Why is it a problem? Large numbers of larvae on young fruit can result in considerable losses through fruit drop. Market value can also be reduced through distortion of fruit shape caused by partial feeding on the apple. Insecticides are needed to manage severe outbreaks. Feeding damage to leaves is not important.
Where and when is it a problem? It is mainly a pest of high altitude areas (such as Bumthang, Ha and Yusipang/Hongtso area of Thimphu). Damage occurs when apples are marble-sized. Losses to this pest have not been quantified.
Adult moths are medium-sized (17 mm long) with a dark head and body and translucent pale wings. Forewings have a tiny orange spot at their base. The apical half of the front wings has a greyish network surrounding pale cells and the posterior edge of the forewings are also greyish. Moths are easily recognisable when flying in the orchard. Caterpillars (up to 20 mm long) are characteristically flat and spiny. Their top (dorsal) side is dark brown with three prominent rows of yellow markings. Underneath (ventrally) they are pale yellow. The head is pinkish-red. Caterpillars secrete a fine web by which they can protect themselves when disturbed. Pupae look like dried-up contracted larvae attached to the underside of leaves and stems. They are often found in groups.
Larvae attack marble-sized fruit in May, gnawing holes. Some apples are largely consumed. These drop from the tree prematurely. In other cases larvae only feed on parts of the apple, resulting in abnormally shaped apples. Larvae also feed on tender leaves, making many holes, but damage is limited.
Confusion with other pests: This pest is one of several feeding on marble-sized fruit, but the flat spiny caterpillars are characteristic.
Lifecycle: Most eggs are probably laid in early May. In May larvae feed on the developing apples and leaves. After early June they appear to feed almost exclusively on leaves. Pupation takes place on the leaves. There may be two to three generations per year depending on the temperature, but only the first generation damages apples.
Dispersal: Adults are active fliers.
When can damage be expected? Only damage to apples is economically important, and only marble-sized apples are susceptible. These are present in May to early June.
Hosts: It is expected that larvae will utilise hosts other than apple, but this has not been confirmed in Bhutan.
Larvae only damage marble-sized fruit. Regular monitoring is therefore essential from May to early June. Insecticides should only be used if the proportion of fruits being damaged is becoming unacceptably high. This is relatively rare.
Monitor orchards weekly in May and early June for gnawing damage on marble-sized apples, and for larvae on apples and leaves. Action should be taken when the proportion of apples being attacked is becoming unacceptably high. Also look for moths hovering in the orchard in high numbers. This can provide an indication that pest numbers will be high.
Effect of variety
There are currently no non-chemical recommendations.
- Insecticide use should be kept to a minimum in apple orchards to avoid the emergence of other pest issues.
- A cover spray of the whole orchard is only necessary if the infestation is severe.
- Do not apply once apples are too large (greater than marble sized) or hard to be damaged. Larvae will move to feeding on leaves at that point so will no longer be of economic importance.
- Either Cypermethrin (1 ml in 1 litres of water) or Chlorpyrifos (4 ml in 1 litre of water) can be used.
Image acknowledgements: NPPC.