Gardening glossary
Thrips
Thrips (order Thysanoptera) are some of the hardest pests to spot because of their size and habit of hiding in flower buds, leaf folds, and growing tips. Adults are 1 to 2 mm long, narrow, and range from pale yellow to brown or black. They have characteristic fringed wings that are hard to see without magnification. Larvae are wingless, slightly smaller, and usually pale yellow or cream.
Unlike aphids and scale, thrips do not pierce phloem. They rake open epidermal cells with asymmetrical mouthparts and feed on the cell contents that leak out. This produces a distinctive silvery or bronze stippling on the upper leaf surface, often accompanied by tiny black dots of frass (excrement). Heavy feeding distorts new leaves, scars flower petals, and can transmit tospoviruses including tomato spotted wilt virus and impatiens necrotic spot virus.
Common species on houseplants and ornamentals include western flower thrips (Frankliniella occidentalis), onion thrips (Thrips tabaci), and chilli thrips (Scirtothrips dorsalis). Outdoor vegetable gardens see them on onions, peppers, tomatoes, beans, and roses. Indoors they are frequent on monstera, anthurium, alocasia, and any flowering plant.
To confirm thrips, tap a leaf or bloom over a sheet of white paper and watch for slender insects scurrying across the surface. Blue sticky cards trap adults and help monitor populations. Treatment is more involved than for aphids because eggs are laid inside plant tissue and pupation happens in the soil. Rotate between insecticidal soap, neem oil, and spinosad sprays every 5 to 7 days for three to four cycles to break the life cycle. Predatory mites such as Amblyseius cucumeris are effective in greenhouses.