Cutworms (Agrotis spp.) are occurring worldwide. Important species are for instance the black cutworm Agrotis ipsilon and the turnip moth Agrotis segetum. The larvae of these moths usually feed on roots and plant parts close to the ground, thereby often cutting the stems of young plants. This is where their common name comes from. Cutworms are vey polyphagous and have a wide host range.
Life cycle and appearance of Cutworms
The adults of Agrotis spp. have pale grey to grey-brown forewings with a faint kidney-shaped marking and a red spot. They have broad hindwings, evenly light or dark grey or orange-yellow with a broad dark marginal stripe. The wingspan is about 40-55 mm and the dorsal thorax is covered with close-lying hairs.
The eggs are white at first but rapidly turn darker. They are laid separately or in batches on the ground, or on the plant close to ground level. The larvae are yellowish when hatching with a dark head capsule and prothoracic shield, later they become earth-brown to dingy grey. They are about 1.5 mm long just after emergence and can reach 4 cm or more when fully grown. The caterpillars may be encountered in the soil in a characteristic, circular position. Pupa are brown to dark brown and 17-25 mm long.
Females are capable of laying several hundred eggs. There are six to seven larval stages. Pupation takes place in the ground. Depending on the temperature, the development from egg to adult takes about 40-60 days.
Early instar cutworm larvae can create 'shotholes' while feeding on tender leaves of seedlings. Third to seventh instars become negatively phototaxic and feed mostly at night and hide in the ground during the day. Damage from these instars is usually observed as a cutting of young seedlings, often causing death of the cut seedlings. Sometimes wilting is observed because of partial cutting. A larva often cuts one plant and quickly moves on to other plants and continues cutting. Therefore, relatively small populations of cutworms can destroy entire stands of crops, such as cotton or maize. As plants become larger, older instars will occasionally tunnel into the growing stalk, disrupting the sap flow in the plant.