Honeybee (Apis mellifera L.) drone size and its effects on aspects of male fitness
Aspects of large and small drone fitness were compared to determine the factors causing the known reproductive advantage of large males. There has been relatively little research into factors that affect drone sperm and fitness. Three predictions were made: (i) larger drones have superior flight performance; (ii) large drones produce more and/or superior spermatozoa; (iii) late season drones have reduced fitness. Large drones did not take more or longer mating flights, but a higher proportion of them took mating flights on a cool (18°C) day. Drone mass was a significant predictor of sperm number but not sperm length. After peaking at 14 to 20 days of age, sperm numbers declined to ~35% of peak numbers in the subsequent 12 days. Mean number of sperm was <2 million; the low numbers are presently unexplainable. Late season drones in October and November had greatly reduced sperm numbers.