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Thrips

By Susan Jones

Many species of thrips feed on orchids; some of the most common include western flower thrips (Frankliniella occidentalis), Cuban laurel thrips (Gynaikothrips ficorum), greenhouse thrips (Heliothrips haemorrhoidalis) and flower thrips (Frankliniella bispinosa).

Thrips are a common problem on vandaceous plants, dendrobiums and to a lesser extent, cattleyas and phalaenopsis. Because they are quite small (about 1/16 to 3/8 inch [1 to 5 mm] long), they are difficult to see with the naked eye. Much more easily detected is the damage to plants, deformed foliage and injured floral tissues caused by their feeding. They most often attack buds and new growths with their rasping mouthparts, sucking the plant sap.


Thrips can make a mess out of flowers you have waited all year to see.

Symptoms
Much like aphids, thrips feed in buds and flowers by using their mouthparts to pierce the surface of the plant tissues and suck up juices from leaves, stems and flowers. Blooms may become prematurely brown, and their petals spotted, streaked, silvery or discolored. Damage to leaves appears as chlorotic spots, wilting and eventually dropping. Plant growth can be stunted, and a severe thrips infestation will kill an orchid. If you suspect that thrips are present, gently blow into an open flower and watch for the insects crawling around inside the blossom.

Because of their method of feeding and ability to travel from plant to plant, thrips, like aphids, may introduce and spread virus through an orchid collection.

Life Cycle
The majority of the pest thrips belong to the family Thripidae. The adults of most species are brown or black. The winged adults (males and females) are found mainly on flowers and developing growths. Females deposit their eggs beneath the surface of the plant tissue. Often the only visible evidence of this is the callus tissue formed by the orchid in response to the wound. The nymphal (immature) stages are creamy yellow to pale orange and resemble adults without any wings. The nymphs feed on the tender young plant growths, then drop to the medium to pupate. The pupae are a darker orange color than the nymphs. As they are generally below the surface of the medium, they are unlikely to be spotted and more difficult to control with pesticides. When they emerge as winged adults, they fly back up to the plant to feed, lay eggs and begin the cycle once again.

Each female is capable of producing 25 to 50 eggs at a time, and many species reproduce at a rate of three to five generations per year. Their reproduction rate is more rapid in warmer temperatures, making thrips a more difficult pest to control in southern climates.

Prevention
Thrips are among the more difficult insect pests to prevent and control, but some measures that help include covering all vents and doorways with insect-proof netting, segregation of infested plants and disposal of all affected loose plant material, and overall good general sanitation ? removal of all weeds and plant debris from the growing area

Thrips can be monitored using blue or yellow sticky traps, which should be checked weekly. Thrips will appear as small dark specks on the traps. This will allow the application of pesticides while populations are small, so as to minimize chances of damage and infestation.

Thrip
Thrips are very small and may go unnoticed until significant damage has been done.

Controls
The nature of the thrips? life cycle places their eggs and pupal stages fairly well out of the reach of most pesticides. Therefore, multiple applications of the chosen control method or pesticide at weekly intervals are needed to control successive generations of these pests.

As with many unwanted insects, monthly rotation of control measures is also recommended, especially when using chemical pesticides. Alternating between at least two different chemicals helps to avoid raising resistance to control measures in the insect pest.

Insecticides such as insecticidal soap, malathion and acephate (Orthene) are all recommended for use on thrips, and are listed as safe for use on orchids as well.

If your growing area is enclosed and is not part of your living space, such as a greenhouse, biological control with a predatory mite is an option. The female Amblyseius cucumeris deposits eggs in thrips. When the young hatch, they parasitize their hosts, killing them.

The use of insecticides is not compatible with employing predatory mites for control, as the insecticides are harmful to the mites as well as the thrips. As always, adhere strictly to the manufacturer?s instructions for safe application and use of chemical pesticides.

As with any spray-on pest control measure, any orchid plants infested with thrips should be managed to allow easy and thorough pesticide application. Arrange the plants in the growing area so that they have adequate space for air circulation and ease of spraying, and be sure to cover all plant surfaces, such as those between and on the undersides of leaves, to maximize the effectiveness of the treatment.



References

Cloyd, Raymond. Orchid Pests and Their Management. Orchids of the World Web site. (http://www.orchids.mu/Problems/Pests/).

Hamon, Avis B., PhD. 2002 Revised Edition. ?Orchid Pests.? Orchid Pests and Diseases. American Orchid Society, Delray Beach.

Laemmlen, Franklin, PhD. Western Flower Thrips on Cymbidium Blossoms. The Coastal Gardener Web site. (http://cesantabarbara.ucdavis.edu/wfth.htm).

Martin, N.A. Thrips Insecticide Resistance Management and Prevention Strategy,Revised January 2003. New Zealand Institute for Crop & Food Research Ltd. Web site. (http://www.hortnet.co.nz/publications/nzpps/thrips.htm).

Pests and Diseases. The Philippine Orchid Society Web Site. (http://www.philippineorchidsociety.org/Pests&Diseases/Philippine%20Orchid%20Society%20-%20Orchid%20Pests.htm).

Plants and Seeds. UK Department for Environment, Food and Rural Affairs, Central Science Laboratory Web site. (http://www.defra.gov.uk/planth/pestnote/thrips.htm).

 

Susan Jones was the editor of Awards Quarterly and assistant editor of Orchids. American Orchid Society, 16700 AOS Lane, Delray Beach, Florida 33446

All reuse must contain the follwing:
Reprinted from the JANUARY 2004 issue of Orchids -- The Bulletin of the American Orchid Society. Copyright American Orchid Society -- www.aos.org