Brood Survival Test

For many years, we have used a simple yet effective method to assess brood survival. We first find a comb where the queen has laid eggs in a patch that is at least 20 cells wide by 12 cells deep. We mark six rows with dressmaker pins. For each row, a pin is inserted into a cell on the left side of the patch and another pin is inserted into the 25th cell to the right of the first pin. We randomize the colors of the pins marking each row and record the colors on a data sheet.

The test area consists of 120 cells (six rows of 20). We record the contents of each cell-empty, honey, nectar, pollen, young larva, old larva, or pupa. The comb is then returned to the center of the brood nest. Two weeks later we take the comb out and again record the contents of each cell.

Assuming that a cell started with an egg or young larva, we should find a pupa in the cell. If not, the pupa either died or was removed by the bees.

Because the bees often try to remove the pins, we mix the colors so that we can find the original area, even if some of the pins have been pulled out of the comb. We use a toothpick to remove the caps from any capped cells. We also record the age of any pupae. We sometimes find pupae that are underage. In other words, the original egg (or larva) did not survive, but the queen replaced it soon enough for the replacement to reach the pupal stage.

We have learned never to assume that all of the initial eggs survived. Capped brood does not guarantee survival. In many industrial areas, we find that brood losses of up to 80% can occur, even though all of the cells may be capped.

The empty row (left) is a positive control. At the time of the initial inspection, we swirl a round dowel in each of the 20 cells of the sixth (bottom) row. This provides another mark to identify the test area, tests the ability of the queen to replace lost eggs and serves as a reference for brood mortality. If no mortality has occurred, all of the pupae should be healthy and similar in age (right).

Hygienic Behavior

The hygienic behavior of a colony influences its susceptibility to microbial pathogens, including natural pathogens such as chalk brood or foul brood and presumably microbial insecticides. Several bee researchers employ a method advocated by Steve Taber to rank colonies according to speed of uncapping and removal of freeze-killed pupae. His method consists of cutting out a piece of brood comb, freezing it overnight in a freezer, and carefully placing the brood back into the comb.

We acknowledge the usefulness of this approach but found that it takes too much time to assess large numbers of colonies. We also had problems getting reproducible results. The act of cutting the comb seems to be sufficient to stimulate our colonies to remove brood.

Therefore, we developed a modification of this technique. We use liquid nitrogen to kill the pupae. 80 ml of liquid nitrogen is poured into a thin-walled metal tube that is lightly pressed against the comb surface. A cloth wrapped around the base of the tube prevents the nitrogen from leaking out and freezing additional parts of the comb. We then have to wait about two minutes for the nitrogen to evaporate and the metal tube to release from the comb. We then place an acetate sheet over the comb and use a permanent marker to mark the positions of groups of 20 undamaged cells. The comb is then placed in the center of the brood nest. We mark the frame with a thumb tack so we can quickly find it. Done correctly, this procedure leaves no visible signs of having been applied other than the scoring of the caps caused by the metal tube.

Twenty-four hours later, we pull out the frame with the tack, index the acetate on the frame, and count the number of uncapped as well as the number of cells from which the bees have removed pupae have been removed by bees.

Additional tests are planned for spring 1996 to determine the optimal number of cells and/or patches to assure consistent results.