Testing For Hygienic Behavior
Hygienic behavior is a genetic trait of some honey bee colonies. Colonies that are hygienic are able to detect diseased larvae and pupae and remove them from the nest before the disease becomes infectious. Hygienic behavior has been found to be a mechanism of resistance to AFB and Chalkbrood. Hygienic behavior may also be a mechanism of defense against Varroa mites.
The following procedure is used to test colonies for hygienic behavior.
1. Find a comb containing sealed brood on both sides of the frame. Cut section of the comb containing 100 cells on each side using a serrated knife. A 2"x2.5" rectangle works. This section of sealed brood will be called an insert.
2. Freeze the insert at -10 degrees F for 24 hours. Alternatively, brood may be frozen in place using a round can filled with liquid nitrogen. This avoids having to remove, freeze and then replace the comb section.
3. Count the number of sealed cells on each side of the insert and record it. Only count whole cells; do not count cells which have been cut or damaged along the edges of the insert.
4. Put the insert back in the comb from where it was cut, and return the frame to the hive putting it in the center of the brood nest. Note the time of day.
5. Forty eight hours after the insert was placed in the colony to be tested, return to the hive and inspect it. Count the number of sealed cells remaining in the insert.
6. If your colony has cleaned over 90% of the cells you can consider it to be hygienic. If your colony appears to be hygienic, it is a wise idea to test it again. There may be some variation in response between tests, particularly if the insert was not fitted back in the comb properly. Also, the lack of a nectar flow may slow the hygienic response to some degree.
There is a correlation between the removal of freeze-killed brood and the removal of diseased and Varroa infested brood.