Monitoring of parasites in bumblebee colonies developed from controlled nesting of wild queens (Hymenoptera: Apidae: Bombus)

Abstract

Bumblebees (Apidae: Bombus spp.) are a major group of wild and domesticated bees that provide crucial ecosystem services through wildflower and crop pollination. However, most of bee populations, including bumblebees, are declining worldwide, partly because of parasite spill-over and spill-back between bumblebee commercial colonies and wild populations. Breeders have to cope with invasions by a vast array of bumblebees’ parasites, and techniques need to be developed to prevent such invasions to support breeders and wild bee populations. Our 10-year study is based on 327 nests of seven bumblebee species (B. humilis, B. hypnorum, B. lapidarius, B. lucorum, B. pascuorum, B. sylvarum, B. terrestris) reared in outdoor boxes. Some boxes were equipped with parasite-preventing techniques, namely (i) an airlock (n = 2) or (ii) an additional chamber with natural fragrances (n = 74). We recorded the invasion of the nests by the wax moth Aphomia sociella, the eulophid Melittobia acasta and the cuckoo bumblebees Bombus subgenus Psithyrus spp. Overall, 8.26 %, 1.53 % and 3.67 % of the colonies were invaded by A. sociella, M. acasta and Psithyrus spp., respectively, without coinfection. Neither the airlock nor the additional chamber with natural fragrances prevented A. sociella infestation. Despite that no nest equipped with an airlock or an additional chamber with natural fragrances was invaded by M. acasta or Psithyrus spp., we lacked replicates to properly demonstrate the efficiency of these techniques. Nest inspection remains a time-consuming but powerful technique to reduce artificial nest spoilage by parasites, yet it is inefficient against tiny invaders (< 1 mm) that are left unnoticed. We therefore encourage further studies to actively seek for parasite-preventing techniques to reduce artificial nest spoilage and to mitigate spill-over towards wild populations.