The effect of sprays on the fauna of apple trees. IV. The re-coloniziilíon of orchard plols by the predatory Mirid Blepharidopierus angulatus and its effect on populations of Panaychus ulmi..
The following is based largely on the author's summary of .this part of a series on investigations in south-eastern f-.ngland [cf. RAE A 54 470]. Following an applícation in Ju! y 1957 of a spray of DDT that almost eliminated the predator Blepharidoplerus angulatus (fall.) from i-acre plots in an apple orchard, populations of Panonychus ulmi (Koch), assessed as number of rnites and eggs per leaf, increased to a máximum of 100 in 1958 and then declined to 8, a level that had been maintained on untreated plots throughout the expirement, in 1960. Adults of B. angtdatus invaded the treated plots in August 1958. In 1959, the numbers were equal to those on the untreated plots. and by 1960 nymphal populations of the Mirid on the plots treated with DDT exceeded those on the control plots. Dispersal of adults of B. angulatus from all the plots occurred in '1960. The predator reduced populations of Cicadellíds, predominantly Erythroneuraalneti (Dhlb.) and Typhlo-cyba froggatti Baker [cf. 52 241], which were further attacked by the parasite A phelopus sp., in 1959.