Influence of ‘parasitic intensity’ onVarroa jacobsoniOud. reproduction

SUMMARYThe influence of ‘parasitic intensity’ (the number of adult female Varroa jacobsoni per cell) on mite reproduction in honey bee (Apis mellifera) colonies was studied during 1991 in Argentina. As the number of mites per cell increased, a clear decrease in the reproductive rate was observed from about three offspring per mite at 1 mite/cell to one offspring per mite at 6 mites/cell. There was also a decrease in the number of females reaching the adult stage. Parasitic intensity. was highest (up to 6 mites/cell) in winter and lowest in summer (up to 2 mites/cell). As the number of male offspring produced was not affected, changes in the sex ratio were observed. At a parasitic intensity of 1 mite/cell, there were 38.7% males in the offspring, but at 6 mites/cell the proportion of males was 51.3%. During winter, a lower number of brood cells were available resulting in a high proportion of highly infested cells and a reduced reproductive rate. It is suggested that exploitative competition could be one factor leading to a high parasitic intensity.