Crops: Apples, walnut
Why is it a problem? Cleorina leaf beetles are not normally a serious problem in apples, but can cause localised damage to developing apples and occasionally completely defoliate young trees.
Where and when is it a problem? This beetle can be commonly found in all apple and walnut growing areas. They can appear quite suddenly from late May onwards, but rarely in sufficient numbers to cause significant damage. They usually disappear towards late July.
There are two species, but they look very similar and are managed in the same way. Adult beetles are quite small, slightly larger than the head of a match stick. They are blackish-blue or dark metallic green. Beetles are very active and fly away as soon as the tree is disturbed. Alternatively they drop down when provoked. Both species are gregarious, and can be seen in small groups on leaves. Larvae have never been found in association with apple or walnut trees.
These beetles are gregarious leaf-feeders that are normally only seen on young apple trees. They usually start feeding on young leaves on tips of branches, ultimately skeletonising them (leaving just the veins).They also feed on the outer skin of marble-sized apples. Heavily attacked apples will turn completely brown and rough and will eventually drop. Because of their gregarious behaviour only a small number of the available apples (up to 20-30) are normally damaged. They can’t feed on mature apples as the skin is too hard.
In walnut trees the leaves are very sensitive to the damage caused by the beetles as they dry up, starting from the edges, and turn black.
Confusion with other pests: Other pests also attack developing apples, including the flat spiny caterpillar and the green apple weevil. Two spotted beetles also skeletonise leaves. However, the Cleorina leaf beetle adults are distinctive.
Lifecycle: Beetles occur in large numbers from late May onwards on the foliage of apple and walnut trees, probably coming in from adjacent forests. They usually disappear towards late July. Their lifecycle is unknown.
Dispersal: Cleorina leaf beetles don’t breed on apple or walnut trees. Adults therefore fly in from their breeding hosts each May.
When can damage be expected? Damage is only seen from late May to late July.
Hosts: Adults are known to feed on apple and walnut trees. The breeding host is unknown.
The Cleorina leaf beetle is one of several pests that can affect young orchards and developing apple fruit. The pest is transitory, but regular monitoring and rapid response is necessary to prevent significant losses if pest numbers are high.
Beetles can appear quite suddenly so monitoring should be regular (three times per week) from May to July as part of broader monitoring of orchard pests (including the flat spiny caterpillar and apple fruit borer). When monitoring survey multiple trees as the pest is often aggregated: just because one tree is heavily attacked it doesn’t mean other trees are.
Effect of variety
- Manual control (removing and destroying adults) is possible if only a small number of trees are affected, but it will need to be repeated for quite a number of days. Adults are easily disturbed so avoid allowing them to drop to the ground and escape.
- Use of insecticides in orchards should be minimised at all times to prevent outbreaks of new pests such as red spider mite. Apple trees should never be sprayed with insecticides during flowering.
- Spraying may be necessary in young apple trees if many leaves have small groups of beetles and skeletonising of leaves starts. Also on adult trees if large numbers of beetles can be seen feeding on large numbers of small apples.
- Only a single spray is generally needed as the pest is transitory.
- Spraying should only be conducted early in the morning when these beetles are still slow and do not fly or drop away.
- Use Chlorpyrifos (4 ml in 1 litre of water) or Cypermethrin (1 ml in 1 litres of water)
Image acknowledgements: NPPC.