Progress report for GS19-210
Sweetpotato whitefly, Bemisia tabaci, is a major economic pest of row crop vegetables causing widespread feeding damage and vectoring many viruses, including tomato yellow leaf curl virus (TYLCV), which leads to considerable yield loss. Growers are facing increasing challenges in controlling B. tabaci as populations during major growing seasons have become increasingly unpredictable and resistant to conventional insecticides. In an effort to develop a more sustainable integrated pest management program, alternative methods for controlling B. tabaci are being explored that take advantage of the whitefly’s natural host seeking behaviors.
Since visual stimuli play a dominant role in host searching behavior, implementing visual traps that display the most attractive wavelengths in the visual spectrum shows great potential in reducing B. tabaci infestations. In addition, many natural repellents including kaolin clay can repel whiteflies visually or mask the attractive volatiles produced by their vegetable host. Preliminary studies have already shown that kaolin clay has proven to act as a moderately successful, natural repellent of B. tabaci adults. However, little to no research has investigated the efficacy of kaolin in combination with other natural repellents and as part of a completed IPM system.
This study will highlight the potential for implementing a “push/pull” system utilizing a combination of natural repellents and visual traps to keep whiteflies below the economic threshold in row crop vegetable. Using this system will reduce the need to use conventional insecticides and lower the associated negative impacts on environmental and human health while increasing benefits for growers.
- Determine how visual attractiveness in TYLCV-infected tomato changes whitefly behavior.
- Determine how B. tabaci behavior is influenced by olfactory cues in healthy tomato vs. TYLCV-infected tomato and compare how this behavior changes when combined with the most attractive visual cues found in Objective 1.
- Determine the efficacy of several natural repellents on whitefly settling in tomato under greenhouse conditions.
- Conduct field trials to test the efficacy of kaolin clay as a natural repellent for B. tabaci nymphs and adults when applied alone and in combination with several botanic oils.
In 2018, we had been conducting field and lab research regarding the effects that kaolin clay has on repelling whitefly, Bemisia tabaci, when sprayed as a particulate barrier on a vegetable host. Our results with this preliminary research showed that kaolin worked best when combined with insecticides. With the potential synergistic effects of kaolin acting as a carrying agent for other chemicals, we conducted a literature review and found several naturals repellents derived from botanic oils that could serve as potential candidates for combining with kaolin. In the end, we chose limonene as a repellent and conducted two large field trials in both watermelon and tomato during Fall, 2019. Our four primary treatments were the untreated control, kaolin alone, limonene alone, and both kaolin and limonene combined.
In addition, we conducted the lab work pertaining to objectives 1 and 2 in the grant proposal. Materials and methods can be obtained from the published paper mentioned in the results below.
The results yielded from our lab work can be found in the following publication:
Johnston, N. and Martini, X., 2020. The Influence of Visual and Olfactory Cues in Host Selection for Bemisia tabaci Biotype B in the Presence or Absence of Tomato Yellow Leaf Curl Virus. Insects, 11(2), p.115.
This paper was recently published, and we have acknowledged the SSARE grant’s contribution to funding this research.
Regarding our field trials in watermelon and tomato, we found that kaolin and limonene combined have an additive effect in repellency, were twice as effective as either product alone, and over four times more effective at reducing whitefly populations compared to the untreated control! This trend was also reflected in our tomato yield, where all tomatoes were processed and graded by industry standards. We found that the total quality weight of all harvested tomatoes from combined kaolin/limonene treatments was more than double the weight harvested from equivalent control tomato plots.
In watermelon, an insecticide treatment was used as an additional treatment for comparison to our repellent (limonene). Importantly, we found that kaolin and limonene combined reduced whitefly populations with the same efficiency as conventional insecticides, however, no yield data was collected since even low whitefly populations were enough to transmit Cucurbit leaf crumple virus (CuLCrV) and destroy the entire yield (across all treatments). As conventional systems rely mostly on insecticides, these new methods of combining kaolin and repellents offer growers a potentially novel, organic method for controlling one of the most destructive agricultural pests in Florida.
Educational & Outreach Activities
Most of the planned talks and presentations regarding this research have either been cancelled or postponed due to the complications caused by COVID-19. As a majority of the data for the project needed to be collected in 2019, more resources were planned to spearhead educational outreach in 2020, which has now been delayed. We are currently organizing an educational symposium for local growers and research scientists in conjunction with another UF/IFAS research station next spring.
We published an IFAS extension article outlining the whitefly behaviors discovered in our lab, the efficacy of kaolin clay, and some practical applications for growers in the field. "Using Kaolin to Manage Whiteflies: A Novel Approach" https://nwdistrict.ifas.ufl.edu/phag/2019/03/01/using-kaolin-to-manage-whiteflies-a-novel-approach/
We gained an increased understanding of how to manage field scale projects in conjunction with other researchers. There is always a learning experience to be gained when realizing that sustainable agricultural practices are easy to theorize but difficult to implement. For my part, it is humbling to realize that my area of expertise (entomology) is only one aspect of all the problems that growers must face. For example, even if whitefly populations are controlled, crops might still have difficulty growing due to poor soil quality, mismanagement of water resources, or even a fungal infection (which happened in our watermelon). These problems have shown me the importance of collaboration between scientists with diverse areas of agricultural expertise.