Field trials on chemical control ofAphis fabaeScop, attacking spring‐sown field beans were carried out during the years 1950–2. The insecticide sprays were applied once only, soon after primary aphid migration into the bean crop had ceased. Destruction of the few aphids present at this early date stops build‐up of the big populations that often develop later.An 0.02% (w/v) parathion spray was used in all three field trials. This gave excellent control ofA. fabaeas did the systemic insecticides Isopestox and Systox at 0.05% (w/v) active ingredient, and nicotine at 0.1% (w/v). Sprays containing allethrin (0.05% (w/v) pure material), pyrethrins (0.05% and 0.02% (w/v) total pyrethrins plus piperonyl butoxide) and an 0.1 (w/v) DDT emulsion gave moderate control.A. fabaewas not controlled in plots treated with an 0.1% (w/v) DDT crystalline suspension, and the aphid population reached a higher peak than in the untreated plots; the suspension is not only relatively ineffective against the aphid, but is more toxic than the DDT emulsion to its Coccinellid predators.On the bean plant the 0.05% (w/v) Systox spray showed some residual toxicity toA. fabaefor at least 5 days after application, but stopped causing 100% kill within 24 hr. 0.02% (w/v) parathion and 0.1 (w/v) DDT emulsion had slight, and 0.02% (w/v) pyrethrins and 0.1% (v/v) nicotine, no residual toxicity.In the year 1950, aphid attack on the field plots was slight and damage insignificant. In 1951, there was a moderate attack and the yield of bean seed was significantly increased by all insecticidal treatments; where aphid control was most efficient (parathion and Isopestox treatments) the yield (16.7–17.1 cwt./acre) was about × 2.7 that of the untreated control (6.3 cwt./acre). In 1952, there was severe aphid attack, and the mean seed yield of the untreated control plots was 1.4 cwt./acre. Plots treated with the DDT suspension yielded 1.3 cwt. seed/acre, but all other insecticides, including the DDT emulsion, increased the seed yield to 10.3–14.8 cwt./acre.All preparations used in 1952, except nicotine, were destructive to adult Coccinellid predators ofA. fabae; Adalia bipunctatawas more susceptible thanCoccinella septempunctata.However, in 1952, predators on the experimental area were too uncommon to be economically