The key will work for slide-mounted winged and wingless adult live-bearing females only; males, egg-laying females, and immature individuals cannot be identified with this key.
The number of aphid species addressed in this tool is only a small percentage of the world aphid fauna which consists of several thousand species. Therefore, there is a chance that your aphid specimen may key to a species that is not the correct match. For example, Anoecia setariae apterae (not included in the key) could be mistakenly identified as Cinara confinis depending on the characters selected. All identifications should be compared to the species pages and an authoritatively identified reference specimen for further assessment.
Aphids come in a great variety of morphs. Some species are known to have over a dozen morphs, and the vast majority have at least five: fundatrix, aptera vivipara, alata vivipara, ovipara, and male. Certain morphs of many species are not well studied. Additionally, aphid nymphs are also not well characterized and are often exceptionally hard to identify. The identification key is only useable for adult aptera vivipara and adult alata vivipara specimens. In some cases, a fundatrix (a special form of vivipara) will also key correctly. However, any other morphs or developmental stages are unidentifiable with this key. It is critical that you first confirm that your specimen is an adult vivipara before using this key.
Aphid species identification uses many continuous characters and ratios and as such this key will require you to make many measurements. Also, aphid individuals of any given species come in a wide range of sizes and proportionality. The identification key includes many continuous characters, all of which include two ranges: one estimates the maximum and minimum possible lengths, counts, or ratios for a species; the other estimates the most likely lengths, counts, or ratios. The accuracy of these character range estimates is limited by the number of specimens that were measured in preparing the key. Ideally, specimens of all possible sizes and proportions would be measured. As this ideal is unrealistic,lease be aware that the specimen you are examining may be unusual in size or proportion and thus cannot be identified correctly.