Family Cecidomyiidae gall midges

Contarinia pisi (Winnertz) Pea midge

This midge is a locally important but sporadic pest of pea; occasionally, infestations also occur on Vicia bean. Larvae cause considerable distortion of growth. New shoots become discoloured and severely distorted; damaged flowers often abort or may produce small, malformed pods. Significant crop losses usually occur only when the first three flower trusses, which contribute most to harvested yields, are attacked. In the British Isles, this midge is most frequent in eastern England.

BIOLOGY

Adult midges first appear in June, but the time of their emergence depends largely on soil moisture and temperature. Mating takes place almost immediately; the mated females (that live for about 4 days) then disperse to seek new host plants. The midges are active in calm conditions, and most dispersal takes place after showers of rain or in the late evening and early morning. Eggs are deposited in batches of about 20-30 on the stipules and buds or beneath the bud scales, and crops remain susceptible to attack throughout the bud and flowering stages. Eggs hatch in about 4 days. The larvae feed on the young tissue for about 10 days. They then drop to the ground (Contarinia larvae typically 'jump' by flexing their bodies) and enter the soil to pupate in small, whitish cocoons. New adults emerge about 2 weeks later, and these eventually give rise to a second generation of larvae. Fully grown second-generation larvae, along with individuals of the first generation which did not pupate, overwinter

Fig. 246 Spatulas of various midge larvae: (a) pea midge, Contariniapisi; (b) yellow wheat blossom midge, C. tritici; (c) saddle gall midge, Haplodiplosis marginata; (d) orange wheat blossom midge, Sitodiplosis mosellana.

in the soil and most of these pupate in May or June; some larvae, however, remain in their cocoons for several years before eventually pupating and producing adults.

DESCRIPTION

Adult greyish-brown with long legs and antennae; wings 2mm long. Egg 0.25mm long, translucent, elongate-oval with a pointed tip. Larva up to 3 mm long, dirty white; sternal spatula broadened anteriorly and strongly cleft (Fig. 246a).

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