Pollen host selection by a broadly polylectic halictid bee in relation to resource availability

Abstract

The relationship between utilized and available resources in the same environment has not yet been studied in most wild bees. In a riparian forest, a total of 15 pollen types from 10 plant families were identified from pollen provisions of 17 nests of the wood-dwelling Augochlora amphitrite (Hymenoptera: Halictidae) for which only floral records have been known. During the foraging period, only five out of 108 available flowering species were visited intensively (more than 10 %) for pollen. As more than three families and 32.2 % of the available plant families were visited for pollen, the broad polylecty category was inferred. Like in other Augochlora species, a variety of floral types was visited by A. amphitrite, in agreement with its broadly polylectic foraging habit. The selection index was positive for the highly abundant Ludwigia (Onagraceae) and the rare Gymnocoronis spilanthoides (Asteraceae). The intensive foraging on Ludwigia could indicate temporary specialization for this abundant pollen resource. The tendency of this bee to visit intensively one flower type for pollen suggests that bee individuals had to learn to handle this abundant flower type. Pollen analysis complemented with field observations on floral resource availability proved to be helpful tools to provide information on the foraging behaviour of a wild bee in its natural environment.