Tobacco thrips (Frankliniella fusca) also have a taste for peanut, and they spread the plant virus causing spotted wilt disease. A new guide in the open-access Journal of Integrated Pest Management details the biology and management of tobacco thrips in peanut crops. (Photo by Jena Johnson, University of Georgia Department of Entomology)

By Gabrielle LaTora

Gabrielle LaTora

Few people other than farmers think about the toll that insect-transmitted viruses have on crop yields. Tomato spotted wilt orthotospovirus (TSWV)—the virus that causes spotted wilt disease in peanut—caused over $27 million (US) in financial losses during the 2020 peanut season in the state of Georgia. Although TSWV infects several crops, it can be devastating for Georgia’s peanut growers, who produce more peanuts than any other state in the U.S.

Peanut plants with spotted wilt disease develop discolored leaflets and abnormal pods and kernels. Often, whole plants become stunted. The primary vector of TSWV in Georgia peanuts is the tobacco thrips (Frankliniella fusca). Besides transmitting TSWV, larvae and adults directly injure peanut plants when feeding, causing additional foliar symptoms and yield losses.

Thrips can be difficult to identify. Life stages of Frankliniella fusca on peanut are shown here: (A) egg; (B) first instar larva; (C) second instar larva; (D) prepupa; (E) pupa; (F) brachypterous adults, female (left) and male. (Scale bar = 0.5 millimeters). (Photos by Yi-Ju Chen and Pin-Chu Lai, Ph.D.)

In “Frankliniella fusca (Thysanoptera: Thripidae), the Vector of Tomato Spotted Wilt Orthotospovirus Infecting Peanut in the Southeastern United States,” published this month in the open-access Journal of Integrated Pest Management, my colleagues at the University of Georgia Vector-Virus Interactions Lab and I provide an overview of F. fusca‘s biology and pest status, including its morphology, life cycle, vector biology, management, and economic impact. Our hope is that this article can be used as a go-to for researchers, extension professionals, farmers, and anyone who wants to learn more about F. fusca. Thrips can be difficult to identify, so we have provided photos and descriptions of each F. fusca life stage and photos of short-winged and long-winged morphs.

Because peanut is an annual crop, F. fusca overwinter in weed hosts surrounding peanut fields until peanuts are planted again in the spring. Many of these plants are also TSWV hosts—F. fusca acquire TSWV as first- and second-instar larvae most likely by feeding on infected weeds before peanuts are available, then moving into croplands and inoculating peanuts in the late spring.

Using TSWV-resistant peanut cultivars has been the most common and successful non-chemical management strategy to date. Resistant cultivars are not immune to the virus, but they exhibit milder symptoms and higher yields than susceptible cultivars. Many growers employ avoidance and disruption strategies, too—they may shift planting dates to avoid peak thrips populations or modify planting patterns to disrupt thrips’ landing cues. Most growers also head off TSWV outbreaks by controlling thrips with prophylactic applications of insecticides, like phorate and imidacloprid. In addition to controlling thrips, phorate—an organophosphate—can actually suppress spotted wilt disease by inducing peanut defenses.

Tomato spotted wilt virus can cause stunted growth in peanut plants, shown in the plants at left shown here, compared with non-infected plants at right. (Photo by Pin-Chu Lai, Ph.D.)

Foliar symptoms associated with tomato spotted wilt virus in peanut include concentric ringspots, chlorosis (yellowing of leaves), and abnormal development of leaflets. (Photo by Pin-Chu Lai, Ph.D.)

Peanut Rx, a disease risk index developed by researchers and extension specialists from southeastern land-grant universities, is a tool used by growers to evaluate the risks of peanut diseases, including spotted wilt, on their farms. Peanut Rx uses individual farm and management characteristics, like plant density, row pattern, irrigation, pesticide programs, and prior disease incidence, to predict disease risks each year.

Although most Georgia peanut growers use a variety of methods to manage F. fusca and TSWV, there are still opportunities to diversify IPM programs. At this time, there are no standardized monitoring protocols or economic thresholds for F. fusca in peanuts. Very few studies have evaluated biological control agents, like thrips-parasitic nematodes and generalist predators, against F. fusca. Although TSWV-resistant cultivars are common, resistance to thrips themselves is not a targeted trait for peanut breeding programs. By “stacking” TSWV and thrips resistance traits, peanut cultivars can become even more resilient.

Gabrielle LaTora is a research professional and lab manager at the Srinivasan Lab at the University of Georgia Griffin Campus in Griffin, Georgia. Twitter: @Gab_LaTora. Email: gabrielle.latora@uga.edu.