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Pitting good mites against bad mitesPitting good mites against bad mites

Clemson entomologist Monica Farfan is studying ways to encourage good, predatory mites, such as phytoseiid mites, to kill pest mites, such as the twospotted spider mite.

Steven Bradley

November 18, 2018

3 Min Read
Predatory mites, such as phytoseiid mites, are natural enemies to notorious crop pests.Clemson University

An entomologist at Clemson University’s Coastal Research and Education Center has been awarded a prestigious fellowship to further her work in understanding how predatory mites can be used to protect South Carolina crops from pests.

The research could lead to a reduction in pesticide use and increased production for South Carolina farmers.

Monica Farfan is studying ways to encourage good, predatory mites, such as phytoseiid mites, to kill pest mites, such as the twospotted spider mite. But first Farfan must learn about the genetic variations and feeding habits of the good mites in an effort to increase their abundance in agricultural ecosystems.

Farfan’s study is the first of its kind in the U.S. and earned her one of 101 National Institute of Food and Agriculture (NIFA) grants that support graduate and postgraduate education in agricultural-related disciplines.

“The twospotted spider mite is a gigantic pest in almost every cropping system you can imagine, from orchard fruit to row crops to veggies,” Farfan said.

Since March, Farfan has been working with assistant professor Rebecca Schmidt-Jeffris in the Vegetable Entomology Lab at the Coastal REC studying how predator-prey dynamics change with food resources and how these dynamics might benefit the two largest specialty vegetable crops in South Carolina: tomatoes and watermelons.

“Natural enemies in vegetable systems have not been as well studied as those in perennial systems, primarily because perennial crops, like fruit trees, are a more permanent habitat, making it easier to get natural enemy populations established and build from year to year,” Schmidt-Jeffris said. “Additionally, it’s more difficult to rely on biological control in the Southeast because our pest pressure is very high. In terms of basic biology research, this means that we’re really pushing boundaries of knowledge by learning about the biodiversity of natural enemies in our vegetable systems in South Carolina.”

 Farfan surveys 23 fields in a season, working with a dozen different growers and regularly traveling 450-plus miles per week from April through June. She also surveys a subset of those fields in the fall when growers do their second plantings.

Some phytoseiids eat spider mites by necessity, while others eat spider mites and a number of other pests and even pollen.

“The basis for this research is that by learning what other resources phytoseiids are utilizing, we can provide recommendations to growers who are interested in promoting these natural enemies in their cropping system, thereby reducing pesticide application costs and any associated hazards,” Farfan said. “There are biocontrol companies that specialize in rearing certain species of phytoseiid mites that growers can purchase in large abundances to disperse in their fields and greenhouses for twospotted spider mite control.”

While the use of phytoseiid mites is a well-known and effective control option against twospotted spider mites, more research is needed. Outbreaks of twospotted spider mites have increased in recent years in incidence and severity in southeastern vegetable crops it is difficult to manage them due to known pesticide resistance.

 While endemic predatory mites show promise for controlling twospotted spider mites, little is known about the factors affecting phytoseiid abundance in open-field vegetable agroecosystems. That’s where Farfan’s research comes in.

“I will do this by determining what the natural abundance and diversity of the phytoseiid community is on tomato and watermelon crops, survey both mildew pathogen and weed species in these cropping systems, test edibility of mildews and pollen of the top three weed species for phytoseiid mites and determine the importance of these alternative resources for phytoseiid survival and reproduction,” Farfan said.

Once Farfan finishes analyzing the results of her surveys from this year, Schmidt-Jeffris believes her lab will be able to determine what predatory mites are common and, through statistical modeling, better understand the landscape features and management practices that affect their abundance.

“After we have that information, future projects in my lab will answer questions like, ‘What pesticides can be used that minimize harm to the most important predator mite species?’ and ‘What are other things that can be done to increase their numbers?’ ‘Do plantings of beneficial flowers help?’” Schmidt-Jeffris said. “We are really fortunate to have Monica with us to do these studies because of her background in mite identification, which is difficult.”

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