Quantifying a Rare Event: Pollen Theft by Honey Bees from Bumble Bees and Other Bees (Apoidea: Apidae, Megachilidae) Foraging at Flowers

Although honey bees (Apis mellifera L.) (Hymenoptera: Apidae) frequently raid conspecific colonies for pollen and nectar stores (Winston, 1987; Downs et al., 2001), they are rarely observed stealing pollen from foraging bees of other species (Laroca and Winston, 1978; Thorp and Briggs, 1980). Here I report observations of honey bees stealing pollen from three species of bee (Bombus impatiens Cresson (Apidae), Megachile montivaga Cresson (Megachilidae), and Melissodes desponsa Smith (Apidae)) at flowers of pasture thistle, Cirsium discolor (Muhl.) Spreng. (Asteraceae) in Indiana. This is the third report of such behavior, and like the others was observed at an Asteraceae species (Thorp and Briggs, 1980; Laroca and Winston, 1978). It is the first report to quantify the rarity of the behavior in Apis; based on this it is no surprise that there are few published reports. In addition, this is the first observation of pollen theft behavior in the eastern United States; previous reports were from California (Thorp and Briggs, 1980) and Kansas (Laroca and Winston, 1978). This is also the first report of a fast-flying (Melissodes) species being subject to cleptolecty (Thorp and Briggs, 1980), the theft of pollen from the pollen collecting apparatus of other bees by honey bees. I also report observations of honey bees collecting pollen from the abdomen of a bumble bee worker and a megachilid forager, similar to the pollen theft previously reported by Laroca and Winston (1978). I made these observations during a three-year (2001-2003) survey of bees in 5 sandy black oak savannas of northwestern Indiana. I netted bees at over 70 species of flowering plants from April-September each year, visiting each site approximately biweekly, and paying special attention to overlap in flower use by honey bees and native bees. Honey bees were commonly observed on flowers of Lupinus perennis L. (Fabaceae), Rubus spp. (Rosaceae), Scrophularia lanceolata Pursh. (Scrophulariaceae), Tradescantia ohiensis Raf. (Commelinaceae), Solidago spp. (Asteraceae) and Cirsium discolor, but pollen theft was only observed on C. discolor at a single site, and then only on three days. Pollen theft was observed on three days (30 August, 5 and 7 September 2003) at Conrad Station, Newton County, a savanna owned by The Nature Conservancy. Here, populations of C. discolor grow along abandoned railroad tracks. Common floral visitors include A. mellifera, B. impatiens, Bombus griseocollis (DeGeer), Melissodes desponsa, Megachile montivaga, and Ceratina spp. (Apidae). Two hives of A. mellifera were maintained 0.5 km from the thistle patch. Cirsium discolor stands 1-2 m high and has a large floral head (2.5-3.5 cm wide; Gleason and Cronquist, 1963) of several hundred blue, tubular florets that produce nectar and bright, white pollen presented on exserted stamens, which is easily seen on pollinators. The corolla tubes are approxi mately 2.5 cm deep, limiting nectar access to long-tongued species. On 30 August, approximately 10 B. impatiens workers were "attacked" by up to 2 Apis workers at a time between 11:00 and 11:30 a.m. At least some pollen appeared to be removed from each victim Bombus. Apis workers sought the corbicula loads on Bombus workers and usually removed a small amount of pollen, but never an entire corbicula load. Bombus responses were complacent and non-aggressive. One honey bee landed on a M. montivaga forager and took pollen from the dorsal portion of the abdomen, causing the victim to fly off. On 5 September at the same patch, six honey bees attempted to steal pollen on six occasions (one individual per occasion) from B. impatiens workers. On 3 of 5 attempts, a single honey bee removed part of a corbicula load. A sixth honey bee removed pollen from a bee's dorsal abdomen. Bumble bee responses were again limited. On three occasions they moved their rear legs back and forth as when grooming, twice they did not respond, and once the bumble bee flew from the flower. On 7 September, I photographed the activity (Fig. 1). Once again, between 10:30 and 11:30 a.m., honey bees robbed pollen from B. impatiens on many occasions. On one occasion a single honey bee attempted to