Soybean Thrips Research Articles

Decision‐making for thrips control in soybean fields using precision agriculture principles

AbstractIn precision agriculture, sub‐areas of fields with similar features are called management zones and the inputs applied similarly in these zones. Such notion of management zones is applicable to high‐output soybean fields where thrips are an emerging problem leading to losses up to 15%. Management zones are an agricultural management strategy that can be used for decision‐making for controlling thrips on soybean fields. Thus, a 2‐year study was carried out on commercial soybean fields aimed at developing a decision‐making system for controlling soybean thrips using management zones. Three control programmes were established and assessed: Cl‐conventional control with insecticide use in the entire field; IPM‐CS‐conventional sampling plan + spray upon reaching the economic injury level (EIL; 3.43 thrips/sample); and IPM‐MZ‐spraying only specific areas of the field where thrips density reached the EIL. The decision to control reached using the IPM‐CS and IPM‐MZ programmes was 3× lower than those of the CI, which incurred in 75% mode decision mistakes. Furthermore, the decision to spray insecticides based on analysis of data for Cl was also incorrect. In 8.5% (3.6% of treated and 4.9% of non‐treated) of the field, the decisions of the IPM‐CS programme were incorrect. The total cost of the Cl programme (US$ 11.4/ha) was higher than that of the IPM‐CS and IPM‐MZ programmes (US$ 3.2 ha−1). Therefore, owing to its technical, economic, and environmental advantages, the establishment of management zones seems worthy of incorporation in integrated thrips management decision‐making systems for soybean fields.

Reduction in productivity of soybean plants infested with Neohyadatothrips variabilis (Thysanoptera: Thripidae) with and without soybean vein necrosis virus

Soybean thrips, Neohyadatothrips variabilis (Beach), a vector of Soybean Vein Necrosis Virus (SVNV), has been recognized as a widespread pest of soybean [Glycine max (L.) Merr.] in USA and Canada. Several experiments investigated the effect on soybean when infested with soybean thrips with and without SVNV. Experiment 1 compared soybean infested at V1 and V5 growth stages (GS) with soybean thrips without SVNV and noninfested plants. For plants infested at GS V1, plant height, number of seeds, and seed weights were reduced by 50, 80, and 75%, respectively. When plants were infested at GSs V1 and V5, the counts of soybean thrips peaked at 1,803 and 4,214 per plant 4 weeks after infestation (WAI), respectively. Experiment 2 used SVNV-infected soybean thrips and compared soybean infested versus control at GS V1 and V5. For plants infested at GS V1, plant height was reduced 77.8%, and plants died before setting pods. For plants infested at GS V5, height, number of seeds, and seed weights were reduced 56, 78, and 92%, respectively. When plants were infested at GSs V1 and V5, the counts of soybean thrips peaked at 282 and 883 per plant 2 WAI, respectively. Experiment 3, five soybean genotypes were infested with SVNV-infected thrips at GS V1. Number and weight of seeds per plant were higher and with lower visual disease ratings (progressive chlorosis, necrosis and rugosity) for the more resistant genotypes Merschman Kennedy and plant introduction (PI) 171451 than for the more susceptible genotypes: soybean breeding line LD12-12734a (Rag1/2), cv Williamsfield Illini 3509N, and PI 417136.

Review of predatory mites as biocontrol agents against thrips in China

Thrips are one of the most destructive pests of vegetables, fruits, and ornamental crops worldwide (Wan et al., 2020; Davari et al., 2021). The more severe species include Frankliniella occidentalis, Frankliniella intonsa, Thrips tabaci, Thrips flavidulus, Pseudodendrotrips mori, Scirtothrips dorsalis, and Megalurothrips usitatus (You et al., 2007; Zheng et al., 2007; Saito et al., 2022). Many thrips have developed resistance to pesticides. For example, Frankliniella occidentalis developed different degrees of resistance to organochlorine, organophosphorus, carbamate, and pyrethroid insecticides and environmentally friendly insecticides (Broadbent and Pree, 1997; Sun et al., 2022). Tobacco thrips have developed resistance to pyrethroid and organic phosphate insecticides (Krob et al., 2022). Soybean thrips also developed varying degrees of resistance to emamectin benzoate, beta-cypermethrin, and imidacloprid (Tang et al., 2016). Therefore, searching and screening effective natural enemies for biological control of thrips is urgent.

Thrips (Insecta: Thysanoptera) Associated with Two Species of Live Birds (Cardinalis cardinalis and Zenaida macroua) in Northeast Arkansas

Dispersal is an important factor in shaping ecosystems and patterns of biodiversity. However, animals use several different modes of dispersal, each of which can have varying impacts on the ecology and evolutionary history of a group. One of these modes is phoresy, when an animal (the phorant) will temporarily attach itself to another animal (the host) as a means of dispersal. This behavior has been described in many groups of animals, but very infrequently in the thrips (Insecta: Thysanoptera). Here, we report the collection of 2 species of live thrips, Hoplothrips sp. and Neohydatothrips variabilis, from 2 species of live birds, Cardinalis cardinalis (Northern Cardinal) and Zenaida macroura (Mourning Dove), respectively, in northeast Arkansas. Most previous records of thrips associated with birds were from nesting material or found on deceased birds. The presence of thrips on live birds suggests some thrips are phoretic on birds, or at the very least that interactions between thrips and birds are more frequent than previously assumed.

Arthropod-Borne Virus Surveillance as a Tool to Study the Australian Mosquito Virome

Mosquitoes (n = 4381 in 198 pools) were collected in March and April 2018 to survey the presence of West Nile virus Kunjin strain in mosquito populations around crocodile farms in the Darwin region of the Northern Territory (NT) of Australia. While no Kunjin virus was detected in these mosquitoes, we applied our viral replicative intermediates screening system termed monoclonal antibodies to viral RNA intermediates in cells or MAVRIC to this set of samples. This resulted in the detection of 28 pools with virus replicating in C6/36 mosquito cells and the identification of three insect viruses from three distinct virus classes. We demonstrate the persistence of the insect-specific flavivirus Palm Creek virus in Coquillettidia xanthogaster mosquitoes from Darwin over almost a decade, with limited genetic drift. We also detected a novel Hubei macula-like virus 3 strain in samples from two mosquito genera, suggesting the virus, for which the sequence was originally detected in spiders and soybean thrips, might be involved in a horizontal transmission cycle between arthropods and plants. Overall, these data demonstrate the strength of the optimized MAVRIC system and contribute to our general knowledge of the mosquito virome and insect viruses.

The Effect of Species Soybean Vein Necrosis Orthotospovirus (SVNV) on Life Table Parameters of Its Vector, Soybean Thrips (Neohydatothrips variabilis Thysanoptera: Thripidae).

Simple SummarySoybean vein necrosis, caused by soybean vein necrosis virus (SVNV) is an important viral disease of soybeans that can be seed borne or insect vectored. This plant viral disease affects seed qualitative parameters, including seed oil content. Increased damage is observed in late planted soybeans. The disease is widespread, and almost all soybean-growing states in USA are affected. Globally, SVNV is reported in Canada, the United States, Egypt and Pakistan. In order to manage the disease, it is important to understand the vector’s biology and the effect of SVNV on life table parameters (survival, longevity, mortality, doubling time, generation, rate of intrinsic increase) of vector soybean thrips, which can help to establish pest management predictive models. We used an age-stage two-sex life table estimation model to define the effect of SVNV on the life parameters of male and female soybean thrips. Overall, we found that SVNV infection increased viruliferous thrips survival, longevity, gross reproduction rate, life expectancy and decreased population doubling time. Overall viruliferous thrips benefit from SVNV infection and transmission due to better survival, longevity and increased fitness.Soybean vein necrosis orthotospovirus (SVNV: Tospoviridae: Orthotospovirus), the causal agent of soybean vein necrosis disease, is vectored by soybean thrips Neohydatothrips variabilis (Beach, 1896), and to a lesser extent by five other thrips species. There is increasing incidence of soybean vein necrosis (SVN) disease in all soybean growing states in the United States, Canada, Egypt and Pakistan, necessitating a study of the system’s ecology and management. We addressed the effect of SVNV on the life table parameters of the vector. We used an ‘age-stage two-sex’ life table approach, which provided detailed life stage durations of each larval instar and adults (both sexes). Our results showed that the intrinsic rate of increase (r), finite rate of increase (λ) and mortality index (qx) were higher in the infected population, while the net reproduction rate (Ro), cumulative probability of survival (lx) and gross reproduction rate (GRR) were lower in the uninfected population. Overall, in both infected and uninfected populations, the number of eggs producing haploid males via arrhenotoky ranged from 9–12 per female. Male to female ratio was female biased in the infected population. Overall, our study provided evidence that virus infection, by decreasing the population doubling time, could enhance the virus and vector populations in soybeans.

Morphology of the Female Reproductive System of the Soybean Thrips, Neohydatothrips variabilis (Beach, 1896) (Thysanoptera: Thripidae).

Simple SummarySoybean thrips are an important vector of Soybean vein necrosis virus disease, found in all soybean-growing regions of the United States and Canada. The disease reduces the seed oil content and fatty acid profiles in infected plants. It is important to know the morphology of the female reproductive system of soybean thrips to understand the egg-laying mechanism and develop strategies for virus vector management. For this purpose, we used fuchsin staining, paraffin-based histology, dissections, serial block-face scanning electron microscopy and confocal laser scanning microscopy techniques to understand the structure and motorization of the internal and external genitalia of soybean thrips. We also investigated the egg-laying behavior of soybean thrips. The female reproductive system is composed of two ovaries, an oviduct, an accessory gland, an appendage gland, a common oviduct and a vagina. Female soybean thrips lay eggs in the parenchymatous tissues near the veins of the leaves. The appendage gland likely secretes lubrication to facilitate the movement of eggs through the external genitalia. Seven muscles support the movement of eggs from the ovaries to the leaf surface. The anatomy and probable role of each muscle is also described.Soybean thrips (Neohydatothrips variabilis) are an important phytophagous vector of the widely recognized Soybean vein necrosis orthotospovirus (SVNV). Understanding the egg-laying behavior of these thrips could aid in developing strategies for the management of the vector and virus. In this study, we described the egg-laying behavior of N. variabilis and reconstructed the three-dimensional morphology of the female terminalia by using serial block-face scanning electron microscopy (SBFSEM) and confocal laser scanning microscopy (CLSM). The female reproductive system consists of two panoistic ovaries consisting of eight ovarioles. The appendage gland is connected to the ovaries by two muscles, and to the body wall by a single muscle. The spermatheca is connected to the eighth tergum through four branched muscles, to the basivalvulae of the ovipositor by one muscle and to the vagina by a single muscle. The external genitalia are operated by seven muscles. The movement of the eggs inside the ovipositor is achieved by the back and forth “rocking” movement of the first valvulae and valvifer. Eggs are deposited into the parenchymatous tissue alongside leaf veins. To the best of our knowledge, this is the first study describing the internal and external genitalia of N. variabilis.

Complexity and Local Specificity of the Virome Associated with Tospovirus-Transmitting Thrips Species.

SUMMARYFrankliniella occidentalis (western flower thrips [WFT]) and Thrips tabaci (onion thrips [OT]) are insect species that greatly impact horticultural crops through direct damage and their efficient vectoring of tomato spotted wilt virus and iris yellow spot virus. In this study, we collected thrips of these species from 12 field populations in various regions in Italy. We also included one field population of Neohydatothrips variabilis (soybean thrips [ST]) from the United States. Total RNA data from high-throughput sequencing (HTS) were used to assemble the virome, and then we assigned putative viral contigs to each thrips sample by real-time reverse transcription-quantitative PCR (qRT-PCR). Excluding plant and fungal viruses, we were able to identify 61 viral segments, corresponding to 41 viruses: 14 were assigned to WFT, 17 to OT, and 1 to ST; 9 viruses could not be assigned to any species based on our stringent criteria. All these viruses are putative representative of new species (with only the exception of a sobemo-like virus that is 100% identical to a virus recently characterized in ST) and some belong to new higher-ranking taxa. These additions to the viral phylogeny suggest previously undescribed evolutionary niches. Most of Baltimore’s classes of RNA viruses were present (positive- and minus-strand and double-stranded RNA viruses), but only one DNA virus was identified in our collection. Repeated sampling in a subset of locations in 2019 and 2020 and further virus characterization in a subset of four thrips populations maintained in the laboratory allowed us to provide evidence of a locally persistent thrips core virome that characterizes each population.IMPORTANCE Harnessing the insect microbiome can result in new approaches to contain their populations or the damage they cause vectoring viruses of medical, veterinary, or agricultural importance. Persistent insect viruses are a neglected component of their microbiota. In this study, for the first time, we characterize the virome associated with the two model systems for tospovirus-transmitting thrips species, of utmost importance for the direct and indirect damage they cause to a number of different crops. The thrips virome characterized includes several novel viruses, which in some cases reveal previously undescribed clades. More importantly, some of the viruses we describe are part of a core virome that is specific and consistently present in distinct geographical locations monitored over the years, hinting at a possible mutualistic symbiotic relationship with their host.

Soybean Thrips (Thysanoptera: Thripidae) Harbor Highly Diverse Populations of Arthropod, Fungal and Plant Viruses.

Soybean thrips (Neohydatothrips variabilis) are one of the most efficient vectors of soybean vein necrosis virus, which can cause severe necrotic symptoms in sensitive soybean plants. To determine which other viruses are associated with soybean thrips, the metatranscriptome of soybean thrips, collected by the Midwest Suction Trap Network during 2018, was analyzed. Contigs assembled from the data revealed a remarkable diversity of virus-like sequences. Of the 181 virus-like sequences identified, 155 were novel and associated primarily with taxa of arthropod-infecting viruses, but sequences similar to plant and fungus-infecting viruses were also identified. The novel viruses were predicted to have positive-sense RNA, negative-stranded RNA, double-stranded RNA, and single-stranded DNA genomes. The assembled sequences included 100 contigs that represented at least 95% coverage of a virus genome or genome segment. Sequences represented 12 previously described arthropod viruses including eight viruses reported from Hubei Province in China, and 12 plant virus sequences of which six have been previously described. The presence of diverse populations of plant viruses within soybean thrips suggests they feed on and acquire viruses from multiple host plant species that could be transmitted to soybean. Assessment of the virome of soybean thrips provides, for the first time, information on the diversity of viruses present in thrips.

Transmission blockage of an orthotospovirus using synthetic peptides.

Orthotospoviruses are acquired by thrips during feeding on infected tissue. Virions travel through the foregut and enter midgut epithelial cells through the interaction between the viral glycoproteins and cellular receptors. Glycoprotein RGD motifs and N-linked glycosylation sites have been predicted to mediate receptor binding or play important roles in virus entry into host cells, yet their function needs to be validated. In this study, peptides derived from the soybean vein necrosis virus N glycoprotein were utilized to identify critical regions in virus-vector interactions. Transmission mediated by single Neohydatothrips variabilis dropped by more than 2/3 when thrips were fed on peptide NASIAAAHEVSQE or the combination of NASIRGDHEVSQE and RLTGECNITKVSLTN when compared to the controls; indicating that this strategy could significantly reduce transmission efficiency, opening new avenues in the control of diseases caused by orthotospoviruses.

Evaluation of Soybean for Resistance to Neohyadatothrips variabilis (Thysanoptera: Thripidae) Noninfected and Infected With Soybean Vein Necrosis Virus.

Soybean vein necrosis virus (SVNV) was first identified in Arkansas and Tennessee in 2008 and is now known to be widespread in the United States and Canada. Multiple species of thrips transmit this and other tospoviruses with Neohydatothrips variabilis (Beach) (soybean thrips) cited as the most efficient vector for SVNV. In this study, 18 soybean, Glycine max (L.) Merr., genotypes were evaluated in four experiments by infesting plants with noninfected and SVNV-infected thrips using choice and no-choice assays. In both choice experiments with noninfected and SVNV-infected thrips, the lowest number of immature soybean thrips occurred on plant introductions (PIs) 229358 and 604464 while cultivars Williams 82 and Williamsfield Illini 3590N supported higher counts of mature thrips. The counts between the two assays (noninfected and SVNV-infected thrips) were positively correlated. In both no-choice experiments with noninfected and SVNV-infected thrips, counts of thrips did not differ by soybean genotypes. Further studies are needed to characterize the inheritance and mechanisms involved in the resistance found in the choice assay.

Assessing soybean genotypes for feeding damage by Neohydatothrips variabilis (Thysanoptera: Thripidae)

The prevalence of soybean vein necrosis virus (SVNV) in soybean (Glycine max (L.), Merr.) across major producing areas in North America and its negative impact on seed oil content demonstrate the need for effective control strategies against the virus. Varieties with resistance to vectors could modify their behavior, reduce transmission and consequently disease incidence. In this study we evaluated feeding preference of viruliferous Neohydatothrips variabilis (Beach), the primary vector of SVNV on selected genotypes with different leaf pubescence. Low feeding genotypes were studied in-depth using imaging software to assess thrips injury in high resolution. We found that damage was reduced among genotypes with low pubescence levels. Given that there is no known SVNV-resistant germplasm, identifying resistance to vectors is a promising alternative strategy. The genotypes identified in this study could be the basis for breeding N. variabilis-resistant cultivars.

Vector Competence of Thrips Species to Transmit Soybean Vein Necrosis Virus.

Soybean vein necrosis virus (SVNV) is a newly discovered species of tospovirus infecting soybean plants that is transmitted by the primary vector, soybean thrips (Neohydatothrips variabilis), and two additional secondary vectors, tobacco thrips (Frankliniella fusca) and eastern flower thrips (F. tritici). This study was undertaken to elucidate the association between virus acquisition [6, 12, 24, and 48 h acquisition access period (AAP)] and transmission efficiency [12, 24, and 48 h inoculation access period (IAP)] in the primary vector, N. variabilis, and to examine the mechanisms of vector competence by analyzing the effect of AAP (6, 12, and 24 h) on virus infection in various tissues. In addition, we examined virus infection in tissues of the two secondary vectors. We found a significant effect of virus acquisition on transmission efficiency, transmission rate post 6 and 48 h AAP was significantly lower than 12 and 24 h AAP. Our analysis did not reveal a correlation between virus transmission rate and virus RNA in corresponding N. variabilis adults. On the contrary, N. variabilis adults harboring higher accumulation of the virus (>104) resulted in lower transmission rates. Analysis of SVNV infection in the tissues revealed the presence of the virus in the foregut, midgut (region 1, 2, and 3), tubular salivary glands and principal salivary glands (PSG) of adults of all three vector species, however, the frequency of infected tissues was highest in N. variabilis followed by F. fusca and F. tritici. The frequency of SVNV infection in individual tissues specifically the salivary glands was lowest after 6 h AAP compared to 12 and 24 h AAP. This finding is in agreement with the transmission assays, where significantly lower virus transmission rate was observed post 6 h AAP. In addition, N. variabilis adults with high PSG infection (12 and 24 h AAP) were likely to have high percentage of foregut and midgut region 2 infection. Overall, results from the transmission assays and immunolabeling experiments suggest that shorter AAP results in reduced virus infection in the various tissues especially PSG, which are important determinants of vector competence in SVNV-thrips interaction.

Monitoring Seasonal Distribution of Thrips Vectors of Soybean Vein Necrosis Virus in Alabama Soybeans.

Soybean vein necrosis virus (SVNV), a new virus in the genus Orthotospovirus, has been found in all soybean-growing regions in the United States and Ontario, Canada. Soybean thrips, Neohydatothrips variabilis (Beach) (Thysanoptera: Thripidae), tobacco thrips, Frankliniella fusca (Hinds) (Thysanoptera: Thripidae), and eastern flower thrips, Frankliniella tritici (Fitch) (Thysanoptera: Thripidae) are reported vectors of this virus, but there are no reports on their distribution in Alabama. A monitoring study was conducted in 2015 and 2016 to determine thrips species composition and abundance in Alabama soybean agroecosystems. Thrips were monitored weekly by collecting them on yellow sticky traps and soybean plant parts including foliage and reproductive structures. All three reported vectors of SVNV were identified in Alabama, with N. variabilis and F. tritici as the predominant species, while F. fusca was not consistently collected from soybean plants. Four additional thrips species were collected, of which Echinothrips americanus (Morgan) (Thysanoptera: Thripidae) was commonly found on soybean at all three locations. Results presented in this study provide new information about seasonal thrips species abundance in soybean agroecosystems in Alabama, and is an important first step to understanding thrips vector species of epidemiological importance in the Southern United States.

First Report of Soybean Vein Necrosis Virus Infecting Kudzu (Pueraria montana) in the United States of America

Soybean vein necrosis virus (SVNV) is a virus originally discovered in Arkansas and Tennessee and is currently present in all major soybean-producing states in the United States and Canada (Zhou and Tzanetakis 2013). Studies were carried out to investigate the role of kudzu (Pueraria montana) in SVNV epidemiology. Kudzu is present in millions of acres in the southeastern United States and is known to host at least another soybean-infecting virus, tobacco ringspot virus (TRSV) (Aboughanem-Sabanadzovic et al. 2014; Khankum et al. 2013). Eighty-five samples collected from 15 Mississippi counties during September 2015 were tested for SVNV infections using DAS-ELISA (Agdia Inc, U.S.A.) and three were infected by the virus. Two of the samples displayed mild deformation of young leaves, whereas the third was symptomless. In order to verify the results, virus-specific RT-PCR tests were performed on nucleic acid extracts from all ELISA-positive samples along with three SVNV-free kudzu plants and controls, represented by SVNV-infected and healthy soybeans. A DNA band of 236 bp corresponding to the NSs gene (Zhou and Tzanetakis 2013) was amplified only from the three ELISA-positive kudzu samples and positive controls. The products were directly sequenced in both directions and confirmed to be SVNV-specific as they shared 96 to 99% nt identity with corresponding region of the SVNV reference isolate (GenBank accession no. GU722319). In a greenhouse-based study, first instar larvae of soybean thrips (Neohydatothrips variabilis Beach) were fed on symptomatic soybean for virus acquisition and transferred to eight SVNV-free kudzu seedlings as described (Zhou and Tzanetakis 2013). Leaf and root tissues were randomly collected from virus-inoculated and mock-inoculated kudzu, respectively, at 6 weeks post inoculation. Total nucleic acids were isolated and RT-PCR was performed using primer set SdetF/SdetR (Zhou et al. 2011). Amplification products corresponding to the complete NP gene (834 bp) were obtained in both leaf and root tissues from five inoculated plants and shared 97 to 99% identity with the reference isolate (GenBank accession no. GU722319), whereas there was no amplification from mock-inoculated controls. Those results were further confirmed by dot blot immunoassay with infected plants remaining asymptomatic for at least a month post inoculation. Our findings represent the first report of SVNV infections of kudzu in the U.S.A. and the world. Kudzu is likely to play a role in the epidemiology of virus and disease. Furthermore, our results expand the range of pathogens (Asian soybean rust, TRSV) and insects (kudzu bug) that kudzu can sustain, indicating its ecological impact as an invasive species.

Factors Affecting Population Dynamics of Thrips Vectors of Soybean vein necrosis virus.

Thrips-infesting soybeans were considered of minor economic importance, but recent evidence of their ability to transmit a newly identified soybean virus, Soybean vein necrosis virus (SVNV), has raised their profile as pests. Season-long surveys were conducted using suction traps to determine the effects of temperature and precipitation on the spatiotemporal patterns of three vector species of SVNV, Neohydatothrips variabilis (Beach) (Thysanoptera: Thripidae) (soybean thrips), Frankliniella tritici (Fitch) (Thysanoptera: Thripidae) (eastern flower thrips), and Frankliniella fusca (Hinds) (Thysanoptera: Thripidae) (tobacco thrips) in soybean fields in Indiana in 2013 and 2014. In addition, soybean fields were surveyed for presence of SVNV in both years. We found that the magnitude and timing of thrips activity varied greatly for the three species. N. variabilis activity peaked in mid-August each year. The peak activity for F. tritici occurred between late-June, and a second peak in activity was observed in early-August, while F. fusca activity remained more or less the same with no peak. There was no gradient in thrips populations from southern to northern locations. This suggests that these insects are not migratory and may overwinter in soil or perennial noncrop host plants and other weed hosts in Indiana. The capture rates of N. variabilis and F. tritici were only related to temperature, and capture rates of F. fusca were not related to either variable. SVNV was first detected in mid-late August, which coincided with the peak of the primary vector, N. variabilis. The virus was not detected earlier in the season despite peaks in F. tritici activity. Our results may be used in weather-based models to predict both thrips dynamics as well as SVNV outbreaks.

Molecular Identification of Thrips Species Infesting Cotton in the Southeastern United States.

Traditional identification of thrips species based on morphology is difficult, laborious, and especially challenging for immature thrips. To support monitoring and management efforts of thrips as consistent and widespread pests of cotton (Gossypium hirsutum L.), a probe-based quantitative PCR (qPCR) assay with crude DNA extraction was developed to allow efficient and specific identification of the primary species of thrips infesting cotton. The assay was applied to identify over 5,000 specimens of thrips (including 3,366 immatures) collected on cotton seedlings from Alabama, Georgia, North Carolina, South Carolina, and Virginia in 2016. One half of all adult samples were examined by morphological identification, which provided a statistically equivalent species composition as the qPCR method. Frankliniella fusca (Hinds) (Thysanoptera: Thripidae) was the dominant species across all the locations (76.8-94.3% of adults and 81.6-98.0% of immatures), followed by Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae) in Georgia, North Carolina, and Virginia (4.6-19% of adults and 1.7-17.3% of immatures) or Frankliniella tritici (Fitch) (Thysanoptera: Thripidae) in South Carolina (10.8% of adults and 7.8% of immatures). Thrips tabaci (Lindeman) (Thysanoptera: Thripidae) and Neohydatothrips variabilis (Beach) (Thysanoptera: Thripidae) were occasionally found among adults but were rarely present among immature thrips. These five species of thrips represented 98.2-100% of samples collected across the Southeast. The qPCR assay was demonstrated to be a valuable tool for large-scale monitoring of species composition of thrips at different life stages in cotton. The tool will contribute to a better understanding of thrips population structure in cotton and could assist with development and application of improved management strategies.

Alternative Hosts for Soybean vein necrosis virus and Feeding Preferences of Its Vector Soybean Thrips

Soybean vein necrosis virus (SVNV), a tospovirus and one of the most widespread soybean viruses in North America, is primarily transmitted by soybean thrips (Neohydatothrips variabilis). Although soybean is not considered the primary plant host for SVNV, there is a dearth of knowledge about alternative host plants for SVNV. We therefore investigated whether commonly present specialty and cover crops in Iowa can serve as alternative hosts for SVNV. Seventeen cover crops and seven specialty crops were tested using mechanical and thrips inoculations. Clear symptoms of SVNV and systemic infection in buckwheat and clear local infection with possible systemic infection on melon were shown. Additionally, we compared soybean thrips feeding on 18 cover crops and determined that they preferred alfalfa, buckwheat, crimson clover, and red clover. Our results suggested that alternative host crops may harbor SVNV and be a possible source of inoculum for soybean.

Within-Plant Distribution and Dynamics of Thrips Species (Thysanoptera: Thripidae) in Cotton.

A 2-yr study in cotton (Gossypium hirsutum L.) was conducted to determine the abundance and species composition of thrips (Thysanoptera: Thripidae) on different plant parts throughout the season in Alabama, Georgia, North Carolina, South Carolina, and Virginia. Plant parts sampled included seedlings, terminals with two expanded leaves, leaves from the upper, middle, and lower sections of the canopy, white flowers, and medium-sized bolls. Adult thrips were significantly more abundant on seedlings and flowers in 2014, and on flowers followed by seedlings and leaves from the middle canopy in 2015. Immature thrips were significantly more abundant on seedlings, followed by flowers in 2014, and on seedlings followed by leaves from the lower canopy and flowers in 2015. Across locations and plant parts, thrips consisted of Frankliniella tritici (Fitch) (46.8%), Frankliniella fusca Hinds (23.5%), Frankliniella occidentalis (Pergande) (17.1%), Neohydatothrips variabilis (Beach) (7.4%), Thrips tabaci (Lindeman) (1.8%), and other species (3.4%). Frankliniella fusca represented 86.7% of all thrips on seedlings, while F. tritici was more abundant on terminals (51.6%), squares (57.5%), and flowers (75.1%). Across all leaf positions, F.fusca was the most abundant species (28.8%), followed by F. tritici (19.2%), N. variabilis (18.8%), F. occidentalis (12.9%), and T.tabaci (5.2%), as well as other species (15.0%). As neonicotinoid insecticides remain a primary tool to manage seedling infestations of F. fusca, our data indicate that mid- to late-season applications of neonicotinoid insecticides targeting other insect pests will intensify selection pressure for resistance on F. fusca, the primary pest of seedling cotton.

Seasonal Population Dynamics of Thrips (Thysanoptera) in Wisconsin and Iowa Soybean Fields.

With the discovery of Neohydatothrips variabilis (Beach) as a vector of Soybean vein necrosis virus (Family Bunyaviridae Genus Tospovirus), a relatively new pathogen of soybean, a multiyear study was initiated in Wisconsin (2013 and 2014) and Iowa (2014 and 2015) to determine the phenology and species composition of thrips in soybean fields. Yellow sticky card traps were used to sample thrips at regular intervals in five counties within each state's primary soybean-growing region. The assemblage of species present in Wisconsin was determined in all site-years, revealing that N. variabilis and other known vectors of tospoviruses were a relatively small percentage of the total thrips captures in 2013 (1.6%) and 2014 (3.6%). A repeated measures analysis was conducted on cumulative proportion thrips capture data within each state's sampling year to investigate differences in phenology, and standardized cumulative insect days were analyzed between sampling years within each state to determine differences in the relative magnitude of populations. Distinct seasonal trends were not detected based on location, as originally hypothesized, and thrips populations varied significantly among locations and between years. These results suggest that thrips populations may be overwintering in northern climates instead of relying solely on migrations to colonize northern soybean fields.