Hosts or Prey
San Jose scale and certain other scale insects, mostly armored scales
Identification
The most obvious evidence of the activity of this tiny wasp or its relatives is that after maturing and emerging as an adult the wasp leaves a rounded hole in the cover of scales it killed. If a scale cover with a hole is gently removed, beneath it can be observed a flat and dehydrated scale body and the parasitoid's dark fecal pellets (meconium) outside of the scale body.
The adult A. aonidiae is about 1/16 inch (1.5 mm) long with a yellow or orange body and head. The broad head has bulging eyes and short, knobby antennae. On top the head are 3 tiny red ocelli (light receptors) arranged in a triangle.
The eggs, larvae, and pupae of A. aonidiae occur on the outside of the host's body, but hidden under the scale cover. Aphytis eggs are 1/125 inch (0.2 mm) long and oval with a distinct stalk. The larvae are yellow to orange and oval or saclike. Larvae have distinct segments and no legs. At maturity the last (third) instar wasp is about 1/32 inch (0.8 mm) long.
The pupa is oblong with distinct segments. As it ages appendages develop folded against the body and the wasp's bulging eyes become apparent.
Lookalikes
Note that numerous other species of Aphytis parasitize San Jose scale and other armored scales. These include Aphytis melinus, the most important parasitoid of California red scale.
Life Cycle
Aphytis aonidiae develops through 4 life stages: egg, larva, pupa, and adult. Males are rare and most females reproduce without mating (parthenogenesis). If honeydew or flower nectar are available to nourish the adults their lifespan is about 6 weeks.
Adult females seek second and third instar hosts on which to lay an egg. If flower nectar or honeydew are available as food the adult female lays an average of about 85 eggs. First she injects venom into the scale to paralyze it and then lays her egg usually singly on the scale body. If more than 1 egg is laid only 1 or sometimes none of the parasitoids complete their development.
In addition to killing scales by parasitism A. aonidiae kills scales by host feeding. The adult female punctures scale bodies with her ovipositor and feeds on the exuding body contents. By host feeding the adult female is able to live longer, lay more eggs, and kill more scales.
The hatching wasp larva develops through three increasingly larger instars. The mature larva (prepupa) excretes its fecal pellets (meconium) then develops into a pupa. The pupa is orange to yellow. As it ages it develops appendages folded against its body. Aphytis aonidiae has several generations per year.
Habitat
Aphytis aonidiae can occur in landscapes, tree and nut crops, and wildlands wherever its scale hosts occur, mostly on woody plants. 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 natural enemies.
- 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 Protecting Natural Enemies and Pollinators and Relative Toxicities of Pesticides Used in Walnuts to Natural Enemies and Honey Bees for more information.
Species
At least 8 Aphytis species parasitize San Jose scale in California: Aphytis aonidiae, A. chilensis, A. diaspidis, A. hispanicus, A. melinus, A. mytilaspidis, A. proclia, and A. vandenboschi. At least 23 Aphytis species occur in California; each parasitizing multiple species of scales. Aphytis aonidiae parasitizes over 30 species of scale insects, mostly armored scales. Its economically important hosts include California red scale, European fruit lecanium, oystershell scale, pittosporum pit scale, and walnut scale.
More Information
- Biological Studies on Aphytis aonidiae (Mercet) (Hymenoptera: Aphelinidae), an Important Parasitoid of the San Jose Scale, UC Riverside, Hilgardia
- Bionomics of Aphelinidae, Annual Review of Entomology
- Universal Chalcidoidea Database, Natural History Museum of London
Scientific classification:
- Phylum: Arthropoda
- Class: Insecta
- Order: Hymenoptera
- Family: Aphelinidae
