Biological Control of Western Flower Thrips

The western flower thrips (WFT), Frankliniella occidentalis, is a difficult to control pest for greenhouse growers. Thrips have a tendency to develop resistance to insecticides making chemical control difficult. Their small size (1/16 inch) and tendency to remain hidden in flower buds makes it difficult to detect the thrips before severe feeding damage is evident.  Thrips feed by piercing plant cells with their mouthparts and feeding on the exuded plant juices. This collapse of plant cells may result in deformed flowers, leaves and shoots. Silvery flecked scars or small black "fecal" spots may be seen on the expanded leaves. In addition to direct feeding injury, WFT may vector (spread) two closely related tospoviruses; impatiens necrotic spot virus (INSV) and tomato spotted wilt virus (TSWV), to uninfected plants. Almost all greenhouse crops with the exception of roses and poinsettias are susceptible to tospoviruses.

Biology and Life Cycle

Most of the thrips in a greenhouse are females. Adult females may live for approximately 30 to 45 days. During their lifetime, female thrips lay from 150 to 300 eggs that are inserted into plant tissue. The first two larval stages remain protected in the tender young growth. After the 2nd instar larvae stops feeding, it drops to the soil or substrate to pupate. Adults emerge in two to five days, depending upon temperature.

The thrips life cycle is dependent upon temperature with development occurring between 50F and 90F. Thrips can survive cooler temperatures than 50F; however, there is no development at that temperature. Robb found that their life cycle varied from seven to 14 days at fluctuating temperatures between 68F to 98F that may be more common in the greenhouse environment (See Table 1).

Table 1. Life Cycle of Western Flower Thrips (Robb, 1988)

Stage

Approximate duration at temperatures between 68o and 98oF

Egg

2-4 days

1st instar (immature)

1-2 days

2nd instar

2-4 days

Prepupal

1-2 days

Pupal

1-3 days

Adult

30-35 days

In the greenhouse, WFT are found year-round whenever temperatures are favorable for their development and host plants (including weeds) are available for food.

Biological controls are best used preventively, when thrips populations are low. Sticky cards may be used to monitor for adult thrips. A 10-20x-hand lens is needed to distinguish the adult thrips from grains of peat moss or other debris. Foliage or flowers can be tapped over a sheet of white paper to detect adult and larval thrips.

Biological controls are more likely to be successful if combined with proper cultural controls such as providing proper irrigation and fertility for the species grown, and sanitation practices.   Prevent pest infestations on incoming plant material by establishing a quarantine area.  Dispose of infected plant material into tightly covered garbage cans. If garbage cans are not tightly covered and removed, infested plant material can be a source of thrips, as well as whiteflies and fungus gnats. Thorough weed control (weeds are a source of thrips and tospoviruses) both inside and outside the greenhouse is vital. Screening may also reduce the influx of thrips from outside.  

There are a number of biological control agents that may be incorporated into your pest management program for western flower thrips.  These include predatory mites, predatory bugs and entomopathogenic fungi.  Beauveria bassiana (sold under the trade names of Botanigard ®, Mycotrol O®) is commercially available. Entomopathogenic nematodes, used primarily against fungus gnat larvae, also attack thrips pupae and prepupae found in the soil.

UK researchers have developed a “Keep Down Strategy” for biological control of thrips in potted crops. The first step is to correctly identify the species of thrips (although WFT is the dominant species, other species such as onion or eastern flower thrips may be present), then anticipate (based upon past scouting records) when thrips are likely to occur. Prophylactic introductions of natural enemies start on young plants or in propagation areas. The predatory mites, Hypoaspis miles and entomopathogenic nematodes are applied to young tranplants. Introductions of additional species of predatory mites begin on young plants and continue through the crop.

Predatory Mites

Neoseilus cucumeris is a small, predatory mite that feeds upon young 1st instar thrips larvae.  Because N. cucumeris only feeds on the young thrips larvae, it is important to start releases preventively, before thrips are detected. N. cucumeris also eats pollen (important in pollen producing crops such as sweet pepper), or they may eat spider mites or spider mite eggs.   Adult predatory mites live for about 3 weeks. Their development from egg to adult takes 8 days at 77F and 11 days at 68F.  Efficacy of N. cucumeris is dependent upon the length of time of the crop, threshold levels, availability of pollen, release methods & rate.

N. cucumeris is available in different formulations including in bulk with a bran carrier, or in “nurse, breeder or slow release sachets” consisting of bran, whitish storage mites (that feed upon the bran), and N. cucumeris which prey upon the storage mites. These sachets were originally developed for preventive releases of this predatory mite on non-pollen producing crops such as cucumber. If using nurse sachets in ornamental hanging baskets, the foliage should be touching, so that the mites can move from plant to plant. Also, periodically check the sachets for the presence of living predatory mites and replace as needed. University of Massachusetts researchers (Van Dreische 2001) found better suppression with a bulk release material than sachets when mites were applied biweekly, 5 times in a 10 week bedding plant crop.

Researchers have found that higher than recommended release rates (3 to 4 times the currently recommended rates) have been successful in a variety of crops including impatiens and cyclamen. Van Driesche (2005) found that a higher release rate of N. cucumeris (3.6 times the recommended release rate) was able to suppress thrips larvae but not adults in a monoculture of garden impatiens in a University of Massachusetts research greenhouse. Van Driesche concluded that this predatory mite provided partial suppression of thrips larvae on short term (7-10 week) crops like impatiens.

N. cucumeris is successfully used in greenhouse vegetables (peppers, tomatoes and cucumbers) as well as ornamentals. 

Tips for Using Neoseilus

·        If high populations of thrips are present, reduce by applying a compatible insecticide first.

·        Apply biweekly, preventive releases to all plants

·        Apply N. cucumeris in bulk to flats and bench top crops. For bedding plants, apply in weeks 1-3, 5, 7 and 9.

·        In week 2 or 3, apply nurse sachets to hanging baskets that cannot be easily reached.  If using nurse sachets, the plants should be touching so the predatory mites can move from one plant to another. Check periodically for living predatory mites (N. cucumeris will be tan in color. The storage mites will be white).

·        For release, temperatures should be 50-85F with 70-90% relative humidity.  

·        Turn and shake tube slightly to distribute the mites evenly in the bran before release.

·        Not compatible with azadirachtin (Spollen & Isman 1996); paraffinic oil (Oetting & Latimer 1995) but predators may safely reenter area after oil spray residues have dried.

·        Spinosad, abamectin and mixtures of these insecticides have the potential to reduce N. cucumeris populations (Lash and Warnock 2006). Adding thiophanate methyl to abamectin and spinosad also increased mortality of the mite nymphs.   

- Pesticide Side Effects Database – www.koppert.com

- Pesticide Side Effects Database - www.biobest.be/  

Hypoaspis miles or H. aculifer are soil dwelling predatory mites that feed upon pupal stages of thrips in the soil as well as fungus gnat larvae. A single preventive release to the media at planting is generally recommended to supplement control with N. cucumeris.   The predatory rove beetles, Athea, are generalist predatory beetles that feed upon thrips as well as shore flies and fungus gnats.  Both of these predators are discussed in more detail in the “Biological Control of Fungus Gnats” fact sheet

Another species of predatory mite, Amblyseius swirskii, feeds upon both thrips and whiteflies. Researchers have noted good results in greenhouse peppers, cucumbers and some ornamental crops. It is available in nurse or breeder sachets, and in bulk. If crops produce sufficient pollen, this predatory mite can be released preventively. The pollen producing caster oil plant, Ricinus communis, can be used as a banker plant in ornamental crops. For more information, see www.allaboutswirskii.com

Predatory bugs

Orius ssp. are minute pirate bugs or flower bugs that search in flowers and feed upon both larval and adult thrips. Orius will also feed upon aphids and spider mites. These predatory bugs need a pollen food source and can be slow to establish (up to 10 or 12 weeks) limiting their effectiveness in short term bedding plant and ornamental crops. Orius have been successfully used in sweet pepper, eggplant, melon and strawberry crops. Researchers are investigating whether the use of pollen producing banker plants, such as sweet peppers, can help their establishment in ornamental crops. Some species of Orius go into reproductive diapause in response to short days. Orius can be used in combination with N. cucumeris but they do prey on the predatory mites.

Entomopathogenic Fungi

Entomopathogenic fungi work by contact; directly penetrating the insect’s cuticle. The fungus then uses the insect as a food source consuming its internal contents and eventually killing it. Once it has killed its host, the fungus emerges and sporulates, covering the insect in a white mold (if conditions are humid enough). Insects may also acquire lethal doses of the Beauveria spores from the surface of a treated leaf. 

Beauveria bassiana is a naturally occurring fungus found in soils. Beauveria sold under the trade names of Botanigard ®, Mycotrol O® is labeled for many foliar pests including whiteflies, aphids, mealybugs and thrips. Beauveria’s effectiveness varies depending upon the humidity levels at the plant surface, life stage of the target pest, crop, temperatures, solar radiation and spray coverage. The larval stage is less susceptible than adults because the molting of the exoskeleton, which removes the spores before they have a chance to penetrate the host tissue, limiting fungal infection. (The addition of an insect growth regulator to the Beauveria may help slow down molting and increase its effectiveness.) It also may be more useful to apply Beauveria early in the cropping cycle before plants flower and produce pollen. (Thrips derive nutrients from the pollen, which increases their egg laying and reproduction. Plants will also be smaller, so it will be easier to obtain more thorough spray coverage.) Due to tendency of thrips to hide in protected places, thorough spray coverage to growing points, flowers and underside of leaves is needed. Repeated applications are also often necessary.  

Beauveria bassiana has been shown to effectively control western flower thrips in roses, carnation, potted sunflowers and has suppressed populations in chrysanthemum. In garden impatiens, Beauveria suppresses populations by about 40%. Most of the thrips are in the impatiens flowers, which may be a drier microenvironment. Garden impatiens also have a waxy leaf, which may also reduce the humidity levels or influence the amount of spores picked up by the thrips.

Tips for Using Beauveria

·        Begin applications early in production, at first sign of thrips.

·        Thorough spray coverage is essential, directing sprays at terminals and buds.

·        Spray to thoroughly wet but not to runoff.  

·        Multiple applications at repeated intervals every 3 to 5 days are often needed.

·         See Bioworks web site (www.bioworksbiocontrol.com) for product label and more information. Do not apply through a thermal pulse fogger.

·        Check with your supplier for pesticide compatibility information

·        Not compatible with Hippodamia convergens (James & Lighthart 1994)   

Entomopathogenic Nematodes

Nematodes are small, colorless, unsegmented, round worms that occur naturally in soils. The term “entomopathogenic” means to cause diseases (“pathogenic”) to insects (“entomon” from the Greek word for insect).  Insect parasitic nematodes are primarily found in the families Steinernema and Heterohabtis.

Applications of Steinernemia feltiae (primarily used against fungus gnat larvae) and S. carpcapsae against the thrips pupal stage in the soil resulted in 75 to 97% mortality in certain studies. For more information on nematodes, see the Biological Control of Fungus Gnats fact sheet.

In summary, predatory mites, predatory bugs, entomopathogenic fungi and  entomopathogenic nematodes  may be incorporated into a biological control program for thrips. 

References:

Heinz, K.M., R.G. Van Driesche, and M.P. Parella (ed). 2004. Bio Control in Protected Culture. Ball Publishing, Batavia, Ill. 522 pp.   

Bennison, J. 2004. Integrated Control of Thrips in the UK. Canadian Greenhouse Conference handout. 2 pp.

Biological Control: A Guide to Natural Enemies of North America. www.nysaes.cornell.edu/ent/biocontrol/pathogens/nematodes.html (accessed 1/08) 

Brodsgaard. H. F. 1995. Keep Down, a concept of thrips biological control in ornamental pot plants. In Thrips Biology and Management, ed. B.L. Parker, M. Skinner, and T. Lewis, 221-4.  

Hogendorp, B. and R. Cloyd. 2006. Sanitation’s Place in an IPM Program. Greenhouse Product News. August 2006. 38-44. 

James, R.R. and B. Lighthart. 1994. Susceptibility of the convergent lady beetle (Coleoptera: Coccinellidae) to four entomogenous fungi. Environmental Entomology 23:190-2.  

Lash, H. and D. Warnock. 2006. Effect of Pesticide Mixtures on the predatory mite, Neoseiulus cucumeris (Oudemans) (Acarina: Phytoseiidae). Poster. Fifth National IPM Symposium, St. Louis, MD.  

Lopes, P. and L. Berg Stack. 2006. New England Greenhouse Floriculture Guide: A Management Guide for Insects, Diseases, Weeds and Growth Regulators. 2007-2008. New England Floriculture, Inc.

Malais, M.H. and W. J. Ravensberg. 2003. Knowing and recognizing: The biology of glasshouse pests and their natural enemies. Koppert Biological Systems and Reed Business Information. The Netherlands.  288 pp.  

Oetting, R. D. and Latimer, J. G. 1995. Effects of soaps, oils and plant growth regulators (PGR”S) on Neoseiulus cucumeris (Oudemans) and PGRs on Orius insidiosus (Say). J. Agric. Entomol. 12:101-109.

Parker, B.L., M. Skinner and T. Lewis (ed). 1995. Thrips Biology and Management. Plenum Press. NY. 593 pp.

Robb, K.L. 1988. Analysis of Frankliniella occidentalis (Pergande) as a Pest of Floricultural Crops in California Greenhouses. P.h.D. dissertation, University of California, Riverside. 135  pp.

Spollen, K.M. and M. B. Isman. 1996. Acute and sublethal effects of a neem insecticide on the commercial biological control agents, Phytoseiulus persimilis and Amblyseius cucumeris (Acari:Phytoseiidae) and Aphidoletes aphidimyza (Diptera: Cecidomyiidae). Journal of Economic Entomology 89:1379-86.

Thomas, C. 2005. Greenhouse IPM with an Emphasis on Biocontrol. Publication No. AGRS-96. 89 pp. Pennsylvania Integrated Pest Management Program.

 

Ugine, T. A., S. P. Wraight, and J.P. Sanderson. 2006. Influences of impatiens pollen and exposure to Beauveria bassiana on bionomics of western flower thrips Frankliniella occidentalis. Biological Control. 37:186-195.  

 

VanDriesche, R. G. and S. Lyon. 2002. Using Predatory Mites to Manage Western Flower Thrips in Bedding Plant Greenhouses. 2 pp. Fact Sheet.  

 

Van Driesche, RG, S. Lyon, EJ Stanek III, Bo Xu, and C. Nunn, 2005. Evaluation of efficacy of Neoseiulus cucumeris for control of western flower thrips in spring bedding crops. Biological Control. 36: 203-215.

 

Van Driesche, S. Lyon, T. Smith, P. Lopes, J. Sanderson, S. MacAvery, T. Rusinek, and G. Couch. 2001. Western Flower Thrips Control in Spring Bedding Plants: Which Formulation of Mites is Best? UMass Floral Notes. March/April 2001. 8-11.

 

1/08 

Leanne Pundt, Extension Educator
University of Connecticut

Information on our site was developed for conditions in the Northeast. Use in other geographical areas may be inappropriate..e.

The information in this material is for educational purposes. The recommendations contained are based on the best available knowledge at the time of printing. Any reference to commercial products, trade or brand names is for information only, and no endorsement or approval is intended. The Cooperative Extension system does not guarantee or warrant the standard of any product referenced or imply approval of the product to the exclusion of others which also may be available.All agrochemicals/pesticides listed are registered for suggested uses in accordance with federal and Connecticut state laws and regulations as of the date of printing. If the information does not agree with current labeling, follow the label instructions. The label is the law.Warning! Agrochemicals/pesticides are dangerous. Read and follow all instructions and safety precautions on labels. Carefully handle and store agrochemicals/pesticides in originally labeled containers immediately in a safe manner and place. Contact the Connecticut Department of Environmental Protection for current regulations.The user of this information assumes all risks for personal injury or property damage.Issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture. Kirklyn M. Kerr, Director, Cooperative Extension System, The University of Connecticut, Storrs. The Connecticut Cooperative Extension System offers its programs to persons regardless of race, color, national origin, sex, age or disability and is an equal opportunity employer.

menu