How to Manage Pests
Identification: Key to Aphids Commonly Found in San Joaquin Valley Alfalfa and Cotton
Note: This key includes only the aphid species that are most commonly found in alfalfa and cotton in California's San Joaquin Valley. If you are unable to identify an aphid using this key, see your local Cooperative Extension farm advisor for assistance.
Aphids may be difficult to identify as they attack California alfalfa and cotton.
The alfalfa aphids, pea aphid (Acyrthosiphon pisum (Harris)) and blue alfalfa aphid (A. kondoi Shinji), are similar in appearance. Recently, the cowpea aphid, Aphis craccivora Koch, has become a pest of alfalfa and has been found colonizing cotton in Californias San Joaquin Valley. The cowpea aphid on cotton is easily confused with cotton aphid, A. gossypii Glover, at certain times of the year.
Since economic thresholds have been developed for individual species, proper aphid management requires accurate identification.
Use this key to identify an aphid. While aphids appear to be very simple insects, they are really very complex, both in their biology and their morphology. As with other insects, external morphological features are used to identify individuals to the species level.