Some studies on the biology of bumblebees (Hymenoptera: Bombidae)

Abstract

The ecological conditions under which bumble bees hibernate have been investigated and differences noted in the type of site chosen for overwintering by certain species. Queens were most often found 8cm. below the surface, but the depths at which hibernacula are constructed vary according to soil conditions. Spring soil temperatures in hibernacular positions typical of early-emerging species such as Bombus lucorum (Linn.) show higher daily maxima than temperatures in positions typical of later-emerging species such as B. lapidarius (Linn.). The characteristics of the adult fat body of bumblebees are described, with particular reference to queens. Both fat and glycogen, but not protein, are stored in the trophocytes. In queens about to enter hibernation, fat forms 34[percent] of their total dry weight. The utilization of both fat body reserves and honey stomach contents during hibernation, particularly in the autumn, has been demonstrated. Investigations of natural incipient colonies of bumblebees have shown that 1st brood adults produced may be divided into two groups according to size. Typically, the larger individuals develop in the centre of the brood clumps and are the first adults to emerge. The number of eggs laid in incipient colonies varies according to the species. In B. agrorum (Fabr.), for example, 8 eggs and in B. hortorum (Linn.) 12 to 14 eggs aregenerally laid. The immature stages of Syntretus splendidus (Marshall), a gregarious endoparasite of adult bumblebees, are described and an account given of its life history. Five larval instars have been recognized. In the late spring and early summer of 1967, the incidence of parasitism among foraging bumblebee queens exceeded 17[percent], and in foraging workers. The brood rearing ability of parasitized queens is impared and parasitic castration occurs. The host dies shortly after the emergence of the full-grown parasite larvae from its body.