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Title: NATURAL AND SUPPRESSED REPRODUCTION OF VARROA MITES

Author
item Harris, Jeffrey
item Harbo, John

Submitted to: Bee Culture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/1/2001
Publication Date: 5/1/2001
Citation: Harris, J.W., Harbo, J.R. 2001. Natural and Suppressed Reproduction of Varroa Mites. Bee Culture. 129(5):34-38.

Interpretive Summary: We have bred honey bees for the ability to suppress the reproduction of varroa mites. This suppression of mite reproduction, or SMR, is a heritable characteristic of bees that probably can be found in any population of honey bees. Selection of this trait involves measuring the percentage of nonreproductive mites from the brood combs in colonies of bees. Worker-sized brood cells containing tan-colored pupae are examined for this purpose, and only singly infested cells are evaluated. Two main types of nonreproductive mites characterize the SMR trait: (a) dead mites that are entrapped between the cocoon of the current host bee and the cell wall, and (b) living mites that do not lay eggs in the brood cell. These non-laying mites often defecate on the host bee rather than on the normal position on the cell wall. In addition, many of the non-laying mites do not contain stored spermatozoa within their spermathecae. Reasons for these abnormalities in mite biology are not known, but the percentages of mites within these two categories of nonreproduction were enhanced through selective breeding of honey bees.

Technical Abstract: We have bred varroa-resistant honey bees by selecting for the ability of a colony of bees to suppress mite reproduction (SMR). Normally reproductive mites produce 1-2 mature daughters during each reproductive cycle in worker brood. Nonreproductive mites produce no mature daughters. A typical unselected colony of bees may have 15-25% nonreproductive mites, but bees selected for the SMR trait have as high as 100% nonreproductive mites (range 50-100%). We measure the percentage of nonreproductive mites by evaluating the reproductive success of about 30 varroa mites from singly infested worker-sized cells for each colony. We examine brood cells containing tan-colored pupae because most mites complete egg laying before this stage of bee development. Bees with the SMR trait have two types of nonreproductive mites:(a) dead mites that are entrapped between the cocoon of the current host bee and the cell wall, and (b) living mites that do not lay eggs in the brood cell. These non-laying mites often defecate on the host bee rather than on the normal position on the cell wall. In addition, many of the non-laying mites do not contain stored spermatozoa within their spermathecae, which suggests that non-mating may cause some of the nonreproduction.