Native Predators and the Control of Potato Aphids

Experiments were done in fields of potato in Fredericton, New Brunswick, in 1981, 1982, and 1984 to determine the effect of native predators on the abundance of aphids. The populations of predators were altered by pitfall trapping within plots enclosed by polythene barriers and by applying a selective insecticide. The abundance of aphids was monitored in the enclosed plots and in unenclosed areas serving as control. The experimental design was successful at significantly reducing the numbers of Carabidae in the enclosures compared with the open plots. Aphid populations tended to be larger in the plots with depleted populations of Carabidae than in the control areas and were significantly larger in the plots where the insecticide depleted the populations of canopy level predators. These results suggest that the Carabidae play a relatively minor role in aphid control on the potato crop compared with specific predators.