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Frankliniella occidentalis (Pergande)

Thripidae, THYSANOPTERA

Description and life cycle

WFT looks like any other thrips to the naked eye. They are very small (1-2cm) thin insects, yellow to pale brown in colour. Adults can fly and have 2 pairs of wings that sit down along the body when at rest. Males are smaller than females and lighter in colour.

The WFT life cycle is mostly continuous. Thrips can be found year-round, at all stages of growth. In greenhouses they may produce 12 – 15+ generations per year. A generation of WFT varies from about 9 days in summer to 15-20 days or more in winter. A female WFT lives 30 - 45 days and can produce 150 to 300 eggs in this time.

The eggs are laid individually, just under the epidermis (skin) of the soft younger parts of leaves, stems, flowers and inside the buds. The eggs hatch in 3 - 4 days, depending on temperature, and the larvae move into more protected areas of the plant to commence feeding. There are four immature stages, two active larval stages, feeding on leaves and in flowers, and two non-feeding pupa stages, usually in the soil. The adults that emerge from the soil are sluggish for the first 24 hours, but become active as they mature. There are usually more females than males in a population. Females do not need to mate to produce fertile eggs. Unfertilised eggs only give rise to male thrips.

Crops attacked and problems caused

This thrips feeds on almost any flowering plant including capsicum, cucumber, lettuce, potatoes tomatoes, strawberries, pome and stone fruit and a very wide range of ornamentals.

WFT affects crop production in two ways:
1) Direct damage from feeding thrips.
Major symptoms of WFT feeding damage on foliage, flowers and fruit include:

• foliage discolouration or silvering
• deformed new growth or flower buds
• halo-spotted foliage - small dark scars surrounded by white tissue
  

2) Transmission of tomato spotted wilt virus.
WFT is a vector of tomato spotted wilt virus (TSWV). Other thrips can transmit this virus but are generally easier to control. The larval stages of WFT pick up the virus while feeding on infected plants; the resultant adult stage is then able to pass the virus on to uninfected plants after about 5 minutes or less of feeding on a plant.

TSWV is known to infect a broad range of vegetables. Plants infected with TSWV can either have no symptoms or they can have a variety of symptoms, depending on plant species, growing conditions and virus strain. Symptoms vary greatly from leaf spots or ring patterns to yellowing, dead tissue, distortion or stunt, reduction in plant vigour, and in some cases plant death.

TSWV is only spread by WFT, Tomato Thrips, Onion thrips in South Australia. Not plague thrips or any other insects. It is no spread by pruning and does not live in the soil.

 Infected capsicum fruit

Reducing the threat of invasion and attack

Reduce the chance of getting TSWV by managing potential sources of infection especially by thoroughly controlling/removing weeds and infected plants. DO NOT LEAVE OLD CROPS, ESPECIALLY IF THEY ARE ALREADY INFESTED WITH THRIPS. They will almost certainly allow thrips to colonise new crops and infect them with TSWV at an early stage.

There are some further simple things that can be done to avoid high WFT numbers:

• Avoid introducing any infested plant material into the crop
• Use seedlings that have been grown away from WFTW and TSWV infested areas, i.e. start with a clean crop.
• Promptly remove TSWV infected plants to reduce the spread of virus – only spread by thrips
• Avoid moving thrips around the crop on staff moving from infested to clean areas.
• Use a fallow period, if possible, when no crop is grown to clear thrips and TSWV levels.
• Use fine mesh/netting to restrict thrips entry if growing in a Greenhouse (400microns or less). Cover all doors (double doors are even better) and vents if the crop is likely to be invaded by thrips from outside. Rolls of yellow sticky tape may be useful in some greenhouse designs if placed near entry points and hot spots.
  

Monitor thrips populations for early control. Use yellow sticky cards to alert you of new infestations and scout plants by turning leaves to look for adults and larvae and signs of thrips feeding damage. Control is simpler and less expensive when plants are young and spray coverage is not an issue.

Crop monitoring:

MAKE INSPECTIONS ROUTINE AND KEEP GOOD RECORDS!

• Get into the habit of walking right through your crops in a set pattern (a M or Z)
• Check about (about 1%) of your plants very carefully
• Hunt for thrips and symptoms of virus disease
• Check underside of leaves for feeding larvae and adults
• Blow gently into flowers or shake flowers over white paper to find more thrips
• Keep good records of pest levels and treatments used
  

Monitoring with sticky traps (only adults with wings are caught on traps):

For insecticide-based control programs economic thresholds need to be worked out from monitoring and spray records using sticky traps, flower checks and virus counts. Decide on a threshold level for thrips in your crop, above which you must spray and below which you can safely withhold spraying.

• Plan the layout of traps to identify hot spots and estimate overall thrips levels
• Place traps just above the plant tops
• Do a weekly count of thrips on each trap and look for virus infected plants. Mark infected plants with tape for removal and replace sticky traps.
• Note any thrips or virus hot spots and check thrips numbers in flowers on nearby plants to find the size of hot spots.
• Check thrips numbers in flowers 1-2 days after spraying to check results
• If able, count the proportion of adult to young thrips in flowers (young thrips, but no adults = spray worked, but high breeding levels still in the crop; adults only = new flight; both adults & larvae = thrips not killed by spray applications indicates resistance/coverage issues)
• Record trap, virus and flower details
• If thrips numbers are above the threshold you must spray ASAP to prevent loss of control
  

Note:

• If you can spot isolated hot spots early you may only need to spray a small area!
• Plan to introduce biological control agents as soon as thrips are found
  

Chemical control

Chemical control of WFT and TSWV outbreaks has been difficult due a number of factors:

• WFT behaviour - hiding in flowers and buds creates difficulties for good spray coverage.
• WFT life cycle – egg and pupal stages not susceptible to chemical control
• High level of resistance to many horticultural insecticides.
• Nearby weed and crop host plants harbouring both WFT and TSWV
  

Many chemicals originally tested and used have now been removed from permit lists including synthetic pyrethroids and most organophosphates due to resistance and OH&S issues.

Include a resistance management strategy into your spray program to reduce the chance of WFT becoming resistant – i.e. correct spray application with rotation of chemical groups after 3-4 sprays. There should be at least a 3 week break (<20 deg C) or a 2 week break (>20 deg C) before another series of sprays is applied. If monitoring indicates the need to spray earlier, then insecticide resistance, inappropriate spray application or inadequate farm hygiene should be suspected and expert advice sought.

Days between sprays Daytime average Temperature Days between sprays Length of life cycle

Daytime Av temp	Length of life cycle	Days between sprays
10-20oC	25-35 days	6
20-30oC	15-25 days	3-5

Spray crop after pruning and training plants to maximise chemical application by improving penetration into the crop.

Current permits are listed on the NSW Department of Primary Industries / Agriculture website (external link).

Relevant beneficial insects

Natural enemies have been investigated and biological control programs using predatory mites and other beneficial insects have been developed. They are very effective if environmental thrips pressure is not too great and they are cared fro properly in the crop.

Predatory mites are now available for use in greenhouses. Typhlodromips montdorensis and Neoseiulus cucumeris are the preferred predators for thrips control in protected environments. These mites are most effective at preventing thrips build-up when applied early in the growing season at the first sign of thrips. These light coloured predatory mites search for prey on the underside of leaves along the veins or inside mature flowers if conditions are not too hot and dry.

Hypoaspis miles mites are used primarily for control of fungus gnats, but they also help with western flower thrips control. Hypoaspis is a generalist predator/scavenger that feeds on small, soil inhabiting insects and mites. It is primarily a predator of fungus gnat larvae in the soil, but it also consumes thrips pupae on the floor and soil surface of the greenhouse. It can also survive by feeding on soil debris in the absence of thrips pupae and fungus gnat larvae. They are a native soil mite and can adapt to a variety of different growth media. They are less than 1 mm (1/20 inch) in size, light brown in colour, and can be seen moving quickly on the soil surface and base of plants.

Commercial suppliers of bio-control agents in Australia can be found listed at the Goodbugs site (external link).  The suppliers on this page will help you develop an IPM program suitable for your crop and situation. Many also provide IPM monitoring services.

You can also boost the numbers of wild beneficial insects in your crop naturally by holding back on broad spectrum insecticides, providing safe plant species as habitat near the crop and maintaining higher levels of organic soil carbon using composted green and animal waste.

 

Download the Western Flower Thrip factsheet (PDF)

Information on other greenhouse pests:
• Greenhouse Whitefly
• Two Spotted Mites
• Broad mites
• Aphids