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Effect of exogenous juvenile hormones on mating behaviour and yellow colour in allatectomized adult male desert locusts

ABSTRACT. A comprehensive dose–response study of exogenous juvenile hormones, JHI and JHIII, on mating behaviour and on yellowing was carried out in allatectomized, crowded adult Schistocerca americana gregaria males. Injections of either hormone induced mating behaviour, but topical applications were almost completely ineffective. In contrast, topical applications were at least as effective as injections for inducing yellow colour. Induction and/or intensity of mating behaviour was dependent on the number of (repeated) administrations (from one to eight) and on the cumulative dose (80 or 160/μg) of the hormone, but these factors, within the above ranges, showed no distinct dose‐response relationship to yellowing. Even 160/μg of cumulative dose, given in the relatively most effective way (eight repeated injections of 20 /μg each), did not fully restore mating behaviour; the level of maximum intensity reached about half of that obtained for non‐allatectomized controls. JHI and JHIII did not differ markedly in this respect, but a 1:1 mixture of the two hormones improved the effect, revealing a mild synergy. JHI induced maximum or near maximum yellowing, but JHIII, under any conditions tested, was unable to induce full yellowing. The effect was always temporary; after cessation of JH administrations mating behaviour rapidly declined and the yellow colour slowly faded. The results indicate that the response of the two physiological systems (male mating behaviour and yellowing) to exogenous JH is completely independent. Although, depending on conditions of administration and on the kind of hormone, exogenous JHs were able to restore mating behaviour and yellowing, effective doses were extremely high. These conclusions are further discussed.