Effect of juvenile hormone treatment on caste differentiation in the honeybee, Apis mellifera

Abstract

Synthetic juvenile hormone (methyl trans,trans,cis-10-epoxy-7-ethyl-3,11-dimethyl-2,6-tridecadienoate, 1 μg/μl acetone per animal) (JH) was topically applied to 2- to 3-day-old worker honeybee larvae in the hive. Eighty per cent of the hormone-treated larvae were removed from their brood cell before pupation. Only 1 out of 42 adults showed characteristics of an intercaste. Fifty per cent of the control larvae (1 μl acetone) developed to adults, all of which were workers. After topical application of JH and feeding on royal jelly under in vitro conditions, the rate of survival is high (up to 85 per cent adults), but up to 67 per cent of queens and 44 per cent of workers exhibit eye malformations with characteristics of somatic mutation. Formation of a more solid web by the spinning larvae, shortening of the diapause by 1 to 2 days, and unusual shapes of mandibles, legs, and abdomen are a consequence of hormone treatment. The effects are less marked after application of 0·1 instead of 1 μg hormone or after its addition to the food (2 μg/g royal jelly). Treatment of the 2- to 3-day-old worker larvae and subsequent rearing on royal jelly is followed by a shift in caste differentiation from queens and workers to intercastes. In no case, are more queens developed after juvenile hormone treatment. Queen bee determinator, partially purified from royal jelly, induces a concentration-dependent shift from workers to queen differentiation. A threefold increase in the natural determinator concentration of royal jelly results in an almost exclusive (98 per cent) queen formation from 2- to 3-day-old worker larvae. In contrast to this direct effect, the influence of JH is explained as an indirect morphogenetic effect not directly coupled with honeybee caste differentiation.