Comparing Host Plant Resistance, Repellent Mulches, and At-Plant Insecticides for Management of Bemisia tabaci MEAM1 (Hemiptera: Aleyrodidae) and Tomato Yellow Leaf Curl Virus

Tomato yellow leaf curl virus: Characteristics, influence, and regulation mechanism

Tomato yellow leaf curl virus (TYLCV), a DNA virus belonging to the genus Begomovirus, significantly impedes the growth and development of numerous host plants, including tomatoes and peppers. Due to its rapid mutation rate and frequent recombination events, achieving complete control of TYLCV proves exceptionally challenging. Consequently, identifying resistance mechanisms become crucial for safeguarding host plants from TYLCV-induced damage. This review article delves into the global distribution, dispersal patterns, and defining characteristics of TYLCV. Moreover, the intricate interplay between TYLCV and various influencing factors, such as insect vectors, susceptible host plants, and abiotic stresses, plays a pivotal role in plant-TYLCV interactions. The review offers an updated perspective on recent investigations focused on plant response mechanisms to TYLCV infection, including the intricate relationship between TYLCV, whiteflies, and regulatory factors. This comprehensive analysis aims to establish a foundation for future research endeavors exploring the molecular mechanisms underlying TYLCV infection and the development of plant resistance through breeding programs.

Evaluation of Biopesticides for Management of Bemisia tabaci Middle East-Asia Minor 1 (Hemiptera: Aleyrodidae) in Florida

The sweetpotato whitefly, Bemisia tabaci MEAM1, is a pest known to significantly impact tomato development and yields through direct damage and virus transmission. To manage this pest, the current study compared the effectiveness of various insecticide rotations. Field trials included rotations involving synthetic insecticides, biochemicals, and microbial agents, applied according to their highest labeled concentrations. The results indicated that while standard synthetic insecticides consistently reduced whitefly egg and nymph counts significantly, microbial biopesticide rotations also achieved reductions, although less consistently. This study demonstrated that while traditional chemical treatments remain highly effective, microbial biopesticides containing Beauveria bassiana and Cordyceps javanica present a viable alternative to manage MEAM1 in tomato fields. The data generated in this study provided baseline information for further investigations to determine the potential for optimizing integrated pest management (IPM) and insecticide resistance management (IRM) strategies by incorporating microbial biopesticides in rotations with a variety of modes of action to sustainably manage B. tabaci MEAM1 populations in agricultural settings.

The amount and chemistry of acylsugars affects sweetpotato whitefly (Bemisia tabaci) oviposition and development, and tomato yellow leaf curl virus incidence, in field grown tomato plants

The objectives of this study were to ascertain the impact of endogenous production of trichome-exuded acylsugars on insects and insect transmitted virus by evaluating tomato lines and their hybrids bred for acylsugar production under field settings on whiteflies and the whitefly-transmitted tomato yellow leaf curl virus. Specifically, we utilized a diverse array of tomato lines and hybrids bred for changes in acylsugar amount or type, grown in three field trials under natural whitefly and virus pressure, to investigate whether the amount of accumulated acylsugars and or the chemical profile of the acylsugars were associated with greater resistance to whiteflies and reduced incidence of tomato yellow leaf curl virus. There was considerable variation in the abundance of whitefly eggs and nymphs and incidence of tomato yellow leaf curl virus across experiments and between entries. Increasing amount of acylsugars accumulated by the tomato entries was associated with a reduction in the abundance of whitefly eggs and nymphs and a reduction in the incidence of tomato yellow leaf curl virus. Additionally, we identified lines with changes in several acylsugar fatty acids that were associated with decreased abundance of whitefly eggs and nymphs and reduced incidence of tomato yellow leaf curl virus. These results inform the utility of acylsugars as a host plant defense system for improving resistance to whiteflies and their transmitted viruses, with potential for reducing insecticides as a control method for whiteflies and provide breeding targets for optimization of existing acylsugar tomato lines to create lines with the most efficacious amount and chemistry of acylsugars.

Sesame as an Alternative Host Plant to Establish and Retain Predatory Mirids in Open-Field Tomatoes

The silverleaf whitefly (Bemisia tabaci) and the South America tomato pinworm (Tuta absoluta) are two of the most destructive pests of tomato. Open-field tomato production frequently relies on chemical treatments, which has been shown to lead to pesticide resistance. The integration of biological control using predatory mirid bugs is an effective alternative method for managing these pests. However, methods to establish and maintain populations of zoophytophagous mirids are not adequately described. We explored the potential use of two mirids naturally occurring in Florida, Nesidiocoris tenuis and Macrolophus praeclarus. We conducted 6 field experiments over 4 consecutive years to develop a strategy to maintain the mirids. Pre-plant inoculation of tomato plants did not lead to their establishment, likely due to the low prevalence of prey. We explored the use of sesame (Sesamum indicum) to retain the mirids. Intercropping sesame maintained the populations of N. tenuis throughout the duration of the crop. Macrolophus praeclarus never established in any of the open-field experiments. Nesidiocoris tenuis damage was minimal (<1 necrotic ring/plant) and mirid damage was reduced in the presence of sesame. Our results show that intercropping sesame may provide a means to utilize mirids to manage B. tabaci, an established pest, and provide options to tomato growers should T. absoluta invade USA.

Biocontrol Potential of Endophytic Plant-Growth-Promoting Bacteria against Phytopathogenic Viruses: Molecular Interaction with the Host Plant and Comparison with Chitosan

Endophytic plant-growth-promoting bacteria (ePGPB) are interesting tools for pest management strategies. However, the molecular interactions underlying specific biocontrol effects, particularly against phytopathogenic viruses, remain unexplored. Herein, we investigated the antiviral effects and triggers of induced systemic resistance mediated by four ePGPB (Paraburkholderia fungorum strain R8, Paenibacillus pasadenensis strain R16, Pantoea agglomerans strain 255-7, and Pseudomonas syringae strain 260-02) against four viruses (Cymbidium Ring Spot Virus-CymRSV; Cucumber Mosaic Virus-CMV; Potato Virus X-PVX; and Potato Virus Y-PVY) on Nicotiana benthamiana plants under controlled conditions and compared them with a chitosan-based resistance inducer product. Our studies indicated that ePGPB- and chitosan-treated plants presented well-defined biocontrol efficacy against CymRSV and CMV, unlike PVX and PVY. They exhibited significant reductions in symptom severity while promoting plant height compared to nontreated, virus-infected controls. However, these phenotypic traits showed no association with relative virus quantification. Moreover, the tested defense-related genes (Enhanced Disease Susceptibility-1 (EDS1), Non-expressor of Pathogenesis-related genes-1 (NPR1), and Pathogenesis-related protein-2B (PR2B)) implied the involvement of a salicylic-acid-related defense pathway triggered by EDS1 gene upregulation.

Combining Cultural Tactics and Insecticides for the Management of the Sweetpotato Whitefly, Bemisia tabaci MEAM1, and Viruses in Yellow Squash

The sweet potato whitefly, Bemisia tabaci MEAM1 Gennadius (Hemiptera: Aleyrodidae), and the complex of viruses it transmits are major limiting factors to squash production in the southeastern United States. At this time, insecticides are extensively relied upon for the management of whiteflies and, indirectly, whitefly-transmitted viruses. The development of a multi-faceted, integrated pest management (IPM) program is needed to increase the sustainability and profitability of squash production. Experiments in 2018 and 2019 evaluated the effects of insect exclusion netting (IEN) in combination with selected pesticides on whitefly population dynamics and virus incidence in greenhouse-grown squash seedlings. Field experiments from 2018 to 2021 evaluated the effects of mulch type (UV-reflective mulch, live mulch, and white plastic mulch), row covers, and insecticides on whitefly population dynamics, silver leaf disorder (SSL) intensity, virus symptom severity, and marketable yield. IEN significantly reduced whiteflies and virus incidence on squash seedlings in the greenhouse study. In the field mulch study, lower whitefly abundance and SSL intensity, as well as reduced virus symptom severity, were observed in plots with reflective mulch compared with white plastic or live mulch. In the insecticide/row cover study, whitefly abundance, SSL intensity, and virus symptom severity were lowest in the row cover and cyantraniliprole- and flupyradifurone-treated plots. Field plots with row covers and those with UV-reflective mulch consistently produced the greatest marketable yields. These findings demonstrate that growers can reduce whitefly and virus pressure and preserve yields in squash production in the southeastern United States by combining cultural and chemical tactics, including row covers, UV-reflective mulch, and select insecticides.

A Maximum Dose Bioassay to Assess Efficacy of Key Insecticides Against Bemisia tabaci MEAM1 (Hemiptera: Aleyrodidae)

The whitefly, Bemisia tabaci MEAM1 Gennadius causes serious losses to Florida vegetable and ornamental production. In 2019, a maximum dose bioassay was administered to 20 field populations of B. tabaci MEAM1 collected from various economic and weed hosts across south Florida to assess insecticide efficacy. The maximum dose bioassay tests the top labeled rate of the insecticide against B. tabaci adults on treated cotton leaves in a Petri dish over a 72-h period. A susceptible laboratory colony of B. tabaci MEAM1 and a colony of B. tabaci MED were also tested. Survival over 72 h was used to produce an area under the maximum dose curve, which was used to compare insecticide effects on different populations. Overall, imidacloprid demonstrated the poorest efficacy, dinotefuran and flupyradifurone were the most effective, and bifenthrin, cyantraniliprole, and thiamethoxam tended to group together, providing intermediate control. Across populations tested, survival in whitefly adults treated with dinotefuran was 50% lower than whiteflies treated with imidacloprid, about 33% lower than whiteflies treated with thiamethoxam, bifenthrin, and cyantraniliprole, and 10% lower than whiteflies treated with flupyradifurone. Efficacy of bifenthrin was less than imidacloprid on some populations, particularly from the Homestead area. Imidacloprid and thiamethoxam had no effect on mortality of the MED population when it was tested after 22 mo in culture without exposure to insecticides, although 7 mo later, these materials resulted in some mortality for the MED population.

Bemisia tabaci on Vegetables in the Southern United States: Incidence, Impact, and Management

Simple Summary

The sweetpotato whitefly, Bemisia tabaci, was initially discovered in the United States in 1894 but was not considered an economic insect pest on various agricultural crops across the southern and western states. After the introduction of B. tabaci Middle East-Asia Minor 1 (MEAM1) into the United States around 1985, the insect rapidly spread throughout the Southern United States to Texas, Arizona, and California. Extreme field outbreaks occurred on vegetable and other crops in those areas. The sweetpotato whitefly is now regarded as one of the most destructive insect pests in vegetable production systems in the Southern United States. The direct and indirect plant damage caused by B. tabaci has led to substantial economic losses in vegetable crops. Bemisia tabaci outbreaks on vegetables in Georgia resulted in significant economic losses of 132.3 and 161.2 million US dollars (USD) in 2016 and 2017, respectively. Therefore, integrated pest management (IPM) tactics are warranted, including cultural control by manipulation of production practices, resistant vegetable varieties, biological control using various natural enemies, and the judicious use of insecticides.

Abstract

Bemisia tabaci Gennadius (Hemiptera: Aleyrodidae) is among the most economically important insect pests of various vegetable crops in the Southern United States. This insect is considered a complex of at least 40 morphologically indistinguishable cryptic species. Bemisia tabaci Middle East-Asia Minor 1 (MEAM1) was initially introduced in the United States around 1985 and has since rapidly spread across the Southern United States to Texas, Arizona, and California, where extreme field outbreaks have occurred on vegetable and other crops. This pest creates extensive plant damage through direct feeding on vegetables, secreting honeydew, causing plant physiological disorders, and vectoring plant viruses. The direct and indirect plant damage in vegetable crops has resulted in enormous economic losses in the Southern United States, especially in Florida, Georgia, and Texas. Effective management of B. tabaci on vegetables relies mainly on the utilization of chemical insecticides, particularly neonicotinoids. However, B. tabaci has developed considerable resistance to most insecticides. Therefore, alternative integrated pest management (IPM) strategies are required, such as cultural control by manipulation of production practices, resistant vegetable varieties, and biological control using a suite of natural enemies for the management of the pest.

Virus Accumulation and Whitefly Performance Modulate the Role of Alternate Host Species as Inoculum Sources of Tomato Yellow Leaf Curl Virus

Evaluating alternate hosts that facilitate the persistence of a virus in the landscape is key to understanding virus epidemics. In this study, we explored the role of several plant species (eggplant, pepper, and Palmer amaranth) as inoculum sources of tomato yellow leaf curl virus (TYLCV) and as reservoirs for its insect vector, Bemisia tabaci (Gennadius). All inoculated species were infected with TYLCV, but whiteflies acquired fewer viral copies via feeding from pepper and eggplant than from tomato and Palmer amaranth. Further, back-transmission assays to recipient tomato resulted in TYLCV infection only when TYLCV was acquired from Palmer amaranth or tomato. Analysis suggested that the role of plant species as TYLCV inoculum sources may be determined by the accumulation of viral copies in the plant, and consequently in the insect vector. In addition, results showed that all three alternate species could sustain populations of B. tabaci, while differentially influencing fitness of whiteflies. Eggplant was a superior host for whiteflies, whereas whitefly survival was compromised on pepper. Together, we demonstrate that both plant-virus and plant-vector interactions could influence the role of an alternate host in TYLCV epidemics, and in our region of study we highlight the potential risk of hosts such as Palmer amaranth in the spread of TYLCV.

Biopesticides for Management of Bemisia tabaci MEAM1 (Hemiptera: Aleyrodidae) and Tomato Yellow Leaf Curl Virus

The sweetpotato whitefly, Bemisia tabaci MEAM1 Gennadius, is a global pest of tomato, transmitting Tomato yellow leaf curl virus (TYLCV). Management of B. tabaci is challenging in part because of its ability to develop resistance to insecticides. Biopesticides include materials that control B. tabaci via mechanisms that do not select for resistance. Field experiments were conducted in the spring and fall of 2016 and 2017 at the University of Florida's Gulf Coast Research and Education Center in west central Florida to compare biopesticides to conventional insecticides for management of B. tabaci and TYLCV. Insecticide rotations were designed in part around the concept that conventional insecticide programs should group modes of action according to 5-wk treatment intervals, corresponding to an estimated 5-wk generation time for the pest. In 2016, when tomato was treated during the first 5-wk treatment interval with either biopesticides or neonicotinoid insecticides, insecticidal soap contributed to a reduction in whitefly egg numbers and percentage TYLCV that was comparable to results achieved with dinotefuran. In contrast, egg numbers and virus incidence in plants treated with kaolin clay tended to be numerically higher than the untreated control. In spring 2017, comparisons of biopesticides and conventional ovicides/nymphicides during the second 5-wk treatment interval showed that biopesticides can provide comparable reduction in nymph numbers to conventional insecticides. While data from these trials confirm that biopesticides can reduce numbers of whitefly eggs and nymphs, they indicate that season-long programs of the biopesticides evaluated may not reduce transmission of TYLCV below economically acceptable levels.

The potential geographical distribution and phenology of Bemisia tabaci Middle East/Asia Minor 1, considering irrigation and glasshouse production

The Bemisia tabaci species complex is one of the most important pests of open field and protected cropping globally. Within this complex, one species (Middle East Asia Minor 1, B. tabaci MEAM1, formerly biotype B) has been especially problematic, invading widely and spreading a large variety of plant pathogens, and developing broad spectrum pesticide resistance. Here, we fit a CLIMEX model to the distribution records of B. tabaci MEAM1, using experimental observations to calibrate its temperature responses. In fitting the model, we consider the effects of irrigation and glasshouses in extending its potential range. The validated niche model estimates its potential distribution as being considerably broader than its present known distribution, especially in the Americas, Africa and Asia. The potential distribution of the fitted model encompasses the known distribution of B. tabaci sensu lato, highlighting the magnitude of the threat posed globally by this invasive pest species complex and the viruses it vectors to open field and protected agriculture.

Priming Melon Defenses with Acibenzolar-S-methyl Attenuates Infections by Phylogenetically Distinct Viruses and Diminishes Vector Preferences for Infected Hosts

Plant virus management is mostly achieved through control of insect vectors using insecticides. However, insecticides are only marginally effective for preventing virus transmission. Furthermore, it is well established that symptoms of virus infections often encourage vector visitation to infected hosts, which exacerbates secondary spread. Plant defense elicitors, phytohormone analogs that prime the plant immune system against attack, may be a viable approach for virus control that complements insecticide use by disrupting pathologies that attract vectors. To explore this, we tested the effect of a commercial plant elicitor, acibenzolar-S-methyl (ASM), on infection rates, virus titers, and symptom development in melon plants inoculated with one of two virus species, Cucumber mosaic virus (CMV) and Cucurbit yellow stunting disorder virus (CYSDV). We also conducted behavioral assays to assess the effect of ASM treatment and virus inoculation on vector behavior. For both pathogens, ASM treatment reduced symptom severity and delayed disease progression. For CYSDV, this resulted in the attenuation of symptoms that encourage vector visitation and virion uptake. We did observe slight trade-offs in growth vs. defense following ASM treatment, but these effects did not translate into reduced yields or plant performance in the field. Our results suggest that immunity priming may be a valuable tool for improving management of insect-transmitted plant viruses.

Spatial and Temporal Physiognomies of Whitefly and Tomato Yellow Leaf Curl Virus Epidemics in Southwestern Florida Tomato Fields

Epidemics of tomato yellow leaf curl virus (TYLCV; species Tomato yellow leaf curl begomovirus) have been problematic to tomato production in the southeastern United States since the first detection of the virus in Florida in the late 1990s. Current strategies for management focus on farm-centric tactics that have had limited success for controlling either TYLCV or its whitefly vector. Areawide pest management (AWPM)-loosely defined as a coordinated effort to implement management strategies on a regional scale-may be a viable management alternative. A prerequisite for development of an AWPM program is an understanding of the spatial and temporal dynamics of the target pathogen and pest populations. The objective of this study was to characterize populations of whitefly and TYLCV in commercial tomato production fields in southwestern Florida and utilize this information to develop predictors of whitefly density and TYLCV disease incidence as a function of environmental and geographical factors. Scouting reports were submitted by cooperating growers located across approximately 20,000 acres in southwestern Florida from 2006 to 2012. Daily weather data were obtained from several local weather stations. Moran's I was used to assess spatial relationships and polynomial distributed lag regression was used to determine the relationship between weather variables, whitefly, and TYLCV. Analyses showed that the incidence of TYLCV increased proportionally with mean whitefly density as the season progressed. Nearest-neighbor analyses showed a strong linear relationship between the logarithms of whitefly densities in neighboring fields. A similar relationship was found with TYLCV incidences. Correlograms based on Moran's I showed that these relationships extended beyond neighboring fields and out to approximately 2.5 km for TYLCV and up to 5 km for whitefly, and that values of I were generally higher during the latter half of the production season for TYLCV. Weather was better at predicting whitefly density than at predicting TYLCV incidence. Whitefly density was best predicted by the number of days with an average temperature between 16 and 24°C (T16to24), relative humidity (RH) over the previous 31 days, and vapor pressure deficit over the last 8 days. TYLCV incidence was best predicted by T16to24, RH, and maximum wind speed over the previous 31 days. Results of this study helped to identify the extent to which populations of whitefly and TYLCV exist over the agricultural landscape of southwestern Florida, and the environmental conditions that favor epidemic growth. This information was used to propose an approach to AWPM for timing control measures for managing TYLCV epidemics.