Olfactory and behavioral response thresholds to odors of diseased brood differ between hygienic and non-hygienic honey bees (Apis mellifera L.)

Through the use of proboscis-extension reflex conditioning, we demonstrate that honey bees (Apis mellifera L.) bred for hygienic behavior (a behaviora l mechanism of disease resistance) are able to discriminate between odors o f healthy and diseased brood at a lower stimulus level than bees from a non -hygienic line. Electroantennogram recordings confirmed that hygienic bees exhibit increased olfactory sensitivity to low concentrations of the odor o f chalkbrood infected pupae (a fungal disease caused by Ascosphaera apis). Three-week-old hygienic bees were able to discriminate between the brood od ors significantly better than three-week old non-hygienic bees. However, th e differential performance in brood odor discrimination was primarily genet ically based, not a direct result of age, experience, or the temporary beha vioral state of the bee. Lower stimulus thresholds for both the olfactory a nd behavioral responses of hygienic bees may facilitate their ability to de tect, uncap and remove diseased brood rapidly from the nest. In contrast., non-hygienic bees, possessing higher response thresholds, may not be able t o detect diseased brood as easily. Our results provide an example of how ph ysiological and behavioral differences between the hygienic and non-hygieni c honey bee lines, operating at the level of the individual, could produce colony-specific behavioral phenotypes.