September 28, 2022

Diamond back moth

Diamond back moth

Trevor HutchinsonThe adult diamond back moth is a small, greyish insect with a wingspan of about 7 mm. Adults are usually seen out at night.

They have a narrow, pale yellow stripe along the back edge of the wing. This stripe has an irregular, wavy black border. With the wings folded in, the stripes form the diamond pattern which gives the moth its name.

The female lays up to 100 light yellow oval cylindrical eggs, usually on the underneath of leaves. Larvae hatch after 5 to 6 days, taking longer in colder weather.  They spend 2 to 7 weeks as caterpillas, then another 10-24 days as a pupae before emerging as the adult moth.

Fully grown caterpillars are usually greenish, and approximately 8mm in length.

The caterpillars feed on brassicas such as  kale, broccoli, and brussels sprouts, cabbage, cauliflower. They also feed on the leaves of turnip and swedes. They bore through the surface of the leaf and mine the tissue underneath. The mines are obvious in the early stages and appear as white markings on the leaves. They then eat out patches which eventually become holes through the leaf. 

Diamondback moth are found throughout NZ and world-wide.