With the thousands of recently planted summer strawberry acres, Parabug has been releasing millions of Phytoseiulus persimilis weekly to help combat Twospotted spider mite infestations. Strawberry plants are especially sensitive to the damage caused by this pest during early development and P. persimilis can eat upwards of twenty Twospotted spider mites per day. Applications of P. persimilis typically occur between the range of 10,000 to 30,000 mites per acre, varying based on infestation levels, and can be repeated over the course of several weeks or months as necessary. It may not be possible for a strawberry grower to delay a chemical application while P. persimilis is still actively foraging for prey in their field. In cases like these it is useful to know what products are potentially harmful to P. persimilis populations.
As P. persimilis are mites just like their preferred prey, they are also susceptible to miticides and insecticides. In most cases, P. persimilis is more susceptible to the effects of miticides than the prey it is trying to control in our agricultural systems. Numerous characteristics of beneficials can be impacted by chemical applications such as prey seeking ability, number of prey consumed, egg laying capacity, and hatch rate. These characteristics are all nearly impossible to measure at the field level and typically a measurement of the percentage of beneficials that died after an application is the most practical metric for pest control professionals. It should also be noted that pesticides affect the different life stages of mites and insects to varying degrees. For example, an ovicide application that specifically targets the egg stage of an insect or mite may not impact the adult life stage when observing effects at the field level.
Chemical | % Mortality | Residual Length |
Hexythiazox | < 25% | < 5 days |
Etoxazole | < 25% | 2 - 4 weeks |
Acequinocyl | < 35% | 1 week |
Bifenazate | 25% - 50% | 1 week - 10 days |
Clyflumetofen | 25% - 50% | < 2 weeks |
Spiromesifen | 50% - 75% | 2 - 3 weeks |
Spirodiclofen | 50% - 75% | < 3 weeks |
Fenazaquin | > 75% | 1 week |
Pyridaben | > 75% | < 2 weeks |
Fenpyroximate | > 75% | 3 - 4 weeks |
Abamectin | > 75% | 2 weeks |
Percent mortality of adult P. Persimilis exposed to various miticides and known residual lengths, synthesized by Anna Howell
Anna Howell and Oleg Daugovish have studied the sublethal effects of miticide applications on predatory mites extensively in a lab setting. Anna and Oleg treated small bean leaves with the field labeled rate of several miticides and placed them in arenas with predatory mites along with their preferred prey. Phytoseuilus persimilis was one of the species they tested in this setting and the chemicals, Acramite, Fujimite, Kanemite, and Nealta were used as treatments. The number of eggs and young produced by P. persimilis was halved in all treatments, four and six days after treatment respectively, when compared to the control. The total number of live predators was also reduced by a minimum of 40% in all treatments when compared to the control only six days after treatment. A reduction like this in a commercial field would be disheartening after purchasing thousands of predatory mites and spending additional resources to have them released.
There are an incredible amount of details that affect predatory mite performance some of which include life stage of the prey, size of the plant canopy, vigor, and temperature and humidity. Failure of P. persimilis to suppress Twospotted spider mites to the desirable level could be due to any one of these factors. Even select fungicides have been proven to impact the egg laying capacity of P. persimilis as showcased in a study by Ditillo, Kennedy, and Walgenbach in 2016. It is important to recognize what management strategies growers can use to best support the predatory mites they are paying for to have released in their fields. Chemical applications are being highlighted here since it is one of the easiest variables that can be altered to promote beneficial activity. Release of P. persimilis after the residual activity window of the miticides listed here have expired will result in the best possible chance of a successful application. Hexythiazox, pyridaben, and spinosyns residuals have been proven to induce an insignificant amount of mortality in P. persimilis compared to control replicates as showcased by Cote, Lewis, and Schultz in 2002.
Parabug can release P. persimilis sourced from any insectary. Most insectaries will even pack specifically for drone release when instructed to do so. Packing P. persimilis in large quantities, up to 250 thousand mites in a single container in the case of P. persimilis, can help reduce the waste associated with smaller packaging and make for an overall more efficient drone application. Please reach out to Parabug with any questions.
References:
Cote, K., Lewis, E., & Schultz, P. (2002). Compatability of Acaricide Residues with Phytoseiulus persimlis and Their Effects on Tetranychus urticae. HortScience, 37(6), 906–909.
Howell, A., & Daugovish, O., Miticide Compatibility with Predatory Mites. Entomological Society of America Joint Annual Meeting Conference 2018.
J. L. Ditillo, G. G. Kennedy, J. F. Walgenbach, Effects of Insecticides and Fungicides Commonly Used in Tomato Production on Phytoseiulus persimilis (Acari: Phtyoseiidae), Journal of Economic Entomology, Volume 109, Issue 6, December 2016, Pages 2298–2308, https://doi.org/10.1093/jee/tow234.
Zalom, F. G., M. P. Bolda, S. K. Dara, and S. V. Joseph. 2018. Strawberry Pest Management Guidelines: Spider Mites. (https://www2.ipm.ucanr.edu/agriculture/strawberry/spider-mites/).
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