The effect of sprays on the fauna of apple trees. IV. The recolonization of orchard plots by the predatory mirid Blepharidopterus angulatus and its effect on populations of Panonychus ulmi.
Abstract
Following a DDT spray in July 1957, which almost eliminated the predatory Blepharidopterus angulatus from 1/4-acre orchard plots, the population of Panonychusulmi increased to a maximum of 100 mites and eggs per leaf in 1958 and then declined to 8 mites and eggs per leaf by 1960, a level which was maintained on untreated plots throughout the period of the experiment. Adults of B. angulatus invaded the treated plots in August 1958; in 1959 the numbers were equal to those on the untreated plots, and by 1960 larval populations of the predator on the DDT-treated plots exceeded those on the controls. Dispersal of adult B. angulatus from all plots occurred in 1960. B. angulatus reduced leaf-hopper populations, which were further attacked by a parasite, Aphelopus sp., in 1959. [For parts I-III see H.A., 35: 7559 and 7560.]-E. Malling Res. Stat., Kent.