Low sperm counts and reduced fecundity of mites in colonies of honey bees (Hymenoptera: Apidae) resistant to Varroa jacobsoni (Mesostigmata: Varroidae)

A breeding program for honey bees, Apis mellifera L., resistant to varroa mites, Varroa jacobsoni Oudemans, selected for bees that maintain low populations of mites with decreased reproduction. This study examines the causes for this suppressed mite reproduction. Nonreproductive mites were classified into 3 groups as follows: (1) mites that were alive but did not lay eggs, (2) mites that began laying eggs later than normal, and (3) mites that died before laying eggs (usually < 2% of mites in worker brood). Mites that did not lay any eggs had significantly fewer spermatozoa (4 +/- 8 [mean +/- SD] n = 33) in their seminal receptacle than normally reproductive mites (27 +/- 14, n = 45). About half of the mites that produced no progeny had no spermatozoa in their seminal receptacles. Hence, the failure to produce progeny was related to fertilization of the female mite. Reproductive mites produced fewer progeny in colonies that had a higher proportion of nonreproductive mites. Therefore, both absolute infertility and reduced fecundity may be associated with the same host-related factors.