Effects of foliar and systemic insecticides on whitefly transmission and incidence of Cucurbit yellow stunting disorder virus

Overview of research on virus-resistant breeding of melon

The development of virus-resistant melon varieties not only poses challenges in balancing melon quality and resistance but also contributes to sustainable agricultural development. This research focuses on the exploration and application of various breeding techniques to enhance the virus resistance of melon varieties. Molecular markers associated with virus resistance genes have been identified and utilized in marker-assisted selection, enabling more efficient and targeted breeding. Genetic engineering approaches have also shown promise, introducing specific resistance genes into melon genomes. In addition, traditional breeding methods, such as hybridization and selection, continue to play an important role in creating virus-resistant melon lines. The combination of these approaches holds great potential for developing melon varieties with improved virus resistance, thereby increasing yield and quality, and reducing the economic losses caused by viral infections in melon production.

Functional orthologs of honeybee CYP6AQ1 in stingless bees degrade the butenolide insecticide flupyradifurone

Flupyradifurone (FPF), a novel butenolide insecticide binding to nicotinic acetylcholine receptors (nAChRs), has been shown to be less acutely toxic to western honey bees (Apis mellifera) than other insecticides such as neonicotinoids sharing the same target-site. A previous study revealed that this is due to enhanced oxidative metabolism of FPF, mediated by three cytochrome P450 monooxygenases (P450s), including CYP6AQ1. Therefore, we followed a toxicogenomics approach and investigated the potential role of functional CYP6AQ1 orthologs in FPF metabolism from eight different bee species, including stingless bees (Tribe: Meliponini). We conducted a phylogenetic analysis on four stingless bee species, including Frieseomelitta varia, Heterotrigona itama, Melipona quadrifasciata and Tetragonula carbonaria to identify CYP6AQ1-like functional orthologs. Three non-Meliponini, but tropical bee species, i.e., Ammobates syriacus, Euglossa dilemma and Megalopta genalis were analyzed as well. We identified candidate P450s in all (neo)tropical species with greater than 61% and 67% predicted protein sequence identities when compared to A. mellifera CYP6AQ1 and Bombus terrestris CYP6AQ26, respectively. Heterologous expression in High Five insect cells of these functional orthologs revealed a common coumarin substrate profile and a preference for the O-debenzylation of bulkier substrates. Competition assays using the fluorescent probe substrate 7-benzyloxymethoxy-4-trifluoromethylcoumarin (BOMFC) with these enzymes indicated inhibition of BOMFC metabolism by increasing concentrations of FPF. Furthermore, UPLC-MS/MS analysis revealed the capacity of all CYP6AQ1-like orthologs to metabolize FPF by hydroxylation in vitro at various levels, indicating a conserved FPF detoxification potential in different (neo)tropical bee species including Meliponini. This research, employing a toxicogenomics approach, provides important insights into the potential of stingless and other tropical bee species to detoxify FPF, and highlights the significance of investigating the detoxification mechanisms of insecticides in non-Apis bee species by molecular tools to inform risk assessment and conservation efforts.

Cutting Dipping Application of Flupyradifurone against Cassava Whiteflies Bemisia tabaci and Impact on Its Parasitism in Cassava

The cassava whitefly Bemisia tabaci causes damage in cassava through the feeding and vectoring of plant viruses that cause cassava mosaic and cassava brown streak diseases. This study sought to explore the efficacy of cutting dipping in flupyradifurone for whitefly control and the impact of the mode of application on whitefly parasitism under farmer field conditions. The insecticide treatment significantly reduced adult whiteflies by 41%, nymphs by 64%, and cassava mosaic disease (CMD) incidence by 16% and increased root yield by 49%. The whitefly parasitism rate by Encarsia spp. parasitoids was 27.3 and 21.1%, while Eretmocerus spp. had 26.7 and 18.0% in control and flupyradifurone, respectively, and these differences were not significant. Electropenetrography recordings of whitefly feeding behaviour on flupyradifurone-treated plants showed significantly reduced probing activity and a delay in reaching the phloem as compared to the control. The findings from this study demonstrated that cassava cutting dipping in flupyradifurone significantly reduces whitefly numbers and cassava mosaic disease incidence, thus contributing to a significant root yield increase in cassava. Flupyradifurone applied through cutting dips does not significantly impact parasitism rates in cassava fields. Routine monitoring of parasitoids and predators in insecticide-treated versus control fields should be emphasized to determine the impact of pesticides on these beneficial non-target organisms.

Survey, Detection, Characterization of Papaya Ringspot Virus from Southern India and Management of Papaya Ringspot Disease

Papaya ringspot virus (PRSV) is a significant threat to global papaya cultivation, causing ringspot disease, and it belongs to the species Papaya ringspot virus, genus Potyvirus, and family Potyviridae. This study aimed to assess the occurrence and severity of papaya ringspot disease (PRSD) in major papaya-growing districts of Karnataka, India, from 2019 to 2021. The incidence of disease in the surveyed districts ranged from 50.5 to 100.0 percent, exhibiting typical PRSV symptoms. 74 PRSV infected samples were tested using specific primers in RT-PCR, confirming the presence of the virus. The complete genome sequence of a representative isolate (PRSV-BGK: OL677454) was determined, showing the highest nucleotide identity (nt) (95.8%) with the PRSV-HYD (KP743981) isolate from Telangana, India. It also shared an amino acid (aa) identity (96.5%) with the PRSV-Pune VC (MF405299) isolate from Maharashtra, India. Based on phylogenetic and species demarcation criteria, the PRSV-BGK isolate was considered a variant of the reported species and designated as PRSV-[IN:Kar:Bgk:Pap:21]. Furthermore, recombination analysis revealed four unique recombination breakpoint events in the genomic region, except for the region from HC-Pro to VPg, which is highly conserved. Interestingly, more recombination events were detected within the first 1710 nt, suggesting that the 5' UTR and P1 regions play an essential role in shaping the PRSV genome. To manage PRSD, a field experiment was conducted over two seasons, testing various treatments, including insecticides, biorationals, and a seaweed extract with micronutrients, alone or in combination. The best treatment involved eight sprays of insecticides and micronutrients at 30-day intervals, resulting in no PRSD incidence up to 180 days after transplanting (DAT). This treatment also exhibited superior growth, yield, and yield parameters, with the highest cost-benefit ratio (1:3.54) and net return. Furthermore, a module comprising 12 sprays of insecticides and micronutrients at 20-day intervals proved to be the most effective in reducing disease incidence and enhancing plant growth, flowering, and fruiting attributes, resulting in a maximized yield of 192.56 t/ha.

(Z)-3-hexenol primes callose deposition against whitefly-mediated begomovirus infection in tomato

Rapid callose accumulation has been shown to mediate defense in certain plant-virus interactions. Exposure to the green leaf volatile (Z)-3-hexenol (Z-3-HOL) can prime tomato (Solanum lycopersicum) for an enhanced defense against subsequent infection by whitefly-transmitted Tomato yellow leaf curl virus (TYLCV). However, the molecular mechanisms affecting Z-3-HOL-induced resistance are poorly understood. Here, we explored the mechanisms underlying Z-3-HOL-induced resistance against whitefly-transmitted TYLCV infection and the role of callose accumulation during this process. Tomato plants pre-treated with Z-3-HOL displayed callose priming upon whitefly infestation. The callose inhibitor 2-deoxy-d-glucose abolished Z-3-HOL-induced resistance, confirming the importance of callose in this induced resistance. We also found that Z-3-HOL pre-treatment enhanced salicylic acid levels and activated sugar signaling in tomato upon whitefly infestation, which increased the expression of the cell wall invertase gene Lin6 to trigger augmented callose deposition against TYLCV infection resulting from whitefly transmission. Using virus-induced gene silencing, we demonstrated the Lin6 expression is relevant for sugar accumulation mediated callose priming in restricting whitefly-transmitted TYLCV infection in plants that have been pre-treated with Z-3-HOL. Moreover, Lin6 induced the expression of the callose synthase gene Cals12, which is also required for Z-3-HOL-induced resistance of tomato against whitefly-transmitted TYLCV infection. These findings highlight the importance of sugar signaling in the priming of callose as a defense mechanism in Z-3-HOL-induced resistance of tomato against whitefly-transmitted TYLCV infection. The results will also increase our understanding of defense priming can be useful for the biological control of viral diseases.

Evaluation of the Efficacy of Flupyradifurone against Bemisia tabaci on Cassava in Tanzania

A novel butenolide insecticide-flupyradifurone (Sivanto SL 200)-was evaluated for efficacy against cassava-colonizing Bemisia tabaci whitefly under laboratory, screenhouse and field conditions. LC50 values from leaf disc spray assays were comparable for both flupyradifurone (12.7 g a.i/100 L) and imidacloprid (12.6 g a.i/100 L). Both insecticides caused high levels of adult whitefly mortality in leaf disc and leaf dip assays when compared to untreated controls. In screenhouse-based trials, longer soaking (60 min) with flupyradifurone or imidacloprid was more effective than shorter soaking durations (15 or 30 min). In field spraying experiments, flupyradifurone significantly reduced whiteflies, and both insecticides demonstrated powerful knockdown effects on whitefly adult abundances over a period up to 24 h. Single cutting dip application of flupyradifurone reduced whitefly adult abundance by 2 to 6 times, and nymphs by 2 to 13 times. Lower whitefly abundances resulting from insecticide application reduced the incidence of CMD or CBSD. In addition, in field experiments, whiteflies were fewer during the long rainy season (Masika) and on cassava variety Mkuranga1. The findings from this study demonstrate that cutting dips with flupyradifurone could be incorporated as a management tactic against cassava whiteflies. This would ideally be combined in an IPM strategy with other cassava virus and virus vector management tactics including host-plant resistance, phytosanitation and the use of clean seed.

A reproducible and sensitive method for generating high-quality transcriptomes from single whitefly salivary glands and other low-input tissues

Transcriptomic studies are an important tool for understanding the molecular pathways underlying host plant use by agricultural pests, including vectors of damaging plant pathogens. Thus far, bulk RNA-Seq has been the main approach for non-model insects. This method relies on pooling large numbers of whole organisms or hundreds of individually dissected organs. The latter approach is logistically challenging, may introduce artifacts of handling and storage, and is not compatible with biological replication. Here, we tested an approach to generate transcriptomes of individual salivary glands and other low-input body tissues from whiteflies (Bemisia tabaci MEAM1), which are major vectors of plant viruses. By comparing our outputs to published bulk RNA-Seq datasets for whole whitefly bodies and pools of salivary glands, we demonstrate that this approach recovers similar numbers of transcripts relative to bulk RNA-Seq in a tissue-specific manner, and for some metrics, exceeds performance of bulk tissue RNA-Seq. Libraries generated from individual salivary glands also yielded additional novel transcripts not identified in pooled salivary gland datasets, and had hundreds of enriched transcripts when compared with whole head tissues. Overall, our study demonstrates that it is feasible to produce high quality, replicated transcriptomes of whitefly salivary glands and other low-input tissues. We anticipate that our approach will expand hypothesis-driven research on salivary glands of whiteflies and other Hemiptera, thus enabling novel control strategies to disrupt feeding and virus transmission.

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 toxicogenomics approach reveals characteristics supporting the honey bee (Apis mellifera L.) safety profile of the butenolide insecticide flupyradifurone

Flupyradifurone, a novel butenolide insecticide, selectively targets insect nicotinic acetylcholine receptors (nAChRs), comparable to structurally different insecticidal chemotypes such as neonicotinoids and sulfoximines. However, flupyradifurone was shown in acute toxicity tests to be several orders of magnitude less toxic to western honey bee (Apis mellifera L.) than many other insecticides targeting insect nAChRs. The underlying reasons for this difference in toxicity remains unknown and were investigated here. Pharmacokinetic studies after contact application of [¹⁴C]flupyradifurone to honey bees revealed slow uptake, with internalized compound degraded into a few metabolites that are all practically non-toxic to honey bees in both oral and contact bioassays. Furthermore, receptor binding studies revealed a lack of high-affinity binding of these metabolites to honey bee nAChRs. Screening of a library of 27 heterologously expressed honey bee cytochrome P450 enzymes (P450s) identified three P450s involved in the detoxification of flupyradifurone: CYP6AQ1, CYP9Q2 and CYP9Q3. Transgenic Drosophila lines ectopically expressing CYP9Q2 and CYP9Q3 were significantly less susceptible to flupyradifurone when compared to control flies, confirming the importance of these P450s for flupyradifurone metabolism in honey bees. Biochemical assays using the fluorescent probe substrate 7-benzyloxymethoxy-4-(trifluoromethyl)-coumarin (BOMFC) indicated a weak, non-competitive inhibition of BOMFC metabolism by flupyradifurone. In contrast, the azole fungicides prochloraz and propiconazole were strong nanomolar inhibitors of these flupyradifurone metabolizing P450s, explaining their highly synergistic effects in combination with flupyradifurone as demonstrated in acute laboratory contact toxicity tests of adult bees. Interestingly, the azole fungicide prothioconazole is only slightly synergistic in combination with flupyradifurone - an observation supported by molecular P450 inhibition assays. Such molecular assays have value in the prediction of potential risks posed to bees by flupyradifurone mixture partners under applied conditions. Quantitative PCR confirmed the expression of the identified P450 genes in all honey bee life-stages, with highest expression levels observed in late larvae and adults, suggesting honey bees have the capacity to metabolize flupyradifurone across all life-stages. These findings provide a biochemical explanation for the low intrinsic toxicity of flupyradifurone to honey bees and offer a new, more holistic approach to support bee pollinator risk assessment by molecular means.

Natural Infection Rate of Known Tomato chlorosis virus-Susceptible Hosts and the Influence of the Host Plant on the Virus Relationship With Bemisia tabaci MEAM1

Tomato chlorosis virus (ToCV; genus Crinivirus, family Closteroviridae) was identified in tomato crops in São Paulo State, Brazil, in 2006. Management strategies to control external sources of inoculum are necessary, because chemical control of the whitefly vector Bemisia tabaci Middle East-Asia Minor 1 (MEAM1) has not efficiently prevented virus infections and no commercial tomato varieties or hybrids are resistant to this crinivirus. We first evaluated the natural infection rate of some known wild and cultivated ToCV-susceptible hosts and their attractiveness for B. tabaci MEAM1 oviposition. Physalis angulata was the most susceptible to natural infection in all six exposures in 2018 and 2019. No plants of Capsicum annuum 'Dahra' or Chenopodium album became infected. Solanum melongena 'Napoli' had only two infected plants of 60 exposed. Capsicum annuum and Chenopodium album were the least preferred, and Nicotiana tabacum and S. melongena were the most preferred for whitefly oviposition. In addition, from 2016 to 2019, we surveyed different tomato crops and the surrounding vegetation to identify ToCV in weeds and cultivated plants in the region of Sumaré, São Paulo State. Only S. americanum, vila vila (S. sisymbriifolium), and Chenopodium album were found naturally infected, with incidences of 18, 20, and 1.4%, respectively. Finally, we estimated the ToCV titer (U.S. and Brazilian isolates ToCV-FL and ToCV-SP, respectively) by quantitative reverse transcription PCR in different ToCV-susceptible host plants and evaluated the relationship between virus acquisition and transmission by B. tabaci MEAM1. The results clearly showed significant differences in ToCV concentrations in the tissues of ToCV-susceptible host plants, which appeared to be influenced by the virus isolate. The concentration of the virus in plant tissues, in turn, directly influenced the ToCV-B. tabaci MEAM1 relationship and subsequent transmission to tomato plants. To minimize or prevent damage from tomato yellowing disease through management of external sources of ToCV, it is necessary to correctly identify potentially important ToCV-susceptible hosts in the vicinity of new plantings.

Defence priming in tomato by the green leaf volatile (Z)-3-hexenol reduces whitefly transmission of a plant virus

Green leaf volatiles (GLVs) can induce defence priming, that is, can enable plants to respond faster or more strongly to future stress. The effects of priming by GLVs on defence against insect herbivores and pathogens have been investigated, but little is known about the potential of GLVs to prime crops against virus transmission by vector insects. Here, we tested the hypothesis that exposure to the GLV Z-3-hexenol (Z-3-HOL) can prime tomato (Solanum lycopersicum) for an enhanced defence against subsequent Tomato yellow leaf curl virus (TYLCV) transmission by the whitefly Bemisia tabaci. Bioassays showed that Z-3-HOL priming reduced subsequent plant susceptibility to TYLCV transmission by whiteflies. Z-3-HOL treatment increased transcripts of jasmonic acid (JA) biosynthetic genes and increased whitefly-induced transcripts of salicylic acid (SA) biosynthetic genes in plants. Using chemical inducers, transgenics and mutants, we demonstrated that induction of JA reduced whitefly settling and successful whitefly inoculation, while induction of SA reduced TYLCV transmission by whiteflies. Defence gene transcripts and flavonoid levels were enhanced when whiteflies fed on Z-3-HOL-treated plants. Moreover, Z-3-HOL treatment reduced the negative impact of whitefly infestation on tomato growth. These findings suggest that Z-3-HOL priming may be a valuable tool for improving management of insect-transmitted plant viruses.

Foliar Spraying of Tomato Plants with Systemic Insecticides: Effects on Feeding Behavior, Mortality and Oviposition of Bemisia tabaci (Hemiptera: Aleyrodidae) and Inoculation Efficiency of Tomato Chlorosis Virus

Simple Summary

The whitefly Bemisia tabaci (Hemiptera: Aleyrodidae) causes serious losses to vegetable, ornamental and fiber crops, including tomato plants, mainly as a vector of economically important viruses. Among the most important viruses affecting tomato is the tomato chlorosis virus (ToCV) (Closteroviridae: Crinivirus), which is semi-persistently transmitted by whiteflies. Effective management of this pest is crucial to reduce the spread of vector-borne diseases and to reduce crop damage and losses. In this study we evaluated the effect of systemic insecticides (cyantraniliprole, acetamiprid and flupyradifurone) on the feeding behavior, mortality and oviposition of B. tabaci MEAM1 and their ability to interfere with the inoculation of ToCV in tomato plants. Our findings indicate that systemic insecticides cause high mortality when compared to untreated plants. Also, we found that flupyradifurone affects stylet activities of B. tabaci and significantly reduce phloem ingestion, a behavior that is closely linked to the transmission of ToCV. Overall, our findings indicate that flupyradifurone may contribute to management of this pest and ToCV in tomato crops.

Abstract

Tomato chlorosis virus (ToCV) is a phloem-limited crinivirus transmitted by whiteflies and seriously affects tomato crops worldwide. As with most vector-borne viral diseases, no cure is available, and the virus is managed primarily by the control of the vector. This study determined the effects of the foliar spraying with the insecticides, acetamiprid, flupyradifurone and cyantraniliprole, on the feeding behavior, mortality, oviposition and transmission efficiency of ToCV by B. tabaci MEAM1 in tomato plants. To evaluate mortality, oviposition and ToCV transmission in greenhouse conditions, viruliferous whiteflies were released on insecticide-treated plants at different time points (3, 24 and 72 h; 7 and 14 days) after spraying. Insect mortality was higher on plants treated with insecticides; however, only cyantraniliprole and flupyradifurone differed from them in all time points. The electrical penetration graph (DC-EPG) technique was used to monitor stylet activities of viruliferous B. tabaci in tomato plants 72 h after insecticide application. Only flupyradifurone affected the stylet activities of B. tabaci, reducing the number and duration of intracellular punctures (pd) and ingestion of phloem sap (E2), a behavior that possibly resulted in the lower percentage of ToCV transmission in this treatment (0–60%) in relation to the control treatment (60–90%) over the periods evaluated. Our results indicate that flupyradifurone may contribute to management of this pest and ToCV in tomato crops.

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.

Imidacloprid Pesticide Regulates Gynaikothrips uzeli (Thysanoptera: Phlaeothripidae) Host Choice Behavior and Immunity Against Lecanicillium lecanii (Hypocreales: Clavicipitaceae)

We attempted to develop an efficient management strategy against gall thrips (Gynaikothrips uzeli Zimmermann (Thysanoptera: Phlaeothripidae)) via the combined application of a systemic insecticide (imidacloprid) and an entomopathogenic fungus (Lecanicillium lecanii Zimmerman (Hypocreales: Clavicipitaceae)). The attraction of G. uzeli to Ficus microcarpa volatiles after imidacloprid treatment was weaker than for untreated plants, which could be due to modulation of volatile metabolite profiles by imidacloprid. The toxicity of L. lecanii against nymph and adult thrips was much higher for those that fed on plants treated with a 50% lethal concentration (LC50) of imidacloprid than for the controls. Phenoloxidase (PO) activity was significantly inhibited in treated G. uzeli, while hemocyte abundances were not different in treated and healthy individuals. Thus, imidacloprid impacted the PO-related humoral immunity of G. uzeli, but not their cellular immunity. Overall, F. microcarpa treated with imidacloprid at LC50 concentrations exhibited volatile profiles that decreased the attraction of G. uzeli and also indirectly increased the pathogenicity of L. lecanni by inhibiting the humoral immunity of gall thrips. The results reported here suggest that combined application of imidacloprid and L. lecanii could be used as a new integrated control strategy against gall thrips.

Validation of a Landscape-Based Model for Whitefly Spread of the Cucurbit Yellow Stunting Disorder Virus to Fall Melons

The cucurbit yellow stunting disorder virus (CYSDV) transmitted by Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) has caused significant reductions in fall melon (Cucumis melo L.) yields in Yuma County, Arizona. In a recent landscape-based study, we found evidence that cotton and spring melon fields increased abundance of B. tabaci and spread of CYSDV infection in fall melon fields. Here, we show that a statistical model derived from data collected in 2011-2012 and based on areas of cotton and spring melon fields located within 1,500 m from edges of fall melon fields was sufficient to retrospectively predict incidence of CYSDV infection in fall melon fields during 2007-2010. Nevertheless, the slope of the association between areas of spring melon fields and incidence of CYSDV infection was three times smaller in 2007-2010 than in 2011-2012, whereas the slope of the association between areas of cotton fields and incidence of CYSDV infection was consistent between study periods. Accordingly, predictions were more accurate when data on areas of cotton alone were used as a basis for prediction than when data on areas of cotton and spring melons were used. Validation of this statistical model confirms that crop isolation has potential for reducing incidence of CYSDV infection in fall melon fields in Yuma County, although isolation from cotton may provide more consistent benefits than isolation from spring melon.

Field evaluation of Cucurbit yellow stunting disorder virus transmission by Bemisia tabaci

Cucurbit yellow stunting disorder virus (CYSDV) is a whitefly-transmitted Crinivirus (Closteroviridae) that impacts melon production in many parts of the world including the USA. It has been responsible for melon crop loss in the southwestern U.S. since 2006 when it was first identified. Control strategies have revolved mainly around chemical control, but research to identify suitable products and approaches to implementing them have lagged. The current study investigated the performance of four systemic insecticides in the field while concurrently tracking CYSDV disease progression after controlled and natural whitefly inoculation of young melon plants. Assessments of virus incidence were made using two different visual observation methods in concert with ELISA analyses of leaf disks samples collected biweekly. Infection rates were consistently lowest in plots treated with the butenolide insecticide flupyradifurone while dinotefuran was second in efficacy measures. Flupyradifurone also held whitefly densities to their lowest numbers relative to the other treatments. Two other insecticides, imidacloprid and cyantraniliprole, exacerbated virus incidence in multiple trials. Further investigation into the anomalous finding of increased virus incidence due to insecticide application is ongoing.