Structural Examination of the Dufour's Gland of the Solitary Bees Osmia lignaria and Megachile rotundata (Hymenoptera: Megachilidae)

TheDufourÕs glandof twosolitarycavity-nestingbees,Osmia lignariaSayandMegachile rotundata (F.) (Hymenoptera: Megachilidae), was examined with microscopy to determine the structure and arrangement of the gland in the sting apparatus. The appearance and relative size of the DufourÕs gland of these two bee species are similar. Unlike the termination of the DufourÕs gland at the base of the sting in the honey bee,ApismelliferaL. (Apidae), the posterior portion of theDufourÕs gland in thesemegachilids enters into the sting bulb alongwith the venomduct.Within the sting bulb, the DufourÕs gland is ventral to and longer than the venom duct. The following evidential Þndings presented here and elsewhere are in support of the hypothesis that the DufourÕs gland is the source of an individual nest recognition cue in these two bee species: 1) the presence of a duct and exit pore at theposterior endof theDufourÕs gland thatmay releaseglandular secretions, 2) the locationof thick, brushymetasomal setae and the setosamembrane that couldbeused to apply a secretion to a substrate, and 3) the observed dragging of the tip of the abdomen during nest-marking.