NC State Extension Publications

Description and Biology

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The diamondback moth, Plutella xylostella, has narrow forewings, conspicuously fringed hind wings, and an ¾ inch wingspan. When at rest, the wings of the male come together to form a line of white or pale yellow diamonds down the middle of the back. Females moths have a crenulated line down the back. Females lay minute oval, pale yellow eggs singly or in groups of two to eight. Each female lays about 150 eggs in her lifetime, but some have laid as many as 300! The caterpillars taper slightly at both ends and are pale green with black heads and scattered black hairs. They grow to about to about 3/8 inch long. Diamondback moth caterpillars thrash rapidly when disturbed, often dropping from the plant and hanging by a silk thread. The yellowish pupa is enclosed within a loosely spun, gauze-like cocoon about 3/8 inch long. Diamondback moths overwinter as adults among field debris of crucifer crops. Although the moths are weak fliers, they can be carried long distances by prevailing winds. In spring, eggs are laid, singly or in groups of two or three on foliage. Tiny caterpillars hatch from eggs a few days later and feed for about 10 to 30 days first as leafminers. They soon emerge to infest the undersides of leaves. Mature caterpillars enclosed themselves in loose cocoons attached to lower leaf surfaces and then pupate. About two weeks later, a new generation of moths emerge. We have five or six generations per year in North Carolina.

Diamondback moth

Diamondback moths are very small and slender.

Diamondback moths

Diamondback moths are about 3/8 inch long.

Diamondback moth caterpillar

Diamondback moth caterpillars are slender and small.

Cocoons of the diamondback

Cocoons of the diamondback moth are flimsy.

Host Plants

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Caterpillars of the diamondback moth feed almost exclusively on cole crops such as broccoli, cabbage and kale (also ornamental varieties) in the vegetable garden and in commercial greenhouses. It is also a pest of alyssum, candytuft, watercress, and stock (a flowering crucifer sometimes grown in ornamental greenhouses). In addition, diamondback moth caterpillars feed on some weeds such as mouse-ear cress, Whitlow grass, shephed's purse, and spring cress that may be growing under the benches or just outside the greenhouses. Diamondback moth caterpillars feed on all plant parts, but prefer the undersides of older leaves, crevices between loose leaves, and young buds. They eat small holes in leaves and buds, or feed superficially.

Diamondback moth caterpillars may cause extensive damage.

Diamondback moth caterpillars may cause extensive damage.

Residential Recommendation

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The diamondback moth has acquired resistance to many kinds of pesticides including some of the Bacillus thuringiensis pesticides that are labeled for the diamondback moth (with three or zero day waiting periods for vegetable crops!). If diamondback caterpillars survive insecticides labeled for use in vegetable gardens or residential landscapes (on flowers), it may be better to consider growing species not in the family Cruciferae.

References

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For assistance with a specific problem, contact your local Cooperative Extension Center.

This Factsheet has not been peer reviewed.

Author

Professor Emeritus
Entomology and Plant Pathology

Publication date: Sept. 26, 2016
Revised: Oct. 25, 2019

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