Juvenile hormone control of oögenesis in bumblebee workers, Bombus terrestris

Abstract

In queenright workers of Bombus terrestris oögenesis is inhibited by the queen, the activity of the corpora allata is suppressed, and the resulting JH titer in the haemolymph remains low. In contrast, in queenless workers the JH production is stimulated on the first day of adult emergence, the JH titer increases, and eggs are rapidly formed. After injection of JH I in newly emerged workers oögenesis can also be induced in the presence of a queen in the same way as in queenless workers. The induced oögenesis is JH dosage dependent, dosages of less than 8 μg stimulate the production of vitellogenins, whereas a complete oögenesis can be induced by high dosages of about 50 μg. From studies on the rate of JH excretion it can be concluded that such high dosages must be injected to obtain the required JH titer during the whole egg maturation of 5 days. It is evident, therefore, that the initiation and the maintenance of oögenesis depends on JH. The injected JH ester is completely degraded to JH acid and JH diol mainly in the hindgut. The excretion starts quickly after the injection, but only traces of unchanged JH are excreted. From these results it can be suggested that a queen inhibits egg maturation in workers by suppressing the JH production in the corpora allata and thus lowering the JH titer. This influence also enables a queen to block oögenesis once stimulated, for instance in queenless workers. Breakdown of JH and excretion are not under the control of the queen and therefore neither of them play any rôle in regulating egg maturation in the worker caste.