Varroa destructor reproduction during the winter in Apis mellifera colonies in UK

The reproductive behaviour of female Varroa destructor mites invading worke r brood cells during the winter months (January to mid-March) was investiga ted in four Apis mellifera colonies in UK. The number of viable offspring p roduced during a reproductive cycle, per mite, was only 0.5 during winter c ompared with 1.0 during the summer. This was mainly due to a large increase in the population of non-reproductive mites (winter 20%, summer 8%). This increase can be explained by the high level of male offspring mortality obs erved in winter (42% vs. 18% in summer), which results in nearly half of th e newly reared female mites being unfertilised. Since mites that do reprodu ce lay a similar number of eggs in winter ((X) over bar = 4.7) as in summer ((X) over bar = 4.9), and the level of mortality suffered by the first fem ale offspring is similar in winter (7%) as in summer (6%), it is probably n ot the internal physiological state of the host which causes the high level of winter non-reproduction, as has been previously suspected.