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The following aspects of Hypoaspis miles' biology were investigated ; development rate of egg to adult at different temperatures, fecundity, longevity and rate of predation on sciarids. With an increase in temperature the time taken for development decreased from 33.7 days at 15 ~ to 9.2 days at 28 ~ The threshold temperature for H. miles to complete its life cycle was between 10 ~ and 12 ~ When fed on Acarus siro, H. miles laid 2-3 eggs a day and unfertilized eoos~,, . only developed into males. Adults of H. miles (0-I day old) survived for 24.0 + 1.4 days without food and if fed for 6 days and then starved, females lived for 65.4 + 2.6 days which was significantly longer than males (45.2 + 3.0 days). With food, 60 % of males and females survived for 142 days. All larval instars of sciarids were attacked by H.miles although the numbers consumed were dependent on the size of the larvae. Egg predation was negligible and pupae were not attacked. In productivity studies of H. miles in culture (fed on A. siro), the time taken for the mites to reach a density of 45-65,000/litre ranged from 76 to 23 days at 15 ~ and 28 ~ respectively.

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JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org. SUMMARY(1) Changes in numbers of cereal aphids were measured inside and outside cages designed to exclude aphid specific predators (certain Coccinellidae, Syrphidae and Chrysopidae) in a field of winter wheat in 1976, 1977 and 1979.(2) In each year, three phases of aphid population development were distinguished; an initial rapid growth phase, a divergence phase, and a decline phase. Populations in the cages increased at the same rate as outside during the growth phase, and during the divergence phase continued to increase to a peak while populations outside increased at a slower rate or decreased. As a result of the divergence, a difference in peak numbers of up to six times was recorded. Populations outside fell rapidly during the decline phase while a slower reduction occurred in the cages.(3) In the 3 years, the divergence phase coincided with an increase in the numbers of aphid specific predators. The consumption rate by predators that would be required to bring about the observed differences between cages and outside was calculated and found to lie within published values. It was concluded that predation was likely to be the major cause of the differences between cages and outside to the time of the population peak. Predation, parasitism, disease and emigration all contributed to the decline phase.(4) Although there was no difference in plant growth stage inside and outside the cages, and the divergence phase occurred at different growth stages in the 3. years, it was not possible to rule out a subtle effect of the caging technique itself on the physiology of the plant or aphid, acting only during the divergence phase.

SUMMARY Winter wheat fields on two farms in West Sussex were sampled in 1980 and 1981 for cereal aphids and their natural enemies. The grain aphid, Sitobion avenae was present in all 19 fields examined, but in no case did the populations increase to densities liable to cause economic damage. The observations strongly suggest that aphid population growth was stopped by aphid‐specific predators, hymenopterous parasitoids and fungal pathogens. In two fields in 1980, S. avenae population densities approximately equalled five aphids per ear at flowering, the threshold at which insecticide application is recommended in the UK, but numbers were then reduced by natural enemies, mainly aphid‐specific predators. In three fields in 1981, S. avenae would probably have exceeded the spray threshold had natural enemies not intervened in late May.