Biotic Factors Involved in Crucifer Aphid Outbreaks Following Insecticide Application1

Applications of carbaryl and cryolite (sodium hexafluoroaluminate) altered the basic structure of the arthropod community associated with collards at Ithaca, N, Y. Population outbreaks of aphids occurred when carbaryl was applied at weekly intervals throughout the season. Aphid populations declined early on plots in which carbaryl applications were stopped in mid-season. Extensive leaf injury caused by flea beetles was associated with low and declining aphid densities. The density of aphid predators increased after carbaryl was withdrawn. However, predators were relatively rare in all treatments. The percent of the aphids parasitized did not differ significantly 011 treated and untreated plots in the late season when the aphid outbreaks occurred. It is suggested that reduced inter specific competition may have been an important factor in the complex chain of events that led to the aphid outbreaks.