Aphids feed on plant sap.
Aphids are small herbivorous insects in the superfamily Aphidoidea, within the order Hemiptera, which also includes cicadas, mosquitoes, and many other “true bugs.” There are ten families of aphids and about 4,000 species. They live all over the world, but are more common in temperate zones. About 250 of the species are considered pests in forests and gardens.
Ladybugs eat aphids.
Although aphids are only 1 to 10 millimeters (about 0.039 to 0.39 inches) long, they can pose a significant problem to plant life. Insects feed on plant sap by piercing the phloem, the vessels through which the sap flows, with a long proboscis. As they feed, they can introduce viruses to plants, sometimes in devastating ways. Even if they don’t introduce disease, insects can destroy the appearance of plants simply through their feeding and reproductive activity. Some feed on a single species of plant, while other types feed on hundreds of different plants.
Insects feed on plant sap by piercing the phloem, the vessels through which the sap flows.
Some of these insects have symbiotic relationships with other species. Some are “raised” by ants, which protect the aphids and feed on the carbohydrate-rich honeydew they secrete. Others harbor Buchnera bacteria, which live in specialized cells within the insects and synthesize amino acids not present in the aphid diet.
Many species have very unusual reproductive methods. The insects usually mate in the fall, and the fertilized female lays eggs. The eggs hatch in spring, but only produce females, each of which may or may not have wings.
Spring-born females produce parthenogenically, without being fertilized. Therefore, daughters are genetically identical to mothers and multiple generations can exist within an individual. Hatchlings at this point can be live or insects can lay eggs. In the fall, some become males and the cycle begins again.
Through parthenogenesis, aphids can reproduce extremely quickly and in large numbers. Those that live in greenhouses or areas with mild winters can continue to reproduce asexually for years. It is easy to see how they can become a threat to their host plants.
Aphids are often controlled by their natural predators, which may be brought into a garden for this purpose. Aphid predators include ladybugs, lacewings, floater larvae, parasitic wasps, and some parasitic fungi. These insects can also be controlled by spraying plants with running or soapy water, pruning affected areas, and using aluminum foil mulch. Pesticides are also an option, although less recommended.