Thrips are tiny insects belonging to the order Thysanoptera, a name that literally means “fringed wings.” They are often overlooked until their impact becomes visible on plants, quickly becoming a concern for gardeners and growers. While the majority of the over 6,000 known species are harmless, those that feed on cultivated plants cause significant economic and aesthetic damage worldwide. Understanding how these insects interact with plant life is important for managing their populations and protecting crops.
Identifying Thrips and Their Feeding Method
Adult thrips are slender insects, measuring less than 2 millimeters in length, and are typically yellowish, brown, or black. A defining characteristic is the two pairs of narrow wings fringed with long, fine hairs, often folded over their back when at rest. The immature stages, called larvae or nymphs, are smaller, wingless, and frequently pale or transparent.
Plant-feeding thrips use a distinctive “rasping and sucking” method. They possess asymmetrical mouthparts, including a single mandible used to puncture the outermost layer of plant tissue, or epidermis. Once breached, a tube-like stylet is inserted to suck out the cell’s internal contents. This process empties the plant cells of chlorophyll and other materials, causing the physical damage observed on leaves and flowers.
The Visible Damage Thrips Cause
The mechanical removal of cell contents causes highly recognizable symptoms on the plant. Leaves where thrips have fed often develop a characteristic silvering or bronzing appearance. This discoloration occurs because the emptied cells fill with air, creating a silvery sheen noticeable against darker green foliage.
Another common sign is stippling, which presents as numerous tiny, light-colored dots across the leaf surface. The presence of small, dark, varnish-like specks of excrement, known as frass, is also an indicator of thrips activity near feeding sites. When thrips feed on developing tissue in flower buds or new shoots, the emerging growth can be severely distorted or stunted. On fruits, feeding leads to cosmetic blemishes such as scabby, silvery, or brownish scarring, reducing the crop’s market value.
Thrips as Vectors for Plant Disease
Beyond the direct mechanical damage, certain thrips species have a devastating role as vectors for plant viruses. They are the exclusive transmitters of viruses belonging to the genus Tospovirus, such as the economically significant Tomato Spotted Wilt Virus (TSWV). This transmission is persistent, meaning the virus multiplies inside the insect and remains infectious throughout the thrips’ life.
The ability to transmit these viruses is acquired only during the early larval stage, specifically the first instar, when the thrips feed on an infected plant. Although adult thrips are the primary inoculators, they can only transmit the virus if they acquired it as a larva. This unique relationship means the subsequent damage is not from the feeding itself, but from the systemic viral infection, which causes severe yield loss and plant death.
Less Common Roles: Predatory Thrips
While many thrips species are considered pests, the order Thysanoptera also includes species that play a beneficial role in natural ecosystems and pest management. Certain families, such as Aeolothripidae and Phlaeothripidae, contain predatory thrips that actively hunt other small arthropods. They use their piercing-sucking mouthparts for consuming the internal fluids of soft-bodied prey, not for feeding on plants.
Predatory thrips species, including those in the genus Franklinothrips, target common agricultural pests. Their diet often consists of the eggs and young stages of mites, whiteflies, and other pest thrips. This natural predation contributes to the biological control of pest populations, particularly where broad-spectrum pesticides are not heavily used.