Male moths are often extremely sensitive and narrowly tuned to the blend of components emitted by conspecific females. The sexual communication channel is therefore under strong stabilizing selective pressure. How then do new female blends and male preferences evolve? We have employed behavioral, neurophysiological and genetic techniques to study this question in two closely related moth species, Heliothis virescens and Heliothis subflexa, that can hybridize under laboratory conditions. Males of these two species prefer qualitatively distinct blends that include either Z9-14:Ald (H. virescens) or Z9-16:Ald (H. subflexa). In addition, H. subflexa males require Z11-16:OH. These behavioral preferences are correlated with the specificity of olfactory receptor neurons and central interneurons arborizing within the glomeruli of the male-specific macroglomerular complex. Wind tunnel studies have shown that Z9-14:Ald/Z9-16:Ald preference segregates in a 1:1 ratio in backcross males. Preliminary genetic (QTL) analyses have revealed that this trait is associated with a single autosomal chromosome suggesting that a major gene may control this phenotype, perhaps coupled to the expression of odorant receptors. Other divergent characters in this system, such as Z11-16:OH-agonism and Z11-16:OAc-antagonism, may involve odorant receptors but also likely involve shifts in the glomerular targets of receptor axons and interpretation of olfactory information by higher brain centers. Supported by NSF IBN-9905683 to NJV.