What is an aphid wasp doing on your plant? If it is Aphidius colemani, it is looking for somewhere to put its next generation. The somewhere is a living aphid.
Colemani is a tiny, narrow-waisted parasitoid used especially against green peach and melon aphids. Its young develop inside a host and eventually kill it. That makes identifying the aphid part of choosing the wasp—not a taxonomic chore we added for entertainment.
Start with the aphid's name
Colemani is an important parasitoid of green peach aphid, Myzus persicae, and melon or cotton aphid, Aphis gossypii. Those are two common greenhouse pests, but they are not interchangeable with every aphid on every plant. Potato and foxglove aphids require a different selection. [1]
Color is particularly unhelpful here. Green peach aphids need not be green, and green aphids need not be green peach aphids. If you are unsure, use the aphid identification guide or obtain a close photograph with a size reference. A mixed parasitoid product broadens coverage only to the hosts supported by the species it contains.
Get a photograph that can answer the question
If you do not yet have a reliable identification, photograph an entire infested shoot first, then a sharp close-up from above and from the side. Use bright, diffuse light and a hand lens or phone macro setting; keep the antenna bases and the two rear tubes, called cornicles, in focus. Put a small ruler beside the leaf, in the same plane as the aphid. Include the plant’s name and photograph colonies on different plants separately. If those features remain indistinct, ask an extension office or an insect supplier to identify a specimen before choosing a host-specific wasp. A blurry green dot is allowed to remain unidentified.
An aphid becomes the nursery
The female uses her egg-laying organ to place an egg in a suitable aphid. The young wasp develops inside. Eventually the aphid becomes a swollen, papery mummy, and a new adult exits through a round opening. You may notice those mummies before you ever get a good look at the wasp. [1, 2]
Leave intact mummies in place when you can. They are potential contributors to the next generation. That does not mean every mummy produces a healthy adult, or that every surviving adult stays on your plant. It means an apparently motionless part of the colony can still be useful.
The greenhouse can keep a spare supply of hosts
One reason colemani is so useful in greenhouse programs is that it can reproduce on bird cherry-oat aphids, Rhopalosiphum padi, maintained on cereal plants. Growers call this a banker-plant system: a separate, managed aphid population supports the wasps between pest outbreaks. The astonishing part is that an aphid-control program can deliberately keep aphids. 4
That is not permission to preserve unidentified aphids on your houseplants. Banker plants use a known plant–aphid–wasp combination and need monitoring. The lesson for a small collection is simpler: colemani needs suitable hosts to produce another generation. Once those hosts disappear, ongoing reproduction stops; adults may linger or disperse rather than providing permanent protection.
When colemani is the useful starting point
Confirmed melon or cotton aphid is a strong reason to choose colemani. Green peach aphid is shared territory with matricariae; the matricariae guide explains when cooler conditions support that alternative. Potato or foxglove aphids point toward ervi. A larger quantity of the wrong wasp does not broaden its host range.
For a few suitable colonies, begin the wasp program early. For leaves already crowded with aphids, reduce removable hotspots and discuss adding an aphid predator while the parasitoid develops. The release guide supplies the actual FGMN quantities and follow-up checks.
Colemani does not sting people. Adults can fly beyond a pot, but they do not build a social-wasp nest in the room. The indoor-use explanation covers what happens after the aphids are gone.
Give a small colony less time to become a large one
Do not wait for mummies before planning the next release. The first attacks are hidden inside aphids, while unparasitized neighbors can keep reproducing. Use the release guide’s weekly checks to compare the live population and protect developing wasps on the plant.
Colemani does not need every aphid to be suitable. It needs the ones on your plant to be suitable.
Sources and further reading
- Prado, Jandricic and Frank (2015). Ecological Interactions Affecting the Efficacy of Aphidius colemani in Greenhouse Crops. Insects 6, 538–575. Host suitability and factors affecting control.
- Cloyd (2024). Aphidius colemani and Aphidius ervi—Biological Control Agents of Aphids. Kansas State University MF3653. Extension guidance on life stages, release and emergence.
- Zamani et al. (2007). Effect of Temperature on Life History of Aphidius colemani and Aphidius matricariae, Two Parasitoids of Aphis gossypii and Myzus persicae. Environmental Entomology 36, 263–271. Constant-temperature laboratory study; development speed and mummification are different measures.
- Banker Plants for Aphid Biological Control in Greenhouses (2018). Journal of Integrated Pest Management. Review of the colemani–bird cherry-oat aphid system.
- Evergreen Growers Supply. Aphidius species technical sheet. Non-stinging adults and shipment formats.
