The ecology of the natural enemies of coroal aphids was investigated at field sites near Norwich, Norfolk during the period when aphids were found on cereals. Field work was supplemented with laboratory studios on one group of predators, the Cioccinollidao. The field studies from 1976 to 1978 had the objective of determining the relative importance of the following natural enemies of cereal aphids, Coccinollidao, Syrphidao, Chrysopidao, . Aphidiidao, polyphagous ground predators and fungal pathoCons. in 1976 Coccinollidao voro the most important predators, followed by Syrphidao and the parasitic Aphidiidao, in 1977 Coccinollidao were again most important, followed by Aphidiidao, fungal pathogons and : "Syrphidao, while in 1978 Aphidiidno and fungal pathogens were the most important cereal aphid natural onomios. Predators were most effective in warm, sunny weather conditions as in 1976, while tunal opizootics occurred in humid weather, Mortality from aphid specific natural enemies was at a maximum late in the aphid population cycle on cereals, honco natural onomios worn unable to prevent economically oignificant outbreaks in 1976 and 1977i though they reduced peak aphid populations and hastened the 'crash' in aphid numbers. The role of polyphagous prodators was difficult to assess because of their low numbers, but exclusion experiments in 1977 showed significantly hij; hor aphid numbers in plots whore thoso prodators were excluded early in the season, though those differences disappeared later, Laboratory studios on Coccinolliclao (mainly Coccixlelln 7-riinetnta with soMo obsorvationa on C'n ac3nQlla 11-runctntn) Cavo inforºaeation on coroal aphid consumption ratos soarchint capacity under different environmento. 1 conditions, ability of adults to survive starvations fecundity of fomalars in relation to aphid conssumptiong and tho effoct of solar radiation on the internal body tewporaturo of adult