The Influence of Insecticides with Differing Specificity on the Structure of the Fauna Associated with Potatoes

Abstract

Population outbreaks of the aphids Macrosiphum euphorbiae and Myzus persicae occurred when potatoes [Solanum tuberosum] at Ithaca, New York [USA], were treated with carbaryl (Sevin) alone and in combination with carbofuran (Furadan) granules. Densities of other herbivore species [insects] and of aphid predators [insects and spiders], especially Orius insidiosus, were suppressed in all carbaryl treatments. Large populations of adult parasitoids and hyperparasitoids [Hymenoptera] were associated with the aphid outbreaks. However, only a small proportion of the aphid populations in all treatments was parasitized. Carbofuran granules, used alone, had little apparent effect on the structure of the potato fauna. Lower tuber yields were associated with the heavy aphid infestations in the carbaryl treatments. These results, as well as those of previous studies, demonstrate that insecticide-induced outbreaks of aphids can have a variety of explanations, including release from interspecific competition, reduced predation pressure, or some combination of these factors. The traditional experimental design used to test insecticide effectiveness is inadequate; it fails to factor out those critical interactions altered by the chemical.