Hosts or Prey
Aphids
Identification
Obvious evidence that D. rapae or another Aphidiidae is present is that about 1 week after being parasitized the aphid becomes a brown, gold, or tan colored mummy. When parasitized by a family Aphelinidae wasp the mummified aphids turn black.
After feeding inside as a larva and pupating the emerging adult wasp leaves a roundish hole in the mummified aphid it killed. The bodies of unparasitized aphids are soft, have no holes visible to the naked eye, and are the color(s) characteristic of the species. However, because the immature parasitoid does not change the aphid's appearance until about a week after the parasitoid egg is laid, the percentage of parasitized aphids can be greater than the percentage of mummified aphids.
The adult D. rapae is about 1/12 inch (2 mm) long varying by the size of the host from which it emerged. It has long, thin, beadlike antennae. The head and thorax are dark brown to black. The abdomen and legs are black to yellowish brown.
Eggs, larvae, and pupae of D. rapae occur hidden inside aphids. The tiny eggs are oblong. Larvae are elongate, legless, and orangish or pale colored with distinct segments. Curved or hooked mouthparts may be apparent on the head.
Pupae are oblong with distinct segments. As they age they develop appendages folded against the body.
Life Cycle
Diaeretiella rapae develops through 4 life stages: egg, larva, pupa, and adult. When temperatures average 68ºF adult longevity is about 1 week during which a female lays about 25 eggs. Adult females can parasitize adults and any instar (nymph) of aphids. But if young first instars are parasitized commonly the aphid is killed but the wasp does not survive to maturity.
After hatching the wasp larva develops through 3 increasingly larger instars as it feeds on the aphid's body contents. About 7 to 10 days after the egg was laid the wasp larva kills the aphid and causes its covering to become mummified. The wasp then pupates into an adult that chews a rounded hole and emerges from the mummy.
Egg to reproductive adult development is about 3 weeks when temperatures average 68ºF. Diaeretiella rapae can be active throughout the year where winters are mild. It has multiple generations per year.
Habitat
Diaeretiella rapae can be found parasitizing aphids in field, tree, and vine crops, gardens, landscapes, and wildlands. The parasitoid is believed to be native to the western United States. Diaeretiella rapae has been introduced throughout much of the world for the classical biological control of aphids.
To improve biological control
- Control ants because they attack natural enemies of aphids and various other pests.
- Grow flowering insectary plants to provide nectar to nourish adult parasitoids.
- Reduce dustiness that disrupts the activities of natural enemies (e.g., irrigate overhead or periodically hose off small plants).
- Avoid the application of broad-spectrum, persistent insecticides for all pests because they are toxic to natural enemies.
For more information see Protecting Natural Enemies and Pollinators and the table of relative toxicities of insecticides and miticides to natural enemies and honey bees for specific crops.
Species
Diaeretiella rapae is the only species in the genus Diaeretiella. It parasitizes at least 100 species of aphids infesting over 180 plant species. Its economically important hosts include bird cherry-oat aphid, cabbage aphid, cotton aphid or melon aphid, and green peach aphid.
More Information
- Biological Notes on Pacific Coast Aphid Parasitoids, and Lists of California Parasitoids (Aphidiidae) and Their Aphid Hosts, UC Riverside, Annals of the Entomological Society of America
- Effects of Temperature on Longevity, Reproduction, and Development of the Asparagus Aphid (Homoptera: Aphididae) and the Parasitoid., Diaeretiella rapae (Hymenoptera: Braconidae), Environmental Entomology
- Host Range and Habitats of the Aphid Parasitoid Diaeretiella rapae (Hymenoptera: Aphidiidae) in Washington State, Environmental Entomology
- Use of the Parasitoid Diaeretiella rapae (McIntoch) to Control the Cabbage Aphid Brevicoryne brassicae (L.), Journal of Applied Entomology
Scientific classification:
- Phylum: Arthropoda
- Class: Insecta
- Order: Hymenoptera
- Family: Aphidiidae
