Thrips

Adults:

• 2mm long
• cigar-shaped
• yellow-orange to grey-black
• narrow wings fringed with hairs carried over the back.

Nymphs are smaller, paler, and wingless.

A microscope is usually required to distinguish between species.

• Maize thrips: maize.
• Onion thrips: cotton, navy bean, mungbean, cereals.
• Plague and tomato thrips: summer pulses.
• Western flower thrips: cotton, navy bean, mungbean, sunflower, canola and peanuts.

Adults and nymphs infest the underside of cotyledons, young leaves and growing points, rasp the plant surface and suck out the cell contents:

• affected areas are silvery-white
• younger leaves become distorted
• growing points can die.

Populations typically peak within 4 weeks of plant emergence. In maize, thrips in the whorl can stop the growth of young plants, particularly if plants are stressed.

Flower thrips inside navy bean and mungbean flowers can cause:

• flower abortion
• pod distortion
• brown marks on pods.

Vigorously growing crops can usually compensate for flower abortion, but deformed pods may be difficult to thresh, resulting in further yield losses.

Western flower thrips life cycle takes 10 days at 20°C:

• eggs are laid in slits made in leaves and growing points
• 2 larval stages, a pre-pupal and pupal stage
• pupation occurs in the soil.

Populations decline at higher temperatures (>30°C).

• Spring-planted crops are at greatest risk, especially those close to maturing host crops.
• Visually examine plants and flowers for signs of thrips. Growing points or flowers can be dipped or stored in alcohol to dislodge thrips for later counting.
• Adults are highly mobile—check for reinfestation post-control.

Predators include pirate bugs, lacewing larvae and ladybird beetles.

• Avoid planting mungbeans next to winter cereals.
• A systemic pesticide applied soon after emergence (within 3–4 days) can greatly reduce seedling damage.
• Western flower thrips are resistant to multiple chemical groups; chemical control of this species is unlikely to be cost-effective.