Submitted to: Annals of the Entomological Society of America
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 2, 2008
Publication Date: November 1, 2008
Citation: Harris, J.W. 2008. Effects of brood type on Varroa-sensitive hygiene (VSH) by worker honey bees (Hymenoptera: Apidae). Annals of the Entomological Society of America 101(6):1137-1144 Interpretive Summary: Removal of diseased brood from capped brood cells is a major defense that honey bees use to combat bacterial and fungal diseases, pests that destroy comb like small hive beetles and the greater waxmoth, and parasitic mites like varroa (Varroa destructor). This is a form of behavioral resistance called hygiene. Hygiene results from the actions of many bees that patrol the broodnest, smell brood cells containing an unusual condition, uncap the cell and remove the affected larva or pupa from the nest. Removal of a varroa-infested pupa interrupts the reproductive cycle of a mite. The adult varroa probably survives removal of her host, but her offspring are killed during hygiene. Bees that are particular good at targeting mite-infested worker brood with hygiene, which is called varroa sensitive hygiene (VSH), were bred at our laboratory. My experiments with VSH bees have involved worker brood, but until now, their abilities to respond to mite-infested drone brood have not been tested. Hygienic responses to drone brood may be important because varroa mites prefer drone brood over worker brood, and they produce more offspring when reproducing in drone cells. Two experiments were used to compare the responses of VSH bees to mite-infested drone and worker brood. VSH bees were much less responsive to mite-infested drone brood than to worker brood. They uncapped some infested drone pupae, but they removed very few of them from brood cells. Mite populations could grow faster in colonies of VSH bees when drone production is high. A third experiment compared the hygienic responses to mite-infested worker brood between colonies of VSH bees caged with or without a queen for 24 hrs. Presence of the queen did not significantly influence VSH during the short test within an incubator; therefore, it may be possible to develop a laboratory method for screening bees for this important form of behavioral resistance to varroa mites.
Technical Abstract: Honey bees have been selectively bred for varroa sensitive hygiene (VSH), which is the removal of pupae that are infested by Varroa destructor 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 non-hygienic 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 to 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. This result suggests that mite populations in VSH colonies could increase more rapidly when drone brood is available. The effects of presence of the queen on the hygienic responses of VSH bees to mite-infested worker brood were also examined in a laboratory test. Presence of the queen had no significant effect on hygienic responses during a 24-h test, and removal of mite-infested pupae and uncapping of pupae were positively correlated to the initial infestation rate of the brood being tested.