CHANGES IN REPRODUCTION OF VARROA MITES AFTER HONEY BEE QUEENS WERE EXCHANGED BETWEEN RESISTANT AND SUSCEPTIBLE COLONIES

Authors: Harris, Jeffrey; Harbo, John

Submitted to: Apidologie
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/27/2000
Publication Date: 11/1/2000
Citation: HARRIS, J.W., HARBO, J.R., CHANGES IN REPRODUCTION OF VARROA MITES AFTER HONEY BEE QUEENS WERE EXCHANGED BETWEEN RESISTANT AND SUSCEPTIBLE COLONIES, APIDOLOGIE, 2000, VOL. 31, pgs. 689-699, EDITION #6.

Interpretive Summary: Varroa jacobsoni is a parasite of honey bees that will kill a colony in 2 years if it is not protected with a miticide. We have bred bees for resistance, and resistance has centered on bees that suppress mite reproduction (SMR trait). Queens with SMR produce colonies of bees in which 50--90% of mites do not reproduce. SMR is expressed 6 weeks after installation of the queen. To determine the mechanism of resistance, we wanted to know which mites are affected, the original mites that begin an experiment or their daughters which are raised in the colony. To that end this study describes changes in mite reproduction when SMR and susceptible queens were exchanged. Half the test colonies were given a susceptible queen, and half were given a SMR queen. After a few weeks queens were exchanged: colonies with susceptible queens were given a SMR queen, and vice versa. Mite reproduction was measured 5 times (2 before and 3 after the exchange). The numbers of mites that did not lay eggs and mites that died increased or decreased by adding or taking away a queen selected for the SMR trait. Changes in mite reproduction became evident after die off of the original mites and their replacement by daughter mites raised in the colony after the exchange. About 20% of daughter mites in SMR colonies were unmated because of the absence of male mites. Unmated mites do not lay eggs. Although the SMR trait was correlated to unmated females, the lack of males in one generation did not predict the number of female mites that did not lay eggs in the next generation.

Technical Abstract: This study examines changes in reproduction and mortality of varroa mites when queens from stocks of honey bees that differ in susceptibility to the mites were exchanged between colonies. Resistant queens were selected for suppression of mite reproduction (SMR). This heritable characteristic of bees causes female mites to produce no progeny after they have entered a brood cell where mite reproduction normally occurs, and it increases mortality of foundress mites. SMR was not apparent until after 5-6 weeks. In two tests uniform colonies of bees were established, each with 1 kg of mite-infested bees and a queen. At the beginning of each test, half the colonies were given a SMR queen and half were given an unselected queen. Queens were exchanged after 7 (experiment 1) and 13 weeks (experiment 2). The percentages of nonreproducing mites and dead mites were determined for each colony at 5 different times (2 before and 3 after exchanging queens). Results showed that mite reproduction in a colony can be increased or decreased by taking away or adding a queen selected for the SMR trait. Two specific characteristics of mites are associated with SMR; mites that lay no eggs and mites that are dead and entrapped by the cocoon. In selecting for this trait, it may be most efficient to count only these two traits and ignore nonreproductive traits such as progeny produced too late to mature, males only, females only, or dead progeny. Lack of males did not predict nonreproduction of mites in subsequent generations.