-spread protocerebral projections organized according to behavioral significance, including a spatial separation of signals representing attraction versus inhibition. The lateral-tract neurons, on the other hand, originating exclusively from the largest MGC-unit, converged onto a distinct protocerebral region. Altogether, the data presented here, indicate the different roles of the parallel tracts – suggesting the involvement of lateral-tract MGC neurons in robust odor evoked flying behavior and the medial-tract neurons in fine-tuned signal processing including identification of attractive versus repulsive signals.