Contarinia nasturtii Kieffer Swede midge

Infestations of this widely distributed midge occur on various members of the Brassicaceae, including cabbage, cauliflower and fodder brassicas; however, they are most important on swede, including fodder crops. The small, delicate, yellowish adults appear in May and June, and eggs are then deposited in the young tissue of host plants. The eggs hatch in about a week and the pale, yellowish-white larvae (up to 2.5 mm long) then feed gregariously. They cause a swelling of flowers, crinkling of leaves ('crumple leaf symptom) and, often and most significantly, death of the main growing point; the latter damage leads to the proliferation of secondary shoots ('many neck' symptom). Larval damage is often followed by bacterial rotting of tissue and tends to be most severe in June, particularly under dry conditions. Fully grown larvae 'jump' to the ground and eventually pupate in cocoons in the soil, the next generation of adults appearing shortly afterwards; some larvae, however, do not pupate but remain in a state of diapause for up to 1 or more years. There are usually from three to five generations each year, depending on temperature.

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