Diamondback Moths are considered pests as they feed on the leaves of cruciferous crops and plants that produce glucosinolates.
Diamondback moth larvae feed on all plants in the mustard family (canola, mustard), cole crops (broccoli, cabbage) and on several greenhouse plants. In Zimbabwe, cabbages are its primary targets.
The adult moth is approximately 8 to 9 mm (1/3 inch) long with a wing span of 12 to 15 mm (½ inch).
At rest, the moth folds its wings over the abdomen in a tent-like manner. The folded wings flare upwards and outward at the tips. The wing tips are fringed with long hairs.
In the male, the forewing margins have a series of yellow wavy markings. When the wings are folded while the moth is at rest, these markings come together to form three yellow diamonds, hence the name diamondback.
Adult females lay an average of 160 eggs during their life span of about 16 days. Egg-laying occurs at night. The greatest number of eggs are laid the first night after emergence and egg-laying continues for about ten days.
In the field, moths will flutter up out of the canopy as the canopy is disturbed.
Immediately after hatching from the egg, larvae burrow into the leaf and begin mining the leaf tissue internally. After feeding within the leaf for about a week, the larvae exit from the underside of the leaf and begin feeding externally.
The larvae are pale yellowish green to green caterpillars covered with fine, scattered, erect hairs. The posterior end of the caterpillar is forked.
Larvae moult three times during the larval stage which lasts about ten to 21 days, depending upon temperature and the availability of food. At maturity the larvae are cigar-shaped and about 12 mm (½ inch) long.
The diamondback moth larva is easily identified by its peculiar reaction to being disturbed. It will wriggle backward violently and may drop from the plant, suspended by a silken thread. After several seconds, the larva will climb back onto the leaf and continue feeding.
Larvae pupate in delicate, white, open-mesh cocoons attached to the leaves, stems or seed pods of the host plant. Initially, the pupae are light green but as they mature, they become brown as the adult moth becomes visible through the cocoon. The pupal stage lasts from five to 15 days, depending on environmental conditions.