Damage. The larvae of the yellow underwing moth, unlike most other moth larvae, live in the soil, nipping off the stems of young plants and eating holes in succulent crops, e.g. bedding plants, lawns, potatoes, celery, turnips and conifer seedlings. The damage resembles that caused by slugs.
Life cycle (see Figure 14.13). The adult moth, 2 cm across, with brown fore-wings and yellow or orange hind wings, emerges from the shiny soil-borne chestnut brown pupa from June to July, and lays about 1000 eggs on the stems of a wide variety of weeds. The first instar caterpillars, having fed on weeds, descend to the soil and in the later instars cause the damage described above, eventually reaching about 3.5 cm in length. They are grey to grey-brown in colour, with black spots along the sides. Several other cutworm species such as heart and dart moth (Agrotis exclamationis) and turnip moth (Agrotis segetum) may cause damage similar to that of the yellow underwing. In all three species, their typical caterpillar-shaped larvae should not be confused with the legless leatherjacket which is also a common underground larva. The cutworm species normally have two life cycles per year, but in hot summers this may increase to three.
For the professional horticulturist, soil drenches of residual insecticides such as chlorpyrifos have proved successful against the larva stage of this pest.
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