The foxglove aphid Aulacorthum solani, also called the glasshouse or potato aphid, is a type of aphid that is most likely native to Europe, but is widespread throughout North America. It feeds on foxglove (Digitalis purpurea) and potato plants, among other species. Like other aphids, foxglove aphids reproduce quickly and are difficult to control once established.
Foxglove aphids are between 0.06 and 0.12 inch long. Their soft, pear-shaped bodies vary in colour from yellow to pale green. They have long, dark-coloured antennae, and long legs with dark-coloured joints. A pair of elongated narrow tubes called siphunculi or cornicles protrude from their back ends. Some foxglove aphids have wings, while others are wingless. Winged foxglove aphids often have dark patterning on their abdomens, while wingless aphids have a rust-coloured or greenish spot at the base of each cornicle.
Foxglove aphids lay tiny black eggs on susceptible plant hosts in the fall; some eggs overwinter on the host and hatch in the spring as nymphs, while other foxglove aphids overwinter in a nymphal stage. Aphid nymphs complete five stages of maturation, or instars, before they reach adulthood. They mature in approximately 2 weeks and begin to lay eggs. Foxglove aphids are all female; they reproduce parthogenically, or without male involvement. Adult winged aphids migrate to other plant hosts and form new colonies, while wingless aphids remain in one location throughout their life cycle.
Adult and nymphal foxglove aphids have piercing and sucking mouth parts. They pierce the foliage and drain sap from susceptible host plants. Their saliva contains toxins that cause leaves to shrivel and curl. Foxglove aphids also transmit approximately 40 different viruses to plants, including the cucumber mosaic virus, beet yellows virus and potato leaf roll virus. Although they rarely cause significant damage by feeding, foxglove aphids cause the most damage in greenhouse plants, particularly bulb species.
Aphids are generally difficult to control with pesticides, according to Leanne Pundt from the University of Connecticut Integrated Pest Management website, because some aphids are resistant to certain insecticides, and it is often difficult to completely cover plants. A number of insects, such as lacewings, midges, lady beetles and flower flies, feed on foxglove aphids. Some species of parasitic wasps lay their eggs in aphids, and the larval wasps devour the aphid from the inside. Greenhouse growers can also use a commercially available fungus called Beauvaria bassiana that sickens and kills aphids.