Orthotospovirus iridimaculaflavi (iris yellow spot virus): An emerging threat to onion cultivation and its transmission by Thrips tabaci in India.

The yellow spot disease caused by the virus species Orthotospovirus iridimaculaflavi (Iris yellow spot virus-IYSV), belonging to the genus Orthotospovirus, the family Tospoviridae, order Bunyavirales and transmitted by Thrips tabaci Lindeman. At present, emerging as a major threat in onion (Allium cepa) in Tamil Nadu, India. The yellow spot disease incidence was found to be 53-73 % in six districts out of eight major onion-growing districts surveyed in Tamil Nadu during 2021-2023. Among the onion cultivars surveyed, the cultivar CO 5 was the most susceptible to IYSV. The population of thrips was nearly 5-9/plant during vegetative and flowering stages. The thrips infestation was 34-60 %. The tospovirus involved was confirmed as IYSV through DAS-ELISA, followed by molecular confirmation through RT-PCR using the nucleocapsid (N) gene. The predominant thrips species present in onion crops throughout the growing seasons was confirmed as Thrips tabaci based on the nucleotide sequence of the MtCOI gene. The mechanical inoculation of IYSV in different hosts viz., Vigna unguiculata, Gomphrena globosa, Chenopodium amaranticolor, Chenopodium quinoa and Nicotiana benthamiana resulted in chlorotic and necrotic lesion symptoms. The electron microscopic studies with partially purified sap from onion lesions revealed the presence of spherical to pleomorphic particles measuring 100-230 nm diameter. The transmission of IYSV was successful with viruliferous adult Thrips tabaci in cowpea (Cv. CO7), which matured from 1st instar larva fed on infected cowpea leaves (24 h AAP). Small brown necrotic symptoms were produced on inoculated plants after an interval of four weeks. The settling preference of non-viruliferous and viruliferous T. tabaci towards healthy and infected onion leaves resulted in the increased preference of non-viruliferous thrips towards infected (onion-61.33 % and viruliferous thrips towards healthy onion leaves (75.33 %). The study isolates shared 99-100 % identity at a nucleotide and amino acid level with Indian isolates of IYSV in the N gene. The multiple alignment of the amino acid sequence of the N gene of IYSV isolates collected from different locations and IYSV isolates from the database revealed amino acid substitution in the isolate ITPR4. All the IYSV isolates from India exhibited characteristic amino acid substitution of serine at the 6th position in the place of threonine in the isolates from Australia, Japan and USA. The phylogenetic analysis revealed the monophyletic origin of the IYSV isolates in India.

Spatiotemporal Patterns of Iris Yellow Spot Virus and Its Onion Thrips Vector, Thrips tabaci, in Transplanted and Seeded Onion Fields in New York.

Onion thrips, Thrips tabaci (Lindeman), transmits iris yellow spot virus (IYSV) and is one of the most important pests of Allium crops. IYSV is a member of the species Tospovirus iridimaculaflavi in the genus Orthotospovirus of the family Tospoviridae. This virus typically reduces overall onion bulb quality and weight but can also prematurely kill onion plants. IYSV is neither seed nor mechanically transmitted. Onion fields are typically established via seeds and transplants. A decade ago, onion thrips tended to colonize transplanted fields before seeded fields because plants in transplanted fields were larger and more attractive to thrips than smaller onions in seeded fields. Therefore, we hypothesized that the incidence of IYSV in transplanted fields would be detected early in the season and be spatially aggregated, whereas IYSV would be absent from seeded fields early in the season and initial epidemic patterns would be spatially random. In 2021 and 2022, IYSV incidence and onion thrips populations were quantified in 12 onion fields (four transplanted fields and eight seeded fields) in New York. Fields were scouted four times throughout the growing season (n = 96 samples), and a geospatial and temporal analysis of aggregation and incidence was conducted to determine spatiotemporal patterns in each field type. Results indicated that spatial patterns of IYSV incidence and onion thrips populations were similar early in the season, indicating that transplanted onion fields are no longer the dominant early-season source of IYSV in New York. These findings suggest the need to identify other important early-season sources of IYSV that impact New York onion fields.

Identifying Onion Fields at Risk of Iris Yellow Spot Virus in New York.

Iris yellow spot virus (IYSV) poses a significant threat to dry bulb onion, Allium cepa L., production and can lead to substantial yield reductions. IYSV is transmitted by onion thrips, Thrips tabaci (Lindeman), but not via seed. Transplanted onion fields have been major early season sources of IYSV epidemics. As onion thrips tend to disperse short distances, seeded onion fields bordering transplanted onion fields may be at greater risk of IYSV infection than seeded fields isolated from transplanted ones. Additionally, seeded onion fields planted early may be at greater risk of IYSV infection than those seeded later. In a 2-year study in New York, we compared IYSV incidence and onion thrips populations in seeded onion fields relative to their proximity to transplanted onion fields. In a second study, we compared IYSV incidence in onion fields with either small or large plants during midseason. Results showed similar IYSV incidence and onion thrips populations in seeded onion fields regardless of their proximity to transplanted onion fields, while IYSV incidence was over four times greater in large onion plants than in small ones during midseason. These findings suggest a greater risk of onion thrips-mediated IYSV infection in onion fields with large plants compared with small ones during midseason and that proximity of seeded fields to transplanted ones is a poor indicator of IYSV risk. Our findings on IYSV spread dynamics provided valuable insights for developing integrated pest and disease management strategies for New York onion growers.

A multiplex PCR assay for rapid identification of major tospovirus vectors reported in India.

BACKGROUND: To date, four thrips vectors have been reported to transmit five different tospoviruses in India. Their identification at an early stage is crucial in formulating appropriate pest management strategies. Since morphometric key-based thrips identification based on the adult stage is time-consuming, there is a need to develop diagnostic tools which are rapid, accurate, and independent of developmental stages. Here, we report a multiplex PCR assay to identify four major thrips vectors viz. Thrips palmi, T. tabaci, Scirtothrips dorsalis, and Frankliniella schultzei present in India. RESULTS: Cytochrome oxidase subunit III and internal transcribed spacer region 2 were utilized to design species-specific primers. Of 38 pairs of primers tested, primer pairs AG35F-AG36R, AG47F-AG48R, AG87F-AG88R, and AG79F-AG80R amplified 568 bp, 713 bp, 388 bp, and 200 bp products from the DNA templates of T. palmi, S. dorsalis, T. tabaci, and F. schultzei, respectively at same PCR conditions. The specificity of the primer pairs was validated with a large number of known specimens and no cross-reactivity was observed with other thrips species. The multiplex PCR assay with a cocktail of all the four primer pairs detected four thrips vectors efficiently and could discriminate all of them concurrently in a single reaction. CONCLUSION: The multiplex PCR reported in this study could identify the major thrips vectors reported in India. The assay will be useful in ascertaining distribution profile of major thrips vectors, disease epidemiology, screening large samples, and quarantine.

A simple molecular identification method of the Thrips tabaci (Thysanoptera: Thripidae) cryptic species complex.

The onion thrips (Thrips tabaci Lindeman, 1889) is a key pest of a wide range of crops because of its ecological attributes such as polyphagy, high reproduction rate, ability to transmit tospoviruses and resistance to insecticides. Recent studies revealed that T. tabaci is a cryptic species complex and it has three lineages (leek-associated arrhenotokous L1-biotype, leek-associated thelytokous L2-biotype and tobacco-associated arrhenotokous T-biotype), however, the adults remain indistinguishable. T. tabaci individuals were collected from different locations of Hungary to create laboratory colonies from each biotypes. Mitochondrial COI (mtCOI) region was sequenced from morphologically identified individuals. After sequence analysis SNPs were identified and used for CAPS marker development, which were suitable for distinguishing the three T. tabaci lineages. Genetic analysis of the T. tabaci species complex based on mtCOI gene confirmed the three well-known biotypes (L1, L2, T) and a new biotype because the new molecular evidence presented in this study suggests T-biotype of T. tabaci forming two distinct (sub)clades (T1 and T2). This genetic finding indicates that the genetic variability of T. tabaci populations is still not fully mapped. We validated our developed marker on thrips individuals from our thrips colonies. The results demonstrated that the new marker effectively identifies the different T. tabaci biotypes. We believe that our reliable genotyping method will be useful in further studies focusing on T. tabaci biotypes and in pest management by scanning the composition of sympatric T. tabaci populations.

Visually and olfactorily enhanced attractive devices for thrips management.

'Lure-and-infect' is an insect pest management strategy with high potential but so far there are few examples of its application. Using traps as surrogates for auto-dissemination devices, we tested the attractiveness to naturally occurring thrips (Thysanoptera: Thripidae) of three trap types differing in colour and structure, with and without the thrips lure methyl isonicotinate (MI), and sticky plate traps as a control. The aim was to find more effective traps that could be further developed into devices for auto-dissemination and lure-and-infect of thrips. The number of thrips captured varied substantially with trap type and the presence of the MI lure. We found a high visual response to a sticky 'white ruffle' trap (i.e., a 30-cm-long cylindrical outline of folded fabric), compared to a commonly used blue sticky plate trap (Bug-scan) as the control. This effect was seen both in a greenhouse with roses (Rosa spp.), where we encountered western flower thrips, Frankliniella occidentalis (Pergande), and in a grass field, where we encountered onion thrips, Thrips tabaci Lindeman, and New Zealand flower thrips, Thrips obscuratus (Crawford). In the absence of MI, the white ruffle trap caught 7-22× more thrips than the control Bug-scan trap. A similarly designed blue ruffle trap and a modified Lynfield trap caught lower thrips numbers than the white ruffle and the control Bug-scan traps. Presence of MI substantially increased the captures of T. tabaci in all three trap types in the field (2.5-18×). In the greenhouse, without MI the white ruffle trap caught 3.5-14× more thrips than the Bug-scan, blue ruffle, or modified Lynfield traps. Presence of MI increased the captures of F. occidentalis males and females in the Lynfield and blue ruffle traps (1.4-2.8×), but not in the white ruffle trap in the greenhouse (ca. 1.1×). The importance of visual and olfactory factors for the design of effective auto-dissemination and lure-and-infect strategies for thrips management is discussed.

RNA sequencing, selection of reference genes and demonstration of feeding RNAi in Thrips tabaci (Lind.) (Thysanoptera: Thripidae).

BACKGROUND: Thrips tabaci is a severe pest of onion and cotton. Due to lack of information on its genome or transcriptome, not much is known about this insect at the molecular level. To initiate molecular studies in this insect, RNA was sequenced; de novo transcriptome assembly and analysis were performed. The RNAseq data was used to identify reference and RNAi pathway genes in this insect. Additionally, feeding RNAi was demonstrated in T. tabaci for the first time. RESULTS: From the assembled transcriptome, 27,836 coding sequence (CDS) with an average size of 1236 bp per CDS were identified. About 85.4% of CDS identified showed positive Blast hits. The homologs of most of the core RNAi machinery genes were identified in this transcriptome. To select reference genes for reverse-transcriptase real-time quantitative PCR (RT-qPCR) experiments, 14 housekeeping genes were identified in the transcriptome and their expression was analyzed by (RT-qPCR). UbiCE in adult, 28s in nymphs and SOD under starvation stress were identified as the most stable reference genes for RT-qPCR. Feeding dsSNF7 and dsAQP caused 16.4- and 14.47-fold reduction in SNF7 and AQP mRNA levels respectively, when compared to their levels in dsGFP fed control insects. Feeding dsSNF7 or dsAQP also caused 62 and 72% mortality in T. tabaci. Interestingly, simultaneous feeding of dsRNAs targeting SNF7 or AQP and one of the RNAi pathway genes (Dicer-2/Aubergine/Staufen) resulted in a significant reduction in RNAi of target genes. These data suggest the existence of robust RNAi machinery in T. tabaci. CONCLUSION: The current research is the first report of the assembled, analyzed and annotated RNAseq resource for T. tabaci, which may be used for future molecular studies in this insect. Reference genes validated across stages and starvation stress provides first-hand information on stable genes in T. tabaci. The information on RNAi machinery genes and significant knockdown of the target gene through dsRNA feeding in synthetic diet confirms the presence of efficient RNAi in this insect. These data provide a solid foundation for further research on developing RNAi as a method to manage this pest.

T929I and K1774N mutation pair and M918L single mutation identified in the voltage-gated sodium channel gene of pyrethroid-resistant Thrips tabaci (Thysanoptera: Thripidae) in Japan.

Pyrethroid-resistance in onion thrips, Thrips tabaci, has been reported in many countries including Japan. Identifying factors of the resistance is important to correctly monitoring the resistance in field populations. To identify pyrethroid-resistance related genes in T. tabaci in Japan, we performed RNA-Seq analysis of seven T. tabaci strains including two pyrethroid-resistant and five pyrethroid-susceptible strains. We identified a pair of single point mutations, T929I and K1774N, introducing two amino acid mutations, in the voltage-gated sodium channel gene, a pyrethroid target gene, in the two resistant strains. The K1774N is a newly identified mutation located in the fourth repeat domain of the sodium channel. Genotyping analysis of field-collected populations showed that most of the T. tabaci individuals in resistant populations carried the mutation pair, indicating that the mutation pair is closely associated with pyrethroid-resistance in Japan. Another resistance-related mutation, M918L, was also identified in part of the resistant populations. Most of the individuals with the mutation pair were arrhenotokous while all individuals with the M918L single mutation were thelytokous. The result of differentially expressed gene analysis revealed a small number of up-regulated detoxification genes in each resistant strain which might be involved in resistance to pyrethroid. However, no up-regulated detoxification genes common to the two resistant strains were detected. Our results indicate that the mutation pair in the sodium channel gene is the most important target for monitoring pyrethroid-resistance in T. tabaci, and that pyrethroid-resistant arrhenotokous individuals with the mutation pair are likely to be widely distributed in Japan.

Maize Chlorotic Mottle Virus Induces Changes in Host Plant Volatiles that Attract Vector Thrips Species.

Maize lethal necrosis is one of the most devastating diseases of maize causing yield losses reaching up to 90% in sub-Saharan Africa. The disease is caused by a combination of maize chlorotic mottle virus (MCMV) and any one of cereal viruses in the Potyviridae group such as sugarcane mosaic virus. MCMV has been reported to be transmitted mainly by maize thrips (Frankliniella williamsi) and onion thrips (Thrips tabaci). To better understand the role of thrips vectors in the epidemiology of the disease, we investigated behavioral responses of F. williamsi and T. tabaci, to volatiles collected from maize seedlings infected with MCMV in a four-arm olfactometer bioassay. Volatile profiles from MCMV-infected and healthy maize plants were compared by gas chromatography (GC) and GC coupled mass spectrometry analyses. In the bioassays, both sexes of F. williamsi and male T. tabaci were significantly attracted to volatiles from maize plants infected with MCMV compared to healthy plants and solvent controls. Moreover, volatile analysis revealed strong induction of (E)-4,8-dimethyl-1,3,7-nonatriene, methyl salicylate and (E,E)-4,8,12-trimethyltrideca-1,3,7,11-tetraene in MCMV-infected maize seedlings. Our findings demonstrate MCMV induces changes in volatile profiles of host plants to elicit attraction of thrips vectors. The increased vector contact rates with MCMV-infected host plants could enhance virus transmission if thrips feed on the infected plants and acquire the pathogen prior to dispersal. Uncovering the mechanisms mediating interactions between vectors, host plants and pathogens provides useful insights for understanding the vector ecology and disease epidemiology, which in turn may contribute in designing integrated vector management strategies.

Heteroplasmy due to coexistence of mtCOI haplotypes from different lineages of the Thrips tabaci cryptic species group.

Heteroplasmy is the existence of multiple mitochondrial DNA haplotypes within the cell. Although the number of reports of heteroplasmy is increasing for arthropods, the occurrence, number of variants, and origins are not well studied. In this research, the occurrence of heteroplasmy was investigated in Thrips tabaci, a putative species complex whose lineages can be distinguished by their mitochondrial DNA haplotypes. The results from this study showed that heteroplasmy was due to the occurrence of mitochondrial cytochrome oxydase I (mtCOI) haplotypes from two different T. tabaci lineages. An assay using flow cytometry and quantitative real-time PCR was then used to quantify the per cell copy number of the two mtCOI haplotypes present in individuals exhibiting heteroplasmy from nine geographically distant populations in India. All of the T. tabaci individuals in this study were found to exhibit heteroplasmy, and in every individual the per cell copy number of mtCOI from lineage 3 comprised 75-98% of the haplotypes detected and was variable among individuals tested. There was no evidence to suggest that the presense of lineage-specific haplotypes was due to nuclear introgression; however, further studies are needed to investigate nuclear introgression and paternal leakage during rare interbreeding between individuals from lineages 2 and 3.

Thrips Settling, Oviposition and IYSV Distribution on Onion Foliage.

Thrips tabaci Lindeman (Thysanoptera: Thripidae) adult and larval settling and oviposition on onion (Allium cepa L.) foliage were investigated in relation to leaf position and leaf length at prebulb plant growth stages under controlled conditions. In the laboratory, four and six adult females of T. tabaci were released on onion plants at three-leaf stage and six- to eight-leaf stage, respectively, and thrips egg, nymph, and adult count data were collected on each of the three inner most leaves at every 2-cm leaf segment. Thrips settling and oviposition parameters were quantified during the light period on the above ground portion of onion plants from the distal end of the bulb or leaf sheath "neck" through the tips of the foliage. Results from studies confirmed that distribution of thrips adults, nymphs, and eggs were skewed toward the base of the plant. The settling distributions of thrips adults and nymphs differed slightly from the egg distribution in that oviposition occurred all the way to the tip of the leaf while adults and nymphs were typically not observed near the tip. In a field study, the foliage was divided into three equal partitions, i.e., top, middle, basal thirds, and thrips adults by species, primarily Frankliniella fusca (Hinds) and T. tabaci, were collected from each partition to determine if there was a similar bias of all adult thrips toward the base of the plant. The results suggested that adults of different species appear to segregate along leaf length. Finally, thrips oviposition on 2-cm segments and Iris yellow spot virus positive leaf segments were quantified in the field, irrespective of thrips species. Both variables demonstrated a very similar pattern of bias toward the base of the plant and were significantly correlated.

Application of the LAMP Assay as a Diagnostic Technique for Rapid Identification of Thrips tabaci (Thysanoptera: Thripidae).

Rapid and accurate identification of potentially invasive taxa that may cause high economic losses or environmental damage is of critical importance. The onion thrips, Thrips tabaci Lindeman, ranks as one of the world's most destructive agricultural pests and commonly found in imported agricultural products and field samples, but is prone to undetected transport because of its minute size as well as cryptic behavior. Although traditional taxonomic methods are pretty useful in straightforward assignment of specimens to the genus Thrips, identification in the species level is much more difficult and requires expertise, knowledge, and experience. Furthermore, it is often difficult or impossible to identify or distinguish this species from other thrips by using material from other stages of development. Based on the foregoings, use of a molecular technique known as loop-mediated isothermal amplification (LAMP) as a rapid and robust alternative species diagnostic tool would be valuable. In this study, a relatively quick and simple method was used to detect the presence of onion thrips DNA rapidly and discriminate it from other species, by using material from different stages of development. Not only LAMP itself required less than 1 h to complete but also amounts of DNA as little as that recovered from a single specimen were adequate for the detection. Another advantage of this identification system is that nonspecialists will be able to make faster and cheaper identifications.

Phylogenetic and population genetic analyses of Thrips tabaci Lindeman (Thysanoptera: Thripidae) on Allium host in India.

Background: Onion thrips (Thrips tabaci) is a complex of cryptic species with subtle morphological differences and distinct genetic backgrounds; thus, species identification using traditional methods remains challenging. The existence of different haplotypes and genotypes within a species can significantly influence various aspects of its biology, including host preference, reproductive capacity, resistance to pesticides, and vector competence for plant viruses. Understanding the genetic diversity and population structure of cryptic species within T. tabaci will not only aid in the development of more effective control strategies tailored to specific genetic variants but also in monitoring population dynamics, tracking invasive species, and implementing quarantine measures to prevent the spread of economically damaging thrips biotypes. Methods: This study aims to explore intraspecies genetic diversity and molecular evolutionary relationships of the mitochondrial cytochrome oxidase gene subunit I (mtCOI) in T. tabaci populations from India. To capture diversity within the Indian T. tabaci populations, amplicon sequencing was performed for the thrips mtCOI gene from eight diverse localities in India. A total of 48 sequences retrieved for the mtCOI gene from the NCBI Nucleotide database were analysed. Results: Multiple insertions and deletions were detected at various genomic positions across the populations from different localities, with the highest variation observed in the 300-400 genome position range. Molecular diversity analyses identified 30 haplotypes within the population, with certain subpopulations exhibiting higher gene flow. Analysis of single nucleotide polymorphism patterns within the mtCOI gene across diverse Indian locales revealed significant intrapopulation genetic heterogeneity and its potential repercussions on gene functionality. Elevated F statistics (Fst) values in the northern-western subpopulations suggested high genetic variability, particularly evident in haplotype networks originating mainly from the northern region, notably Delhi. While most populations displayed stable and ancient evolutionary histories, thrips populations from northern, western, and north-eastern regions indicated rapid growth.

Thrips Species Composition in Ontario Greenhouse Floriculture: Innovative Identification Tools and Implications for Integrated Pest Management.

Proper species identification is the keystone of successful integrated pest management (IPM). However, efforts to identify thrips species in Canadian greenhouses have not been formally made since the 1980s. In response to recent increases in crop damage, we sampled thrips communities from eight commercial floriculture greenhouses in the Niagara region (Ontario, Canada) from May until August 2016. Selected sites were revisited in 2017, 2018, and 2019 to determine changes in species composition over time. Western flower thrips (Frankliniella occidentalis (Pergande)), along with onion thrips (Thrips tabaci Lindeman), constituted the majority of species found. Other pest species (less than 8% of specimens across all sampling years) included poinsettia thrips (Echinothrips americanus Morgan), chrysanthemum thrips (Thrips nigropilosus Uzel), and Frankliniella fusca (Hinds). Further investigations of thrips outbreaks in Ontario from 2016 to 2023 revealed other important species, including Thrips parvispinus (Karny), Hercinothrips femoralis (Reuter), and Scirtothrips dorsalis Hood. The current biocontrol strategies used in Ontario floriculture crops for western flower thrips do not adequately control onion thrips or other thrips pests in ornamental crops, making identification a fundamental step in determining whether biocontrol or chemical control strategies should be implemented. However, traditional taxonomic keys are inaccessible to non-specialists due to their technical difficulty. Using the data gathered in these surveys, we developed a simplified, illustrated identification key for use by growers and IPM consultants.

Unravelling the synergistic interaction of Thrips tabaci and newly recorded, Thrips parvispinus with Alternaria porri (Ellis.) Cif., inciting onion purple blotch.

Onion purple blotch is the most indispensable foliar disease of crop and has become a major concern for farmers and research fraternity. An attempt to investigate the role of injury in parasitism by Alternaria porri indicated that disease incidence and severity enhance considerably with injury. Thrips injured plants inoculated with A. porri presented 100% incidence and 52-72% severity while mechanically injured plants inoculated with A. porri showed 60-70% incidence and 28-34% severity. The uninjured plants showed considerably less disease incidence (30-40%) and severity (10-16%). Injured inoculated plants presented reduced leaf length and leaf area while the leaf diameter remained unaffected. The lesion number, lesion length and size was substantially enhanced with concomitant infestation of pest and pathogen. Thrips tabaci injury led to more pronounced symptoms of purple blotch compared to Thrips parvispinus injury. There was substantial decrease in photosynthetic rate and chlorophyll content with stress imposed on plant whilst the relative stress injury was enhanced. The induction of injury and inoculation of A. porri had an impact on the concentration of total phenolics, total soluble sugars, total proteins and hydrogen peroxide in onion leaves. A. porri combined with injury caused a more pronounced decrease in total soluble sugars and total protein content while enhancement in total phenolics and hydrogen peroxide content compared to uninjured plants. The dynamic nature of morpho-physiological and biochemical changes owing to stress conditions imposed on onion plant adds an extra layer of complexity in understanding the onion plant physiology and their ability to work out in response to challenging environment conditions.

Thripidae pest species community identification and population genetic diversity analyses of 2 dominant thrips in cotton fields of China.

Thrips are devastating pests for various crops, and they can rasp tender leaves, terminal buds, and flowers, which specifically causing huge economic losses to cotton production. However, there is very little knowledge about the species composition of thrips in mainland China, as well as the genetic structure of the thrips populations, particularly in the cotton-producing regions. In this study, thrips were collected from 40 geographical locations at 8 different provinces which representing majority cotton-producing belts in China, and mitochondrial cytochrome oxidase subunit I sequence was used to identify species composition and evaluate the genetic diversity of collected thrips individuals. Based on experimental results proven that overall, 10 and 8 species of thrips were identified in seedling and flowering stage respectively, which is corresponding dominant species are Thrip tabaci (Lindeman) and Frankliniella intonsa (Trybom). Genetically, 24 haplotypes were identified in 310 T. tabaci individuals from 10 locations, and 263 haplotypes were detected in 1,861 F. intonsa individuals from 40 locations. Hap1 (T. tabaci) is the most widely distributed haplotype among all the T. tabaci samples. Likewise, Hap 2 is the most widely distributed and abundant haplotype among all samples of F. intonsa. The genetic differentiation degrees of T. tabaci between SXYC population and other 9 populations were high, but its gene flow in these 10 regions was relatively low, which might be due to geographical barriers. The Mantel tests showed no correlation between genetic distance and geographic distance of the 2 thrip species. Demographic analysis results showed that both T. tabaci and F. intonsa experienced population expansion in China. Taken together, this study identifies the species composition of thrips in major cotton-producing regions at different growth periods and evaluates effects of geomorphology on the geographical distribution of haplotypes of dominant thrips T. tabaci and F. intonsa.

Efficacy of entomopathogenic fungi, nematodes and spinetoram combinations for integrated management of Thrips tabaci.

BACKGROUND: Two consecutive field trials using a blend of entomopathogens in combination with a new chemistry insecticide were conducted to determine treatment effects on onion thrips (Thrips tabaci Lindeman) populations, crop damage, plant development, crop yield and impact on natural enemies. Products were tested in an onion cropping system and included the insect pathogenic fungus Beauveria bassiana (isolate WG-11), an entomopathogenic nematode Heterorhabditis bacteriophora (strain VS) and the new-chemistry chemical insecticide spinetoram. RESULTS: In all treatments, a significant decrease in thrips per plant population was detected in both trials. Overall, dual application of entomopathogens and insecticide was more effective than singly applied treatments. The lowest number of thrips larvae (1.96 and 3.85) and adults (0.00 and 0.00) were recorded when treated with dual application of B. bassiana and spinetoram at 7 days post application (DPA) after the second spray application in 2017and 2018, respectively. Damage on onion plants was considerably decreased in all treatments relative to the control. The lowest damage was observed on onion plants treated with B. bassiana + spinetoram at 7 DPA after the second spray application during both years. A significant decrease in the number of natural enemies (beetles, spiders, mites, lacewings, ants and bugs) on onion plants was recorded during both years. Insect pathogens when applied alone and in combination with each other considerably protected arthropod natural enemies compared to insecticide application applied alone. Significant increase in plant agronomic traits was observed compared to the control. Among all the treatments, B. bassiana + spinetoram produced maximum leaf length, leaf weight, total leaves, neck diameter, bulb diameter, number of rings per bulb, bulb weight, dry matter and plant yield following the 2017and 2018 applications, respectively. CONCLUSION: The findings of the study reveal the potential of using insect pathogens and insecticide for control of T. tabaci. However, combinations containing spinetoram are harmful to nontarget organisms, whereas biological control agents help in protecting biodiversity in onion agroecosystems. © 2023 Society of Chemical Industry.

Development of Insecticide Resistance in Field Populations of Onion Thrips, Thrips tabaci (Thysanoptera: Thripidae).

The present study evaluated insecticide resistance in field populations of onion thrips, Thrips tabaci Lindeman (Thysanoptera: Thripidae), collected from eight different onion-growing regions of Punjab, Pakistan. These field-collected populations were assessed for resistance development against eight commonly used active ingredients including deltamethrin, lambda-cyhalothrin, imidacloprid, acetamiprid, spinosad, spinetoram, cypermethrin, and abamectin. In leaf dip bioassays, T. tabaci adults showed varied levels of resistance towards different insecticides. Moderate or high levels of resistance to deltamethrin (58-86 fold), lambda-cyhalothrin (20-63 fold), and cypermethrin (22-54 fold) were observed in T. tabaci field populations. There were very low to moderate resistance levels to imidacloprid (10-38 fold), acetamiprid (5-29 fold), and abamectin (10-30 fold). The lowest levels of resistance were detected in thrips exposed to spinosad (3-13 fold) and spinetoram (3-8 fold). Insecticide resistance levels varied among populations collected from various geographic locations, but all populations exhibited elevated levels of resistance to deltamethrin. Thrips tabaci populations with higher resistance levels were most commonly found from the southern part of Punjab, Pakistan. Our findings revealed that spinosyns could be used as alternatives to conventional insecticides for the successful management of T. tabaci in onion fields.

There Is No Influence of Egg Size on Sex Allocation in Arrhenotokous Lineages of Thrips tabaci Lindeman.

In two haplodiploid species, sex allocation in young arrhenotokous females is mediated by egg size. We tested if sex allocation is mediated by egg size in two arrhenotokous lineages of the haplodiploid species complex of T. tabaci: L1 and T. We measured the size of eggs produced by very young mothers, 3-5-day-old mothers (just like in the case of Tetranychus urticae) and 7-10-day-old mothers (as in Pezothrips kellyanus). Moreover, we measured the size of eggs oviposited by mothers in their entire lifespan. We found that in T. tabaci, sex allocation is not mediated by egg size. Egg size and gender were independent of maternal age in the L1 lineage, whilst in the T lineage, the observed egg size difference between males and females was only present in the progeny of young females (7-10-day-old mothers). Furthermore, we found that male eggs produced by mated mothers were larger than those produced by virgin mothers in the L1 lineage, but in the T lineage, there were no differences in the size of male eggs produced by mated and virgin mothers. Our results indicate that these two subspecies have different resource allocation strategies in response to maternal mating status.

Comparison of Bioassays Used to Determine Onion Thrips (Thysanoptera: Thripidae) Susceptibility to Spinetoram.

Onion thrips (Thrips tabaci Lindeman) is one of onion's most damaging insect pests and has a history of developing resistance across insecticide classes. The susceptibility of T. tabaci populations to insecticides can be determined using laboratory bioassays. Three types of bioassays have been documented in the literature specifically for use with T. tabaci: vial assay (contact only), feeding assay (ingestion only), and leaf-dip assay (contact + ingestion). The objectives of this study were to 1) compare insecticide susceptibility levels of a T. tabaci population using these three assays and 2) determine which bioassay's results were most similar to those generated from exposing thrips to whole plants treated with insecticide. All experiments were conducted using a colony of T. tabaci known to be susceptible to insecticides and all were evaluated for their susceptibility to spinetoram (Radiant SC). Results indicated that 1) each bioassay generated a unique concentration-mortality relationship and LC50 value (0.01, 0.03 and 1.6 ppm for leaf-dip, vial, and feeding assays, respectively), and 2) all bioassays overestimated the susceptibility of the population relative to the whole-plant assay (LC50 = 5.3 ppm). Attributes of these bioassays are discussed relative to their future use in insecticide resistance monitoring programs for T. tabaci.