Seasonal phenology and abundance of early-, mid- and long-season bumble bees in southern England, 1985–1989

Abstract

SUMMARYThe seasonal phenology of six Bombus species and four Psithyrus species is given for a site to the west of London, UK, for five years from 1985 to 1989. The emergence in spring of Bombus spp. queens was linked to periods with air temperatures above 11°C. During the five-year survey a mean maximum temperature of 12.1°C occurred during the week of initial oviposition, an increase of 1.9°C from the week preceding ovipositon. The colonies of Bombus spp. matured at different times: early-season during June, mid-season in early August and late-season in August or early September. The period between the emergence of queens and of their workers and males was on a progressive scale, from species maturing early to those maturing in mid-season. This is consistent with the increasing lengths of their colony cycles. Workers and males of the long-season bumble bees emerged in a shorter period than those of the mid-season species. When profiles for the three groups are shown separately they show a regular outline and are distinct. Density profiles of the mid- and long-season bumble bees show a trough which occurs in early July each year. This trough is a phase in the cycle and is probably caused by the rearing of reproductives. However, no trough occurs in the profiles of the early- maturing bumble bees. In some years periods of heavy precipitation or prolonged drought considerably reduced the population of the mid- and long-season bumble bees.