TARGET PESTS: Melon aphid (Aphis gossypii)
FOR YOUR FILES: Aphidius Tech Sheet (PDF)
Aphidius species are a group of native parasitic wasps, frequently found parasitizing aphids in greenhouses and outdoor crops. Adults are tiny, dark colored, non-stinging wasps, up to 1/8 inch (2-3 mm) long. Larvae develop entirely inside host aphids, 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. Optimum conditions are daytime temperatures of 64-77 ºF (18-25 ºC) and relative humidity 60-80%. Aphidius is not affected by short-day induced diapause, so it can be used year round.
Aphidius alone will not provide control when aphid populations are high, but can be used with Aphidoletes to provide control. Effectiveness may be reduced in late summer when Aphidius itself may be attacked by naturally occurring parasitic wasps (called hyperparasites).
A complete life cycle takes 10 days at 77ºF (25ºC) and 2 weeks at 70ºF (21 ºC). 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 to 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. The larvae pupate inside the aphid’s body, which 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.
1-25 per 100 sf., weekly
Before aphids are detected — 400 Aphidius/acre weekly (1,000/ha)
After aphids are established — 2,000 Aphidius/acre (5,000/ha) 2-3 times, one week apart.
Greenhouse peppers — Before aphids are detected: 400 Aphidius/acr
(1,000/ha) weekly. After aphids are established: 2000 Aphidius/acre (5000 /ha)
2-3 times or until 10% of aphids on plants are mummies.
Greenhouse tomatoes — 1 Aphidius/10 plants, weekly for 2 weeks.
Greenhouse cucumbers — 1 Aphidius/plant, weekly until established.
Ornamentals and outdoors — 0.1-3 Aphidius/10 ft2 (m2)or 0.1-5 Aphidius/plant, weekly or until control is evident.
Remove sticky cards prior to release. If you must continue to monitor with sticky cards, hang for only 2 days per week. Release contents into your grow space and leave bottle in space turned upside down for continued emergence from mummies.Aphidius is shipped either as parasitized aphid mummies (pupae) from which adults will emerge, or as newly emerged adults. The advantage of shipping adults is that they usually arrive pre-mated and the supplier can ensure they are sent without hyperparasites.
If necessary, parasitized aphid mummies may be held at 39-50 ºF (4-10 ºC) for up to 3 days.
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 two releases one 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, that the population should soon collapse (Ramakers, 1989).
Note: The yellow sticky traps used for monitoring pest also trap Aphidius. If yellow traps are necessary for monitoring whitefly, do not release near the yellow traps and use no more than 1 yellow trap per 100 plants. Aphidius are not attracted to blue sticky traps, which can be used for monitoring thrips where Aphidius is being released for aphid control.
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 aphidimyza.
In gardens, wash high populations of aphids from plants with a strong water spray before introducing the aphid parasite. Note: Aphidius does not attack many common aphid species, such as potato aphid so if mummies are not present check aphid identification.
Aphidius matricariae is likely to be sensitive to the same pesticides as Encarsia formosa.
Growth regulators used in crop production should not be harmful to Aphidius.
Spreader-stickers are likely to be harmful to Aphidius on contact, but do not have residual effect.
Insecticidal soap and pirimicarb (e.g., Pirliss®) can be used to reduce aphid numbers in hot spots without harming the pupal stage of Aphidius.