Aphidius colemani

Target Pest: Aphids

Description: Aphidius species are a group of native parasitic wasps, frequently found parasitizing aphids in greenhouses and outdoor crops. Adults are tiny (2-3 mm long), dark colored wasps that do not sting. The larvae develop entirely inside the host aphid, which eventually become rigid mummies when the larvae pupate. Aphidius is an outstanding searcher, and can locate new aphid colonies even when aphid populations are low.

Use in Biological Control: When aphid populations are high, Aphidius colemani alone will not provide adequate control, but they work well in conjunction with Aphidoletes and ladybugs to provide control. Effectiveness may be reduced in late summer when "Colemani" itself may be attacked by naturally occurring hyperparasites. These are even smaller parasitic wasps that will parasitize the Colemani as well as the aphid, and will emerge instead of the Colemani. While this can be damaging to a biocontrol program, modern processes can ensure that this is a rare situation. 

Life Cycle: A complete life cycle takes 10 days at 77°F (25°C) and 2 weeks at 70°F (21°C). The sex ratio in the population is about equal, although there may be slightly more females than males (50-60% females). Each female lays about 100 eggs in aphids, but may attack 200-300 aphids in the process.

The larvae develop entirely inside the aphids, and do not kill their host until the wasp larva is ready to pupate. Once the larva pupates, the aphid’s body will become a rigid, leathery, golden-brown mummy. Adults emerge from the mummies by cutting an exit hole in the top. The empty mummy remains on the leaf surface. The size of the adult parasite and the number of eggs it can lay depends on the size of the aphid it came from. 

For Best Results: During spring and summer, aphid populations grow too fast to be controlled by the parasite alone. Therefore, it is advisable to introduce additional aphid predators such as Aphidoletes and ladybugs. In gardens, wash high populations of aphids from plants with a strong water spray before introducing the aphid parasite.

Colemani does not attack many common aphid species, such as potato aphid, so if mummies are not present, check aphid identification. 

Introduction Rates: Aphidius is most effective when aphid populations are low. Parasites can be introduced at low rates before aphids are detected in greenhouses or when aphids are likely to move onto crops outdoors. When aphids have been detected in a crop, higher release rates should be used over a period of at least 3 weeks. Because of the time it takes for larvae to develop inside aphid mummies, use at least 2 releases, 1 week apart to establish overlapping generations of the parasite. Most of the parasitized aphids leave the plant before mummies are formed, and it has been found that if 10% of aphids found on leaves are mummies, then the population should soon collapse

General Introduction Rates: Before aphids are detected: 1,000 Aphidius per hectare, weekly (400/acre) After aphids are established: 5,000 Aphidius per hectare, 2-3 times, one week apart (2,000/acre)

Greenhouse peppers: Use general introduction rates, until 10% of aphids on plants are mummies (if aphids are established)

Greenhouse tomatoes: 1 Aphidius per 10 plants, weekly for 2 weeks Greenhouse cucumbers: 1 Aphidius per plant, weekly until established

Ornamentals and outdoors: 0.1-3.0 Aphidius per 10 ft2 (m2 ) or 0.1-5.0 Aphidius per plant, weekly or until control is evident Important

Note: Yellow sticky traps used for monitoring pests will also trap Aphidius. If yellow traps are necessary for monitoring whitefly, do not release Aphidius near the yellow traps, and use no more than 1 yellow card per 100 plants. Aphidius are not attracted to blue sticky traps (which can be used for monitoring thrips where Aphidius is being released).