British Insects: Bumblebees and Cuckoo-bees
Subspecies campestris s. str., swynnertoni Richards.
Biology. Solitary insects, parasitic on social bumblebees; the adult populations comprising males and fertile females only; the larvae parasitic in the nests of host Bombus species; hosted by B. muscorum, B. pascuorum, B. ruderarius, and B. sylvarum (long known to be associated with B. pascuorum, but probably parasitizing all Carder bumblebees).
Adult morphology. Adults about 14–20 mm long (females about 18 mm, males about 15 mm). The hair coats of abdomen and thorax conspicuously colour-patterned (usually), or more or less homogeneously coloured or merely shaded darker to lighter; predominently when unpatterned, more or less all-black (melanism being fairly common, especially in males); all black except for a contrasting abdominal tail, or not all black anterior to a contrasting abdominal tail. Face at least as wide as long, or wider. The facial hairs of males black; vertex black haired. The facial hairs of females black; vertex black haired. The mandibles of the females obliquely-ended. Antennae of the male with the third segment shorter than the fifth (the 5th about 2/3 as long as the 3rd and 4th together); with the third segment equalling or only slightly longer than the fourth. Thorax banded (black, with a gingery (female) or yellow (male) anterior band and a greyish or yellowish-grey one posteriorly; or both bands darkly yellowish-grey in dark forms of the male); when banded, black posteriorly, with a pale anterior band only, or black across the middle, with pale anterior and posterior bands; the light thoracic hairs mid-yellow, or yellowish grey, or gingerish yellow, or pale greyish whitish. The outer surface of the hind tibiae of females with no pollen basket, strongly and uniformly convex, dull and uniformly covered with stout hairs. The hind tibiae of the males having a fringe of short hairs along the outer margin. The hind basitarsus narrower than the tibia.
The abdomen black, only shortly tailed gingerish in females, but gingerish over the posterior half in light males. Abdomen not conspicuously patterned (in dark forms of the male), or conspicuously patterned (in females and light males); with a contrasting tail. The tail ginger. The tail with some black hairs (in males), or without black hairs. Abdomen without conspicuous banding between the anterior of the tail and the thorax. Abdomen without a line of yellowish hairs between the black ones and the white tail. Sternite 6 of females without a reflexed spiny process at the tip; without a median keel; with ventro-lateral keels; with large, conspicuous, bulging callosities associated with the ventro-lateral keels; the callosities separate, not coalescing and not visible from above. Sternite 6 of males with a black ventro-lateral hair-tuft on each side; posteriorly rounded, without bulges near the tip.
Male genitalia. The sagittae curved inwards around the spatha; with a small hook externally around the middle or somewhat above; apices apically turned slightly outwards and obliquely truncate, not hooked, or apically minutely punctate, not hooked (i.e., almost symmetrical and scarcely truncate). The ends of the claspers much expanded to somwhat expanded; pale and soft; not or only slightly emarginate, without teeth (but fringed); with the volsella readily visible at their ends (the visible tip broadly triangular and scarcely incurved, internally fringed).
British representation. Recorded from England, Wales, Mainland Scotland, Channel Isles, and Ireland. Widespread throughout the British Isles, less frequent in northwestern Scotland, and now perhaps confined in Ireland to the extreme south and west. The adults abroad during April to September (females), or June to September (males). In divers habitats.
Illustrations. • Psithyrus rupestris, P. vestalis, P. campestris, P. sylvestris, P. barbutellus: Saunders. • Comparing females of P. campestris and P. rupestris with their hosts (B. pascuorum and B. lapidarius). • Male genital capsules of Bombus and Psithyrus.
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Cite this publication as: ‘Watson, L., and Dallwitz, M.J. 2003 onwards. British insects: Bumblebees and Cuckoobees. Version: 1st January 2012. http://delta-intkey.com’.