In a previous paper (Clark and Brown, 1959) a field cage was described for rearing syrphid larvae and other predators of the balsam woolly aphid. The cages proved satisfactory in the field but some method was necessary to supplement the results with data for individual predators reared in the laboratory under controlled conditions.

In the past, attempts to rear predator larvae in the laboratory on small pieces of infested bark proved unsatisfactory because of the difficulties of keeping the bark moist and suitable for prey development and preventing the growth of moulds on the prey, the bark, and the containers. In most cases when small petri dishes or other containers were used the prey or predators died before rearing was complete or the individuals which survived were unhealthy and not representative of normal prey or predator development.