Diamondback Moth

Adults are small, slender greyish-brown moths; when the wings are folded, pale markings along the back can form a series of diamond shapes, giving the insect its name. Larvae are small, green, and tapered at both ends, and they wriggle actively and may drop on a silk thread when disturbed. Pale, mesh-like pupal cocoons are found on the foliage.

Young larvae may mine briefly within the leaf, while older larvae chew small holes, often leaving the upper leaf surface intact to create a "window-pane" effect. These signs, plus the wriggling larvae and lacy cocoons, help separate diamondback moth from other brassica caterpillars.

Females lay tiny eggs on the foliage, and larvae develop through several instars before spinning a cocoon and pupating on the plant. The life cycle is short in warm weather, allowing many overlapping generations per year and rapid population growth, which also accelerates the selection of resistant individuals under repeated spraying.

The moth is highly mobile and can migrate, recolonizing areas where cold limits year-round survival. Continuous availability of brassica hosts, including weeds and crop residues, supports carry-over between crops.

Larval feeding produces small holes and window-pane patches on leaves; heavy feeding can defoliate seedlings and contaminate or damage the marketable heads of crops such as cabbage and broccoli. Because damage to the growing point or head is especially costly, even modest larval numbers can matter at sensitive stages.

Hosts are brassicas, including cabbage, broccoli, cauliflower, and kale, as well as other cabbage-family crops such as mustard and oilseed rape. Damage severity varies with crop stage, variety, and natural-enemy activity.

Pheromone traps track adult male flight to signal activity and generations, while direct plant inspection counts larvae and assesses feeding damage relative to crop stage. Checking for parasitized larvae and cocoons helps gauge natural control. Decisions are guided by local economic thresholds rather than fixed schedules.

Given the pest’s resistance history, management stresses non-chemical tactics and strict resistance management within integrated pest management.

• Conserve parasitoid wasps and other natural enemies that provide substantial control
• Use crop rotation, field sanitation, and control of brassica weeds to reduce carry-over
• Consider selective biological products, such as microbial insecticides, that spare natural enemies
• Rotate modes of action and avoid overuse to slow resistance development
• Base any intervention on trapping and scouting against local thresholds