checking hive health
Photo A. Hygienic bees detect, uncap and remove a sealed, 5th instar larva that is infected with either American foulbrood or chalkbrood disease. Hygienic bees are able to detect that the larva is diseased before it reaches the infectious stage; in this way, hygienic bees eliminate the pathogen and avoid further disease transmission through the colony.

Breeding for Resistance
We have been breeding honey bees for resistance to diseases and Varroa destructor since 1994. The most devastating disease of honey bees is American foulbrood (AFB), a highly infectious bacterial disease of brood (larvae). We have demonstrated that honey bees bred for hygienic behavior, a genetic trait, demonstrate good resistance to AFB and also to a fungal disease, chalkbrood [1]. Bees bred for hygienic behavior are able to detect and physically remove disease-infected brood from the colony before it becomes infectious. Hygienic bees are able to detect and remove diseased brood before the human eye can detect any sign of disease symptoms. When bees remove the disease in the non-infectious stage, it prevents the disease from spreading throughout the colony.

Our research has shown that bees bred for hygienic behavior also display resistance to V. destructor mites because they are able to detect and remove broods infested with the mites [2]. This mite parasite alternates between feeding on blood of adult bees, and feeding and reproducing on the pupal stage of bees. Bees that remove mite-infested pupae from the nest interrupt the reproductive cycle of the mite by eliminating the offspring of the mite developing within a wax-sealed cell (Photo A).

We have bred hygienic behavior into an Italian line of honey bees. However, the behavior is present in all races and lines of honey bees in the US (and the world!), and can be easily selected for, using the methods described below. Our “MN Hygienic Line” of bees is available commercially in the US and has become widely accepted by beekeepers. However, our hope is that beekeepers select for hygienic behavior from among their favorite line of honey bee, whether it be Carniolan, Italian, Caucasian or other species. In this way, there will be a number of resistant lines available within the U.S. to maintain genetic diversity — the perfect way to promote the vitality of our pollinators.

Much of our research effort is in evaluating our MN Hygienic Line against other lines of commercially available honey bees to ensure that it is resistant to diseases and can actively defend itself against the mite pests, resulting in lower mite levels. We also evaluate the honey production, gentleness and wintering ability of our line to ensure that it is acceptable to both commercial and hobby beekeepers [3, 4]. In the last several years, we have made great strides in increasing the degree of resistance of our line to the mites, so that the frequency of treatments to control the mites can be greatly reduced and alternative treatments (such as organic acids and botanical oils) can be used to reduce mite loads.