Integrated Pest Management Program Department of Plant Science and Landscape Architecture UConn Extension Biological Control of Western Flower Thrips The western flower thrips (WFT), Frankliniella occidentalis, is a difficult to control pest for greenhouse growers for a number of reasons. 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. Rapid development of resistance to many commonly used insecticides has also made thrips difficult to control. Figure 1: Thrips larvae and feeding damage on Aster, Photo by L. Pundt
Figure 2: Thrips feeding damage to verbena. Photo by L. Pundt 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 50 F and 90 F. Thrips can survive cooler temperatures than 50 F; however, there is no development at that temperature. Robb found that their life cycle varied from seven to 14 days at fluctuating temperatures between 68 F to 98 F that may be more common in the greenhouse environment. In the greenhouse, WFT are found year-round whenever temperatures are favorable for their development and host plants (including weeds) are available for food. Scouting A regular monitoring program is needed for early detection and to insure the success of a biological control program. Sticky cards may be used to monitor for adult thrips. Check yellow sticky cards weekly. See: Identifying Some Pest and Beneficial Insects on Your Sticky Cards on the UConn IPM website.
Figure 3: Adult male (on left) and female thrips (on right) on sticky card. Photo by L. Pundt 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. Figure 4: Adult thrips (in red circle) compared to grains of peat moss. Photo by L. Pundt
Cultural Controls 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. See Greenhouse Weed Control on the IPM Website. Insect screening may also reduce the influx of thrips from outside; however, careful design and maintenance is needed. Biological Controls Predatory mites, predatory bugs, entomopathogenic nematodes and entomopathogenic fungi can all be used in your biological control program. In addition, Atheta (=Dalotia) coriaria, and Hypoaspis miles (= Stratiolaelaps scimitus) used primarily for fungus gnat larvae will also feed upon thrips pupae found in the growing media. Both of these predators are discussed in more detail in the Biological Control of Fungus Gnats fact sheet on the UConn IPM website. Predatory Mites Neoseilus (Amblyseius) cucumeris and Amblyseius swirskii are generalist predatory mites that primarily feed upon first instar thrips larvae. Neoseilus (Amblyseius) cucumeris Neoseilus (Amblyseius) cucumeris is a small, generalist predatory mite that feeds upon young 1 st instar thrips larvae. Second instar thrips are too large for the predatory mites to kill. However, recent research has shown that the second instar thrips spend less time feeding (about 30% in this study) so that thrips feeding damage to plants was reduced. Because N. cucumeris only preys on the young thrips larvae, it is important to start releases preventively, at planting, before thrips are detected. N. cucumeris also eats pollen (important in pollen producing crops such as sweet pepper), or they may prey upon spider mites or spider mite eggs as well as broad or cyclamen mites. Adult predatory mites live for about 3 weeks. Their development from egg to adult takes 8 days at 77 F and 11 days at 68 F. Efficacy of N. cucumeris is dependent upon the length of time of the crop, threshold levels, and availability of pollen, release methods & rate. Optimum conditions are temperatures between 75 and 85 F and relative humidity levels greater than 65% (ideally 75%).
N. cucumeris is available in different formulations including in bulk with a bran carrier that can be placed on the foliage or with a vermiculite carrier so that the mites can be blown onto the foliage with a mite blower. They are also available in slow release breeding piles placed on the growing media. Figure 5: Releasing bulk N. cucumeris onto plant foliage. Photo by L. Pundt Figure 6: Breeding piles of N. cucumeris. Photo by L. Pundt Slow release sachets consist of bran, whitish storage mites (that feed upon the bran), and N. cucumeris which prey upon the storage mites. Predatory mites should emerge from the sachets for 4 to 6 weeks unto the crop. If using sachets in bench crops, the foliage should be touching, forming a bridge so that the mites can move from plant to plant. These small predatory mites do not disperse well between isolated plants.
Another option would be to apply the predatory mites in a carrier that can be placed on the foliage or in breeder piles on the growing media surface. Sachets are also now available in smaller sizes as mini-sachets which are less expensive with fewer predatory mites so they can be placed onto individual hanging baskets. (Leaves would not be touching so the predators cannot move from hanging basket to hanging basket). Recent research has shown that these mini-sachets are best placed in the plant canopy where they are protected from bright sunlight. If the mini-sachets are placed in bright sunlight, high temperatures and low relative humidity in the sachets adversely affects the reproduction and egg hatch of the predatory mites. (Eggs will shrivel and die at low relative humidity). If mini sachets are placed within the plant canopy, the temperature peaks less, with higher relative humidity needed for the reproduction of these predatory mites. Tips for Using Neoseilus (Amblyseius) cucumeris If using mites with a carrier, turn and shake tube slightly to distribute the mites evenly in the bran before release. If using sachets check periodically for living predatory mites (N. cucumeris will be tan in color. The storage mites will be white). Place mini-sachets in the plant canopy so they are shaded. Optimum conditions are temperatures between 75 and 85 F and relative humidity levels greater than 65% (ideally 75%). Consult with your supplier for information on recommended release rates. For more detailed information on pesticide compatibility: consult with your supplier or with the following resources on the Internet: - Pesticide Side Effects Database www.koppert.com - Pesticide Side Effects Database - www.biobest.be/ Amblyseius swirskii The generalist predatory mite, Amblyseius swirskii, feeds upon thrips and whiteflies as well as eriophyid mites, broad mites, spider mites and pollen in the absence of prey. Both A. swirskii and N. cucumeris feed upon first instar thrips larvae, however, A. swirksii is more expensive than N. cucumeris. Recent research compared releases of N. cucumeris to A. swirskii and found that during the winter conditions (short days) both species reduced thrips and controlled heavy thrips feeding damage on chrysanthemum. Therefore, researchers concluded it was more economical for growers to use N. cucumeris under winter conditions. During the summer with higher temperatures, light intensity and long days, releases of A. swirksii resulted in more predation and egg laying of the Swirskii mite than N. cucumeris. Consider releases of A. swirksii during summer conditions as it is most effective at warmer temperatures (70 F to 80 F) and a relative humidity of 70 %. This generalist predatory mite is available in an inert carrier, in a breeding system with an inert carrier and storage mites, as individual sachets or as sachets in ribbons or strips. They can be used in a variety of crops but are not suitable for use on greenhouse tomatoes. Consult with your supplier for recommended release rates.
Hypoaspis miles Hypoaspis miles (= Stratiolaelaps scimitus) is a soil dwelling predatory mite 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. Predatory bugs Orius species commonly known as minute pirate bugs feed upon both larval and adult thrips as well as aphids, spider mites and other small arthropods. Minute pirate bugs need pollen as a food source and can be slow to establish (up to 8 to 10 weeks) limiting their effectiveness in shorter term ornamental crops. Orius have been successfully used in a variety of crops but they are not suitable for use on greenhouse tomatoes. Both adult and nymphs are predacious. Nymphs may be observed on leaves whereas adults can be seen on open flowers. Orius is most effective at temperatures between 68 and 85 F. Orius species are commercially available as adults and nymphs mixed with inert materials that can be shaken over plants. Some species enter diapause (a resting period) during shorter daylights, but not others. Orius can be used in combination with N. cucumeris but they do prey on the predatory mites. Figure 7: Minute pirate bug adult, Orius spp. Tips for Using Orius Available as adults and nymphs in a inert carrier mixture Shake over plants, especially in hot spots of thrips activity and over banker plants Release in the early morning or late evening, when greenhouse vents are closed Avoid releases in bright sunlight Consult with your supplier on recommended release rates
Thrips Banker/ Habitat Plants Researchers are investigating how the use of pollen producing banker plants, such as sweet peppers, can help Orius establishment in ornamental crops. Banker plants would both provide an addition food source (pollen) and habitat for the Orius to reproduce when short term ornamental crops are shipped. Canadian researchers found that the ornamental pepper variety Purple Flash produced the greatest number of flowers per plant compared to Black Pearl pepper, Lemon Gem Marigold, Feverfew, Gerbera Daisy, Choco Sun sunflower and Castor Bean. With more flowers, there will be more Orius. After Orius is released unto banker plants, you may see nymphs in about 2 to 3 weeks. Pepper plants are started from seed, and are slow to grow to maturity. Canadian researchers suggest sowing the pepper seed in October, so the ornamental peppers flower in late January. Orius can then be released onto the banker plants starting in late February. Supplemental food (sterile moth eggs or Ephestia) available from your biological control supplier can also help in the establishment of Orius on the pepper banker plants. Some growers have also used habitat planters containing pollen producing plants such as Cosmos Sensation White with African marigolds and other pollen producing plants. It can be labor intensive to remove the pepper fruits so the ornamental peppers continue to flower. Figure 8: Habitat planter with pollen producing plants. Photo by L. Pundt Entomopathogenic Nematodes Steinernema feltiae Drench applications of this beneficial nematode against fungus gnat larvae can also be used against thrips pupae in growing media. Start with a drench application to the growing medium followed by weekly spray or sprench applications. Apply nematodes in the early morning or late evening to avoid desiccation (from ultra-violet light) and when thrips mobility is generally slow. Use blackcloth curtains to minimize ultra-violet (UV) light and heat exposure and turn-off artificial lights for at least two hours after applying the nematodes. Spray adjuvants may
improve application uniformity especially on plants with waxy leaves. See Beneficial Nematodes: An Easy way to Begin Using Biological Control in the Greenhouse for specific tips on their use. Entomopathogenic Fungi Beauveria bassiana and Metahizium anisopliae (strain 52) are commercially available entomopathogenic (insect-killing) 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 fungal 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, and Mycotrol O. 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. This fungus works best with a relative humidity >90%. 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. 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. Do not apply through a thermal pulse fogger. Check with your supplier for pesticide compatibility information Not compatible with Hippodamia convergens (ladybird beetles) Metahizium anisopliae (strain 52): This fungus infects insects on contact and is commercially available as rice-based granular and an EC formulation. It may be used against thrips pupae in growing media as it will infect and kill thrips entering soil to pupate. In recent research, thrips populations were lower on plants receiving both Met 52 and nematodes. In summary, predatory mites, predatory bugs, entomopathogenic fungi and entomopathogenic nematodes may be incorporated into a biological control program for thrips.
By Leanne Pundt, Extension Educator, University of Connecticut, 2007, Revised 2014. References: Buitenhuis, R. 2013. A Novel Approach to Controlling Thrips, Vineland Research and Innovation Center. http://www.vinelandresearch.com/pub/docs/vric%20-%20biocontrol%20eng%20- %20colour.pdf Buitenhuis, R., E. Glemser and A. Brommit. 2014. Practical placement improves the performance of slow release sachets of Neoseiulus cucumeris. Biocontrol Science and Technology. 24(10): 1153-1166. Gillett-Kaufman. 2013. Swirski mite: Amblyseius swirskii Athias-Henriot in Featured Creatures: University of Florida: Entomology and Nematology/FDACS/DPI/ EDIs http://entnemdept.ufl.edu/creatures/beneficial/swirksi_mite.htm Heinz, K.M., R.G. Van Driesche, and M.P. Parella (Ed). 2004. Bio Control in Protected Culture. Ball Publishing, Batavia, Ill. 522 pp Hewet, L. 2013. Seasonal Climatic Variations Influence Efficacy of Predatory Mites used for Control of Western Flower Thrips in Greehouse Ornamental Crops. MS. University of Guelph. Ontario, Canada. James, R.R. and B. Lighthart. 1994. Susceptibility of the convergent lady beetle (Coleoptera: Coccinellidae) to four entomogenous fungi. Environmental Entomology 23:190-2. Jandricic, S. and S. Frank. 2014. Too scared to eat: non-consumptive effects of predatory mites reduce plant damage by Western flower thrips larvae. IOBC-WPRS Bulletin 102: 111-115. Lamb, E. and B. Eshenaur. 2014. Greenhouse Biocontrol Workbook. NYS Integrated Pest Management Program. Cornell University Cooperative Extension. 84 pp. http://www.nysipm.cornell.edu/ Available online at: http://www.nysipm.cornell.edu/nursery_ghouse/biocontrol_wkbk_10-31-13.pdf 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. Robb, K.L. 1988. Analysis of Frankliniella occidentalis (Pergande) as a Pest of Floricultural Crops in California Greenhouses. PhD. dissertation, University of California, Riverside. 135 pp. Smith, T. and L. Pundt. 2014. Greenhouse Pest Guide web App. http://tiny.cc/greenhousepestguide.
Stack, Lois Berg. (Ed). 2015-2016. New England Greenhouse Floriculture Guide. A Management Guide for Insects, Diseases, Weeds and Growth Regulators. New England Floriculture Inc and the New England State Universities. Thomas, C. 2005. Greenhouse IPM with an Emphasis on Biocontrol. Publication No. AGRS-96. 89 pp. Pennsylvania Integrated Pest Management Program. http://extension.psu.edu/pests/ipm/agriculture/copy_of_greenhouse/greenhouse-manual Van Driesche, R. 1998. Western Flower Thrips in Greenhouses: A Review of its Biological Control and Other Methods. Check year http://biocontrol.ucr.edu/wft.html Waite, M., C. Scott-Dupree, G. Murphy, M. Brownbridge and R. Buitenhuis. 2012. Benefiting from bankers. Greenhouse Canada. Feb. 2012. 28-30.
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