Thrips are minute, slender insects that possess narrow, fringed wings. Belonging to the insect order Thysanoptera, only a small fraction of the thousands of existing species cause significant damage to cultivated plants worldwide. They are a major concern for both home gardeners and commercial agriculture due to their ability to rapidly colonize a wide range of host plants. Infestations lead to severe aesthetic defects on ornamental plants and substantial reductions in the yield and marketability of food crops.
The Thrips’ Menu: General Feeding Habits
Many damaging thrips species exhibit polyphagy, meaning they feed on diverse, unrelated plant families. This broad diet enables generalist species, such as the Western Flower Thrips (Frankliniella occidentalis), to thrive in various environments, from indoor spaces to large agricultural fields. Their feeding mechanism involves unique, asymmetrical mouthparts that function like a rasping-sucking tool. The thrips use a single elongated mandible to puncture the plant’s outer cell wall, then suck up the contents of the damaged cells. This feeding concentrates on the softest parts of the plant, including developing buds, new leaf growth, and flower petals, making early detection difficult.
Highly Susceptible Indoor and Ornamental Plants
The protected, warm environment of a home or greenhouse often creates ideal conditions for thrips to reproduce rapidly, leading to sustained infestations. Roses are a frequent target; feeding causes buds to become distorted or fail to open, and petals develop characteristic brown or streaked patches.
Many herbaceous bedding plants are also vulnerable:
- Impatiens
- Gladiolus
- Chrysanthemums
- African violets (where feeding leads to premature flower drop and pollen deposits)
Ficus species, including the weeping fig (Ficus benjamina), can host gall-forming thrips, causing new terminals to become tightly bunched and twisted. Foliage plants like Monstera and Philodendron are also at risk, with damage often appearing on unfurling new leaves.
Vulnerable Edible Crops
Thrips attack reproductive tissues and transmit devastating plant viruses, causing significant crop loss in food production. The Onion Thrips (Thrips tabaci) is a major agricultural pest that severely affects allium crops, including onions and garlic. Feeding causes leaves to develop silvery streaks and stunts growth, resulting in undersized, poor-quality bulbs.
In greenhouse and field settings, the Western Flower Thrips is a major threat to fruiting vegetables:
- Tomatoes
- Peppers
- Cucumbers
- Strawberries
Thrips often feed on flowers, causing them to abort or develop into malformed fruit. This species vectors tospoviruses, such as Tomato Spotted Wilt Virus (TSWV), which can be fatal to young plants. Citrus fruit is also susceptible, with feeding on the developing rind leading to silvery or brown scarring that reduces the produce’s market grade.
Recognizing Thrips Damage Across Different Hosts
Visual identification of thrips damage is the first step in diagnosing an infestation. The characteristic symptom on leaves is a silvery or bronzed appearance, which results from the thrips emptying the chlorophyll-containing cells. This damage frequently manifests as tiny pale spots known as stippling, which can merge into larger bleached patches over time.
Small, dark, varnish-like specks of excrement, or frass, are often found within the damaged areas on the leaf surface. When thrips feed on flowers, the petals may exhibit a “color break,” where the tissue dies before the bud opens, leaving streaks or spots. On fruit and new growth, feeding causes scarring, distortion, and crinkling as the damaged cells fail to expand properly.