The nature and development of sex attractant specificity in cockroaches of the genus Periplaneta . II. Juvenile hormone regulates sexual dimorphism in the distribution of antennal olfactory receptors

Sexual dimorphism of antennal sense organs appears only at the adult stage during normal development of the cockroach, Periplaneta americana. Adult males acquire approximately twice as many olfactory sensilla as females at the terminal ecdysis. When terminal instar larvae are subjected to unilateral antennectomy, most ecdyse to supernumerary larvae rather than adults. Sexual dimorphism is not evident in the intact (unamputated) antenna during the extra larval stage, but appears at the following ecdysis which leads to the adult stage. Allatectomy of male and female larvae in the penultimate instar produces adultoids which show antennal sexual dimorphism. Whole‐body treatment of terminal instar larvae with exogenous juvenile hormone‐mimic (JH‐M) results in supernmerary larvae which lack antennal sexual dimorphism. When these superlarvae are removed from the influence of JH‐M, they ecdyse to adults with antennal sexual dimorphism. Topical application of JH‐M to male antennae early in the terminal larval instar results in the emergence of adults which lack the total male complement of antennal sensilla, but are otherwise normal‐appearing. These results indicate that an inhibitory action of juvenile hormone prevents the appearance of antennal sexual dimorphism during normal larval development.