Rates of juvenile hormone synthesis control caste differentiation in the stingless bee Scaptotrigona postica depilis.

In social insects the expression of caste-specific characters is controlled by juvenile hormone (JH) during definite sensitive periods in preimaginal development. For a number of stingless bee species the existence of such a JH-sensitive period has already been demonstrated. Queen development can be induced by topical JH applications during the cocoon spinning phase of the last larval instar. Neither JH titers nor rates of JH synthesis were known so far for this subfamily of eusocial bees distinguished by a pronounced caste dimorphism. As the pantropically distributed stingless bees with approximately 400 recent species are the largest group of social bees, JH synthesis was studied in one of the species that can be kept under laboratory conditions. An in vitro radiochemical assay was used to measure stage- and caste-specific activities of the corpora allata (CA). For the first time in a eusocial hymenopteran species it was demonstrated how the endocrine system is reacting to trophogenic stimuli capable to induce caste differentiation during larval development. Generally JH synthesis in queen CA was found to be 30-80% higher than in workers during the penultimate and last larval instar, but a strong and distinct caste-specific modulation of JH synthesis was only observed right before the onset of a JH-sensitive period in the cocoon spinning phase of the fifth instar.