Light brown apple moth

Distribution

The light brown apple moth is a native insect of Australia. It has been introduced and now also lives in New Caledonia, the British Isles, Hawaii, and New Zealand. In March 2007 the moth was positively identified in California by DNA samples across hundreds of miles, from Los Angeles to Napa, north of San Francisco.

Behavior

Light brown apple moth pass through three generations annually with a partial fourth generation in some years. The moth has no winter resting stage. There is considerable overlap in the generations. In warmer areas, four or even five generations are completed annually, with major flight periods occurring during September–October, December–January, February–March, and April–May. In cooler climates, the number of complete generations may be reduced to two.

Eggs are laid in clusters of 3–150 on leaves or fruit. A single female might lay hundreds of eggs. Adults produced by the overwintering larval generation emerge during October and November. These give rise to the first summer generation, in which final instar larvae mature between January and mid February. Second generation larvae reach maturity during March and April, and the adults from this generation provide third generation eggs. Normally, the rate of larval development is slowed considerably during the winter, particularly when temperatures approach freezing; thus the majority of larvae over-winter in the prolonged early juvenile phases of the second third, and fourth instars. During this period they normally feed on herbaceous plants. Re-invasion of apple trees takes place during October–December, when moths of the third generation start laying eggs again on apple leaves.

Reproduction

Larvae are not easily distinguished from the larvae of other tortricid leafrollers; only DNA testing is a certain identification method. The first larval instar has a dark brown head; all other instars have a light fawn head and prothoracic plate. Overwintering larvae are darker. First instar larvae are approximately 1.6 mm long, and final instar larvae range from 10–18 mm in length. The body of a mature larva is medium green with a darker green central stripe and two side stripes.

Food

The insect is regarded as an herbivorous generalist, and the larvae feed on numerous horticultural crops in Australia and New Zealand, where they have limited natural predators. It is known to feed on 123 dicotyledonous plant species, including 22 Australian natives, belonging to 55 different families. In New Zealand, over 250 host species have been recorded. It feeds on nearly all types of fruit crops, ornamentals, vegetables, glasshouse crops, and occasionally young pine seedlings.

The larvae cause significant damage to foliage and fruit. Early instars feed on tissue beneath the upper epidermis of leaves, while protected under self-constructed silken webs on the undersurface of leaves. Larger larvae migrate from these positions to construct feeding niches between adjacent leaves, between a leaf and a fruit, in the developing bud, or on a single leaf, where the leaf roll develops. The late stage larvae feed on all leaf tissue except main veins, and can often be found tunneling into berry fruits such as strawberries and caneberries.

Superficial fruit damage is common in apple varieties which form compact fruit clusters, though more significant damage may also occur such that crops are no longer commercially viable. Leaves are webbed to the fruit and feeding injury takes place under the protection of the leaf; or larvae spin up between fruits of a cluster. Internal damage to apple, pear, and citrus fruits is less common, but a young larva may enter the interior of an apple or pear fruit through the calyx or beneath the stem of a citrus fruit. Excreta are usually ejected on to the outside of the fruit.

In sharp contrast to most affected regions, the Hawaii Department of Agriculture says the moth "has not been a significant pest in Hawaii" and finds it beneficial in a few cases, because it kills some invasive plants, including gorse and blackberry.

In April 2008, an attorney for the California Department of Agriculture acknowledged in court papers that there were "no documented crop losses in California at this time".