Impacts of commercialization on the developmental characteristics of native Bombus terrestris (L.) colonies

Bombus terrestris (L.) is naturally distributed mainly in Europe, and since 1988, it has been used commercially as a valuable pollinator of greenhouse crops in many countries, far beyond its natural range. Although the possible ecological impacts of this invasive species have been intensely discussed with respect to hybridization, we know little about the consequences of this nearly 30-year period of commercialization. We examined and compared the developmental characteristics of native and commercial colonies and their first-generation hybrids under the same laboratory conditions. Young queens and males produced in both native and commercial colonies were mated to generate four genotype groups: Native x Native (N-a (TM) Euro x N-a (TM),N-), Native x Commercial (N-a (TM) Euro x C-a (TM),C-), Commercial x Commercial (C-a (TM) Euro x C-a (TM),C-), and Commercial x Native (C-a (TM) Euro x N-a (TM),N-). The commercial genotype produced significantly more gynes and workers than did the native genotype. However, average gyne number of N-a (TM) Euro x N-a (TM),N- was not significantly different from the pooled N-a (TM) Euro x C-a (TM),C- and C-a (TM) Euro x N-a (TM),N-. The commercial genotype constructed more egg cells in the first brood and commenced egg laying earlier. Hybridization between commercial and native genotypes generally resulted in intermediate expression of the colony traits. Our data suggest that the maternal genotype primarily determines these colony traits. Our results imply that hybridization with the commercial genotype affected some colony traits of native B. terrestris colonies.