Popillia species and Protaetia neglecta
Why is it a problem? The adults of six species of apple fruit beetles all feed on developing and developed apples, making them unmarketable. Although feeding damage can be conspicuous, the economic impact is not important unless beetles arrive in large numbers. They can be managed without pesticides.
Where and when is it a problem? Beetles arrive and begin feeding on apples from about June. Popillia beetles occur in all apple growing regions but are reported to be particularly abundant around Bumthang. Outbreaks are uncommon and generally localised.
Apple fruit beetles include five Popillia species and Protaetia neglecta. Adult Popillia are 8-12 mm long and are metallic green to blue in colour. Adult Protaetia neglecta are larger (18-23 mm long) and are dull metallic green in colour. Larvae have never been found in association with apple trees.
On fruit the large adult beetles usually feed in groups of three to ten. Feeding damage is conspicuous. They feed on larger developing apples and fully grown apples.
Confusion with other pests: They are the only pest to feed on maturing apples. They are also the largest beetle to feed on apples.
Lifecycle: Adults appear in apple orchards in June where they feed on leaves, flowers and fruit (developing, ripe and rotting). Lifecycle duration is not known, but is likely to take at least one year in Bhutan. Adults usually feed on flowers and ripe and rotting fruits.
Dispersal: Adults fly.
When can damage be expected? Most damage occurs when fruits are maturing or ripe.
Hosts: Popillia larvae feed on the roots of grasses and probably also other plants. Circumstantial evidence suggests that clover might also be a host for larvae. In Bhutan adults appear to feed on the leaves and fruits of various plants including apple, peach, apricot, plum and cabbage. However, they are only reported to cause significant damage on apples. Protaetia neglecta adults have only been reported on apples in Bhutan and their breeding host is not known.
Apple fruit beetles are an occasional pest that should be easily detected through regular orchard monitoring, and be readily managed.
Monitor fruit weekly in the orchard from June through to harvest for the presence of feeding adults and damaged fruit.
Effect of variety
- Adults can be hand-picked off fruit into a container, together with infested apples if need be, then immersed in a bucket of water with a few drops of kerosene. Alternatively, the beetles can be shaken from the fruit tree into the bucket, leaving the damaged apple to attract other beetles.
Chemical control is not needed. Contact NPPC in the event of an exceptional outbreak.
Image acknowledgements: Bugwood.org