Scale insect populations are host to a complex of natural enemies.
Parasitic wasps
The minute chalcid wasp Aphytis mytilaspidis is a common external parasite of mussel, oyster and pear scales.
- The egg of the parasite, usually one per scale, is laid under the waxy scale, close to the body of the insect.
- The wasp has two generations per year and can feed on the second nymphal stage as well as on the adult female.
- The greatest extent of parasitism of mussel scale recorded is 26%, but in most cases parasitism is much lower.
Several other species of parasitic wasp also attack mussel and other scale insects.
- Levels of parasitism can be assessed by looking for small circular holes in the old scales from which the adult wasps have emerged.
- However, natural populations of the parasitic wasps do not constitute a significant or reliable regulatory mechanism.
Predatory insects
Ladybird adults and larvae, mirid and anthocorid bugs, earwigs and predatory mites often destroy large numbers of scales, particularly the vulnerable young stages.