Aphids 101 for All Gardeners

Aphids are also called greenflies, or plant lice. There are over 4,000 species of this insect worldwide but only five per cent are considered a major threat in agriculture and gardens. Aphids multiply at light speed and blend into their host plant so they are easy to overlook until they have reached mob status.

Aphids do not discriminate much and can be found almost anywhere plants are growing. They range in size from 0.03 to 0.3 inches(1-10 millimeters) in length and can be many colors. Some aphids change color mimicking the host plant as they age. While aphids have a survival advantage from sheer numbers, they are also tasty morsels for predators. Small, plump, pear shaped, succulent aphids, being near the bottom of the food chain, are a favored food for ladybug larvae, lacewings, parasitic wasps and other insects. Aphids damage plants through their feeding by sucking phloem sap through their beaks-particularly from the most tender young stems, leaves and flower buds. Aphids secrete a saliva toxin back into the plant that causes twisting and curling of leaves, eventually stunting the host. Aphids also leave a honeydew waste substance. This dripping honeydew waste is particularly distasteful when it lands on patio furniture or cars. On leaves it blocks sunlight from reaching the leaves, slowing photosynthesis. Light infestations can have little or no impact on host plants so early detection and control is important.

Soft-bodied, with or without wings, most species of aphid have a pair of tube-like structures called cornicles that project backwards (like tailpipes) from their behinds. These cornicles distinguish aphids from all other insects. Only gall-forming and woolly aphids do not have them. The cornicles are thought to secrete defensive substances to warn off predators. Most aphid species reproduce by overwintering as fertilized eggs, often glued onto host plants. Young nymphs hatch from these eggs in spring and evolve into wingless females. There are no males present at this time. Wingless young are born alive, are all female and soon begin to reproduce in a like manner. As the season progresses with shorter days and cooler temperatures, both male and females are born. After mating, the females begin laying fertilized eggs and the cycle begins again.

Non-chemical control includes washing them away, using the two fingered squishing method, laying

out sticky traps, pruning the host plant, and giving up. Sometimes a plant cannot be saved. Other methods of control include use of biological predators such as parasitic wasps and other beneficial insects that feed on aphids. The safest chemical control includes use of insecticidal soap, horticultural or neem oil. Monitor your plants to determine if aphids are present. Doing this allows one to begin control while the numbers are still small. Examining indoor and outdoor plants while caring for them is one way to head off major infestations. Isolate plants when taking them into the house for the winter to prevent spreading aphids and other insects that may be hiding in the plant but willing to jump to other hosts. Never use a feather duster to clean indoor plants as this may carry eggs or larvae to other plants.