Thrips

Thrips are slender, spindle-shaped insects that are easily overlooked without close inspection or a hand lens. Adults of many pest species are pale yellow to dark brown or black, and winged individuals have two pairs of narrow wings fringed with long hairs, a feature reflected in the order name Thysanoptera ("fringed wing").

• Silvery or bronzed stippling on leaf and fruit surfaces where cell contents have been removed
• Tiny black flecks of excrement (frass) on leaves
• Distorted, streaked, or discoloured flowers and growing points
• Insects visible when flowers or leaf whorls are shaken over a white surface

Thrips develop through an egg stage, two active larval instars, and non-feeding prepupal and pupal stages before becoming adults. Eggs are typically inserted into plant tissue with a saw-like ovipositor, while the prepupal and pupal stages often occur in soil, leaf litter, or sheltered plant structures such as flowers.

Egg

Inserted into plant tissue; not visible without dissection.

Larva (two instars)

Active, feeding stage resembling a small, wingless adult.

Prepupa and pupa

Non-feeding, largely immobile stages, often found in soil or sheltered plant sites.

Adult

Winged or wingless depending on species; capable of dispersal and, in some species, virus transmission.

Many pest thrips can build populations quickly under favourable temperatures, and colonies often develop unnoticed within concealed sites such as flowers and leaf whorls before damage becomes obvious.

Thrips feeding punctures individual plant cells and removes their contents, leaving behind characteristic silvery or bronzed scarring as air replaces the emptied cells. Heavy feeding can distort leaves, flowers, and fruit, and feeding on growing points can stunt or deform new growth.

A smaller number of thrips species, including the western flower thrips, are recognized as efficient vectors of tospoviruses such as tomato spotted wilt virus. Transmission generally requires larvae to acquire the virus while feeding on an infected plant; the virus is then carried through to the adult stage, which can spread it further. Host crops affected by thrips and thrips-vectored viruses include a wide range of vegetables and ornamentals, with tomato and potato among the notable examples.

Because thrips are small and often hide within flowers, leaf whorls, and other sheltered plant parts, monitoring typically combines several methods rather than relying on visual inspection alone.

• Blue or yellow sticky traps placed within or above the canopy to catch dispersing adults
• Tapping or shaking flowers and foliage over a white surface or beat sheet to dislodge and count insects
• Direct inspection of flowers and new growth, where thrips often concentrate
• Tracking trends over time and comparing counts with locally established thresholds

Thrips management fits within an integrated pest management framework that favours prevention and monitoring over reliance on any single tactic.

• Conserve natural enemies such as minute pirate bugs, predatory mites, and lacewings
• Remove or manage weeds and volunteer plants that can host thrips or the viruses they transmit
• Use virus-tested or certified planting material where thrips-vectored viruses are a concern
• Monitor regularly with traps and direct inspection, and use local thresholds to guide any response