Hosts or Prey
California red scale, San Jose scale, and certain other armored scales
Identification
Obvious evidence of the activity of E. perniciosi or other scale parasitoids is a relatively large, roundish hole in the cover of armored scales. If the cover of the dead scale is removed, underneath will be the crusty, puffy (mummified) orange body of the dead scale that also has a roundish emergence hole of the adult parasitoid. Within the empty body will be dark pellets of excrement (meconium) of the last-instar (larval) wasp.
Another way to confirm the wasp is present is to place out a commercially available sticky trap baited with the pheromone (sex attractant) of California red scale or San Jose scale. In addition to attracting male scales of these species these pheromones also attract E. perniciosi adults.
The adult female E. perniciosi is 1/60 inch (0.4 mm) or less in length and mostly black to dark brown. Males if present are somewhat smaller and black. The antennae and on top the head and thorax are yellowish brown. The rear of the body has a bluntly pointed tip.
Eggs, larvae, and pupae occur hidden inside host scales. The pale egg is about 1/300 inch (0.08 mm) long and ovate spherical with a short projection on one end. The first instar has distinct mouthparts and is elongate with a thin tail-like projection. At the time the larva molts to the second instar it causes the host to turn orange and become a puffy mummy. The second instar is tail-less and becomes plump or saclike.
After becoming a mature third instar the wasp develops distinct segments and identifiable abdomen, head, and thorax. It then pupates and as the wasp ages it darkens and develops distinct appendages folded against the body.
Life Cycle
Encarsia perniciosi develops through 4 life stages: egg, larva, pupa, and adult. The adult female parasitizes all scale stages but it prefers to lay eggs in first and second instars. During her 2 week lifespan a female can lay over 100 eggs. Although more than 1 egg may be laid in a host, only 1 wasp per host survives to maturity.
Encarsia perniciosi has more than one biotype; populations that differ in their reproduction. On California red scale E. perniciosi reproduces parthenogenetically; only females are present. On San Jose scale there is both a parthenogenetic (females-only) biotype and a form that produces both female and male parasitoids. In the latter females are produced from fertilized eggs and males from unfertilized eggs. The males are autoparasitoids, meaning they develop on female E. perniciosi or the larvae of other species of internal parasitoids of armored scales.
Encarsia perniciosi overwinters as an egg or first instar in armored scale nymphs. Egg to reproductive adult development time is 3 to 4 weeks during the summer. The wasp has multiple generations per year.
Habitat
In 1949 E. perniciosi (then named Prospaltella perniciosi) was introduced from Southern China and Taiwan into California to control California red scale infesting citrus. Encarsia perniciosi now occurs on citrus in Coastal California and Southern California but is uncommon on citrus in inland valleys. On walnut and various other woody plants infested with its host armored scales, E. perniciosi can occur throughout California. It mostly occurs on scale-infested fruit and nut trees, landscape trees and shrubs, and woody wildland plants.
Parasitic wasps especially Aphytis species and Encarsia species and predatory beetles including twicestabbed lady beetle, (ladybug or ladybird beetle, Chilocorus orbus), and a smaller black beetle (Cybocephalus californicus) can provide biological control of various pest scales. To improve biological control
- Control ants because they attack natural enemies of scales and other pests.
- Grow flowering insectary plants to provide nectar to nourish adult parasitoids.
- Reduce dustiness that disrupts the activities of natural enemies (e.g., periodically hose off small plants).
- Avoid the application of broad-spectrum, persistent insecticides for all pests because they are toxic to natural enemies.
See the citrus table Selectivity of Insecticides and Miticides and Relative Toxicities of Pesticides Used in Walnuts to Natural Enemies and Honey Bees to learn which pesticides are most compatible with biological control. To learn additional ways to improve the effectiveness of natural enemies see Protecting Natural Enemies and Pollinators.
Species
At least 30 Encarsia species occur in California, many of which parasitize multiple species of scale insects, whiteflies, or other plant-sucking insects formerly called Homoptera. Encarsia perniciosi parasitizes at least 14 species of armored scales.
More Information
- Competition, Resource Partitioning and Coexistence of an Endoparasitoid Encarsia perniciosi and an Ectoparasitoid Aphytis melinus of the California Red Scale, UC Riverside, Ecological Entomology
- Integrated Pest Management for Citrus, UC Integrated Pest Management Program
- Life Stages of California Red Scale and Its Parasitoids, UC Agriculture and Natural Resources
- Transition from Bisexual to Unisexual Cultures in Encarsia perniciosi (Hymenoptera: Aphelinidae): New Data and a Reinterpretation, UC Riverside, Annals of the Entomological Society of America
- Universal Chalcidoidea Database, Natural History Museum of London
Scientific classification:
- Phylum: Arthropoda
- Class: Insecta
- Order: Hymenoptera
- Family: Aphelinidae
