Thrips (order Thysanoptera) are tiny, slender insects that are often overlooked due to their minute size — most species measure just 1–2 mm in length. Despite their small stature, they are enormously abundant and economically significant. There are roughly 6,000 described species worldwide and around 150 species in the UK. In Britain, they are colloquially known as “thunderbugs” or “thunderflies” because they tend to swarm in large numbers during warm, humid, thundery weather.
Identification
Thrips have a distinctive appearance, though you may need a hand lens or microscope to appreciate their features:
Key Identification Features
- Size: 0.5–5 mm (most UK species 1–2 mm)
- Body shape: Elongated and narrow, somewhat flattened
- Colour: Typically yellow, brown, or black; some species bicoloured
- Wings: Four narrow wings fringed with long hairs (the name Thysanoptera means “fringe-wing”). Some species are wingless or have reduced wings.
- Mouthparts: Asymmetrical, punch-and-suck type — one mandible is a sharp stylet used to pierce plant cells
- Antennae: Short, with 6–9 segments
Life Cycle
Thrips have an unusual life cycle that combines features of both incomplete and complete metamorphosis. It is sometimes described as “remetabolous” or intermediate metamorphosis.
| Stage | Description | Duration |
|---|---|---|
| Egg | Inserted into plant tissue (leaves, petals, or fruit) | 3–16 days |
| Larva (2 instars) | Resembles a small, wingless adult; actively feeds on plant cells | 5–14 days |
| Prepupa | Non-feeding resting stage, often in soil or leaf litter | 1–4 days |
| Pupa | Non-feeding; wing buds develop externally | 2–7 days |
| Adult | Fully winged (usually); feeds and reproduces | Several weeks |
Many thrips species reproduce by parthenogenesis (females produce offspring without mating), which allows populations to build rapidly. In some species, unfertilised eggs produce males (arrhenotoky), while in others, all offspring from unfertilised eggs are female (thelytoky).
Feeding and Damage
Most thrips feed on plants by piercing individual cells with their asymmetrical mouthparts and sucking out the contents. This creates characteristic silvery or bronze streaking, stippling, and scarring on leaves, petals, and fruits. Heavily infested plants may show distorted growth, discoloured flowers, and reduced fruit quality.
Economically Important Pest Species
Several thrips species are significant agricultural and horticultural pests:
- Western flower thrips (Frankliniella occidentalis) — a major glasshouse pest worldwide; damages ornamental flowers and vegetables; vectors tomato spotted wilt virus (TSWV).
- Onion thrips (Thrips tabaci) — attacks onions, leeks, and other alliums; one of the most widespread thrips globally.
- Glasshouse thrips (Heliothrips haemorrhoidalis) — common on houseplants and greenhouse ornamentals in the UK.
- Pea thrips (Kakothrips pisivorus) — damages pea and bean crops; causes silvering of pods.
- Grain thrips (Limothrips cerealium) — feeds on cereal crops, particularly wheat and barley.
Did you know? The word “thrips” is both singular and plural. A single individual is “a thrips,” not “a thrip.” The name comes from the Greek thrips, meaning “woodworm.”
Thrips as Virus Vectors
Some thrips species transmit plant viruses in the genus Tospovirus, including tomato spotted wilt virus (TSWV), which affects over 1,000 plant species. The virus is acquired by the larval stage and transmitted by the adult, making control particularly challenging. TSWV causes billions of pounds in crop losses globally each year.
Beneficial Thrips
Not all thrips are pests. Some species are predatory, feeding on mites, other thrips, and small insects. Predatory thrips in the genus Aeolothrips are used in biological control. Some thrips species also contribute to pollination, particularly of heathers (Ericaceae) and some tropical crops. In Australian Cycas plants, thrips are the primary pollinators.
Control Methods
Managing Thrips in the Garden
- Biological control: Predatory mites (Amblyseius cucumeris), predatory bugs (Orius), and lacewing larvae
- Sticky traps: Blue sticky traps are particularly effective for monitoring and reducing thrips numbers
- Cultural practices: Remove plant debris, avoid over-fertilising (lush growth attracts thrips), maintain good air circulation
- Water sprays: A strong jet of water dislodges thrips from plants
- Chemical control: Use targeted insecticides only as a last resort, as thrips readily develop resistance
Key Takeaway
Thrips are tiny, fringed-winged insects that are major pests of crops and ornamental plants. They cause damage by piercing plant cells and sucking out contents, and some species transmit devastating plant viruses. However, some thrips species are beneficial predators or pollinators. Identification and management require attention to these minute but economically significant insects.