Interactions between two species of recently-sympatric invasive honeybees: Apis cerana induces aggression in Apis mellifera during foraging

Honeybees Apis mellifera (European honeybee) and Apis cerana (Asian honeybee) are cosmopolitan, having colonized continents beyond their natural ranges. In tropical Australia, these alien species have recently become sympatric. The environmental and economic impacts of these species when in sympatry remain to be seen; however, any interspecific competition may be of significance. We examined conspecific and heterospecific interactions between honeybees foraging at the nectar- and pollen-providing flowers of Antipogon leptopus (Polygonaceae). We cross-classified 554 encounters by three variables; incoming bee species, resident bee species, and one of four potential responses: (1) incoming defers to resident; (2) incoming procures the flower from resident; (3) incoming and resident share the flower; or (4) both incoming and resident abandon the flower. We also measured aggression and foraging rates of workers at flowers. Both species visited similar numbers of flowers in a foraging bout and spent similar foraging times on individual flowers. Incoming A. mellifera were more likely to procure flowers from resident A. cerana, and incoming A. cerana were more likely to defer to resident A. mellifera. A. mellifera were more aggressive toward heterospecifics than conspecifics, with heterospecifics 4.5 times more likely to provoke an aggressive response. However, no significant difference between conspecific and heterospecific aggression was observed for incoming A. cerana. A. mellifera were less abundant, yet overall more likely to acquire flowers and use aggression to do so. Costs of aggression may help explain the population-scale dominance of A. cerana over A. mellifera in this study.

西方蜜蜂（Apis mellifera，European honeybee）与东方蜜蜂（Apis cerana，Asian honeybee）均为广布性物种，其已成功拓殖其自然分布区之外的各大陆。在澳大利亚热带地区，这两种外来蜜蜂现已形成同域共存的分布格局。二者同域共存时所产生的环境与经济影响尚待探明，但二者间的种间竞争极可能具有重要生态学意义。本研究针对在蓼科（Polygonaceae）Antipogon leptopus提供花蜜与花粉的花朵上觅食的蜜蜂，开展了种内与种间互动行为的观察分析。我们通过三个变量对554次蜜蜂互动事件进行交叉分类：到访蜂物种、驻留蜂物种，以及四种可能的互动结果之一：(1) 到访蜂避让驻留蜂；(2) 到访蜂从驻留蜂处获取该花朵的访问权；(3) 到访蜂与驻留蜂共享该花朵；(4) 到访蜂与驻留蜂均放弃该花朵。此外，本研究还测定了工蜂在花朵处的攻击行为与觅食速率。两种蜜蜂在单次觅食事件中访问的花朵数量相近，且在单朵花上的觅食时长也无显著差异。当驻留蜂为东方蜜蜂时，到访的西方蜜蜂更易获取该花朵的访问权；而当驻留蜂为西方蜜蜂时，到访的东方蜜蜂更易选择避让。西方蜜蜂对异种个体的攻击意愿显著高于同种个体，异种个体引发其攻击行为的概率是同种个体的4.5倍。但对于到访的东方蜜蜂而言，其针对同种与异种个体的攻击行为并无显著差异。西方蜜蜂的种群丰度较低，但整体上更易获取花朵访问权，且会通过攻击行为达成这一目的。攻击行为的代价或可解释本研究中东方蜜蜂在种群规模上优于西方蜜蜂的现象。