The effect of sprays on the fauna of apple trees. II. Some aspects of the interaction between populations of Blepharidopterus angulatus (Fall.) (Heteroptera: Miridae) and its prey, Panonychus ulmi (Koch) (Acariña: Tetranychidae).
Part II: P. ulmi hatched 4-5 weeks before B. angulatus, and in years when the predator severely checked the mite predation was effective at the beginning of the second mite generation. In 1956, following treatment with either winter wash+lime-sulphur or captan, the numbers of mites and eggs increased at a similar rate before B. angulatus hatched, but declined rapidly when the predator appeared, the rate of decrease being proportional to the numbers of the predator. There was no evidence of effective predation by any other species before B. angulatus hatched. In 1958, when mite density was greater than 30 mites plus eggs per leaf, there was a clear relationship between the rate of mite increase and the mean density of B. angulatus. The rate of mite increase in the absence of predation was calculated to be 5.3% per day, and the mean number of predators required to stabilize the mite population was 57 per tree. From estimates of total numbers of mites and predators per tree it was shown that one predator could stabilize a population of approximately 2, 000 mites and eggs, of which 40% were mites. The egg density of B. angulatus was low following seasons when the mite was scarce due to heavy predation, and higher when mite density increased. [From author's summary].-E. Malling Res. Stat., Kent.