Nest Structure, Colony Composition and Foraging Activity of a Tropical-Montane Bumblebee, Bombus senex (Hymenoptera : Apidae), in West Sumatra

We described the nest architecture, colony composition and for-aging activity of an oriental tropical-montane bumblebee, Bombus (Senexibom-bus) senex VOLLENHOVEN, with a nest collected at Mt. Singgalang, West Sumatra. The underground nest contained 212 bees (one queen and 211 workers), 195 eggs in 21 egg cells, 98 larvae in 18 larval cells, 228 pupae and prepupae in cocoons, and 218 vacated cocoons. This species was a pocket maker. After the collection of the nest, 158 bees emerged in the laboratory (6 queens, 150 workers, and 2 males). The size distribution of females was unimodal, and bees with head width ≥ 5.9 mm were considered to be queens. The females showed a marked, continuous variation in the pattern of pubescence color, correlated with size. While queens and large workers had thoraces and abdomens covered with whitish pubescence, small intranidal workers were entirely black, and intermediate-sized workers had intermediate color patterns. Foraging activity of the colony continued throughout the day time. The number of departures per 10 min was negatively correlated with relative humidity.