Quick Facts

  • Adults overwinter in plant debris until April when the temperature reaches 9.5°C
  • Mating takes place within 24 hours of emergence
  • Females are considered monogamous and live approximately 23 days
  • Adults are nocturnal—flights and mating are usually restricted to the hours of darkness
  • On average there are three generations per year
  • Female moths lay eggs mostly on the lower leaf surface, usually near the base of the plant
  • Eggs hatch 4-6 days in the spring and 8-11 days in the fall

Species Facts:

The Leek Moth, Acrolepiopsis assectella, is a serious pest that causes damage to all parts of Allium plants (e.g. leeks, onions, etc.) except for their flowers. Symptoms on younger plants in early summer include mines and perforations. The larvae and pupae of Leek Moths are often hidden in Allium tops in the new growth near the crown. Visual inspection for larval damage is most effective for plants with very small tops. It is common to find both old and recent feeding damage on a plant.
On leek, they prefer to feed on the youngest leaves, but can consume leaves more than two months old. They bore through the folded leaves to the center of the plant, causing a series of pinholes, and feed on the inner leaves. When the larva develops on 1st-year leek, it is the leaves that suffer. The lacerated appearance makes the leeks unfit for sale and the lesions facilitate rotting.

In onions, larvae remain in the leaf cone and cause partial desiccation from feeding on the hollow leaves. The damage in itself is of minor importance, but, under unfavorable conditions, the onion ages too quickly and the larvae reach the more turgescent bulb and form galleries. Harvested crops containing damaged bulbs will be rejected, because hidden damage causes sales-loss in markets.

On seed-crop, the larvae feed mainly at the base of the inflorescences and cause the flower stems to fall off in large numbers. Losses frequently reach 70 to 90% of the harvest. Under field conditions the damage is more prevalent at the field perimeter than toward the center.

The adult Leek Moths have a wing span of approximately 15 mm. The forewings are pale brown to black in color. The forewing has a large triangular white mark with smaller white markings. The hindwings are pale gray to light black in color. The egg is white in color, oval and about 0.4 mm in diameter. The larvae are yellowish-green in color with gray-brown patches, possessing a yellowish-brown head; mature larvae are 13-14 mm in length. The 5th instar larvae emerge from the leaves to pupate, the pupal case is reddish-brown in color. The cocoon is white in color and is composed of a loose "net-like" structure. Pupation occurs mainly on the food plant but can also occur on the soil or neighboring plants, or among plant debris. In the field, the pupal stage lasts about three weeks, or it may overwinter.

Portions of this article courtesy of: Canadian Food Inspection Agency
Image of a Leek Moth larva (Photo from: www.bugwood.org Credit to: Mariusz Sobieski)