Aberrant splicing of a nicotinic acetylcholine receptor alpha 6 subunit is associated with spinosad tolerance in the thrips predator Orius laevigatus.

Susceptibility to insecticides is one of the limiting factors preventing wider adoption of natural enemies to control insect pest populations. Identification and selective breeding of insecticide tolerant strains of commercially used biological control agents (BCAs) is one of the approaches to overcome this constraint. Although a number of beneficial insects have been selected for increased tolerance to insecticides the molecular mechanisms underpinning these shifts in tolerance are not well characterised. Here we investigated the molecular mechanisms of enhanced tolerance of a lab selected strain of Orius laevigatus (Fieber) to the commonly used biopesticide spinosad. Transcriptomic analysis showed that spinosad tolerance is not a result of overexpressed detoxification genes. Molecular analysis of the target site for spinosyns, the nicotinic acetylcholine receptor (nAChR), revealed increased expression of truncated transcripts of the nAChR α6 subunit in the spinosad selected strain, a mechanism of resistance which was described previously in insect pest species. Collectively, our results demonstrate the mechanisms by which some beneficial biological control agents can evolve insecticide tolerance and will inform the development and deployment of insecticide-tolerant natural enemies in integrated pest management strategies.

Revisiting a pollen-transmitted ilarvirus previously associated with angular mosaic of grapevine.

We report the characterization of a novel tri-segmented RNA virus infecting Mercurialis annua, a common crop weed and model species in plant science. The virus, named "Mercurialis latent virus" (MeLaV) was first identified in a mixed infection with the recently described Mercurialis orthotospovirus 1 (MerV1) on symptomatic plants grown in glasshouses in Lausanne (Switzerland). Both viruses were found to be transmitted by Thrips tabaci, which presumably help the inoculation of infected pollen in the case of MeLaV. Complete genome sequencing of the latter revealed a typical ilarviral architecture and close phylogenetic relationship with members of the Ilarvirus subgroup 1. Surprisingly, a short portion of MeLaV replicase was found to be identical to the partial sequence of grapevine angular mosaic virus (GAMV) reported in Greece in the early 1990s. However, we have compiled data that challenge the involvement of GAMV in angular mosaic of grapevine, and we propose alternative causal agents for this disorder. In parallel, three highly-conserved MeLaV isolates were identified in symptomatic leaf samples in The Netherlands, including a herbarium sample collected in 1991. The virus was also traced in diverse RNA sequencing datasets from 2013 to 2020, corresponding to transcriptomic analyses of M. annua and other plant species from five European countries, as well as metaviromics analyses of bees in Belgium. Additional hosts are thus expected for MeLaV, yet we argue that infected pollen grains have likely contaminated several sequencing datasets and may have caused the initial characterization of MeLaV as GAMV.

Genome-wide identification of cuticle protein superfamily in Frankliniella occidentalis provide insight into the control of both insect vectors and plant virus.

The structural cuticle proteins (CPs) play important roles in the development and fitness of insects. However, knowledge about CP gene superfamily is limited in virus-transmitting insect vectors, although its importance on transmission of plant virus has been gradually emphasized. In this study, the genome-wide identification of CP superfamily was conducted in western flower thrips Frankliniella occidentalis that is the globally invasive pest and plant virus vector pest. The pest transmits notorious tomato spotted wilt virus (TSWV) around the world, causing large damage to a wide array of plants. One hundred and twenty-eight F. occidentalis CP genes (FoCPs) were annotated in this study and they were classified into 10 distinct families, including 68 CPRs, 16 CPAP1s, 6 CPAP3s, 2 CPCFCs, 10 Tweedles, 4 CPFs, 16 CPLCPs, and 6 CPGs. The comprehensive analysis was performed including phylogenetic relationship, gene location and gene expression profiles during different development stages of F. occidentalis. Transcriptome analysis revealed more than 30% FoCPs were upregulated at least 1.5-fold when F. occidentalis was infected by TSWV, indicating their potential involvement in TSWV interactions. Our study provided an overview of F. occidentalis CP superfamily. The study gave a better understand of CP's role in development and virus transmission, which provided clues for reducing viral damages through silencing CP genes in insect vectors.

Inbreeding effects on different lineages of Thrips tabaci (Thysanoptera: Thripidae).

Inbreeding can have detrimental effects on reproductive fitness, but the extent of lineage-specific variation in these effects remains poorly understood. This study investigated the effects of brother and sister inbreeding on reproductive fitness in 2 lineages (L1 and T) of T. tabaci. Inbred females from both lineages exhibited a significant reduction in longevity compared with the control group. The L1 lineage experienced a 27% and 43% decrease in longevity in the F2 and F3 generations, respectively, while the T lineage showed a similar trend with a 30% and 44% decrease. The T lineage consistently displayed slightly longer lifespans than the L1 lineage across all generations. Brother and sister inbreeding also led to a decrease in fecundity rates in both lineages. In the F3 generation, the number of eggs laid decreased by 59% compared with the F2 generation. The T lineage consistently exhibited slightly lower fecundity rates compared with the L1 lineage. Egg hatchability rates declined with subsequent inbreeding, with the F3 generation showing lower rates compared with the F2 generation. However, the T lineage did not exhibit a significant difference in inbreeding depression for egg hatchability rates, while the L1 lineage demonstrated a noticeable decrease. Deformities observed in male L1 lineage resulting from inbreeding were consistent with disruptions in normal developmental processes, affecting various body parts such as legs, antennae, and wings. Continued inbreeding increased susceptibility to inbreeding depression in terms of longevity, fecundity, and egg hatchability.

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.

Leaf-feeding species of the genus Liothrips from China (Thysanoptera, Phlaeothripinae).

The 250 species of the second largest genus of Thysanoptera, Liothrips, are known as feeding mainly on green leaves, with many inducing galls or associated with galls. In China, 33 species are recognized including L. brevis sp. n., L. elongatus sp. n., L. longistylus sp. n., L. motuoensis sp. n., L. piceae sp. n., L. populi sp. n. and L. tibetanus sp. n., also seven species are recorded from this country for the first time. Four Hans Liothrips species are considered as new synonymies of L. vaneeckei that might be widespread in the Holarctic region. Three species are newly combined as Liothrips aporosae comb.n., Teuchothrips fuscus comb.n. and T. turkestanicus comb.n. The illustrated identification key to Chinese Liothrips species excludes L. hsuae but includes L. mirabilis due to its potential as a pest of Piper plants are growing throughout Southern China. Biology, structural variation, and generic relationships are also discussed.

A chromosome-level genome for the flower thrips Frankliniella intonsa.

The flower thrips Frankliniella intonsa (Thysanoptera: Thripidae) is a common insect found in flowers of many plants. Sometimes, F. intonsa causes damage to crops through direct feeding and transmission of plant viruses. Here, we assembled a chromosomal level genome of F. intonsa using the Illumina, Oxford Nanopore (ONT), and Hi-C technologies. The assembled genome had a size of 209.09 Mb, with a contig N50 of 997 bp, scaffold N50 of 13.415 Mb, and BUSCO completeness of 92.5%. The assembled contigs were anchored on 15 chromosomes. A set of 14,109 protein-coding genes were annotated in the genome with a BUSCO completeness of 95.0%. The genome contained 491 non-coding RNA and 0.57% of interspersed repeats. This high-quality genome provides a valuable resource for understanding the ecology, genetics, and evolution of F. intonsa, as well as for controlling thrips pests.

Predator-Prey Interaction Between Xylocoris sordidus (Hemiptera: Anthocoridae) and Enneothrips enigmaticus (Thysanoptera: Thripidae).

The peanut thrips, Enneothrips enigmaticus (Thysanoptera: Thrypidae), is an important pest of the peanut (Arachis hypogaea) in South America. Due to concerns about the environment and human health induced by the extensive use of pesticides in the management control of pests, environmentally and friendlier tactics must be targeted. Thus, this study investigates, for the first time, the behavior of Xylocoris sordidus (Hemiptera: Anthocoridae) as a biological control agent for E. enigmaticus. The methodology included no-choice tests to assess whether the predation rate varies according to the developmental stage of the prey, as well as the predator's developmental stage with the highest predation capacity. Additionally, an analysis of the functional response of adult and 5th instar nymphs of X. sordidus exposed to different densities of E. enigmaticus nymphs (1, 2, 4, 8, 16, and 32) was conducted. The results confirm the predation of peanut thrips by X. sordidus, with a higher predation rate in the nymphal stages of the prey. There was no difference in predation capacity between predator nymphs and adults, and exhibiting a type II functional response. Therefore, the potential of X. sordidus as a biological control agent for E. enigmaticus is confirmed, showing the importance of adopting measures to preserve this predator in peanut crops.

Control effect and field application of four predatory Orius species on Megalurothrips usitatus (Thysanoptera: Thripidae).

Megalurothrips usitatus (Bagrall) is one of the most important pests of cowpea, Vigna unguiculata (Linn.) Walp in South China. Four Orius species, including Orius minutus (L.), Orius nagaii (Yasunaga), Orius sauteri (Poppius), and Orius strigicollis (Poppius), have been commercially produced and widely used as natural enemies of pests in China. In this study, we evaluated the control efficiency of these Orius species on M. usitatus in tropical Hainan Province, China, by recording the survival rates, developmental times, and predation effects in laboratory and semi-field conditions. Laboratory experiments showed that all these 4 Orius species preyed on M. usitatus under the experimental temperatures (25, 30, and 35 °C), and O. strigicollis exhibited the highest survival rate and predation effect. Semi-field cage experiments showed that the control effect of 4 Orius species on M. usitatus was significantly higher than that under normal chemical control, with O. strigicollis having the highest effect. Greenhouse experiments in Hainan Province, China, confirmed that O. strigicollis had a significant control effect on M. usitatus. Our study indicated that O. strigicollis has a significant potential for the control of M. usitatus in cowpea fields in southern China.

Changes in primary metabolite content may affect thrips feeding preference in soybean crops.

Past research has characterized the induction of plant defenses in response to chewing insect damage. However, little is known about plant responses to piercing-sucking insects that feed on plant cell-contents like thrips (Caliothrips phaseoli). In this study, we used NMR spectroscopy to measure metabolite changes in response to six days of thrips damage from two field-grown soybean cultivars (cv.), known for their different susceptibility to Caliothrips phaseoli. We observed that thrips damage reduces sucrose concentration in both cultivars, while pinitol, the most abundant leaf soluble carbohydrate, is induced in cv. Charata but not in cv. Williams. Thrips did not show preference for leaves where sucrose or pinitol were externally added, at tested concentration. In addition, we also noted that cv. Charata was less naturally colonized and contained higher levels of trigonelline, tyrosine as well as several compounds that we have not yet identified. We have established that preference-feeding clues are not dependent on the plants major soluble carbohydrates but may depend on other types of compounds or leaf physical characteristics.

Plasticity of cold and heat stress tolerance induced by hardening and acclimation in the melon thrips.

Extreme temperatures threaten species under climate change and can limit range expansions. Many species cope with changing environments through plastic changes. This study tested phenotypic changes in heat and cold tolerance under hardening and acclimation in the melon thrips, Thrips palmi Karny (Thysanoptera: Thripidae), an agricultural pest of many vegetables. We first measured the critical thermal maximum (CTmax) of the species by the knockdown time under static temperatures and found support for an injury accumulation model of heat stress. The inferred knockdown time at 39 °C was 82.22 min. Rapid heat hardening for 1 h at 35 °C slightly increased CTmax by 1.04 min but decreased it following exposure to 31 °C by 3.46 min and 39 °C by 6.78 min. Heat acclimation for 2 and 4 days significantly increased CTmax at 35 °C by 1.83, and 6.83 min, respectively. Rapid cold hardening at 0 °C and 4 °C for 2 h, and cold acclimation at 10 °C for 3 days also significantly increased cold tolerance by 6.09, 5.82, and 2.00 min, respectively, while cold hardening at 8 °C for 2 h and acclimation at 4 °C and 10 °C for 5 days did not change cold stress tolerance. Mortality at 4 °C for 3 and 5 days reached 24.07 % and 43.22 % respectively. Our study showed plasticity for heat and cold stress tolerance in T. palmi, but the thermal and temporal space for heat stress induction is narrower than for cold stress induction.

Advanced methods for insect nets: red-colored nets contribute to sustainable agriculture.

Development of advanced pest control methods that do not rely on insecticides is an important issue for sustainable agriculture. Particularly with regards to micro pests that are not only highly resistant to various insecticides but also because we are running out of options for which insecticide to use against them, resulting in enormous economic damage worldwide. Here we report that the effectiveness of the conventional insect net can be greatly advanced by changing their color to red that helps significantly reduce pesticide use. We demonstrate the red effect using Onion thrips, Thrips tabaci a main vector of Iris Yellow Spot Virus (IYSV) and Tomato Spotted Wilt Virus (TSWV) that cause serious damage to various vegetables. New red nets succeeded in suppressing the invasion rates and damages (white spots on the leaves) in a Welsh onion greenhouse with minimum use of pesticides. We discuss how red nets are compatible with labor-saving, sustainable agriculture and the future potential of "optical pest control" based on insect color vision and its behavioral response.

Evolutionary origin and distribution of amino acid mutations associated with resistance to sodium channel modulators in onion thrips, Thrips tabaci.

In onion thrips Thrips tabaci, reduced sensitivity of the sodium channel caused by several sodium channel mutations have been correlated with pyrethroid resistance. For this study, using mitochondrial cytochrome c oxidase subunit I gene sequences, we examined the phylogenetic relation among a total of 52 thelytokous and arrhenotokous strains with different genotypes of the sodium channel mutations. Then, we used flow cytometry to estimate their ploidy. Results showed that the strains are divisible into three groups: diploid thelytoky, triploid thelytoky, and diploid arrhenotoky. Using 23 whole genome resequencing data obtained from 20 strains out of 52, we examined their genetic relation further using principal component analysis, admixture analysis, and a fixation index. Results showed that diploid and triploid thelytokous groups are further classifiable into two based on the sodium channel mutations harbored by the respective group members (strains). The greatest genetic divergence was observed between thelytokous and arrhenotokous groups with a pair of T929I and K1774N. Nevertheless, they shared a genomic region with virtually no polymorphism around the sodium channel gene loci, suggesting a hard selective sweep. Based on these findings, we discuss the evolutionary origin and distribution of the sodium channel mutations in T. tabaci.

Emerging challenges in the management of Orthotospoviruses in Indian agriculture.

Orthotospoviruses, a genera of negative-sense ssRNA viruses transmitted by thrips, have gained significant attention in recent years due to their detrimental impact on diverse crops, causing substantial economic losses and posing threats to food security. Orthotospoviruses are characterised by a wide range of symptoms in plants, including chlorotic/necrotic spots, vein banding, and fruit deformation. Seven species, including four definite and three tentative species in the genus Orthotospovirus, have so far been documented on the crops of the Indian subcontinent. Management of Orthotospoviruses under field conditions is challenging since they have a wide host range, adaptation to versatile environmental conditions, a lack of promising resistance sources, and the ubiquitous nature of thrips and their transmission through a propagative manner. Our present review elucidates the significance, molecular biology and evolutionary relationship of Orthotospoviruses; vector population; and possible management strategies for Orthotospoviruses and their vectors in the scenario of the Indian subcontinent.

The extraordinary rearrangement of mitochondrial genome of the wheat pest, Aptinothrips stylifer and the mitochondrial phylogeny of Thripidae (Thysanoptera).

The mitochondrial gene order in Thysanoptera is notably distinct and highly rearranged, with each species exhibiting its own unique arrangement. To elucidate the relationship between gene rearrangements and phylogeny, the complete mitochondrial genome (mitogenome) of the wheat pest, Aptinothrips stylifer, was sequenced and assembled, spanning a total length of 16,033 bp. Compared with the ancestral arthropod mitogenome, significant rearrangement differences were evident in A. stylifer, whereas the gene order between A. stylifer and Anaphothrips obscurus was similar. Phylogenetic trees were reconstructed based on all 13 protein-coding gene sequences using Bayesian inference and maximum-likelihood methods, both yielding similar topological structures. Notably, A. stylifer was robustly clustered with A. obscurus, affirming its classification within Anaphothrips genus group. This exemplifies the potential correlation between gene rearrangements and phylogeny in the Thripidae family. Additionally, the mitogenome of A. stylifer exhibited several atypical features, including: (1) Three putative control regions (CRs) in close proximity, with CR2 and CR3 displaying partial similarity, and CR1 differing in base composition; (2) Two transfer RNAs (tRNAs), trnS1 and trnV, lacking the DHU arm; (3) Two ribosomal RNA (rRNA) genes inverted and positioned distant from each other; (4) Negative AT and GC skew (AT skew = -0.001, GC skew = -0.077); (5) One transposition (nad6), one inverse transposition (trnQ), four inversions (trnF, trnH, trnC, and gene block nad1-trnL1-rrnL-trnV-rrnS), and four tandem duplication random loss events; and (6) Two protein-coding genes, nad2 and atp8, terminated with an incomplete stop codon "T".

Evaluation of fumigant toxicity of cyclohexanone to 5 species of insect pests.

Cyclohexanone is a major precursor for nylon production and is also used as a pesticide solvent. In this study, cyclohexanone was evaluated as a fumigant against rice weevil adults, confused flour beetle adults, western flower thrips larvae and adults, spotted wing drosophila adults, and subterranean termite workers. Cyclohexanone fumigation was effective against all 5 insects, and there were considerable variations in susceptibility to cyclohexanone fumigation among the 5 species. At 20 °C, complete control of spotted wing drosophila adults was achieved in 1-h fumigation with 25 µl/l of cyclohexanone and complete control of eastern subterranean termite workers was achieved in 3-h fumigations with 50 µl/l dose of cyclohexanone. Stored-product insects confused flour beetle, and rice weevil adults were more tolerant to cyclohexanone fumigation. Fumigations of 24 h with 75 µl/l dose of cyclohexanone caused 100% mortality of rice weevil adults and 98% mortality of confused flower beetle adults. Even at a 100 µl/l dose, the 24-h fumigations did not achieve 100% mortality of confused flour beetle adults. At 5 °C, complete control of western flower thrips was achieved in 3- and 6-h fumigations with 100 and 50 µl/l doses of cyclohexanone, respectively. Cyclohexanone vapor concentrations were measured using cyclohexanone detector tubes. Vapor concentrations were far below the expected saturation concentration indicating that most cyclohexanone did not exist as vapor in fumigation chambers. The results of effective control of all 5 insect species suggest that cyclohexanone has the potential to be used as a fumigant for postharvest pest control.

Uridine diphosphate glucosyltransferases are involved in spinosad resistance in western flower thrips Frankliniella occidentalis (Pergande).

Uridine diphosphate glucosyltransferases (UGTs) play crucial roles in the insect detoxification system and are associated with pesticide resistance. Our previous transcriptomic analysis of spinosad-susceptible (Ivf03) and resistant (NIL-R) Frankliniella occidentalis revealed numerous upregulated UGT genes in the NIL-R strain, suggesting their potential contribution to spinosad resistance. To investigate this hypothesis, here we conducted UGT activity assays and spinosad induction experiments, employing RNA interference (RNAi) techniques for gene function validation. We found significantly elevated UGT activity in the NIL-R strain compared to Ivf03, with 5-nitrouracil showing a substantial synergistic effect on the resistant strain. Eighteen UGT genes were identified in F. occidentalis, with gene expansion and duplication observed within families UGT466, 467, and 468. Ten out of the eighteen UGTs exhibited higher expression levels in NIL-R, specifically FoUGT466B1, FoUGT468A3, and FoUGT468A4 consistently being upregulated across nymphs, males, and females. RNAi-based functional validation targeting these three UGT genes led to increased susceptibility to spinosad in a life stage-, sex-, and dose-dependent manner. These results indicate that UGTs are indeed involved in spinosad resistance in F. occidentalis, and the effects are dependent on life stage, sex, and dose. Therefore, sustainable control for F. occidentalis resistance should always consider these differential responses.

Delayed spinetoram application is useful in managing Scirtothrips dorsalis Hood (Thysanoptera: Thripidae) in Florida strawberry.

Scirtothrips dorsalis Hood (Thysanoptera: Thripidae) is an invasive, early-season pest of strawberry in Florida, causing feeding injury to young foliage that results in stunted plant growth and yield loss. Spinetoram, an effective insecticide for thrips pests with up to 3 applications per season permitted in strawberry, is often applied repeatedly during the early-season (Oct-Nov) to manage S. dorsalis, leaving few or no applications for flower thrips pests later in the season (Dec-Mar). Therefore, new strategies are needed to manage S. dorsalis with less insecticide, with the hypothesis that the first insecticide application can be delayed because young strawberry plants can compensate for minor feeding injury without compromising strawberry yield. Experiments conducted in strawberry field plots in Balm, FL, during 2018 and 2019 showed that delaying a spinetoram application for 14 days after infesting a plant with zero, 5, 10, or 20 S. dorsalis adults did not reduce the plant vigor and yield compared to spinetoram application after 4 days. Furthermore, young plants recovered from injury (10-30% bronzing injury on leaf veins and petioles) due to 1 or 2 S. dorsalis adults or larvae per trifoliate. A strategy of delaying the first spinetoram application when plants have 4-5 trifoliates should help reduce the number of insecticide applications needed for S. dorsalis management and reserve spinetoram applications for later in the season. Lower input costs in Florida strawberry without compromising yields due to thrips damage will improve the economics and sustainability of production systems.

Enneothrips Hood: a Neotropical genus of leaf-feeding thrips (Thysanoptera: Thripidae) with generic diagnosis and four new species.

Enneothrips is a lineage of leaf-feeding thrips conventionally placed in the Anaphothrips genus-group (Thripinae) and exclusively found in the Neotropics. Here we describe E. amazonicus sp. n., E. fulbrightae sp. n. and E. manauara sp. n. from the Brazilian Amazon and E. atlanticus sp. n. from the Brazilian Atlantic Forest, together with an illustrated key to all ten species now recognized in the genus.

A new species of the genus Scirtothrips (Thysanoptera, Thripidae) from India.

A new species of Scirtothrips is described from India, S. donumdei, collected on leaves of Senegalia pennata (Fabaceae). Partial mitochondrial cytochrome c oxidase subunit 1 (mtCOI) gene sequence of the species was sequenced and the annotated sequence was submitted to NCBI GenBank.