Invariance and sex-specific variations of the glomerular organization in the antennal lobes of a moth, Mamestra brassicae, and a butterfly, Pieris brassicae.

The glomerular organization of the antennal lobes was analyzed in the moth Mamestra brassicae and comparatively in the butterfly Pieris brassicae. The invariance of the lobes in number, position, and size of the glomeruli was verified quantitatively in the moth for all the glomeruli in individuals of the same sex (67 in males, 68 in females) and for 56 sex-invariant glomeruli which can be identified in all individuals whatever their sex. In the butterfly, the positional variability is greater than in the moth and hinders identification. The most conspicuous sex-variant glomeruli are two adjoining macroglomeruli in the male moth which have homologs of very small size in the female. No such dimorphism was observed in Pieris, a species in which males are attracted to female by visual stimuli and not by a sex pheromone as in Mamestra. There are other sex-variant glomeruli in Mamestra: four varying in location, three subdivided in the female, two found only in the male, and three found only in the female. Consequently, differing olfactory sensitivity related to species and sex could correlate with detectable modifications in the glomerular organization. A hypothesis on the function of glomeruli is discussed in which most of the glomeruli are viewed as "olfactory generalists" giving rise collectively to proposed "across-glomeruli patterns."