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.
Where and when is it a problem?
Around June, beetles arrive and begin feeding on apples. Popillia beetles occur in all apple-growing regions but are reported to be particularly abundant in Bumthang. Outbreaks are uncommon and generally localized.
Apple fruit beetles include five Popillia species and Protaetia neglecta. Adult Popillia are 8–12 mm long and are metallic green to blue in color. Adult Protaetia neglecta are larger (18–23 mm long) and are dull metallic green in color. Larvae have never been found in association with apple trees.
Beetles feed in groups (often 10) on 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.
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 to 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.
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.
Chemical control is not needed. However, during outbreaks, applications of cypermethrin (1 ml per 1 liter of water) or chlorpyrifos (4 ml per 1 liter of water) can be made.
Image acknowledgements: Bugwood.org