![Lady beetle on a squash leaf, with a small cluster of pale green aphids nearby.](https://blogs.cornell.edu/biocontrolbytes/files/2019/06/1-IMG_3180-972x1024.jpg)
Practicing good integrated pest management in the greenhouse requires correct identification of the pest. Accurate pest ID is also critical to successful use of biocontrol. Aphids are a good example. Biocontrol of aphids works best when you match the biocontrol agent to the aphid species you have. When I first learned this, I was a bit intimidated, because aphids are pretty small, and I’m not an entomologist. But the four aphid species you are most likely to encounter in your greenhouse are actually pretty easy to differentiate.
Anatomy of an aphid
In order to successfully ID aphids, you need to know (just a little) about aphid anatomy. All aphids are pretty small (between approximately 1/16 and 1/8 inches long). In addition to six legs and a body, aphids have antennae. Antennae attach near their eyes and are angled back over their bodies. They also have two little “spikes” that protrude from their rear end. These are called cornicles. Not so bad, right?
![Diagram identifying the antennae on the aphid’s head and the cornicles attached at the rear of the abdomen.](https://blogs.cornell.edu/biocontrolbytes/files/2019/06/2-aphid-anatomy.jpeg)
Green peach aphid
![Enlarged photo of a light green, green peach aphid with identifying characteristics (indentation between antennae and cornicles that match the color of the body but with dark tips) labeled.](https://blogs.cornell.edu/biocontrolbytes/files/2019/06/3-green-peach-Sanderson-1024x773.jpeg)
Green peach aphids come in different colors (from green to, well, peachy pink) and they are one of the smaller species. Their cornicles are the same color as their body (whatever that color is), and have dark tips on the ends. Green peach aphids also have an indentation in their head between the bases of their antennae.
Melon (or cotton) aphid
![Enlarged photo of a dark green melon aphid with the distinguishing dark cornicles labeled.](https://blogs.cornell.edu/biocontrolbytes/files/2019/06/4-melon-Sanderson.jpeg)
Melon aphids (also called cotton aphids) also come in a range of colors that include light yellow, green, dark green, or almost black. Regardless of the body color, the cornicles will always be dark. Also, there’s no indentation in their head between the bases of the antennae. This is another small aphid species.
Foxglove aphid
![Enlarged photo of a shiny green foxglove aphid with the distinguishing dark-spotted long antennae, dark leg joints, and darker green spots at the base of the cornicles labeled.](https://blogs.cornell.edu/biocontrolbytes/files/2019/06/5-foxglove-Gilrein.jpg)
Foxglove aphids are large (for an aphid). Their bodies are light green, but often shiny. There is an indentation in their head between their antennae. Their antennae are extra-long, extending well beyond the end of their body, and appear to have dark spots on them because the joints of the antennae are dark. The joints of their legs are also dark. Check where the cornicles attach to the body of the aphid. Foxglove aphids have darker green spots on their bodies at the base of the cornicles. These aphids usually like to hang out on the lower leaves of a plant, though they will infest flower petals sometimes.
Potato aphid
![Enlarged photo of a potato aphid showing the segmented appearance and dark stripe running the length of the body.](https://blogs.cornell.edu/biocontrolbytes/files/2019/06/6-potato-Sanderson-1024x735.jpeg)
Another large aphid, potato aphids come in pink and green. They look like they have a dark stripe running down the middle of their backs, and their body appears faintly segmented. They also have an indentation in their head between the antennae. Of the four species we’re discussing here, only the melon aphids lack this indentation.
To see these features, you will need a little magnification, but you don’t need a fancy microscope. Find a hand lens or a magnifier with 10X magnification. I like to keep one in my backpack so I’m always prepared.
![Picture of a 10X hand lens. The lens folds out from a protective metal cover.](https://blogs.cornell.edu/biocontrolbytes/files/2019/06/7-IMG_4277-1024x798.jpg)
There are even some relatively inexpensive 10X lenses you can snap on to your smartphone or tablet. Not only does this turn your device into a little microscope, but you can take a picture to document what you see (and show to an expert, later).
![Picture of a macro lens that clips on to a smart phone or tablet.](https://blogs.cornell.edu/biocontrolbytes/files/2019/06/8-IMG_4278-1024x991.jpg)
You can also find (at least some of) these four aphid species outside. Last summer I spotted the aphid below on an acorn squash plant in August. Now that you know what to look for, what species do you think it might be?
![Enlarged photo of a light green aphid with black cornicles. Do you know what species it is?](https://blogs.cornell.edu/biocontrolbytes/files/2019/06/9-IMG_3067.jpg)
One minor complication: Each of these four aphid species can either have wings, or be without wings. Usually aphids you find in a greenhouse have no wings, so you can stick with the above descriptions. But winged aphids can appear in the greenhouse, particularly when populations get very high. If you find aphids with wings in your greenhouse, the above descriptions won’t apply; ask for some help from your local extension office.
![Enlarged photo of a winged (right) and non-winged (left) green peach aphid. The winged aphid is mostly black and looks very different from the pale green aphid without wings.](https://blogs.cornell.edu/biocontrolbytes/files/2019/06/10-1326230-LGPT-1024x850.jpg)
Choosing the right natural enemy
![Enlarged photo of a tiny parasitoid wasp surrounded by green aphids that appear to be covered in white wax. The wasp is inserting an egg into one of the aphids.](https://blogs.cornell.edu/biocontrolbytes/files/2019/06/11-5490036-LGPT-1024x724.jpg)
A good biocontrol option for aphids is a parasitoid wasp from the genus Aphidius. These tiny wasps are called parasitoids because they lay their eggs inside of aphids. As the young wasp grows, it kills the aphid and turns it into a mummy.
![Enlarged photo of the tan shell of an aphid (mummy) with a hole in it, still sitting on a leaf](https://blogs.cornell.edu/biocontrolbytes/files/2019/06/12-Aphid-Mum.jpeg)
But if you want to purchase Aphidius wasps to release in your greenhouse (or the banker plants and prey that support them; read more here), you’ll need to know which Aphidius species to use. Aphidius colemani works well against green peach and melon aphids, while Aphidius ervi works well against foxglove and potato aphids. Another natural enemy you can use is Aphidoletes aphidimyza. This is a tiny fly whose larvae are voracious aphid predators. Although it seems to be less effective against foxglove aphid, it may work well in combination with another natural enemy.
![An enlarged picture of what looks like a segmented worm (the larva of Aphidoletes aphidomyza), surrounded by pale green aphids](https://blogs.cornell.edu/biocontrolbytes/files/2019/06/13-aphidoletes-Sanderson.jpg)
Like all biocontrols, Aphidius wasps and Aphidoletes larvae need to be released while your aphid population is very small, before it gets out of hand. Aphid infestations can explode very quickly! Scout your crop regularly, and keep records so you know which aphid species you are likely to have. (Consider the Pocket IPM Greenhouse Scout app to help you with your scouting and pest management.) Then plan your biocontrol releases accordingly. Parasitoids and predators for aphids should be released preventatively on crops that are prone to aphids.
If you’ve inspected your aphids at 10X magnification, and still aren’t sure which species you have, contact your local extension office for help with ID. If you are planning to send a picture, make sure that it is clear and shows the features of the aphid that you now know are important (antennae, body, cornicles).
You can learn more about aphid biocontrol in this factsheet from John Sanderson (Department of Entomology, Cornell University) on managing aphids in a greenhouse. Identification of these four common aphid species and which biocontrols you can use against them are also summarized here. The natural enemies listed in the chart are meant to be a starting place. Maximizing the efficacy of your aphid biocontrol program takes some trial and error and willingness to fine-tune your program to the crop and environmental conditions you’re dealing with. Suppliers of aphid natural enemies also have great information about how to use these biocontrol agents most effectively.
Happy aphid hunting!
This post was written by Amara Dunn and Betsy Lamb (NYS IPM) and John Sanderson (Entomology, Cornell University).