The larvae of this pest produce holes in the carrot roots, creating points of entry for root diseases. The tops of the foliage acquire a rust coloration. The fly may affect related species, such as parsley and parsnip, but this is less common. Carrot flies overwinter as pupae in the soil close to the roots on which they have fed. The adult flies emerge in May and, attracted by the smell of the roots, they lay their eggs near to the carrots. The eggs hatch and the insect progresses rapidly through its life cycle. The new flies lay their eggs and a second brood, present in far greater numbers, do much more damage. During autumn they pupate in the soil around the roots. There is much that can be done to thwart the pests. Carrots can be planted on raised beds as the flies are incapable of flying above 45cm/18in. The egg-laying females are attracted to the carrots by smell. Complementary planting of onions between the rows of carrots will divert but not always prevent the pests. Sow the seed thinly and try to prevent the need for thinning, which results in the bruising of the little roots which emits the odorous attractants into the air. Delay sowing maincrop as late as possible, to prevent the first brood from building up numbers. Where carrot fly is a persistent problem, cover crop with crop protection mesh. Fly-resistant varieties such as ‘Resistafly’ or Flyaway’ in which the chemical attractant has been bred out will also help and these can drastically reduce the problem especially when sown between rows of standard varieties to act as sacraficial crops. There is also a biological control, a ground beetle, which is available from specialists.