Bumblebee infestation status and interspecific competition between bumblebees and honeybees increase with proximity to honeybee hives

Bumblebees are key pollinators in temperate regions of the northern hemisphere. Niche overlap and competition between bumblebees and honeybees may represent a significant stressor to bumblebees by reducing nutrient acquisition and facilitating spillover of pathogens and parasites from honeybees. One of these parasites is the bumblebee wax moth (Aphomia sociella), whose larvae can be found in bumblebee and wasp nests, as well as weakened commercial honeybee hives. Using Bombus terrestris colonies as experimental models, we expected that young queen and worker bumblebee immunity (measured by encapsulation response) would become weaker under both competitive (i.e., proximity to honeybee hives) and parasite (A. sociella infestation) pressure and, specifically, that the immunity of bumblebees in closest proximity to honeybee hives would be weakest in nests infested by A. sociella. We observed increased infestation, lower reproductive output, and weaker encapsulation response in bumblebee colonies that were near honeybee hives. Our data provide insights on the ecology of A. sociella infestations where honeybees and bumblebees coexist. Our observations of reduced immune response in bumblebees inhabiting colonies nearer to honeybee hives are of critical importance, as this reduction in immune response could facilitate additional infestations of other parasites and pathogens within bumblebee colonies.熊蜂（bumblebee）是北半球温带区域的关键传粉者。熊蜂与蜜蜂（honeybee）之间的生态位重叠与种间竞争，可通过降低营养获取效率、促进病原体与寄生虫从蜜蜂向熊蜂的跨宿主传播，对熊蜂构成显著胁迫。其中一类寄生虫为蜂蜡螟（Aphomia sociella），其幼虫可寄生于熊蜂、黄蜂巢穴以及衰弱的商业蜜蜂蜂箱中。本研究以大地熊蜂（Bombus terrestris）蜂群作为实验模型，假设在竞争胁迫（即与蜜蜂蜂箱近距离接触）与寄生虫（蜂蜡螟侵染）双重压力下，熊蜂处女蜂王与工蜂的免疫能力（以包囊反应为检测指标）会出现下降；且具体而言，距离蜜蜂蜂箱最近且同时遭受蜂蜡螟侵染的熊蜂蜂群，其免疫能力最弱。研究团队观测到，相较于远离蜜蜂蜂箱的熊蜂蜂群，近距离接触蜜蜂蜂箱的熊蜂蜂群其侵染率更高、繁殖力更低，且包囊反应更弱。本研究数据为蜜蜂与熊蜂共存环境下的蜂蜡螟侵染生态学提供了新的认知视角。我们观测到栖息于距离蜜蜂蜂箱较近的熊蜂蜂群免疫反应有所降低，这一发现具有关键意义：免疫反应的减弱可能会进一步加剧熊蜂蜂群内其他寄生虫与病原体的侵染风险。