Nest Marking Behavior and Chemical Composition of Olfactory Cues Involved in Nest Recognition inMegachile rotundata

Abstract

In-nest observations of the solitary bee, Megachile rotundata (F.), revealed that nesting females apply olfactory cues to nests for nest recognition. On their way in and out of the nest, females drag the abdomen along the entire length of the nest, and sometimes deposit fluid droplets from the tip of the abdomen. The removal of bee-marked sections of the nest resulted in hesitation and searching behavior by females, indicating the loss of olfactory cues used for nest recognition. Chemical analysis of female cuticles and the deposits inside marked nesting tubes revealed the presence of hydrocarbons, wax esters, fatty aldehydes, and fatty alcohol acetate esters. Chemical compositions were similar across tube samples, but proportionally different from cuticular extracts. These findings reveal the importance of lipids as chemical signals for nest recognition and suggest that the nest-marking cues are derived from a source in addition to, or other than, the female cuticle.

Comparison of the Chemical Compositions of the Cuticle and Dufour’s Gland of Two Solitary Bee Species from Laboratory and Field Conditions

“…Individual lipid components were separated by capillary gas chromatography (GC), quantified by their flame ionization detector (FID) response, and identified by GC-mass spectrometry (GC-MS) (Guédot et al 2013). For both species, GC-MS analyses were performed as previously described in Buckner et al (2009).…”

“…Long-range cues are visual, while short-range cues are olfactory (Guédot et al 2006, 2007, 2013; Steinmann 1973). At times, bees are visually misguided and attempt to enter cavities belonging to conspecifics.…”

“…In manipulative experiments, whole or sections of glass tube nests being used by actively nesting M. rotundata and O. lignaria females were removed and replaced with new, unused tubes while the foraging females were away. Upon returning to the nest sites, these females had difficulty finding their own nests and reluctantly reentered them (Steinmann 1973; Guédot et al 2006, 2013). Guédot et al (2006, 2013) also observed female bees inside their nests displaying body movements and positions consistent with employing the abdomen for nest-marking and concluded that replacement of the used tubes had removed discriminating, individual recognition cues that were applied intentionally by the bees.…”

“…Upon returning to the nest sites, these females had difficulty finding their own nests and reluctantly reentered them (Steinmann 1973; Guédot et al 2006, 2013). Guédot et al (2006, 2013) also observed female bees inside their nests displaying body movements and positions consistent with employing the abdomen for nest-marking and concluded that replacement of the used tubes had removed discriminating, individual recognition cues that were applied intentionally by the bees. The definitive source of the chemical cues was not revealed in that study, but was suspected to be lipids from the cuticle, the Dufour’s gland, or both.…”

“…The cuticular lipids of just-emerged as well as nesting M. rotundata and O. lignaria females have been reported (Buckner et al 2009; Guédot et al 2006, 2013), but how a female’s cuticular lipids compare to her Dufour’s gland content is unknown. The contents of the Dufour’s gland of four ground-nesting and two cavity-nesting Megachile species contain triglycerides with 2–16-carbon fatty acids (Cane and Carlson 1984; Williams et al 1986), but it cannot be assumed that the Dufour’s glands of all bees share common chemistry, nor that all analytical chemistry is performed using identical techniques with similar levels of detection and sensitivity.…”