Long-range dispersal of small hive beetles

Aethina tumida, bumble bees, honey bees, stingless bees Journal of Apicultural Research 51(2): 214-215 (2012) © IBRA 2012 DOI 10.3896/IBRA.1. 51.2. 11 Small hive beetles (SHB), Aethina tumida, are parasites and scavengers of social bee colonies in their endemic range in Africa as well as in the USA and Australia (Neumann and Ellis, 2008; cf. Hoffmann et al., 2008; Halcroft et al., 2011). It is currently unknown whether adult SHB which have emerged from the soil but have not yet conducted any flights are attracted to neighbouring host colonies or conduct long range dispersal instead. Here we studied whether the presence of neighbouring host colonies distracts migrating SHB. We conducted a field trial (Experiment A) in the USA using a circle of alternating honey bee (Apis mellifera) and native bumble bee (Bombus impatiens) colonies. In Australia (Experiment B), we also arranged A. mellifera and native stingless bee (Trigona carbonaria) colonies (Bombus spp. do not occur in mainland Australia) in a circle but within a greenhouse, to enforce host choice by SHB. In both experiments, all colonies remained in their original colony boxes (mating nuclei for A. mellifera, cardboard boxes for the bumble bees and wooden OATH hives (Dollin & Heard, 1999) for the stingless bees), but were placed in new unused standard single ten-frame Langstroth hive boxes to give them a similar external appearance. Honey bee mating nuclei were chosen to match the size of the bumble bee and stingless bee colonies, so as to provide a similar amount of odour cues for beetle orientation (Torto et al., 2005). We used laboratory-reared, 2-3 weeks old SHB adults (Neumann et al., 2001), which were maintained on a honey/pollen diet (Hoffmann et al., 2008). Those SHB had neither any prior contact with any of the tested host bees nor had a chance to conduct any dispersal flights whatsoever. The SHB were released at dusk from boxes (N = 3,000 each) in the centre of the circles (AE = ~15m). Twenty-four hours later, the release boxes as well as all colonies were sealed, transported to the laboratories, freeze-killed and thoroughly dissected for the number of bees and adult beetles. LED lights were used to detect the dark adult SHB inside of the nests, because their colour camouflages them, especially in used darkish honey bee combs or stingless bee nest constructions. The data clearly show that the presence of neighbouring host colonies does not distract adult SHB, which have previously emerged from the soil, from conducting long-range dispersal flights. The results further suggest that SHB seem to prefer B. impatiens over A. mellifera and A. mellifera over T. carbonaria host colonies (Table 1). This must be interpreted with caution, however, because the vast majority of SHB (>92% in both experiments) did not enter any host colony and instead either left the entire apiary or remained in the corners or at the ceiling of the greenhouse. The age and mating status of the tested SHB appears less relevant, because 2-3 week old SHB were used in both experiments, which were sexually mature and had probably already mated (casual observations during the laboratory rearing). The findings therefore strongly support that, indeed, adult SHB initially conduct long-range dispersal flights (Spiewok et al., 2008) regardless of the presence of host colonies in close proximity (<15 m). This appears adaptive in the light of destructive SHB mass reproduction, which can produce thousands of beetles in a given area, as well as absconding and the dispersed distribution of host colonies. SHB often, however, use cryptic low-level reproduction and beetle dispersal behaviour could differ under less crowded conditions and, thus, deserves further research.