SUMMARYObservations on the biology of carrot fly (Psila rosae(F.)) were made in the important carrot‐growing areas of eastern England in the period 1948–72.Adults of the spring generation usually emerged in May and peak numbers were usually swept during the third and fourth weeks of May. Eggs were found from the end of May and larval damage was evident from late June. Calculations of accumulated day‐degrees of air temperature above 42°F (5.6°C) showed that peak emergence could generally be associated with a total of 422 day‐degrees commencing on 1 April. Both separate and combined totals of accumulated day‐degrees for February and March were markedly different in years of early and late fly emergence. Adults of the second generation appeared from late July onwards and oviposition occurred mainly during August and September, although in some years eggs were found much later. Resulting larval damage was present by October and increased in severity until the crop wa
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