Dorothee Hoffmann, Dept. of Zoology, Martin-Luther University Halle-Wittenberg, Hoher Weg 4, 06099 Halle (Saale), Germany, Peter Neumann, Swiss Bee Research Centre, Eidgenössische Forschungsanstalt für Nutztiere und Milchwirtschaft (ALP), Schwarzenburgstrasse 161, CH-3003 Bern, Switzerland, and Jeffery S. Pettis, USDA-ARS Bee Research Laboratory, Bldg. 476 BARC-E, Beltsville, MD 20705.
Invasive parasite species, such as the small hive beetle (= SHB), may switch to alternative hosts in their new ranges. Bumblebees do not occur in the natural range of the SHB in sub-Saharan Africa, but in its new range in North America. It has been shown that in the field SHB do infest commercial bumblebee colonies, and that they can complete an entire life cycle in artificially infested Bombus impatiens colonies in the laboratory. We investigated the host preference of SHB by releasing 1000 adults in a flight room with four commercial bumblebee colonies, four honeybee nucleus colonies and four empty control boxes. After 36 hours the colonies were euthanized and the infestation level was determined. There were significantly more beetles in the bumblebee colonies than in the controls. In all four bumblebee colonies, SHB had started to lay eggs. We also assessed bumblebee defensive behaviour at the colony level. SHB eggs and larvae were introduced into ten commercial bumblebee colonies, and removal rates were monitored for 24 hours. A large proportion of unprotected eggs and of larvae was removed by the workers, but most of the protected eggs remained in the colonies. Bumblebees showed aggressive behaviour towards SHB larvae such as grabbing, biting and stinging. We conclude that commercial bumblebee colonies are attractive to small hive beetles and may serve as alternative hosts, but do show behavioural defence mechanisms. The vulnerability of wild soil-dwelling Bombus colonies to SHB needs to be assessed in field studies.
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