2. An optimal colony configuration
In establishing colonies for experiments, it is useful to have some guidance on how colony population size can be expected to affect colony growth, behaviour, and survivorship. The best guidance in this matter comes from John Harbo (1986) who compared brood production, worker survival, and honey gain in colonies begun with no brood and 2,300, 4,500, 9,000, 17,000, or 35,000 bees while fixing bee density at ca. 230 per 1000 cm3 hive space. The experiment was repeated in each of the months of Feb, Apr, Jun, Aug, and Oct and terminated before brood emerged. Worker survival (22 days) was significantly higher in colonies with 2,300-9,000 bees than in colonies with 35,000 bees. Larger populations tended to store more nectar per bee during times of nectar flow and consume less during times of nectar dearth. However, smaller populations produced more brood per bee. Harbo concluded that colonies established with 9,000 bees are a good optimum between the honey hoarding efficiency of large populations and the brood rearing efficiency of small colonies. Colonies that are significantly larger than this are costly and labour-intensive to set up and less suitable for measures of population growth because they are already near their maximum. Colonies significantly smaller than this may do well at the height of the season, but they are more vulnerable to winter and summer stresses. Bees are normalized for colony-source genetics and parasite loads if colonies are set up with the common pool of bees as described in section 3.1. If colony growth is a measure of interest, the investigator can invite a greater range of expansion if colonies are begun with no brood. But if one prefers to provide colonies with brood, it is reasonable to stock colonies of 9,000 bees with no more than two combs of brood of various ages, allowing plenty of open cells to accommodate growth.