Tiny Insects on Indoor Plants

Aphids

• Aphids, often called plant lice, are tiny, soft-bodied insects that feed on houseplants. They pierce plant parts, including leaves, stems and flowers, with a needle-like stylet and suck plant sap. Inordinate loss of sap will compromise the health of houseplants. As aphids walk along plants while feeding, they excrete a sticky, sugary liquid called “honeydew.” Sooty mold fungi can grow on this honeydew and leave dark splotches over the leaves. At first sight of aphids, gardeners should remove them by dabbing them with alcohol-soaked cotton swabs.

Spider Mites

• Spider mites are among the most serious houseplant pests, according to the University of Minnesota, and can cause plant injury, escalating rapidly to plant death if left untreated. Only 1/50th of 1 inch long, first detection is usually made by observing signs of plant injury. Stippling on plant leaves, leading to yellowish discoloration, is often an early indicator of the presence of spider mites. Closer inspection of plants reveals fine webbing. Spider mites do not spin webs to catch prey, since they feed on plant parts, but they produce webbing as protection against predators. Insecticidal soaps and horticultural oils formulated for houseplants will control mites.

Mealybugs

• Mealybugs appear as white, cottony spots on houseplants. If disturbed, they jump to other plant parts. They suck sap, which stunts plant growth and can lead to plant death. Like aphids, mealybugs excrete honeydew. These excretions create a favorable environment for plant molds to grow, causing a secondary plant problem that can also lead to plant death. Treating light infestations with jets of water or alcohol-dipped cotton swabs is usually effective. Heavy infestations may require treatment with insecticidal soap.

Fungus Gnats and Whiteflies

• Flying houseplant insects include whiteflies and fungus gnats. A waxy white covering gives whiteflies their cottony appearance. Fungus gnats are dark brown and, unlike whiteflies, they do not feed on plants. Their larvae are small translucent worms that live in potting soil and feed on plant roots. Yellow sticky traps are attractive to whiteflies and gnats and are helpful in reducing populations of flying pests. Trap cropping is an effective control for fungus gnats, which are attracted to wheatgrass sprouts as a place to lay their eggs. Setting out disposable pans of wheatgrass for two to three days and then removing them to an outside trash receptacle disposes of eggs and breaks the life cycle of fungus gnats.