Pea midge
Contarinia pisi

Identification
The adult midges are very small, 3 mm long, weak fliers and black / yellow in colour.  The larvae are white and 2 - 3 mm long.

Symptoms
The larvae feed at the base of the flowers leading to flower abortion or small misshapen pods which fail to develop normally.  Feeding can also occur on the growing point causing distortion which has been described as `nettle heading`.