Endocrine manipulations and ontogenesis of male sexual behaviour in Locusta: studies on precocene-induced early adultiforms

ABSTRACT. Fourth- and third-instar permanent adultiforms of Locusta migratoria migratorioides (R.&F.) were produced by applying 7-ethoxy-precocene II (precocene III) to hoppers in earlier stages. The mating behaviour of male adultiforms and the effects of injected exogenous juvenile hormone III (JH) on this behaviour were investigated quantitatively and the results were compared to those obtained for normal adult males and for adult males chemically allatectomized by precocene III. Fourth- and third-instar adultiform males exhibited sexual behaviour and injections of JH intensified this behaviour in a dose-dependent manner, though the number of repeated injections in which a cumulative dose is administered was found to be not less important than the amount of the cumulative dose itself. Huge repeated doses (6×144=864 μg) of JH temporarily induced normal intensity of mating behaviour in fourth-instar male adultiforms. The same doses of JH intensified mating behaviour also in third-instar adultiform males, but less markedly so than in fourth-instar ones. For restoring temporarily normal intensity of mating behaviour in chemically allatectomized but morphogenetically normal adult males, much smaller doses (2×36=72, or 2×72=144μg) of JH were sufficient. In contrast, even huge doses of JH were unable to induce mating behaviour in normal (no precocene-treated) male hoppers. Thus, the ethological ontogenesis (='ethogenesis') of the male's mating behaviour, including the response of the system to JH, is clearly accelerated by precocious metamorphosis. However, this is not a simple 'all or none' effect, because adultiforms in earlier stadia exhibit less intense male mating behaviour and more limited response to JH than adultiforms in later stadia or adults.