CASTE DETERMINATION IN BOMBUS-TERRESTRIS - DIFFERENCES IN DEVELOPMENTAND RATES OF JH BIOSYNTHESIS BETWEEN QUEEN AND WORKER LARVAE

To study the possible role of juvenile hormone in caste determination in Bombus terrestris, we measured development and rates of juvenile ho rmone biosynthesis in vitro in larvae destined to develop into either workers or queens, Larvae of both castes developed through four instar s and had the same growth rates, However, the duration of the instars was longer for queen larvae, and their head width at the third and fou rth instars was significantly larger, After validating the well-known radiochemical assay of JH for bumble bee larvae, we show that worker l arvae corpora allata exhibited a constant and low rate of JH biosynthe sis, never more than 5 pmol JH/h/pair, Queen larvae, in contrast, had two peaks of JH biosynthesis: a small one during the first instar, whi ch has previously been correlated with caste determination; and a larg e peak, previously undetected, above 40 pmol JH/h/pair, during the sec ond and third instars, We suggest that caste determination in this spe cies is mediated by JH and that the duration of larval instars is a ke y factor, The possibility that the queen influences caste determinatio n via an effect on instar duration is also discussed. (C) 1997 Elsevie r Science Ltd.