The use of drone congregation behaviour for population surveys of the honey bee Apis cerana

Honey bees (Apis spp.) are important pollinators in many natural and agro-ecosystems across the world. Effective means of surveying wild populations are therefore key to their conservation and management. One available survey method infers honey bee colony density from the genotype of drones (males) sampled from sites known as Drone Congregation Areas (DCAs). While this approach has been commonly used for the Western honey bee (A. mellifera), its feasibility for other Apis species is unknown. Here, we investigate drone congregation behaviour in the Asian honey bee Apis cerana in north-east Australia and its suitability for inferring colony density. As this A. cerana population is invasive, surveys in this case can aid in monitoring the population’s growth and spread. Over 5 years, we identified 30 DCAs, many of which were stable across time. DCAs were sheltered areas beside tree-lines or openings in the forest canopy. A. cerana drones joined DCAs during 1–2-h afternoon intervals and could be sampled at heights of 2–24 m via adhesive lines attached to helium balloons carrying lures coated in queen pheromone. Drones were more likely to be present at a DCA as temperature increased, though abiotic factors did not predict overall drone abundance. Drones could be sampled in low numbers even where colony density was extremely low. Based on the genotyping and inferred sibship of drones sampled at DCAs between 2016 and 2021, we estimate population density in Australia’s A. cerana to be in the range 1.1–8.1 colonies/km2. This extrapolates to a total population size in the range 11,000–83,000 colonies, with more refined estimates requiring better knowledge of drone flight distance and the effect of habitat on colony density. We conclude that population surveys based on drones from DCAs are possible for A. cerana and propose that this approach be part of a toolkit of methods used to monitor Asian honey bee populations in both their native and invasive ranges.