Why is it a problem? Large beetle numbers can defoliate trees. This is mainly a problem with young trees and newly established orchards where it can retard growth.
Where and when is it a problem? Problems have been recorded in Thimphu and Paro valley from late April to July. Outbreaks are rare and localised, but can quickly cause significant damage when they do occur.
Adult beetles are tiny, about 5 mm long. The hard forewings (elytra) are yellowish-brown with two black spots in the middle. Immature stages have not been found on apples.
Adults feed on the green parts of the leaf. In large numbers they skeletonise leaves such that only the veins remain. Young trees can be totally defoliated. On older trees feeding tends to concentrate on only one or two branches and serious damage is rare.
Confusion with other pests: Cleorina leaf beetles also skeletonise leaves. However, adults are characteristic.
Lifecycle: Very little is known of the lifecycle. Adults occur on apple trees from late April to July, and probably spend the rest of the year in adjacent forests. Beetles are very sensitive and fall to the ground to hide in the surrounding debris as soon as the tree is disturbed. Sometimes they can be observed flying in a dense cloud around apple trees.
Dispersal: Adults are winged and probably fly into apple orchards from surrounding forests.
When can damage be expected? Damage mostly occurs during flushing in April and May.
Hosts: They probably utilise a wide range of hosts as adults of the same species have been observed on Phaseolus bean plants and wild Melia trees. It is not known what they breed on.
The two-spotted apple beetle is only an occasional pest, and chemical control is only needed on young trees and then only under exceptional circumstances.
Weekly monitoring of young orchards (especially those with many new seedlings) need to be carried out from late April to end of July to ensure the beetle presence is noted in time. Beetles can occur quite suddenly and in large numbers so damage can occur very quickly. Look for feeding damage on the leaves, and for any associated beetles.
Effect of variety
Currently no recommendations.
- Use of insecticides in orchards should be minimised at all times to prevent outbreaks of new pests such as red spider mite. However, insecticides may be needed in young orchards if the outbreak is severe.
- Spaying is not needed once leaves are fully matured and hardened.
- Normally only a single treatment will be needed. Use either Chlorpyrifos (4 ml in 1 litre of water) or Cypermethrin (1 ml in 1 litre of water). Be careful not to knock the beetles to the ground prior to spraying.
Image acknowledgements: NPPC.