Juvenile hormone inhibits differentiation of olfactory sense organs during postembryonic development of cockroaches

The density of olfactory sense organs on the antenna of the cockroach, Leucophaea maderae, is relatively constant throughout larval development (average 400 sensilla/mm 2), but undergoes a substantial increase at the adult state (to about 620 sensilla/mm 2). Experimental manipulations of juvenile hormone (JH) activity result in either supernumerary larval instars (induced by unilaterla antennectomy or addition of exogenous JH), or premature adulthood (induced by allatectomy). The density of antennal sensilla remains at the larval level during the extra instars, but increases to the adult level or surpasses it at the terminal ecdysis following the induction of extra instars. Adultoids resulting from allatectomized sixth instars also have the high density of antennal olfactory sensilla characteristic of the normal adult. These data suggest that an interplay of surface area effects and an inhibitory action of JH controls the pattern of postembryonic development of antennal olfactory sensilla. Limited behavioural observations of the insects resulting from these experiments are consistent with the hypothesis that sex attractant-specific olfactory receptors appear only at the adult stage. However, electrophysiological data will be needed to confirm or negate this hypothesis.