Flower Thrips Research Articles

The role of ornamental plants as hosts of Tomato chlorotic spot virus and its vector thrips affecting tomato production

The tomato industry in South Florida (USA) is seriously affected by recently emerging Tomato chlorotic spot virus (TCSV). Western flower thrips, Frankliniella occidentalis (Pergande), and common blossom thrips, Frankliniella schultzei (Trybom) (Thysanoptera: Thripidae), are the two known vectors of TCSV in Florida. In the present study, the presence of thrips vectors and TCSV in 24 flowering ornamental plant species was observed in South Florida. The two thrips vectors, as well as melon thrips, Thrips palmi Karny (Thysanoptera: Thripidae), were abundant in the area; they were observed with a range from high (83.1 per sample of 10 flowers) in Hibiscus rosa-sinensis L. to low (3.7 per sample of 10 flowers) in Catharanthus roseus (L.) G. Don in a nursery study. In a subsequent greenhouse study, we selected seven species of ornamentals, among which the species with the highest thrips abundance, and planted them next to tomato, to determine their effects on TCSV incidence and thrips abundance in tomatoes. Tomatoes with Portulaca oleracea L. next to them showed a higher number of TCSV-infected plants (4.25 plants per plot in 2017, and 3.25 plants per plot in 2018) compared to tomatoes with some of the other ornamentals next to them. We report the presence of TCSV through reverse transcriptase polymerase chain reaction (RT-PCR) analysis in Lantana camara L., H. rosa-sinensis, Mandevilla spec., Gazania linearis (Thunb.) Druce, Hemerocallis spec., Agastache spec., and P. oleracea. Identification of alternative hosts of TCSV and thrips vectors can be helpful to evaluate the ongoing management programs and develop future programs in local tomato-growing areas.

Efecto de un insecticida sintético y un botánico sobre plagas, enemigos naturales y productividad del melón

Melon is attacked by pests such as the whitefly, Bemisia tabaci (Gennadius), the cotton aphid, Aphis gossypii Glover, the flower thrips, Frankliniella occidentalis (Pergande) as well as Diaphania worms that can affect yield and crop productivity. To control it, frequent spraying of organo-synthetic insecticides is carried out, which can generate ecological imbalances. During two productive cycles, experimental plots were established to test the effect of an organo-synthetic insecticide and a botanical one on some pests, a natural enemy and on melon productivity. The treatments tested were, 1. Organo-synthetic insecticide: lambda-cyhalothrin + thiamethoxam. 2. Botanical insecticide: azadirachtin. 3. Untreated plot. The populations of A. gossypii, B. tabaci, F. occidentalis, percentage of fruits damaged by Diaphania spp. (% FDD), and the effect on parasitism in B. tabaci (% PBT), as well as on yield (t.ha-1) and crop productivity. The populations of A. gossypii, B. tabaci, F. occidentalis, fruits damaged by Diaphania spp. (% FDD), and the effect on parasitism in B. tabaci (% PBT), as well as on crop yield and productivity. The % FDD, the populations of A. gossypii and F. occidentalis did not show differences between treatments. The yields were higher in plots treated with azadirachtin, where there were lower populations of B. tabaci and higher % PBT. Productivity presented a negative correlation with the populations of B. tabaci. Despite the control exerted by azadirachtin on B. tabaci, there was a decrease in productivity, which added to the damage of Diaphania spp. suggest the importance of these pests and for their management other alternatives should be tested that reduce populations to levels that do not affect yield and at the same time guarantee sustainable production.

A narrow host-range and lack of persistence in two non-target insect species of a bacterial symbiont exploited to deliver insecticidal RNAi in Western Flower Thrips.

Insecticidal RNAi is a targeted pest insect population control measure. The specificity of insecticidal RNAi can theoretically be enhanced by using symbiotic bacteria with a narrow host range to deliver RNAi, an approach termed symbiont-mediated RNAi (SMR), a technology we have previously demonstrated in the globally-invasive pest species Western Flower Thrips (WFT). Here we examine distribution of the two predominant bacterial symbionts of WFT, BFo1 and BFo2, among genome-sequenced insects. Moreover, we have challenged two non-target insect species with both bacterial species, namely the pollinating European bumblebee, Bombus terrestris, and an insect predator of WFT, the pirate bug Orius laevigatus. Our data indicate a very limited distribution of either symbiont among insects other than WFT. Moreover, whereas BFo1 could establish itself in both bees and pirate bugs, albeit with no significant effects on insect fitness, BFo2 was unable to persist in either species. In terms of biosafety, these data, together with its more specific growth requirements, vindicate the choice of BFo2 for delivery of RNAi and precision pest management of WFT.

Semiochemicals Associated with the Western Flower Thrips Attraction: A Systematic Literature Review and Meta-Analysis

The study of the semiochemicals of the western flower thrips (WFT), Frankliniella occidentalis, Pergande (Thysanoptera: Thripidae), is a relevant topic that spans the last two decades. Approximately a hundred articles published on this subject from 2000 to 2022 can be found in academic databases, representing approximately 5% of the research on this important pest. These topics have generated a platform for novel research with a high potential for development. However, to move on to a new research step, an effectiveness evaluation of the compounds discovered so far is necessary. This review conducted a systematic analysis of the research focused on the semiochemicals (kairomones, pheromones, and attractants) for this pest. Papers from the past three decades on WFT attraction to semiochemicals were collected from databases using the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) guidelines. The number of individuals attracted to compounds was extracted from the papers and compiled for analysis. With this information, an attraction ratio was calculated. Forty-one possible attractants were found in the literature, with methyl isonicotinate being the most-studied compound so far, with the third-highest attraction ratio. δ-Decalactone was the compound with the highest attraction ratio, but it was one of the least studied. A meta-analysis of the WFT choosing proportion was performed for the compounds with more trials found in the literature. The predicted mean choice percentages for methyl isonicotinate (MIN) and Lurem-TR, the MIN's commercial product, were 76.6% and 66.6%, respectively. There was a convergence among the analyzed studies showing a high degree of research focus on the same group of nitrogen-containing compounds (mainly the pyridine structure). These findings call for future research to diversify the discovery and evaluation of attractive compounds in this relevant study area.

Efficacy of Oil and Photosensitizer against Frankliniella occidentalis in Greenhouse Sweet Pepper.

Many common insect pests have developed resistance against the pesticides currently available, to the point where pest and disease management has become extremely difficult and expensive, increasing pressure on agriculture and food production. There is an urgent need to explore and utilize alternatives. Due to their unique mode of action, photosensitizers may be able to control insect pests effectively, especially in combination with oil-based products, without the risk of resistance build-up. In this study, the efficacy of a mineral oil-based horticultural spray oil, PureSpray™ Green (PSG), and a sodium magnesium chlorophyllin photosensitizer formulation, SUN-D-06 PS, were evaluated and compared to a registered cyantraniliprole insecticide (as positive control) and a negative control against western flower thrips (WFT), Frankliniella occidentalis. In detached leaf ingestion assays, PSG at high concentration was more effective than low concentration, causing >70% WFT mortality, whilst SUN-D-06 PS + PSG caused higher mortality than cyantraniliprole after five days of feeding. The same combination was as effective as cyantraniliprole in the contact assay. In greenhouse pepper, the photosensitizer decreased the WFT more than mineral oil applied alone, whilst a combination treatment of SUN-D-06 PS + PSG was most effective, decreasing the WFT population to fewer than four WFT per plant. SUN-D-06 PS + PSG shows promise as a sustainable, economical way of controlling WFT, with the potential to be incorporated into existing integrated pest (and disease) management (IPM) programs with ease.

Multigenerational variation in the nutrients and digestion of western flower thrips (Frankliniella occidentalis) depends on the nutritive quality of different foods

Western flower thrips (WFTs), Frankliniella occidentalis (Thysanoptera, Thripidae), is one of the most serious pests that attack rose flowers. Little is known about the effect of different parts of the rose flower on nutritional contents and digestive enzyme activities in thrips. This study assessed variations in the nutritional contents and digestive enzyme activities in the second-instar larvae and adults WFTs fed on 3 food types (rose petals, rose flowers, and honey solution + kidney bean pods) for multiple generations. The highest contents of soluble sugar (in 10% honey solution + kidney bean pods), amino acid (in rose flowers), and protein (in rose flowers) were observed, respectively. Soluble sugar and protein contents in the second-instar larvae and adults fed on rose petals decreased in the F1 generation but increased in the F2 generation and remained at higher levels until the F7 generation. Feeding of thrips with 3 food types increased the lipid content in the F1 generation, which peaked in the F2 generation and remained high until the F7 generation. In most cases, α-amylase and trypsin activities significantly decreased in the F1 generation after feeding on rose petals and then prominently increased in the F2 generation. In contrast, chymotrypsin activity remarkably increased and peaked in the F1 generation after second-instar larvae thrips fed on rose petals. There were correlations among the contents of 3 nutrient related positively with the activities of α-amylase and trypsin in WFTs second-instar larvae and adults, respectively. Overall, variations in the nutrient properties of the 3 food types caused changes in nutrient contents and digestive enzyme activities in thrips.

A push-pull strategy to control the western flower thrips, Frankliniella occidentalis, using alarm and aggregation pheromones.

Since the first report in 1993 in Korea, the western flower thrips, Frankliniella occidentalis, has been found in various crops throughout the country. Although more than 20 different chemical insecticides are registered to control this insect pest, its outbreaks seriously damage crop yields, especially in greenhouses. This study developed a non-chemical technique to control F. occidentalis infesting hot peppers cultivated in greenhouses. The method was based on behavioral control using an alarm pheromone ("Push") to prevent the entry of the thrips into greenhouses and an aggregation pheromone ("Pull") for mass trapping inside the greenhouses. The greenhouse fences were treated with a wax formulation of the alarm pheromone and a yellow CAN trap covered with sticky material containing the aggregation pheromone was constructed and deployed inside the greenhouses. Field assay demonstrated the efficacy of the push-pull tactics by reducing thrips density in flowers of the hot peppers as well as in the monitoring traps. Especially, the enhanced mass trapping to the CAN trap compared to the conventional yellow sticky trap led to significant reduction in the thrips population. This novel push-pull technique would be applicable to effectively control F. occidentalis in field conditions.

Snake River alfalfa virus, a persistent virus infecting alfalfa (Medicago sativa L.) in Washington State, USA

Here we report an occurrence of Snake River alfalfa virus (SRAV) in Washington state, USA. SRAV was recently identified in alfalfa (Medicago sativa L.) plants and western flower thrips in south-central Idaho and proposed to be a first flavi-like virus identified in a plant host. We argue that the SRAV, based on its prevalence in alfalfa plants, readily detectable dsRNA, genome structure, presence in alfalfa seeds, and seed-mediated transmission is a persistent new virus distantly resembling members of the family Endornaviridae.

FIRST REPORT OF COMMON BEAN FLOWER THRIPS Megalurothrips usitatus Bagnall IN COSTA RICA

<p><strong>Background: </strong>The species <em>Megalurothrips usitatus</em> is a thrips insect that has been recorded in Asia, Oceania, Australia and recently in America, attacking legume crops.<strong> Objective: </strong>to report <em>Megalurothrips usitatus</em> as species associated with flowers of common bean plants in Costa Rica.<strong> Methodology: </strong>the thrips from three growing bean locations were sampled and characterized through light microscopy in Costa Rica. Furthermore, a phylogenetic analysis of the COI gene compared with the databases of the National Center for Biotechnology Information (NCBI) was performed.<strong> Results: </strong>The species was recorded in three bean growing areas (Sardinal of Guanacaste, Estación Experimental Agrícola Fabio Baudrit Moreno in Alajuela and La Managua in Quepos).<strong> Implications:</strong> the new report of the insect in flowers of <em>Phaseolus vulgaris</em> implies future monitoring actions and respective integrated management; ignoring thrips populations could cause losses in the bean's regional production.<strong> Conclusion: </strong>the bean flower thrips is reported for the first time in Costa Rica. <strong></strong></p>

Temporal decline of genetic differentiation among populations of western flower thrips across an invaded range

Temporal decline of genetic differentiation among populations of western flower thrips across an invaded range

Two Alimentary Canal Proteins, Fo-GN and Fo-Cyp1, Act in Western Flower Thrips, Frankliniella occidentalis TSWV Infection.

Tomato spotted wilt virus (TSWV) is a plant virus that causes massive economic damage to high-valued crops. This virus is transmitted by specific thrips, including the western flower thrips, Frankliniella occidentalis. TSWV is acquired by the young larvae during feeding on infected host plants. TSWV infects the gut epithelium through hypothetical receptor(s) and multiplies within the cells for subsequent horizontal transmission to other plant hosts via the salivary glands during feeding. Two alimentary canal proteins, glycoprotein (Fo-GN) and cyclophilin (Fo-Cyp1), are thought to be associated with the TSWV entry into the gut epithelium of F. occidentalis. Fo-GN possesses a chitin-binding domain, and its transcript was localized on the larval gut epithelium by fluorescence in situ hybridization (FISH) analysis. Phylogenetic analysis indicated that F. occidentalis encodes six cyclophilins, in which Fo-Cyp1 is closely related to a human cyclophilin A, an immune modulator. The Fo-Cyp1 transcript was also detected in the larval gut epithelium. Expression of these two genes was suppressed by feeding their cognate RNA interference (RNAi) to young larvae. The RNAi efficiencies were confirmed by the disappearance of the target gene transcripts from the gut epithelium by FISH analyses. The RNAi treatments directed to Fo-GN or Fo-Cyp1 prevented the typical TSWV titer increase after the virus feeding, compared to control RNAi treatment. Our immunofluorescence assay using a specific antibody to TSWV documented the reduction of TSWV in the larval gut and adult salivary gland after the RNAi treatments. These results support our hypothesis that the candidate proteins Fo-GN and Fo-Cyp1 act in TSWV entry and multiplication in F. occidentalis.

Special issue: Relationship between insect vectors and plant pathogens

Special issue: Relationship between insect vectors and plant pathogens

Repellency and Toxicity of Eight Plant Extracts against the Western Flower Thrips, Frankliniella occidentalis

We investigated the repellency and toxicity of eight plant extracts containing celangulin, cnidium lactone, matrine, nicotine, pyrethrins, rotenone, stemonine and veratrine against the western flower thrips (Frankliniella occidentalis Pergande; Thysanoptera: Thripidae). Flowers treated with 0.05% nicotine, pyrethrins, stemonine and rotenone harbored fewer western flower thrips in two- and multiple-choice repellency bioassays. When evaluated at concentrations varying from 0.005% to 0.1% in two-choice repellency bioassays, pyrethrins and rotenone were most repellent at 0.01% to 0.1%, and nicotine was most repellent at 0.025%. Mortality was 76% with 0.1% nicotine at 48 h, 78% with 0.5% stemonine at 72 h, and 100% with 0.1% pyrethrins and 0.5% rotenone at 48 h after contact with fresh (<1-d-old) residue. Effective residue age was 1 d for nicotine, pyrethrins and rotenone, and 5 d for stemonine in aged residual toxicity bioassays. Celangulin, cnidium lactone, matrine and veratrine did not provide sufficient repellency and toxicity. Stemonine had inconsistent results. Therefore, additional evaluation of its potential as a botanical insecticide will be needed. When sprayed onto whole plants, plant extracts containing nicotine, pyrethrins, rotenone and stemonine caused unacceptable damage to flowers, suggesting that the final formulation will need to be modified to improve crop safety.

Seasonal Incidence of Insect Pests and Predatory Fauna in Black Gram

The succession and seasonal incidence of insect pests and predatory fauna in black gram were studied in a field experiment at the Agronomy farm, Anand Agricultural University, Anand during kharif 2019 and 2020. The results revealed nine species of insects (7 pests and 2 predators) from seedling to pod maturity stage. Besides, the peak incidence of whitefly, jassid, flower thrips, tobacco caterpillar, Bihar hairy caterpillar, and spiders were observed during 37th standard meteorological week (SMW); with spotted pod borer and coccinellids, maximum incidence was observed during 38th SMW, and the green stink bug during 35th SMW. Correlation coefficients revealed that tobacco caterpillar had a significant positive correlation with minimum temperature, morning RH and evening vapour pressure; and the incidence of spotted pod borer showed a significant negative correlation with bright sunshine hours and rainfall.

Side effects of Zataria multiflora Boiss (Lamiaceae) essential oil on predation and life table parameters of Amblyseius swirskii Athias-Henriot (Acari: Phytoseiidae)

The predatory mite, Amblyseius swirskii Athias-Henriot (Acari: Phytoseiidae) is one of the most promising candidates for biological control of some economically important mites and insect pests such as spider mites, whiteflies, and thrips. Western Flower Thrips (WFT), Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae) is a severe economic pest for many crops in the world. In this study the lethal concentrations of Shirazicum thymus: Zataria multiflora Boiss (Lamiaceae) essential oil was calculated to the adult stage of the WFT. Side effects LC30 and LC50 of the essential oil were assessed on life table parameters and functional response of A. swirskii. Experiments were carried out in growth chambers at 25 ± 1 °C, 60 ± 10% RH, and 16: 8 h (Light: Dark) photoperiod. We utilized the age-stage, two-sex life table method to evaluate the life history features and population growth of A. swirskii on WFT. For assessing the functional response, the first instar of WFT was offered as prey to the adult female of A. swirskii with densities of 2, 4, 8, 16, 32, and 64. The LC50 concentration of the essential oil resulted in lower fecundity (15.05 eggs/female) in comparison with the control (19.8 eggs/female). The application of LC50 and LC30 concentrations also resulted in a significant decrease in net reproductive rate (R0) (8.9, 6.6, and 4.5 eggs per individuals), intrinsic rate of increase (rm) (0.116, 0.093, and 0.077 day -1), finite rate of increase (λ) (1.123, 1.097, and 1.079 day -1), but an increase in mean generation time (T) (18.5, 20.1, and 19.5 days) (for control, LC30, and LC50, applications, respectively). A type II functional response was detected for A. swirskii fed on WFT first instar in all treatments. Adult females of A.swirskii had the highest attack rate (a) (0.11± 0.01 h-1) and shortest handling time (1.61± 0.46h) on control treatment. In conclusion, although Z. multiflora essential oil had potential against F. occidentalis to be applied in integrated pest management programs, the lethal side effects of selected essential oil on the predatory mite, A. swirskii should be considered.

Cadmium contamination triggers negative bottom-up effects on the growth and reproduction of Frankliniella occidentalis (Thysanoptera: Thripidae) without disrupting the foraging behavior of its predator, Orius sauteri (Heteroptera: Anthocoridae).

Heavy metal contaminants may influence tri-trophic interactions among plants, herbivores, and their natural enemies and affect the results of pest management practices. We examined how the widely distributed heavy metal cadmium (Cd) could modify interactions between kidney bean, Phaseolus vulgaris L., western flower thrips, Frankliniella occidentalis Pergande, and a predator, Orius sauteri (Poppius) by examining Cd effects on the feeding damage on leaves, the growth and reproduction of the thrips, and the feeding and plant location selection behaviors of predators. Leaf feeding damage was significantly reduced only at the highest Cd treatment (625mg L-1). Survival, reproduction, and population growth of thrips decreased with the increase of Cd treatment concentration (0, 25, and 625mg L-1). The reproduction rate of thrips from the highest Cd treatment group was reduced to less than 30% of the controls. Predator choice of plants was not impacted at the lowest level of Cd treatment (25mg L-1) when prey were excluded, but the predators were deterred from plants treated at the high level of Cd (625mg L-1). However, the predators responded strongly to the presence of prey, and the Cd-based deterrence was effectively eliminated when prey were added. Thus, the presence of Cd can cause a bottom-up effect on the fitness of pests without disrupting the foraging behavior of its predator. Our results provide baseline data on the toxic impacts on the pest and predator, and indicate that the ecology of the system and the biological control efficiency would be potentially impacted by high levels of Cd (625mg L-1).

Weak genetic structure of flower thrips Frankliniella intonsa in China revealed by mitochondrial genomes

Human activities facilitate long-distance dispersal of insects beyond their native range. In particular, the transportation of live plants offers diffusion opportunities for some insects with weak flight abilities. The increase in urban afforestation also help insect reside in urban habitats. The flower thrips, Frankliniella intonsa, is a widespread pest that causes serious damage to many economically important plants. Human activities are likely to facilitate the dispersal of this pest, however, the population genetic structure of this pest remains unclear. Herein, high-throughput sequencing was used to obtain 149 whole mitochondrial genomes of flower thrips from 28 geographic populations in China. Population genetic analyses, phylogenetic reconstruction, and inference of demographic history were then performed. A weak genetic structure was found among all populations across large geographic distance in China, in which five mitochondrial haplotype lineages were resolved. One of the lineages was identified to be shared among most samples collected from central city areas, which may be derived from the surrounding areas. Demographic history analyses suggested a recent population expansion of F. intonsa. Overall, the present population genetic structure of flower thrips in China may be promoted by human-mediated urban afforestation across the country.

Molecular diagnostics for monitoring insecticide resistance in the western flower thrips Frankliniella occidentalis.

Insecticide resistance has emerged in various western flower thrips (WFT) populations across the world, threatening the efficiency of chemical control applications. Elucidation of insecticide resistance mechanisms at the molecular level provides markers for the development of diagnostics to monitor the trait and support evidence-based resistance management. TaqMan and Droplet Digital polymerase chain reaction (ddPCR) diagnostics were developed and validated, against Sanger sequencing, in individual and pooled WFT samples respectively, for the G275E mutation (nicotinic acetylcholine receptor α6 gene, nAChR α6) associated with resistance to nAChR allosteric modulators, site I (spinosyns); L1014F, T929I, T929C and T292V mutations (voltage-gated sodium channel gene, vgsc) linked with pyrethroid resistance; and I1017M (chitin synthase 1 gene, chs1) conferring resistance to growth inhibitors affecting CHS1 (benzoylureas). The detection limits of ddPCR assays for mutant allelic frequencies (MAF) were in the range of 0.1%-0.2%. The assays were applied in nine WFT field populations from Crete, Greece. The G275E (MAF=29.66%-100.0%), T929I and T929V (combined MAF=100%), L1014F (MAF=11.01%-37.29%), and I1017M (MAF=17.74%-51.07%) mutations were present in all populations. The molecular diagnostics panel that was developed in this study can facilitate the quick and sensitive resistance monitoring of WFT populations at the molecular level, to support evidence-based insecticide resistance management strategies. © 2022 Society of Chemical Industry.

Enhanced β-glucosidase in Western flower thrips affects its interaction with the redox-based strategies of kidney beans under elevated CO2.

β-Glucosidase is validated as an elicitor for early immune responses in plants and it was detected in the salivary glands of Frankliniella occidentalis in previous research. Seven differentially expressed genes encoding β-glucosidase were obtained by comparing the transcriptomes of F. occidentalis adults grown under two different CO2 concentrations (800 vs. 400 ppm), which might be associated with the differences in the interaction between F. occidentalis adults and its host plant, Phaseolus vulgaris under different CO2 levels. To verify this speculation, changes in defense responses based on the production and elimination of reactive oxygen species (ROS) in P. vulgaris leaves treated with three levels of β-glucosidase activity under ambient CO2 (aCO2 ) and elevated CO2 (eCO2 ) were measured in this study. According to the results, significantly higher levels of ROS were noticed under eCO2 compared to aCO2 , which was caused by the increased β-glucosidase activity in thrips due to increased cellulose content in P. vulgaris leaves under eCO2 . Together with the lower activities of superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT)in injured leaves under eCO2 , P. vulgaris leaves would be negatively affected on redox-based defense by eCO2 , thus facilitating thrips damage under climate change.

Specificity of vectoring and non-vectoring flower thrips species to pathogen-induced plant volatiles

Specificity of vectoring and non-vectoring flower thrips species to pathogen-induced plant volatiles