Using salicylic acid-responsive promoters to drive the expression of jasmonic acid-regulated genes enhances plant resistance to whiteflies

BACKGROUND

Jasmonic acid (JA) is an important phytohormone used to defend against herbivores, but it does not respond to whitefly feeding. Conversely, another phytohormone, salicylic acid (SA), is induced when plants are fed upon by whiteflies. JA has a better anti-whitefly effect than SA; however, there is limited research on how to effectively improve plant resistance by utilizing the different responses of these phytohormones to whitefly feeding.

RESULTS

We discovered that protease inhibitors 8 (PI8) and terpene synthase 10 (TPS10) located downstream of the JA-regulated pathway in plants have anti-whitefly effects, but these two genes were not induced by whitefly feeding. To identify whitefly-inducible promoters, we compared the transcriptome data of tobacco fed upon by Bemisia tabaci with the control. We focused on pathogenesis-related (PR) genes because they are known to be induced by SA. Among these PR genes, we found that expression levels of pathogenes-related protein 1C-like (PR1) and glucose endo-1,3-beta-glucosidase (BGL) can be significantly induced by whitefly feeding and regulated by SA. We then engineered the whitefly-inducible promoters of BGL and PR1 to drive the expression of PI8 and TPS10. We found that compared with control plants that did not induce the expression of PI8 or TPS10, transformed plants expressing PI8 or TPS10 under the PR1 or BGL promoter showed a significant increase in the expression levels of PI8 and TPS10 after whitefly infection, significantly improving their resistance to whiteflies.

CONCLUSION

Our findings suggest that using SA-inducible promoters as tools to drive the expression of JA-regulated defense genes can enhance plant resistance to whiteflies. Our study provides a novel pathway for the enhancement of plant resistance against insects. © 2024 Society of Chemical Industry.

Emergence of watermelon chlorotic stunt virus in melon and watermelon in the southwestern United States

Watermelon (Citrullus lanatus) and melon (Cucumis melo) plants with leaves exhibiting mosaic symptoms or chlorotic spotting, respectively, along with limited foliar distortion, predominantly on newer growth, were observed in commercial fields throughout Yuma County, AZ, and Imperial County, CA, in fall 2023. Older leaves also exhibited yellowing typical of infection by whitefly-transmitted viruses common in the region, and whiteflies (Bemisia tabaci) were prevalent in fields. Symptomatic plants were tested using a multiplex RT-PCR for cucurbit yellow stunting disorder virus (CYSDV), cucurbit chlorotic yellows virus (CCYV), squash vein yellowing virus (SqVYV), and cucurbit aphid-borne yellows virus (CABYV) (Mondal et al., 2023), and separately for cucurbit leaf crumple virus (CuLCrV; F: TCAAAGGTTTCCCGCTCTGC, R: TCAAAGGTTTCCCGCTCTGC). Most plants were infected with CYSDV, which has been widely prevalent during the fall production season since its emergence in 2006, but not with the other tested viruses. Although the yellowing of older leaves near the crown was typical of symptoms resulting from CYSDV infection, the unusual symptoms on newer growth suggested the possibility of infection by a begomovirus. Rolling circle amplification and DNA sequencing of nucleic acid extract from a symptomatic melon plant collected in Dome Valley, AZ, identified the presence of watermelon chlorotic stunt virus (WmCSV), a bipartite begomovirus (Geminiviridae) (Jones et al., 1988; Lecoq, 2017), but no other begomoviruses. Sequencing of the complete WmCSV genome from this melon plant determined that DNA A (GenBank accession #PQ399661) shared 99% identity with WmCSV isolates from cactus (MW588390) and melon (KY124280) in Sonora, Mexico, and DNA B (PQ399662) shared 96% and 94% identity with WmCSV isolates from watermelon in Palestine (KC462553) and Sonora (KY124281), respectively. PCR with primers targeting WmCSV DNA A (F: CATGGAGATGAGGTTCCCCATTCT and R: GCTCGTAGGTCGATTCAACGGCCT) and DNA B (F: AGATACAACGTATGGGCAGCATT and R: TACAGATCCCARTCGATGAGACT) was used for secondary confirmation. Sequencing of amplified products confirmed both WmCSV DNA A and B in 12/15 initial melon samples. PCR using the DNA A or B primers confirmed the presence of WmCSV from additional watermelon and melon samples collected from Yuma County (31 positive/37 tested) and Imperial County (20/22). This is the first report of WmCSV in cucurbits in the United States (U.S.); the virus was previously identified in watermelon (Domínguez-Durán et al., 2018) and cactus (Opuntia auberi) from Sonora, Mexico, and from one cactus (O. cochenillifera), lamb's ears (Stachys byzantine), and an unknown Solanum plant from a botanical garden in Arizona (Fontanelle et al., 2021). The geographic distribution of WmCSV and the presence of similar symptoms in melon in 2022 suggests that it may have been present in the U.S. for at least a year. Interestingly, nearly all melon and some watermelon plants infected with WmCSV were co-infected with CYSDV. Most fall cucurbits in the Sonoran Desert production region become infected with CYSDV, and many are also infected with CCYV and/or SqVYV (Mondal et al., 2023). However, incidence of CCYV (4/63) and SqVYV (2/63) in the region was extremely low during fall 2023. Research is in progress to determine the potential impact of WmCSV on the cucurbit virus complex in the Sonoran Desert and the U.S. as a whole, and to understand the epidemiological factors that influence WmCSV infection and spread.

Cotton leaf curl Multan virus subverts the processing of hydroxyproline-rich systemin to suppress tobacco defenses against insect vectors

Insect vector-virus-plant interactions have important ecological and evolutionary implications. The constant struggle of plants against viruses and insect vectors has driven the evolution of multiple defense strategies in the host as well as counter-defense strategies in the viruses and insect vectors. Cotton leaf curl Multan virus (CLCuMuV) is a major causal agent of cotton leaf curl disease in Asia and is exclusively transmitted by the whitefly Bemisia tabaci. Here, we report that plants infected with CLCuMuV and its betasatellite CLCuMuB enhance the performance of the B. tabaci vector, and βC1 encoded by CLCuMuB plays an important role in begomovirus-whitefly-tobacco tripartite interactions. We showed that CLCuMuB βC1 suppresses the jasmonic acid signaling pathway by interacting with the subtilisin-like protease 1.7 (NtSBT1.7) protein, thereby enhancing whitefly performance on tobacco plants. Further studies revealed that in wild-type plants, NtSBT1.7 could process tobacco preprohydroxyproline-rich systemin B (NtpreproHypSysB). After CLCuMuB infection, CLCuMuB βC1 could interfere with the processing of NtpreproHypSysB by NtSBT1.7, thereby impairing plant defenses against whitefly. These results contribute to our understanding of tripartite interactions among virus, plant, and whitefly, thus offering ecological insights into the spread of vector insect populations and the prevalence of viral diseases.

Occurrence and Distribution of Major Cassava Pests and Diseases in Cultivated Cassava Varieties in Western Kenya

Cassava is an important food crop in western Kenya, yet its production is challenged by pests and diseases that require routine monitoring to guide development and deployment of control strategies. Field surveys were conducted in 2022 and 2023 to determine the prevalence, incidence and severity of cassava mosaic disease (CMD) and cassava brown streak disease (CBSD), whitefly numbers and incidence of cassava green mite (CGM) in six counties of western Kenya. Details of the encountered cassava varieties were carefully recorded to determine the adoption of improved varieties. A total of 29 varieties were recorded, out of which 13 were improved, although the improved varieties were predominant in 60% of fields and the most widely grown variety was MM96/4271. The CMD incidence was higher in 2022 (26.4%) compared to 2023 (10.1%), although the proportion of CMD attributable to whitefly infection was greater (50.6%) in 2023 than in 2022 (18.0%). The CBSD incidence in 2022 was 6.4%, while in 2023 it was 4.1%. The CMD incidence was significantly lower (5.9%) for the improved varieties than it was for the local varieties (35.9%), although the CBSD incidence did not differ significantly between the improved (2.3%) and local varieties (9.7%). Cassava brown streak virus (CBSV) and Ugandan cassava brown streak virus (UCBSV) were both detected. Most infections were single CBSV infections (82.9%), followed by single UCBSV (34.3%) and coinfection with both viruses (16.7%). Whiteflies were more abundant in 2023, in which 28% of the fields had super-abundant populations of >100/plant, compared to 5% in 2022. KASP SNP genotyping designated 92.8% of the specimens as SSA-ECA for 2022, while it was 94.4% for 2023. The cassava green mite incidence was 65.4% in 2022 compared to 79.9% in 2023. This study demonstrates that cassava viruses, whiteflies and cassava green mites continue to be important constraints to cassava production in western Kenya, although the widespread cultivation of improved varieties is reducing the impact of cassava viruses. The more widespread application of high-quality seed delivery mechanisms could further enhance the management of these pests/diseases, coupled with wider application of IPM measures for whiteflies and mites.

Cucurbit Leaf Crumple Virus (CuLCrV) is Seed Transmitted in Yellow Squash (Cucurbita pepo L.)

The traditional understanding of begomovirus transmission exclusively through the whitefly Bemisia tabaci (Gennadius) has shifted with findings of seed transmission in some begomoviruses over the last decade. We investigated the seed transmissibility of cucurbit leaf crumple virus (CuLCrV), a bipartite begomovirus that has recently emerged as a severe constraint for yellow squash (Cucurbita pepo L.) production in the southeastern United States. We found high concentration of CuLCrV in male and female flower tissues of infected squash, including pollen and ovules. The virus infiltrated the fruit tissues including the endocarp and funiculus, which are anatomically positioned adjacent to the seeds. In seeds, CuLCrV was detected in the endosperm and embryo where there are no vascular connections, in addition to the seed coat. The virus was detected in the radicle, plumule, cotyledonary leaves, and true leaves of seedlings grown from seeds collected from infected fruits. In the grow-out test conducted, CuLCrV infections ranged from 17-56% of the progeny plants. To ensure that partial viral genome fragments were not being mistaken for replicative forms of the virus, we performed RCA ̶ PCR and amplified complete DNA-A and DNA-B of CuLCrV from seed tissues, seedlings, progeny plants of CuLCrV infected squash. Near complete DNA-A and DNA-B sequences of CuLCrV were recovered from a progeny plant, further validating our findings. Our results demonstrate that CuLCrV can translocate from vegetative to reproductive tissues of yellow squash, persist within the seeds, and subsequently induce infection in progeny plants, confirming its capacity for seed transmission.

Biological and physiological effects in Bemisia tabaci feeding on tomatoes endophytically colonized by Beauveria bassiana

BACKGROUND

Entomopathogenic fungi (EPF) treatment of plants may affect the survival and feeding preferences of herbivorous pests. However, comprehensive studies on the fitness across their entire life cycle, feeding behavior, and physiological changes in herbivores consuming EPF-treated plants within the tripartite interactions of EPF, plants, and pests are still limited. In this study, we utilized life tables, electrical penetration graph (EPG), and metabolomics to uncover the biological and physiological characteristics of Bemisia tabaci on tomato plants inoculated with Beauveria bassiana through root irrigation.

RESULTS

Our study indicated that Beauveria bassiana Bb252 can penetrate the entire tissue from the point of inoculation, primarily colonizing the intercellular spaces and vascular tissue. However, this colonization is temporary, lasting no more than 35 days. Moreover, the population fitness and feeding behavior of Bemisia tabaci on tomato plants treated with Beauveria bassiana via root irrigation were significantly affected, showing a substantial 41.4% decrease in net reproductive rate (R0), a notable reduction in watery salivation, and shortened phloem ingestion. Lastly, we observed a significant decrease in hormones and amino acids of whiteflies that fed on Beauveria bassiana-treated tomato plants by root irrigation.

CONCLUSIONS

Our results indicated that the endophyte, Beauveria bassiana Bb252, reduced demographic fitness of Bemisia tabaci by altering its hormones and amino acids levels. These findings enhance our understanding of multitrophic interactions in integrated pest management. © 2024 Society of Chemical Industry.

Composition and abundance of midgut plasma membrane proteins in two major hemipteran vectors of plant viruses, Bemisia tabaci and Myzus persicae

Multiple species within the order Hemiptera cause severe agricultural losses on a global scale. Aphids and whiteflies are of particular importance due to their role as vectors for hundreds of plant viruses, many of which enter the insect via the gut. To facilitate the identification of novel targets for disruption of plant virus transmission, we compared the relative abundance and composition of the gut plasma membrane proteomes of adult Bemisia tabaci (Hemiptera: Aleyrodidae) and Myzus persicae (Hemiptera: Aphididae), representing the first study comparing the gut plasma membrane proteomes of two different insect species. Brush border membrane vesicles were prepared from dissected guts, and proteins extracted, identified and quantified from triplicate samples via timsTOF mass spectrometry. A total of 1699 B. tabaci and 1175 M. persicae proteins were identified. Following bioinformatics analysis and manual curation, 151 B. tabaci and 115 M. persicae proteins were predicted to localize to the plasma membrane of the gut microvilli. These proteins were further categorized based on molecular function and biological process according to Gene Ontology terms. The most abundant gut plasma membrane proteins were identified. The ten plasma membrane proteins that differed in abundance between the two insect species were associated with the terms "protein binding" and "viral processes." In addition to providing insight into the gut physiology of hemipteran insects, these gut plasma membrane proteomes provide context for appropriate identification of plant virus receptors based on a combination of bioinformatic prediction and protein localization on the surface of the insect gut.

Transcriptome data reveal beneficial effects of Rickettsia (Rickettsiales: Rickettsiaceae) on Bemisia tabaci(Hemiptera: Aleyrodidae) through nutritional factors and defense mechanisms

Whitefly Bemisia tabaci (Hemiptera: Aleyrodidae) is a destructive insect pest of many crops. Rickettsia infection in different cryptic species of B. tabaci has been observed worldwide. Understanding the interactions between these 2 organisms is critical to developing Rickettsia-based strategies to control B. tabaci and thereby reduce the transmission of related vector-borne viruses. In this study, we investigated the effects of Rickettsia infection on the biological characteristics of the Middle East Asia Minor 1 (MEAM1) strain of B. tabaci through biological analysis of infected and uninfected individuals. The results of this study suggest that Rickettsia may confer fitness benefits. These benefits include increased fertility, improved survival rates, accelerated development, and resulted in female bias. We also investigated the transcriptomics impact of Rickettsia infection on B. tabaci by performing a comparative RNA-seq analysis of nymphs and adult females, both with and without the infection. Our analysis revealed 218 significant differentially expressed genes (DEGs) in infected nymphs compared to uninfected ones and 748 significant DEGs in infected female adults compared to their uninfected whiteflies. Pathway analysis further revealed that Rickettsia can affect many important metabolic pathways in whiteflies. The results suggest that Rickettsia plays an essential role in energy metabolism, and nutrient synthesis in the B. tabaci MEAM1, and depends on metabolites obtained from the host to ensure its survival. Overall, our findings suggest that Rickettsia has beneficial effects on B. tabaci and offered insights into the potential molecular mechanisms governing the interactions between Rickettsia and B. tabaci MEAM1.

Susceptibility of Yellow Squash and Zucchini Cultivars to the Sweetpotato Whitefly, Bemisia tabaci Gennadius (MEAM1), in the Southeastern United States

The sweetpotato whitefly, Bemisia tabaci (Gennadius) Middle East-Asia Minor 1 (MEAM1), causes significant losses to vegetable crops directly by sap-feeding, inducing plant physiological disorders, and elevating the build-up of sooty mold, and indirectly by transmitting plant viruses. In this study, we evaluated the susceptibility of 20 yellow squash and zucchini (Cucurbita pepo) cultivars to MEAM1, across three growing seasons in the southeastern United States. Weekly sampling of the numbers of MEAM1 adults, nymphs, and eggs were conducted from the fourth week after seed sowing and across 6 weeks during the summer and fall of 2021 and five weeks during the fall of 2022. In general, adult whitefly populations were high during the first week of sampling but decreased as the seasons progressed. The zucchini cultivar 'Black Beauty' harbored the most adults, while 'Green Eclipse Zucchini' was the least attractive zucchini cultivar to the adults in fall 2022. For yellow squash, 'Early Summer' (summer 2021) and 'Amberpic 8455' (summer 2021 and fall 2022) were the cultivars with the highest adult populations, while 'Lioness' (summer 2021) and 'Gourmet Gold Hybrid' (fall 2022) harbored the lowest adult counts. The whitefly egg counts across both vegetables trailed those of adults and peaked in the second week of sampling. The counts of nymphs increased as the seasons progressed, but there was a decline after the second week during fall 2021. For the yellow squash cultivars, 'Gourmet Gold Hybrid', (summer 2021 and fall 2022), 'Lioness', and 'Fortune' (summer 2021) recorded the highest yields. For zucchini, 'Golden Glory' (summer 2021) was the top performer. These results provide valuable information for whitefly management in yellow squash and zucchini based on host plant susceptibility and yield.

Role of aminopeptidase N-like in the acquisition of begomoviruses by Bemisia tabaci, the whitefly vector

Sri Lankan cassava mosaic virus (SLCMV) is a prominent causative agent of cassava mosaic disease in Asia and relies on the whitefly Bemisia tabaci cryptic complex for its transmission. However, the molecular mechanisms involved in SLCMV transmission by B. tabaci have yet to be understood. In this study, we identified an aminopeptidase N-like protein (BtAPN) in B. tabaci Asia II 1, an efficient vector of SLCMV, which is involved in the SLCMV transmission process. Through the use of glutathione S-transferase pull-down assay and LC-MS/MS analysis, we demonstrated the interaction between BtAPN and the coat protein (CP) of SLCMV. This interaction was further confirmed in vitro, and we observed an induction of BtAPN gene expression following SLCMV infection. By interfering with the function of BtAPN, the quantities of SLCMV were significantly reduced in various parts of B. tabaci Asia II 1, including the whole body, midgut, hemolymph, and primary salivary gland. Furthermore, we discovered that BtAPN is conserved in B. tabaci Middle East-Asia Minor 1 (MEAM1) and interacts with the CP of tomato yellow leaf curl virus (TYLCV), a begomovirus known to cause severe damage to tomato production. Blocking BtAPN with antibody led to a significant reduction in the quantities of TYLCV in whitefly whole body and organs/tissues. These results demonstrate that BtAPN plays a generic role in interacting with the CP of begomoviruses and positively regulates their acquisition by the whitefly.

Assessment of Prickly Sida as a Potential Inoculum Source for Sida Golden Mosaic Virus in Commercial Snap Bean Farms in Georgia, United States

Sida golden mosaic virus (SiGMV), an obligate pathogen that infects snap beans (Phaseolus vulgaris), is known to infect prickly sida (Sida spinosa L.), which is a common weed in agricultural farms in Georgia. Prickly sida has also been reported as a suitable host of sweetpotato whitefly (Bemisia tabaci), the vector of SiGMV. Despite being a host for both SiGMV and its vector, the role of prickly sida as a reservoir and inoculum source for SiGMV in snap bean farms has not been evaluated. This study was conducted to document the occurrence of SiGMV-infected prickly sida plants and to assess its potential role as a source of SiGMV inoculum in snap bean farms. A survey of 17 commercial snap bean farms conducted in spring 2021 confirmed the presence of SiGMV-infected prickly sida in southern Georgia. In fall 2021 and 2022, on-farm field trials were conducted in four commercial farms where SiGMV-infected prickly sida plants were documented earlier as a part of survey in spring 2021. The spatial distribution and temporal patterns of adult whiteflies and SiGMV on snap bean were compared between macroplots (13.7 × 30.5 m) "with prickly sida" or "without prickly sida" that were at least 232 m apart from each other. We did not observe any consistent differences in counts of adult whiteflies between macroplots with or without prickly sida in the four commercial farms. SiGMV infection was detected earlier and with higher incidences in snap bean macroplots "with prickly sida" compared with macroplots "without prickly sida." An apparent disease gradient was observed in two of the four farms assessed. Higher SiGMV incidences were observed on the edges of macroplots "with prickly sida." These findings indicate prickly sida as a potential natural reservoir and a source for SiGMV spread in snap bean farms in southern Georgia.

Temporal changes in the levels of virus and betasatellite DNA in B. tabaci feeding on CLCuD affected cotton during the growing season

Cotton, a key source of income for Pakistan, has suffered significantly by cotton leaf curl disease (CLCuD) since 1990. This disease is caused by a complex of phylogenetically-related begomovirus (genus Begomovirus, family Geminiviridae) species and a specific betasatellite (genus Betasatellite, family Tolecusatellitidae), cotton leaf curl Multan betasatellite. Additionally, another DNA satellite called alphasatellite (family Alphasatellitidae), is also frequently associated. All these virus components are vectored by a single species of whitefly (Bemisia tabaci). While many factors affect cotton productivity, including cotton variety, sowing time, and environmental cues such as temperature, humidity, and rainfall, CLCuD is a major biotic constraint. Although the understanding of begomoviruses transmission by whiteflies has advanced significantly over the past three decades, however, the in-field seasonal dynamics of the viruses in the insect vector remained an enigma. This study aimed to assess the levels of virus and betasatellite in whiteflies collected from cotton plants throughout the cotton growing season from 2014 to 2016. Notably, begomovirus levels showed no consistent pattern, with minimal variations, ranging from 0.0017 to 0.0074 ng.μg-1 of the genomic DNA in 2014, 0.0356 to 0.113 ng.μg-1 of the genomic DNA in 2015, and 0.0517 to 0.0791 ng.μg-1 of the genomic DNA in 2016. However, betasatellite levels exhibited a distinct pattern. During 2014 and 2015, it steadily increased throughout the sampling period (May to September). While 2016 showed a similar trend from the start of sampling (July) to September but a decline in October (end of sampling). Such a study has not been conducted previously, and could potentially provide valuable insights about the epidemiology of the virus complex causing CLCuD and possible means of controlling losses due to it.

A new pest suction machine to control Bemisia tabaci (Hemiptera: Aleyrodidae) in tomato greenhouses

The sweetpotato whitefly Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) is challenging to control using chemical pesticides owing to its resistance to many insecticides. Thus, there has been an increasing demand for alternative control measures. Thus, this study evaluated the efficacy of a newly designed pest suction machine to manage whiteflies on tomato plants (Solanum lycopersicum L.) (Solanales: Solanaceae) in greenhouses over 2 seasons. The suction machine comprised a battery-powered cart with a mounted suction unit, an ultrasonic device, and green lights. Ultrasonic irradiation provided non-contact vibration, facilitating the movement of adult whiteflies away from the plants, and green lights attracted them to the suction device. This combination effectively captured whitefly adults, even with a weak suction force, saving electricity consumption. The efficacy of suction machine was further evaluated by measuring the number of whitefly adults caught by the machine and the number of adults and nymphs remaining on the tomato leaves. The whitefly population was considerably lower in the treated blocks than in the non-treated blocks in the autumn trial. The machine reduced the density of whitefly adults without using chemical pesticides. Although a lot of optimizations would be required, suction control is an additional and alternative strategy that may be incorporated in the integrated pest management of whiteflies on greenhouse tomato plants.

Tracking Sweet Potato Leaf Curl Virus through Field Production: Implications for Sustainable Sweetpotato Production and Breeding Practices

Sweet potato leaf curl virus (SPLCV) is a whitefly-transmitted begomovirus infecting sweetpotato and other morning glory (Convolvulaceae) species worldwide. The virus is widespread at the USDA, ARS, U.S. Vegetable Laboratory (USVL), and testing of germplasm maintained in the breeding program indicates nearly 100% infection in storage roots of materials propagated for at least four years. Prior to the public release of new germplasm, viruses must be eliminated via laborious and time-consuming meristem-tip culture. The identification of virus-free seedlings early in the selection process can offer an alternative to meristem-tip culture. In this study, we investigated the transmission of SPLCV over two years of consecutive field plantings (early and late) of sweetpotato. While SPLCV is endemic at the USVL, virus transmission pressure over the typical cultivation season is unknown, and avoidance of virus transmission paired with the selection and maintenance of clean material may be a viable alternative to virus elimination. In 2022, the storage roots of 39 first-year seedling (FYS) selections were tested for SPLCV after early-season cultivation, revealing a single selection (2.6%) with a positive test. Similar testing was conducted in 2023 with no SPLCV-positive FYS selections detected. To further assess SPLCV acquisition in the field, replicated late-season plantings of each selected FYS (n = 37) were monitored from planting to harvest. Testing was conducted at 60 and 120 days after planting (DAP). Approximately 35% of the bulk samples were infected at 60 DAP, and infection increased to 52.3% by 120 DAP. Testing of individuals within selected positive bulked samples did not support 100% infection at harvest. Altogether, these results demonstrate that SPLCV transmission during early planting is sufficiently low to facilitate the maintenance of virus-free selections, offering an alternative to virus cleaning and a cultivation strategy that may be leveraged for production.

Influence of Alternative Prey on the Functional Response of a Predator in Two Contexts: With and without Intraguild Predation

In biological control, joint releases of predators and parasitoids are standard. However, intraguild predation (IGP) can occur when a predator attacks a parasitoid, potentially affecting pest control dynamics. In addition to the focal prey (FP), Trialeurodes vaporariorum, the intraguild predator (IG-predator) Geocoris punctipes can consume the parasitoid Eretmocerus eremicus (IG-prey). In this IGP context with multiple prey, an alternative prey (AP), like the aphid Myzus persicae, may influence interactions. Theory predicts that, in simple interactions, a predator's functional response (FR) to the FP changes with the presence of an AP. However, whether this holds in an IGP context is unknown. In this study, we empirically tested that prediction. Our results show that without IGP, G. punctipes exhibits a generalized FR with and without AP. Nevertheless, with IGP, the predator exhibited a Type II FR at low and high AP densities, increasing pressure on the FP and potentially favoring short-term biological control strategies. However, when 25 AP were offered, the predator's response shifted, underscoring the importance of monitoring AP densities to prevent potential disruptions in FP control. In both contexts, the increase in AP produced a handling time increase and a decrease in consumption rate. These results indicate that the theoretical prediction of the effect of AP on the FR is met only under specific conditions, and the complexity of multitrophic interactions must be considered.

The Synergistic Effect of Lemongrass Essential Oil and Flometoquin, Flonicamid, and Sulfoxaflor on Bemisia tabaci (Genn.) (Hemiptera: Aleyrodidae): Insights into Toxicity, Biochemical Impact, and Molecular Docking

The whitefly, Bemisia tabaci (Genn.), is one of the most dangerous polyphagous pests in the world. Eco-friendly compounds and new chemical insecticides have gained recognition for whitefly control. In this study, the toxicity and biochemical impact of flometoquin, flonicamid, and sulfoxaflor, alone or combined with lemongrass essential oil (EO), against B. tabaci was studied. In addition, a molecular docking study was conducted to assess the binding affinity of the tested compounds to AchE. Based on the LC values, the descending order of the toxicity of the tested compounds to B. tabaci adults was as follows: sulfoxaflor > flonicamid > flometoquin > lemongrass EO. The binary mixtures of each of the tested compounds with lemongrass EO exhibited synergism in all combinations, with observed mortalities ranging from 15.09 to 22.94% higher than expected for an additive effect. Sulfoxaflor and flonicamid, alone or in combination with lemongrass EO, significantly inhibited AchE activity while only flonicamid demonstrated a significant impact on α-esterase, and none of the tested compounds affected cytochrome P450 or GST. However, the specific activity of P450 was significantly inhibited by the lemongrass/sulfoxaflor mixture while α-esterase activity was significantly inhibited by the lemongrass/flometoquin mixture. Moreover, the lemongrass EO and all the tested insecticides exhibited significant binding affinity to AchE with energy scores ranging from -4.69 to -7.06 kcal/mol. The current findings provide a foundation for utilizing combinations of essential oils and insecticides in the integrated pest management (IPM) of B. tabaci.

Functional response of Franklinothrips vespiformis (Thysanoptera: Aeolothripidae) to eggs and nymphs of Bemisia tabaci (Hemiptera: Aleyrodidae)

The Middle East Asia Minor 1 biotype of Bemisia tabaci Gennadius (Hemiptera: Aleyrodidae) is a greenhouse and field crop pest of global significance. The objective of this study was to assess the potential of the generalist predatory thrips, Franklinothrips vespiformis Crawford (Thysanoptera: Aeolothripidae), as a biological control agent for B. tabaci. This was achieved by determining the functional responses of F. vespiformis larvae and adults to the egg and nymphal stages of B. tabaci under laboratory conditions. Analyses consisted of 10 replicates of each predator and prey stage combination on bean leaf discs for a 24-h period. Following logistic regression analyses to determine the functional response type exhibited, response parameters were estimated with nonlinear least squares regression using Roger's equation. Results showed that F. vespiformis larvae and adults exhibited a Type II functional response when feeding on immature B. tabaci. The handling times (Th) of F. vespiformis larvae and adults were magnitudes higher for B. tabaci nymphs than they were for eggs, which were in part driven by the higher attack rates (a) observed on eggs. The maximum attack rate (T/Th) for B. tabaci eggs and nymphs exhibited by first-stage larvae, second-stage larvae, and adult F. vespiformis increased with increasing predator age. Results from this study suggest that F. vespiformis larvae and particularly adults are promising biological control agents for B. tabaci and are efficient predators at both low and high prey densities.

Control of sweet potato whitefly (Bemisia tabaci) using entomopathogenic fungi under optimal and suboptimal relative humidity conditions

BACKGROUND

Sweet potato whitefly (Bemisia tabaci) is one of the most destructive pests to an extensive range of crops and vegetables. Pesticide-dependent management programs have led to severe health problems, including pesticide poisoning and cancer in human beings, as well as pesticide resistance in insect pests. Entomopathogenic fungi (EPF) are considered safe and highly effective against many pests. Therefore, identifying the pathogenicity and virulence of EPFs against Bemisia tabaci is a valuable addition to the management of their infestations. In this study, we investigated the efficacy of conidia suspensions of Aschersonia aleyrodis, Isaria fumosorosea, Beauveria bassiana, and Akanthomyces muscarius (= Lecanicillium muscarium) against nymphal stages of Bemisia tabaci in cucumber seedlings under both optimal and suboptimal conditions.

RESULTS

All of the EPFs demonstrated significant ovicidal effects, with the highest cumulative mortalities observed in Aschersonia aleyrodis (96.46%) and I. fumosorosea-treated (94.60%) seedlings against host eggs and crawlers. Similarly, in the L4-instars experiment, Aschersonia aleyrodis and I. fumosorosea were the most efficient, resulting in cumulative mortalities of 94.82% and 94.75%, respectively. However, Bemisia tabaci cumulative mortalities on seedlings treated with Akanthomyces muscarius (78.36%) and Beauveria bassiana (85.90%) were also significantly different from untreated seedlings (7.10%). Under suboptimal relative humidity (RH) conditions (≤ 45% RH), Aschersonia aleyrodis exhibited greater tolerance to harsh conditions, causing a significantly higher infection rate in L1-L2 nymphs (~92%) compared to the approximately 32% infected young nymphs observed in I. fumosorosea-treated seedlings.

CONCLUSION

All the selected EPF were more effective against the young nymphal instars. Our results also highlight the efficacy of Aschersonia aleyrodis under suboptimal conditions. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Whitefly-Transmitted Viruses of Cucurbits in the Southern United States

Cucurbits are economically important crops that are widely cultivated in many parts of the world, including the southern US. In recent years, higher temperatures have favored the rapid build-up of whiteflies in the fall-grown cucurbits in this region. As a result, whitefly-transmitted viruses (WTVs) have severely impacted the marketable yield of cucurbits. In this review, we discuss three major groups of WTVs negatively impacting cucurbit cultivation in the southern US, including begomoviruses, criniviruses, and ipomoviruses. Here, we discuss the available information on the biology, epidemiology and advances made toward detecting and managing these viruses, including sources of resistance and cultural practices.

Enhancing Coccinella Beetle Biological Pest Control via a Floral Approach in Cucumber Greenhouse

Flower-rich habitats are crucial for promoting biodiversity and ecosystem services within agricultural ecosystems, such as pollination and pest control. The present study investigates the efficacy of employing floral structures as a criterion for the selection of plant species in order to enhance the attraction of natural enemies within cucumber greenhouses, consequently augmenting floral resources. The results of our study provide evidence that flower strips have a beneficial effect on the fitness of critical natural predators, while not facilitating the proliferation of detrimental insect species. These findings exhibit potential for enhancing pest-management services in the agricultural sector. The findings of our study demonstrate that pest levels within greenhouse environments closely resemble those observed in real-world commercial cropping systems. As a result, the introduction of Coccinella septempunctata and Menochilus sexmaculatus biocontrol agents is confirmed to be a reliable and efficient method for pest management. The phenomenon of predator-prey density dependency is recognized as a crucial element in the implementation of biological control strategies. Furthermore, we investigate the impact of floral resources on the reproductive capacity of indigenous predators. The impact of Coriandrum sativum on fertility is substantial, indicating that the presence of a varied plant assortment with overlapping flowering periods can prolong the availability of floral resources. This study highlights the significance of flower-rich habitats and deliberate plant selection in augmenting biodiversity, ecosystem services, and pest management within agricultural settings. The implementation of conservation biological control technologies presents supplementary ecological advantages, thus offering practical implications for the promotion of sustainable agricultural practices.

A temperature-dependent phenology model for Bemisia tabaci MEAM1 (Hemiptera: Aleyrodidae)

The sweetpotato whitefly, Bemisia tabaci (Gennadius) Middle East-Asia Minor 1 (MEAM1), is widespread across tropical and subtropical regions, affecting hundreds of cultivated and wild plant species. Because the species transmits a variety of viruses, the whitefly has become one of the most economically significant insect pests in the world. Determining a pest's population growth potential as a function of temperature is critical for understanding a species population dynamics, predicting the potential range of the species and its associated diseases, and designing adaptive pest management strategies. The life history of B. tabaci MEAM1 was studied in life-table experiments at 7 constant temperatures ranging from 12 to 35 °C. Nonlinear equations were fitted to development, mortality, and reproduction data and compiled into an overall phenology rate-summation model using Insect Life Cycle Modeling (ILCYM) software, to simulate life-table parameters based on temperature. Life tables of B. tabaci MEAM1 observed at naturally variable temperature in La Molina, Lima, during different seasons, covering the entire temperature range of the species' predicted performance curve, were used to validate the model. Simulations predicted population growth within temperature between 13.9 and 33.4 °C, revealing a maximum finite rate of population increase (λ = 1.163), with a generation time of 33.3 days at 26.4 °C. Predicted species performance agreed well when compared against observed life tables and published data. The process-based physiological model presented here for B. tabaci MEAM1 should prove useful to predict the potential spatial distribution of the species based on temperature and to adjust pest control measures taking different population growth potentials due to prevailing temperature regimes into account.

Pyrifluquinazon baseline susceptibility and inhibition of Tomato chlorosis virus transmission by Bemisia tabaci

BACKGROUND

Tomato chlorosis virus (ToCV) is associated with tomato yellow leaf disorder diseases in more than 20 countries. ToCV can be transmitted in a semipersistent manner by whitefly vectors such as Bemisia tabaci. Controlling the vector pests by using chemical insecticides is an efficient and effective approach to reduce and interrupt the virus transmission. Pyrifluquinazon is a new pyridine azomethine derivative, showing insecticidal toxicity to sucking pests by disturbing their feeding behavior. However, limited attention has been paid to the performance of pyrifluquinazon against B. tabaci and ToCV transmission.

RESULT

This study showed the lethal concentration of 50% (LC50 ) values of pyrifluquinazon to 22 B. tabaci field populations ranged from 0.54 to 2.44 mg L-1 , and the baseline susceptibility of B. tabaci to pyrifluquinazon was 1.24 mg L-1 with a 95% confidence limit of 0.35-1.85 mg L-1 . Pyrifluquinazon and afidopyropen did not show cross-resistance to dinotefuran and pymetrozine in B. tabaci, which both inhibited the feeding activities of B. tabaci. The antifeedant concentration of 50% (AFC50 ) values at 48 h were 0.70 mg L-1 for pyrifluquinazon and 2.13 mg L-1 for afidopyropen. Foliar application of pyrifluquinazon and afidopyropen reduced the ToCV transmission by 40.91% and 33.33%, respectively and significantly decreased the ToCV loads in tomato plants under laboratory conditions.

CONCLUSION

These results provided new information about the effects of modulators of the vanilloid-type transient receptor potential channel on the toxicity to B. tabaci and inhibition of ToCV transmission. © 2023 Society of Chemical Industry.

Catalase promotes whitefly adaptation to high temperature by eliminating reactive oxygen species

Thermal stress usually leads to excessive production of reactive oxygen species (ROS) in all aerobic organisms. Catalases (CAT) are the key antioxidant enzymes, which act as the first line of defense against ROS in the antioxidant pathway. The highly invasive and widely distributed whitefly Bemisia tabaci MED damages plants by feeding as well as by transmitting many plant viruses. Previous studies have shown that strong adaptability to high temperature helps explain the spread of MED around the world. However, the mechanism underlying high temperature adaptation of this pest is not well understood. In this study, 6 CAT genes were identified from the MED genome and transcriptome dataset, among which BtCAT1, BtCAT2, and BtCAT3 were found to be highly expressed in adults. The expression of BtCAT1, BtCAT2, or BtCAT3 increased with induction temperature and induction time. The MED was exposed with mean high temperature (30 °C or 35 °C) and a short-term extremely high temperature (39 °C or 41 °C) after the silencing of BtCAT1, BtCAT2, or BtCAT3 to significantly increased ROS levels by at least 0.5 times and significantly decreased survival rate and fecundity of MED adults. The ROS level in the treated specimens gradually returned to a normal level after 24 h at 25 °C, but the survival rate still declined significantly. Taken together, our results demonstrate that CAT could help B. tabaci adapt to long-term mean high temperatures and short-term extremely high temperatures by eliminating excessive ROS.

Lytic Polysaccharide Monooxygenase Activity of Tma12 Is Critical for Its Toxicity to Whitefly

Lytic polysaccharide monooxygenases (LPMOs) are powerful redox enzymes that transform complex carbohydrates through oxidation and make them suitable for saccharification by canonical hydrolases. Due to this property, LPMOs are considered to be a valuable component of enzymatic consortia for industrial biorefineries. Tma12 is a fern entomotoxic protein that kills whitefly and has structural similarities with chitinolytic LPMO. However, its enzymatic activity is poorly understood. Studying the role of the LPMO-like activity in the insecticidal function of Tma12 can be of considerable importance. Our results show that Tma12 preferentially binds and digests β-chitin. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis shows that the digestion of chitin produces chitin oligosaccharides of various lengths (DP2-DP7). The Michaelis constant (km) and catalytic constant (kcat) for hydrocoerulignone are 0.022 mM and 0.044 s-1, respectively. The attenuation of catalytic activity through diethylpyrocarbonate modification abolishes the insecticidal activity of the protein. Our findings reveal that (a) Tma12 is an active LPMO and (b) LPMO activity is indispensable for its function as a bioinsecticide.

Differential Seasonal Prevalence of Yellowing Viruses Infecting Melon Crops in Southern California and Arizona Determined by Multiplex RT-PCR and RT-qPCR

Viruses transmitted by the whitefly (Bemisia tabaci) are an increasing threat to cucurbit production in the southwestern United States and many other cucurbit production regions of the world. The crinivirus cucurbit yellow stunting disorder virus (CYSDV) has severely impacted melon production in California and Arizona since its 2006 introduction to the region. Within the past few years, another crinivirus, cucurbit chlorotic yellows virus (CCYV), and the whitefly-transmitted ipomovirus squash vein yellowing virus (SqVYV) were found infecting melon plants in California's Imperial Valley. CYSDV, CCYV, and an aphid-transmitted polerovirus, cucurbit aphid-borne yellows virus (CABYV), occur together in the region and produce identical yellowing symptoms on cucurbit plants. Mixed infections of these four viruses in the Sonoran Desert and other regions pose challenges for disease management and efforts to develop resistant varieties. A multiplex single-step RT-PCR method was developed that differentiates among these viruses, and this was used to determine the prevalence and distribution of the viruses in melon samples from fields in the Sonoran Desert melon production region of California and Arizona during the spring and fall melon seasons from 2019 through 2021. TaqMan probes were developed, optimized, and applied in a single-step multiplex RT-qPCR to quantify titers of these four viruses in plant samples, which frequently carry mixed infections. Results of the multiplex RT-PCR analysis demonstrated that CYSDV is the predominant virus during the fall, whereas CCYV was by far the most prevalent virus during the spring each year. Multiplex RT-qPCR was used to evaluate differential accumulation and spatiotemporal distribution of viruses within plants and suggested differences in competitive accumulation of CCYV and CYSDV within melon. This study provides the first official report of SqVYV in Arizona and offers an efficient method for virus detection and quantification for breeding and disease management in areas impacted by cucurbit yellowing viruses.