Most growers have experienced aphid outbreaks in their crops. Often, they are found on the young, new growth of many types of plants. However, there are also aphids that grow and feed from the root system of several plant species and are classified as root aphids. These aphids are not the same as those that feed from the upper parts of the plants.
There are several species of root aphids, most of which are Pemphigus species. Each individual species feeds on a limited number of plant species, but some have a wider plant host range. Root aphids vary in color, but most are white, whitish yellow or brown in color. Adults look somewhat like aphids you find on new stems and leaves, except most are pear-shaped and have shorter antennae and legs. Most root aphids have cornicles, or “tail pipes”, protruding from the end of the abdomen, like their aboveground counterparts.
Like all aphids, they have piercing, sucking mouthparts that extract sugar-rich sap from underground structures such as roots, bulbs and rhizomes. Root aphids produce a white, waxy secretion later in their lifecycle that covers them, and some is left behind as they move through the growing medium. This is often mistaken for mealybugs that are also covered with a white waxy or threadlike substance. It is best to use a hand lens and observe the roots to see the actual insect.