Biological Control of Two-Spotted Spider Mites

The two-spotted spider mite (TSSM), Tetranychus urticae, is a common pest in greenhouses. This mite has a wide host range including many different annuals, herbaceous perennials, greenhouse vegetables and herbs. Its short generation time, and potential for rapid increase has lead to many populations developing resistance to some commonly used miticides.

Adult female two-spotted spider mites can live for about one month. During this time, they may lay from 100 to 200 eggs. Mite eggs are small, spherical in shape and are laid on the underside of leaves. Eggs hatch in about three days and develop into pale green to light-yellow 6-legged larvae. The larvae develop into eight-legged nymphal stages with a  feeding and resting stage. Optimum temperatures for mite development are between 85 to 95oF; with a lower threshold for development of 54°F and an upper threshold of 104° F.  The life cycle from egg to adult varies depending upon greenhouse temperatures, relative humidity levels, and age and quality of the host plant. For example, on roses at temperatures of 77/95° F (Day/Night), spider mites developed from egg to adult at 8 days, and 50/68°F (Day/Night), mites developed at 28 days. 

Female mites are three times more abundant than males. Fertilized adult females produce both males and females. Unfertilized adult females only produce males. Males have only one set of genes, so mutations such as pesticide resistance, are immediately expressed. Incorporating biological control strategies into your pest management program, can help slow down the development of resistance.

Biological control agents are best used preventatively, when pest populations are low. A regular monitoring program is needed for early detection of spider mites, and to insure the success of a biological control program. Weekly scouting and random plant inspections are needed to detect populations early before feeding damage occurs. Carefully inspect plants in hot, dry areas of a greenhouse or where there is no overhead irrigation that wets the foliage that may wash some of the mites off the leaves. Regularly inspect the most susceptible cultivars or species, and look for signs of plant damage. As spider mites insert their stylet-like mouthparts into plant tissue, they suck out plant juices removing the chlorophyll. At first, you see a slight flecking or stippling (chlorotic spot) on the leaves. Thin-leaved plants such as garden impatiens may show injury more quickly than thick-leaved plants such as ivy geraniums. Mite feeding damage on ivy geraniums is also often mistaken for oedema. As spider mite feeding continues, leaves turn yellow, bronzed and drop from the plant. When high mite populations develop, the fine webbing is extensive. Tag pest-infested plants as indicator plants to determine the effectiveness of biological control measures. A 10x to 16x hand lens is helpful to detect all stages of the mites. Because mites are easily carried on workers or their clothing, do routine greenhouse tasks and scout in mite-infested areas at the end of the day.

There are a number of biological control agents that may be incorporated into your pest management program for two-spotted spider mites. These include different species of predatory mites (Phytoseiulus persimilis, a specialist predator and Neoseilus californicus, a more generalist predator), and predatory midges (Feltiella acarisuga).  No parasitoids are commercially available. Outdoors, natural enemies such as predatory mites, predatory thrips, predatory ladybeetles (Stethorus punctum), predatory midges, lacewings and pathogenic fungi may help to keep the spider mite populations low.

Phytoseiulus persimilis, a predatory mite

Adult Phytoseiulus persimilis feeds on all stages of two-spotted spider mites. Nymphs feed on spider mite eggs, larvae or spider mite nymphs. This specialist predator can only survive by feeding upon two-spotted spider mites.  The adult P. persimilis is bright red in color, pear shaped, long-legged and slightly larger and more active than spider mites. Adult females lay eggs that are about 2 to 3x the size of two-spotted spider mite eggs.

The development time for P. persimilis is shorter than for spider mites; about 5 days at 86°F, 9 days at 68°F, and 25 days at 59°F. This predatory mite has a development threshold of 52°F. At temperatures above 86°F, P. persimilis can’t keep up with the reproduction of spider mites. At low relative humidity (less than 60%), eggs shrivel and do not hatch. 

P. persimilis is attracted to the chemical odors produced by plants infected with spider mites as it searches for its prey by touch and scent.  P. persimilis can spread through a greenhouse as long as plants are in contact with each other. Researchers have demonstrated its effectiveness on ivies, roses, dieffenbachia, and schefflera.  P. persimilis has difficulty climbing the vertical leaves of cut flower carnations and doesn’t survive and reproduce well on greenhouse tomatoes. This biological control agent has been used in commercial greenhouses (primarily vegetable crops) since the 1960’s.

Tips for Use

·        Release early when mite populations are low and spider mites are first noticed.

·        This voracious, specialist predatory mite needs to have spider mite prey or it will disperse or starve.

·        Gently roll the tube to mix the predatory mites in the carrier before application.

·        Sprinkle material on leaves. Concentrate releases near hot spots of mite activity.

·        Relative humidity should be greater than 75% and temperature above 68°F for some hours of the day.

·        Adults and nymphs actively search for prey and suck them dry.

·        Spider mite colonies should be reduced in 2 to 3 weeks. 

·        Suppliers recommend releases every 1 to 2 weeks on mixed ornamental crops. 

·        Supplier recommended release rates vary depending upon susceptibility of crops or cultivars to spider mites, length of crop time and infestation levels.

·        To evaluate effectiveness, look for dead spider mites that have been fed upon

·        Compatible pesticides reported in the literature include: spinosad (Conserve)(Holt et al. 2006), diflubenzuron (Blumel and Stolz 1993),  pymetrozine (Endeavor), clofentezine (Ovation) (Cloyd 2007) 

·        However, Cloyd 2007 reported that bifenazate (Floramite), spiromesifen (Judo) and chlorfenapyr (Pylon) were not compatible with P. persimilis.  Osborne and Petit 1985 reported that insecticidal soap is not compatible with P. persmilis.

·        For more detailed information on pesticide compatibility: consult with your supplier or with the following resources on the Internet:

o       Pesticide Side Effects Database- www.koppert.com

o       Pesticide Side Effects Database – www.biobest.be

For more information:

Biobest Technical Sheet http://207.5.17.151/biobest/en/productfiches/Phytoseiulus-System.pdf

Neoseilus californicus, a predatory mite 

Neoseilus californicus is slower acting than P. persimilis, but can survive longer in the absence of prey. It is useful for keeping low spider mite populations under control. In situations where high temperature or relative humidity variations can occur, N. californicus may be a better choice than P. persmilis. At low pest densities, it declines less than P. persmilis, for N. californicus can survive on other mites, thrips, molds and nectar. N. californicus can also be introduced preventively. You can also release N. californicus in combination with P. persmilis. N. californicus may also feed upon broad mites and cyclamen mites.

Tips for Use

·        Release as soon as possible after receiving.

·        Gently roll the tub to mix the predatory mites in the carrier before application.

·        N. californicus is active at temperatures between 46°F to 95°F, 40-80% RH. 

·        Repeat applications every 2 to 3 weeks.

N. californicus is compatible with bifenazate (Floramite), chlorfenapyr (Pylon), spiromesifen (Judo) (Cloyd et al. 2006), spinosad (Conserve)(Miles and Dutton 2003) 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.comPesticide Side Effects Database – www.biobest.be  

For more information:

Biobest Technical Sheet: http://207.5.17.151/biobest/en/productfiches/Californicus-System.pdf

Feltiella acarisuga, a predatory midge

A tiny predatory gall midge Feltiella acarisuga feeds on two-spotted spider mites. (Another species of gall midge is commercially available for use against aphids.) Adults live for 2 or 3 days, are more active at night and rest during the day on the underside of leaves. Adults search out spider mite colonies where they deposit 30 to100 eggs. Eggs hatch into small larvae that eat eggs, nymphs and adults of two-spotted spider mites. After about a week of feeding, larvae pupate on the underside of leaves forming tiny, white fluffy cocoons. Feltella develops from egg to adult in 10 days at 80° F to 34 days at 59°F with relative humidity between 60 to 95%. The minimum developmental threshold is 46 °F.  This predatory mite is active year round.

This predatory gall midge is shipped in the pupal stage and hatches into midge adults upon arrival. Felitella can be used with P. persmilis (depending upon the crop and pest levels).  Researchers have reported good control of two-spotted spider mites with Feltiella in hydrangea, datura, and roses. Adults can fly, so they may be able to reach hanging baskets and other hard to reach ornamental crops.  Feltiella is also able to forage on the hairy leaves of greenhouse tomatoes whereas the tomato’s glandular hairs reduce the survival and reproduction of P. persmilis.

Tips for Use

·        Commercially available as pupae on paper pieces in pots or boxes. Pierce paper disc on the cover, so adult midges can emerge.

·        Open the box containing the predatory midges, place close to spider mite infestations. Let box stand for one week until adults have emerged.

·        Larvae, pupae and adults are visible when scouting.

·        For more detailed information on pesticide compatibility: consult with your supplier or with the following resources on the Internet:

o       Pesticide Side Effects Database- www.koppert.com

o       Pesticide Side Effects Database – www.biobest.be

For more information:

Biobest Technical sheet: http://207.5.17.151/biobest/en/productfiches/Feltiella-System% 20(LV).PDF

In summary, beneficial predatory mites (P. persmilis and N. californicus), and predatory gall midges (Feltiella) can be part of a biological control program for two-spotted spider mites. Regular monitoring, in conjunction with cultural controls help insure their successful use.

References:

Blumel, S. and M. Stolz. 1993. Investigations on the effect of insect growth regulators and inhibitors on the predatory mite Phytoseiulus persimilis A.H. with particular emphasis on cyromazine. J. Plant Dis. Protect. 100:150-154.

Cloyd, R. A., C.L. Galle and S. R. Keith. 2006. Compatibility of Three Miticides with the Predatory Mites Neoseiulus californicus McGregor and Phytoseiulus persimilis Athias-Henriot (Acari: Phytoseiidae) HortScience. 41(3):707-710.

Cloyd R. 2007. Compatibility Conflict: The use of Pesticides with Biological Control Agents. 2007AERGC Annual Meeting. July 31, 2007. University of Connecticut. Storrs, CT. 13 pp.

Gillespie, D. R., G. Opit and B. Roitberg. 2000. Effects of Temperature and Relative humidity on Development, Reproduction, and Predation in Feltiella acarisuga (Vallot) (Diptera: Cecidomyiidae). Biological Control. 17. 132-138.

Glenister, C. 2005. Midge Out-Muscles Spider Mites. GMPro. Feb 2005. 35-38.

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

Holt, K.M, G. Opit, J. R. Nechols and D. C. Margolies. 2006. Testing for Non-target Effects of Spinosad on Twospotted Spider Mites and their Predator Phytoseiulus persimilis under Greenhouse Conditions. Experimental and Applied Acarology 38:141-149.  

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.

Miles M., Dutton R. 2003. Testing the effects of spinosad to predatory mites in laboratory, extended laboratory, semi-field and field studies. Vogt H., Heimbach U., Vinuela E. Pesticides and beneficial organisms. IOBC/WPRS Bull. 26: 2003. 9–20.  

Opit, G. P., G.K. Fitch, D.C. Margolies, J. R. Nechols, and K. A. Williams. 2006. Overhead and Drip-tube Irrigation Affect Twospotted Spider Mites and their Biological Control by a Predatory Mite on Impatiens. HortScience. 41(3):691-694

Osborne, L. S., L. E. Ehler, and J. R. Nechols. 1999. Biological Control of the Twospotted Spider Mite in Greenhouses. University of Florida. Bulletin 853. http://www.mrec.ifas.ufl.edu/lso/SpMite/b853a1.htm

Osborne, L. S. and F.L. Petitt. 1985. Insecticidal Soap and the Predatory Mite, Phytoseiulus persimilis (Acari: Phytoseiidae), Used in Management of the Twospotted Spider Mite (Acari: Tetranychidae) on Greenhouse Grown Foliage Plants. Journal of Economic Entomology. 78(3):687-691.

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

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Leanne Pundt Extension Educator
University of Connecticut 

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