Nesting Biology, Seasonality, and Mating Behavior of Epicharis metatarsalis (Hymenoptera: Apidae) in Northeastern Costa Rica

We investigated several aspects of the nesting biology of Epicharis metatarsalis Friese (Hymenoptera: Apidae) in a lowland wet-forest of northeastern Costa Rica. Five large aggregations were found 30Ð100 m from larger rivers at the La Selva Biological Station. The relatively short nesting season, from May to August, indicates that E. metatarsalis is probably univoltine. Four nests were excavated to study nest architecture, and Þve brood cells from three different nests were analyzed for pollen composition. Additionally, we analyzed pollen loads from 33 females returning from pollen-collecting trips, and we observed male patrolling behavior. The canopy treeApeibamembranacea Spruce ex Benth (Tiliaceae)was found to be the principal pollen source, representing an average proportion of 98.5% of each pollen load and 93.4% of the larval provisions. The brood cell with the lowest proportion of A. membranacea pollen contained 89.3% A. membranacea pollen, which was 98.5% by relative volume. Pollen of Byrsonima crispa A. Juss. (Malpighiaceae) was the second most frequently encountered pollen with average proportions of 1.3 and 4.9% in pollen loads and larval provisions, respectively. E. metatarsalis can thus be considered oligolectic. The E. metatarsalis nesting season coincides with the relatively short ßowering season of B. crispa, perhaps because of the importance of B. crispa as a source of oils rather than nectar.