Gardening glossary
Aphid
Aphids (family Aphididae) are among the most common garden and houseplant pests worldwide, with more than 4,000 known species. Adults are soft-bodied, roughly 1 to 3 mm long, and come in green, black, brown, pink, yellow, or grey forms depending on species and host plant. Most have a pair of small tube-like cornicles projecting from the rear of the abdomen, which is a reliable identification feature when viewed with a hand lens.
They feed by inserting needle-like mouthparts into phloem tissue and drawing out sugar-rich sap. Heavy feeding distorts new shoots, curls leaves downward or inward, stunts buds, and can transmit plant viruses such as cucumber mosaic virus. As they feed they excrete honeydew, a sticky transparent residue that drips onto lower leaves and surfaces, attracts ants, and supports sooty mold growth.
Aphids reproduce by parthenogenesis through most of the growing season, meaning females give birth to live clones without mating. A single founder can produce dozens of offspring in a week, which is why populations seem to explode overnight. Look for them on tender new growth, flower stems, and the undersides of young leaves first.
Cast white skins on leaves are another diagnostic sign and are often mistaken for the insects themselves. Natural predators include ladybird beetles, lacewing larvae, hoverfly larvae, and parasitic wasps. For light infestations a strong spray of water knocks them off; persistent populations respond to insecticidal soap or neem oil applied to leaf undersides every 5 to 7 days.