The leek moth is present throughout Europe. It is also found in some Asian countries and has been introduced to parts of Canada. The larvae of Acrolepiopsis assectella feed on cultivated Allium species, primarily leek and onion, but also garlic and chives.
Life cycle and appearance of Leek moth
The leek moth (Acrolepiopsis assectella) goes through eight stages, namely egg, five larval stages, a pupa and the adult moth. The eggs are small, white and elliptical and are laid singly on the leaf of Allium plants. After a wandering period on the leaves, first instar larvae penetrate into the green leaves where they bore galleries. Third, fourth and fifth instars bore into the central yellow leaves of the leek and produce the most severe damage.
First instar larvae are ca 1 mm long, but mature larvae are ca 10 mm with a brown head capsule and . a yellowish-white body. Pupation takes place in a 10-mm-long, cream-coloured, silk cocoon made of characteristic meshes spun on the surface of the leaves or on the flower-stalk of the host plant. The pupa is 7-8 mm long, its colour varies from light yellow in the beginning to brown before adult emergence.
Male and female moth are 8-9 mm long, with a wing span of 15-16 mm. Their general colour is grey-brown with a typical white triangle in the middle of the posterior edge of the forewings. The hindwings are uniformly grey. The moth are active at night and rest during the day.
Development time is temperature dependent. At 25°C, eggs hatch after 3-4 days. Larval development takes 2 weeks, pupal development 1 week and adults can survive 7-10 days. The moths overwinter as diapausing adults.
The vegetative and flowering stages are most widely affected, but the seedling stage is sometimes affected in nurseries. Stored onions and garlic are also damaged.
After hatching, the young larva explores the surface and mines the green leaves. On reaching the third instar, the larva penetrates the young leaves, the flower stalk or the inflorescence of the host plant. Feeding on the leaf tissue by the caterpillars causes a reduction in plant growth; if larvae are numerous, weakening or withering of the plant can occur. On old leaves, open galleries can be seen which decrease the economic value of the plant.
Severe damage also occurs on inflorescences of plants cultivated for seed production where serious seed loss can occur.
- On leeks, larvae mine the central leaves which have long, longitudinal grooves when growing.
- On onion leaves, the larvae feed on the parenchyma inside the hollow leaves, forming white windows closed by the epidermis. When feeding takes place at the base of the hollow flower stalk, this can be broken easily.
- On inflorescences, damage is characterized by the fall of the flowers where moth larvae have eaten the floral peduncles.