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 matricariae is an outstanding searcher, and can locate new aphid colonies even when aphid populations are low.
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.
A. matricariae are shipped as mummies in a sawdust carrier. 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).
- Optimum conditions are daytime temperatures of 64-71.5 ºF (18-22 ºC) and relative humidity 60-80%. Aphidius is not affected by short-day induced diapause, so it can be used year round.
Preventative applications: 0.025 per square foot weekly.
Light curative applications: 0.1 per square foot weekly, minimum of 3 applications.
High curative applications: 0.2 per square foot weekly, minimum of 6 applications. Use release boxes to concentrate the wasps near hotspots.
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 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).
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 matricariae do 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.