Phenology of the specialist bee Colletes hederae and its dependence on Hedera helix L. in comparison to a generalist, Apis mellifera

Abstract

Colletes hederae, the ivy bee, (Hymenoptera: Colletidae) has undergone large range expansions in Europe in recent years, including colonising Britain in 2001 with its original distribution limited to Western mainland Europe and the Channel Islands. It is thought to specialise on Hedera helix L. (Apiales: Ariliaceae), common ivy. However, some research has questioned this dependence. This study quantifies the foraging ecology of C. hederae to determine its relationship with ivy in Sussex. We quantified the phenology of ivy bloom, C. hederae activity and flower visitation, and pollen collection of females through pollen analysis. We also gathered equivalent data on Apis mellifera both as a comparison and to assess alternative pollen sources. The phenology of female C. hederae activity was highly correlated with and phonologically contained within the ivy bloom period. Pollen analysis from C. hederae identified ivy pollen was 98.5% of samples, significantly more than for A. mellifera (90%). Two other plant species were identified and more common in C. hederae samples when ivy bloom was not at its peak. Surveys of ivy flowers surrounding the aggregations found that C. hederae were the most common insect (26%) foraging on ivy. Although C. hederae can forage on other species, ivy was found to be an important floral resource. The results also suggest the potential for competition with A. mellifera, the only other bee present in more than small numbers on H. helix flowers, as although A. mellifera is a generalist, in autumn it mainly forages on ivy.