SATTLER, A.L.*; FOSTER, R.L.; HANNAFORD, S.; Univ. of Puget Sound; Univ. of Puget Sound; Univ. of Puget Sound: Odor conditioning success differs between nurse and forager bumblebees
Classical conditioning of the proboscis extension reflex (PER) is a common laboratory paradigm for studying mechanisms of learning in insects, but has only recently been applied to odor learning in bumblebees. This study compared the effectiveness of PER conditioning in 10 foragers, 10 nurse bees, and 9 controls of the bumblebee Bombus huntii; all bees were selected from free-foraging colonies. Conditioning trials paired 1-hexanol as the conditioned odor stimulus (CS) with sucrose, which naturally elicits and rewards the PER response. Following a 20 h sucrose deprivation, bees completed 40 conditioning trials, divided into two sessions over consecutive days. Learning was defined as proboscis extension to the odor, i.e., conditioned response (CR). Because foragers must learn visual and olfactory qualities of flowers, we predicted that they would be easier to condition than nurse bees. However, CR rates were significantly higher in nurse bees (M=21.8%) than in foragers (M=7.0%) (p=.045) and controls (M=0.8%) (p=.005); foragers did not perform significantly better than controls (p=.593). Electroantennogram response strength to 1-hexanol was unrelated to group affiliation, ruling out differences in the ability to detect the odor stimulus as an explanation for superior conditioning in nurse bees. CR rates did not differ between session 1 and session 2, but were significantly correlated (r=.51, p=.005). We propose that experiences during foraging may inhibit olfactory PER conditioning. In a recent odor discrimination study, Laloi and Pham-Del�gue (2004) proposed that exposure to a biologically relevant odor may inhibit conditioning to a second odor. In this study prior exposure and/or conditioning to floral odors by free-foraging bees, but not by nurse bees, may likewise have inhibited later conditioning to a non-biologically relevant odor 1-hexanol.
