Acrolepiopsis assectella (leek moth)

On inflorescences, damage is characterized by the fall of the flowers where moth larvae have eaten the floral peduncles. 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.

Cultural Control

Some cultural methods may influence leek moth damage on annual Allium plants (Rahn, 1982b). They have less activity on biennial plants such as leek.

Biological Control

Work on the specialist solitary endoparasitoid Diadromus pulchellus has been undertaken in the laboratory (Lecomte and Thibout, 1983, 1986, 1993; Thibout et al., 1988, 1993). No field studies have been undertaken.

Host-Plant Resistance

Some Allium varieties are considered more resistant than others to the leek moth. However, leeks and onions are selected according to flower stalk length, leaf colour, taste, winter hardiness or tendency to bulbiness (Brewster, 1994) and not on resistance to insects.

Chemical Control

Chemical control of the leek moth is very efficient when applied at the most appropriate time. Sexual trapping by means of the synthetic female pheromone (Z 11 HDAL) can be used to predict potential damage and dates of egg laying. However, some abnormally low captures have shown that this technique is not entirely reliable (Rahn, 1982a). The use of five pyrethrinoids and two organophosphorous insecticides, and of Bacillus thuringiensis toxin is possible in France under certain conditions (ACTA, 2000). No resistance of the leek moth to these insecticide treatments has been indicated. Film-coating leek seeds with fipronil and imidacloprid provided protection against A. assectella at low population densities (Ester and Huiting, 2001).

Cultivated Allium plants, particularly leek and onion, from the south of Norway and Sweden to Italy, Spain and Algeria, are frequently attacked by A. assectella. 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 parenchyma by the moth larva 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. Without control, moth populations can reach so high a level at the third generation that 100% of the plants are damaged (Bouchet, 1964).Very important damage also occurs on inflorescences in plants cultivated for seed production where serious seed loss can occur. In France, damage can reach >70% in Brittany (Rahn, 1982b), and 60-80% on leek and 40-50% on onion in Vaucluse (Nepveu and Hoffman, 1950).The number of leek moths in a population depends on climatic conditions. The population increases with successive generations and damage is more important in summer and at the beginning of autumn than in the spring.Sometimes moth galleries are colonized by maggots of Drosophilidae or of the onion fly, Delia antiqua, which introduce fungal and bacterial pathogens.