Effect of Brood Type on Varroa-Sensitive Hygiene by Worker Honey Bees (Hymenoptera: Apidae)

Honey bees (Apis mellifera L.) (Hymenoptera: Apidae) have been selectively bred for varroa-sensitive hygiene (VSH), which is the removal of pupae that are infested by Varroa destructor Anderson & Trueman from capped brood cells. This hygienic behavior is a complex interaction of bees and brood in which brood cells are inspected, and then brood is either removed or recapped. Previous work has shown that VSH bees uncap and remove significantly more varroa-infested worker pupae than nonhygienic bees do, but nothing is known about the reactions of VSH bees to mite-infested drone brood. This study compared the reactions of VSH bees with mite-infested worker and drone brood in a laboratory test and a field test. VSH bees inspected brood cells containing mite-infested pupae of both types of brood, but they removed significantly fewer mite-infested drone pupae than mite-infested worker pupae after 1 wk. This result suggests that mite populations in VSH colonies could increase more rapidly when drone brood is available. Additionally, the percentages of uncapped pupae and uncapped mite-infested pupae were positively correlated to the natural infestation rate of brood after a 24-h exposure, but not after an exposure of 1 wk. This result suggests that the rate of uncapping brood by hygienic bees may depend on the infestation rate, which gradually decreases with longer exposures to bees that remove mite-infested pupae from capped brood.