There are many species of aphids, varying in size, color, and habitat. As individuals, they do little harm to a host plant, but large infestations can produce severe damage. Their behavior is determined largely by food preference and feeding site. Most are seen on the leaves, stems, and foliage of plants, especially on the new growth, but there are species that feed underground on roots and bulbs. Some produce galls or other deformities. Fortunately, there are many effective management methods available.
A soft-bodied, pear-shaped insect, the aphid is generally very small, with most species under 1/8 inch in length. Aphids can be almost any color, but green, black, white, and gray are the most common. Some are covered with a threadlike white material, which makes them appear woolly, while others may be covered in a fine dust. There are both winged and wingless individuals of most species.
Aphids can be identified by a beak or rostrum that sits far back on the underside of the head. Their antennae are rather long and placed in the front of the head, between the eyes. The feet are two-jointed and terminate in claws. Many aphids have a pair of projections called cornicles on each side of their posterior through which they emit a sticky substance commonly referred to as ‘honeydew’.
Aphids live in large colonies and reproduce rapidly, having numerous generations each season. Life cycles vary with species but, generally, only female aphids are present during the summer and can give birth to living young without mating. This wingless form of aphid is known as the stem mother. After one or two generations, winged forms are born and fly off to other plants. Males are produced in the fall, at which time mating does occur and females lay eggs that overwinter in bark or ground litter. Larvae will emerge at the end of May or early June in the Chicago region. On average, an aphid lives for about one month and each female produces 80-100 offspring.