Abstract
As a signature of reproductive interference (RI), we reviewed hybrid production in eusocial bumblebees in Japan, by comparing introduced Bombus terrestris with native B. ignitus in Honshu (main island of Japan) and with native B. hypocrita sapporoensis in Hokkaido (northern island of Japan). In this review, we present additional new data showing hybrid production between introduced B. terrestris and native B. ignitus in Honshu. Interspecific mating with introduced B. terrestris disrupts the reproduction of native B. h. sapporoensis and B. ignitus, which belong to the same subgenus of Bombus, through inviable egg production. This interference appears to facilitate species replacement on Hokkaido. Simultaneously, the mating frequencies for queens of B. terrestris have increased, suggesting that polyandry might evolve in response to the extent of RI between B. terrestris and B. h. sapporoensis. To suppress the population size of B. terrestris in Hokkaido, two methods have been proposed: the mass release of B. h. sapporoensis males to induce RI between the two species and the spraying of insecticides against foraging workers so that the workers will carry the insecticides back to their colonies, killing the immature bees within the colonies. A candidate insecticide type is insect growth regulator, which may disrupt larval development without any apparent effect on foraging workers.
Highlights
Negative interspecific interactions between closely related species during the process of mating can lead to species exclusion [1,2,3,4,5,6]
Colonies of B. terrestris were reared from mated queens, which were held for 3 months at 2 ◦ C before nest initiation and introduced into a rearing chamber maintained at 28 ◦ C and 60% relative humidity (RH) with a B. terrestris pupa to elicit oviposition and provided with sufficient pollen and sugar solution
Until the introduction of B. terrestris, allopatric distribution alone was sufficient to prevent interspecific mating between B. terrestris and B. h. hypocrita or B. h. sapporoensis. This finding is a good example of an introduced alien species breaking down a reproductive barrier that was constructed through a long evolutionary history. These findings indicate that reproductive interference (RI) by B. terrestris disrupts the reproduction of B. h. hypocrita, B. h. sapporoensis and B. ignitus, which all belong to the subgenus Bombus
Summary
Negative interspecific interactions between closely related species during the process of mating can lead to species exclusion [1,2,3,4,5,6]. Such sexual interactions, known as reproductive interference (RI), have been suggested to protect the coexistence of the two interacting species, leading to parapatry [1,2]. Hybrid inviability and/or infertility is more likely to have negative impacts on the less abundant subspecies or species within the pair. RI was proposed as a promising method to eradicate the invasive melon fly using the sterile insect technique
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