Morph identification in natural populations of alate female bird cherry aphids, Rhopalosiphum padi L., by multivariate methods

The effects of six burning treatments combined with two insecticide treatments of alfalfa (Medicago sativa L.) stubble on alfalfa plant bug, Adelphocoris lineolatus (Goeze) and Lygus spp. populations were evaluated over an 8-yr period (1982–1989). The burn treatments were: burning every spring and autumn, burning in alternate springs, burning at 50–100 mm and 150–200 mm of spring growth, and an unburned control. Alfalfa plant bug, which overwinters in the egg stage in alfalfa stems, were reduced by the spring burns. First generation populations of Lygus spp., were enhanced by the burn treatments before spring growth appeared, but were reduced when alfalfa was burned over 50 mm of spring growth. Counts of the minute pirate bug, Onus tristicolor White, were enhanced in 1983 by all burn treatments, and in 1985 by some of the burn treatments. Of all the predators, only spiders were significantly reduced and only in 1986 by the burned every autumn and spring treatments.