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.

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.

Development and application of reverse transcription-loop mediated isothermal amplification assay for sensitive detection of groundnut bud necrosis virus infecting potato

Reverse-transcription loop-mediated isothermal amplification (RT-LAMP) assay was developed for detection of groundnut bud necrosis virus (GBNV) causing potato stem necrosis disease. The isothermal temperatures, reaction periods and concentrations of reaction mixture were optimized where, the assay worked well at 65 °C for 50 min, 6 U of WarmStart Bst 2.0 DNA polymerase, 1.4 mM dNTPs and 2.0 mM MgSO4. The optimized assay proved to be specific to GBNV with no cross reactivity to other viruses infecting potato in India. The specificity of RT-LAMP assay was found to be 100 fold more sensitive than that of RT-PCR. The developed assay was applied for the detection of GBNV from 80 potato leaf samples where 24 samples were found infected which was confirmed by RT-PCR. It was concluded that the RT-LAMP assay developed for detection of GBNV was specific, sensitive and suitable for its use in virus indexing under potato seed production programme.

Extant thrips diverged in the early tertiary period

Thysanoptera, commonly known as thrips, are diverse tiny insects whose earliest fossil record dates back to the Triassic period. Since there are few studies on the divergence time of taxa under Thysanoptera, this study used 13 mitochondrial coding protein genes to reconstruct the phylogenetic tree with divergence time of 26 species of this order and show a reliable phylogenetic relationship of thrips species. The time tree of this study shows that most extant thrips diverged in the early Tertiary period, while the fossil records also support that most extinct thrips appeared in this period. This study expands our understanding of the evolution of thrips and provides a feasible way of using multiple mitochondrial genes to establish robust phylogenetic relationships and explore divergence time between species.

Pest status, molecular evolution, and epigenetic factors derived from the genome assembly of Frankliniella fusca, a thysanopteran phytovirus vector

BACKGROUND

The tobacco thrips (Frankliniella fusca Hinds; family Thripidae; order Thysanoptera) is an important pest that can transmit viruses such as the tomato spotted wilt orthotospovirus to numerous economically important agricultural row crops and vegetables. The structural and functional genomics within the order Thysanoptera has only begun to be explored. Within the > 7000 known thysanopteran species, the melon thrips (Thrips palmi Karny) and the western flower thrips (Frankliniella occidentalis Pergrande) are the only two thysanopteran species with assembled genomes.

RESULTS

A genome of F. fusca was assembled by long-read sequencing of DNA from an inbred line. The final assembly size was 370 Mb with a single copy ortholog completeness of ~ 99% with respect to Insecta. The annotated genome of F. fusca was compared with the genome of its congener, F. occidentalis. Results revealed many instances of lineage-specific differences in gene content. Analyses of sequence divergence between the two Frankliniella species' genomes revealed substitution patterns consistent with positive selection in ~ 5% of the protein-coding genes with 1:1 orthologs. Further, gene content related to its pest status, such as xenobiotic detoxification and response to an ambisense-tripartite RNA virus (orthotospovirus) infection was compared with F. occidentalis. Several F. fusca genes related to virus infection possessed signatures of positive selection. Estimation of CpG depletion, a mutational consequence of DNA methylation, revealed that F. fusca genes that were downregulated and alternatively spliced in response to virus infection were preferentially targeted by DNA methylation. As in many other insects, DNA methylation was enriched in exons in Frankliniella, but gene copies with homology to DNA methyltransferase 3 were numerous and fragmented. This phenomenon seems to be relatively unique to thrips among other insect groups.

CONCLUSIONS

The F. fusca genome assembly provides an important resource for comparative genomic analyses of thysanopterans. This genomic foundation allows for insights into molecular evolution, gene regulation, and loci important to agricultural pest status.

Whether curse or blessing: A counterintuitive perspective on global pest thrips infestation under climatic change with implications to agricultural economics

The improvement and application of pest models to predict yield losses is still a challenge for the scientific community. However, pest models were targeted chiefly towards scheduling scouting or pesticide applications to deal with pest infestation. Thysanoptera (thrips) significantly impact the productivity of many economically important crops worldwide. Until now, no comprehensive study is available on the global distribution of pest thrips, as well as on the extent of cropland vulnerability worldwide. Further, nothing is known about the climate change impacts on these insects. Thus the present study was designed to map the global distribution and quantify the extent of cropland vulnerability in the present and future climate scenarios using data of identified pest thrips within the genus, i.e., Thrips, Frankliniella, and Scirtothrips. Our found significant niche contraction under the climate change scenarios and thrips may reside primarily in their thermal tolerance thresholds. About 3,98,160 km² of cropland globally was found to be affected in the present scenario. However, it may significantly reduce to 5530 Km² by 2050 and 1990 km² by 2070. Further, the thrips distribution mostly getting restricted to Eastern North America, the North-western of the Indian sub-continent, and the north of Europe. Among all realms, thrips may lose ground in the Indo-Malayan realm at the most and get restricted to only 27 out of 825 terrestrial ecoregions. The agrarian communities of the infested regions may get benefit if these pests get wiped out, but on the contrary, we may lose species diversity. Moreover, the vacated niche may attract other invasive species, which may seriously impact the species composition and agricultural productivity. The present study findings can be used in making informed decisions about prioritizing future economic and research investments on the thrips in light of anticipated climate change impacts.

Pantoea Bacteria Isolated from Three Thrips (Frankliniella occidentalis, Frankliniella intonsa, and Thrips tabaci) in Korea and Their Symbiotic Roles in Host Insect Development

Gut symbionts play crucial roles in host development by producing nutrients and defending against pathogens. Phloem-feeding insects in particular lack essential nutrients in their diets, and thus, gut symbionts are required for their development. Gram-negative Pantoea spp. are known to be symbiotic to the western flower thrips (Frankliniella occidentalis). However, their bacterial characteristics have not been thoroughly investigated. In this study, we isolated three different bacteria (BFoK1, BFiK1, and BTtK1) from F. occidentalis, F. intonsa, and T. tabaci. The bacterial isolates of all three species contained Pantoea spp. Their 16S rRNA sequences indicated that BFoK1 and BTtK1 were similar to P. agglomerans, while BFiK1 was similar to P. dispersa. These predictions were supported by the biochemical characteristics assessed by fatty acid composition and organic carbon utilization. In the bacterial morphological analysis, BFoK1 and BTtK1 were distinct from BFiK1. All these bacteria were relatively resistant to tetracycline compared to ampicillin and kanamycin, in which BFoK1 and BTtK1 were different from BFiK1. Feeding ampicillin (100,000 ppm) reduced the bacterial density in thrips and retarded the development of F. occidentalis. The addition of BFoK1 bacteria, however, rescued the retarded development. These findings indicate that Pantoea bacteria are symbionts to different species of thrips.

Gene arrangement, phylogeny and divergence time estimation of mitogenomes in Thrips

BACKGROUND

The metazoan mitogenomes usually display conserved gene arrangement while thrips are known for their extensive gene rearrangement, and duplication of the control region.

METHODS AND RESULT

We sequenced complete mitogenomes of eight species of thrips to determine the gene arrangement, phylogeny and divergence time estimation. All contain 37 genes and one control region, (CR) except four species with two CRs. Duplicated tRNAs were detected in Mycterothrips nilgiriensis and Thrips florum. nad4-nad4L were not found adjacent to each other in Phibalothrips peringueyi and Plicothrips apicalis. Both Bayesian and likelihood phylogenetic analyses of thrips mitogenomes supported the monophyly of two suborders (Terebrantia and Tubulifera) and the two largest families (Phlaeothripidae and Thripidae). Out of seven earlier proposed ancestral gene blocks, six are conserved in Panchaetothripinae, three in Thripinae and two in Phlaeothripidae. Additionally, eight Thrips Gene Blocks were identified, of which, three conserved in Tubulifera, four in Terebrantia, and one only in Aeolothripidae. Forty-two gene boundaries (15 from previous study + 27 new) were identified. The molecular divergence time is estimated for the order Thysanoptera and suggested that these insects may have been diversified from hemipterans in the late Permian period. The most recent ancestors belong to family Thripidae and Phlaeothripidae, which were diversified in upper Cretaceous period and showed higher rates of rearrangement from the ancestral gene order.

CONCLUSIONS

The current study is the first largest effort to provide the new insights into the mitogenomic features, gene arrangement, phylogeny and divergence time estimation of thrips belonging to the order Thysanoptera.

Problems with the Concept of "Pest" among the Diversity of Pestiferous Thrips

Almost all of the thrips species that are considered pests are members of a single subfamily of Thripidae, the Thripinae, a group that represents less than 30% of the species in the insect Order Thysanoptera. Three of the five major Families of Thysanoptera (Aeolothripidae, Heterothripidae, Melanthripidae) are not known to include any pest species. The Phlaeothripidae that includes more than 50% of the 6300 thrips species listed includes very few that are considered to be pests. Within the Thripidae, the members of the three smaller subfamilies, Panchaetothripinae, Dendrothripinae and Sericothripinae, include remarkably few species that result in serious crop losses. It is only in the subfamily Thripinae, and particularly among species of the Frankliniella genus-group and the Thrips genus-group that the major thrips species are found, including all but one of the vectors of Orthotospovirus infections. It is argued that the concept of pest is a socio-economic problem, with the pest status of any particular species being dependent on geographical area, cultivation practices, and market expectations as much as the intrinsic biology of any thrips species.

A new brood-pollination mutualism between Stellera chamaejasme and flower thrips Frankliniella intonsa

BACKGROUND

Brood pollination mutualism is a special type of plant-pollinator interaction in which adult insects pollinate plants, and the plants provide breeding sites for the insects as a reward. To manifest such a mutualism between Stellera chamaejasme and flower thrips of Frankliniella intonsa, the study tested the mutualistic association of the thrips life cycle with the plant flowering phenology and determined the pollination effectiveness of adult thrips and their relative contribution to the host's fitness by experimental pollinator manipulation.

RESULTS

The adult thrips of F. intonsa, along with some long-tongue Lepidoptera, could serve as efficient pollinators of the host S. chamaejasme. The thrips preferentially foraged half-flowering inflorescences of the plants and oviposited in floral tubes. The floral longevity was 11.8 ± 0.55 (mean ± se) days, which might precisely accommodate the thrips life cycle from spawning to prepupation. The exclusion of adult thrips from foraging flowers led to a significant decrease in the fitness (i.e., seed set) of host plants, with a corresponding reduction in thrips fecundity (i.e., larva no.) in the flowers.

CONCLUSIONS

The thrips of F. intonsa and the host S. chamaejasme mutualistically interact to contribute to each other's fitness such that the thrips pollinate host plants and, as a reward, the plants provide the insects with brooding sites and food, indicating the coevolution of the thrips life cycle and the reproductive traits (e.g., floral longevity and morphology) of S. chamaejasme.

The complete mitochondrial genome of Taeniothrips tigris Bhatti, 1995 (Thysanoptera: Thripidae)

In this study, we sequenced complete mitogenome of Taeniothrips tigris Bhatti 1995. It was 15,501 bp in length containing 13 protein-coding genes, 22 transfer RNA genes, and 2 ribosomal RNA genes along with two non-coding regions. The overall base composition of Ta. tigris is 43.66% A, 35.20% T, 11.46% C, and 9.68% G, with a high AT bias of 78.86%. The constructed phylogeny using 19 mitogenomes revealed that the genus Taeniothrips is in close relationship with genus Thrips. This mitogenome data would help in deducing phylogenetic relationships studies in the order Thysanoptera.

Interspecific variation in bristle number on forewings of tiny insects does not influence clap-and-fling aerodynamics

Miniature insects must overcome significant viscous resistance in order to fly. They typically possess wings with long bristles on the fringes and use clap-and-fling mechanism to augment lift. These unique solutions to the extreme conditions of flight at tiny sizes (< 2 mm body length) suggest that natural selection has optimized wing design for better aerodynamic performance. However, species vary in wingspan, number of bristles (n), and bristle gap (G) to diameter (D) ratio (G/D). How this variation relates to body length (BL) and its effects on aerodynamics remain unknown. We measured forewing images of 38 species of thrips and 21 species of fairyflies. Our phylogenetic comparative analyses showed that n and wingspan scaled positively and similarly with body length across both groups, whereas G/D decreased with BL, with a sharper decline in thrips. We next measured aerodynamic forces and visualized flow on physical models of bristled wings performing clap-and-fling kinematics at chord-based Reynolds number of 10 using a dynamically scaled robotic platform. We examined the effects of dimensional (G, D, wingspan) and non-dimensional (n, G/D) geometric variables on dimensionless lift and drag. We found that: (a) increasing G reduced drag more than decreasing D; (b) changing n had minimal impact on lift generation; and (c) varying G/D minimally affected aerodynamic forces. These aerodynamic results suggest little pressure to functionally optimize n and G/D. Combined with the scaling relationships between wing variables and BL, much wing variation in tiny flying insects might be best explained by underlying shared growth factors.

Natural variation in wild tomato trichomes; selecting metabolites that contribute to insect resistance using a random forest approach

BACKGROUND

Plant-produced specialised metabolites are a powerful part of a plant's first line of defence against herbivorous insects, bacteria and fungi. Wild ancestors of present-day cultivated tomato produce a plethora of acylsugars in their type-I/IV trichomes and volatiles in their type-VI trichomes that have a potential role in plant resistance against insects. However, metabolic profiles are often complex mixtures making identification of the functionally interesting metabolites challenging. Here, we aimed to identify specialised metabolites from a wide range of wild tomato genotypes that could explain resistance to vector insects whitefly (Bemisia tabaci) and Western flower thrips (Frankliniella occidentalis). We evaluated plant resistance, determined trichome density and obtained metabolite profiles of the glandular trichomes by LC-MS (acylsugars) and GC-MS (volatiles). Using a customised Random Forest learning algorithm, we determined the contribution of specific specialised metabolites to the resistance phenotypes observed.

RESULTS

The selected wild tomato accessions showed different levels of resistance to both whiteflies and thrips. Accessions resistant to one insect can be susceptible to another. Glandular trichome density is not necessarily a good predictor for plant resistance although the density of type-I/IV trichomes, related to the production of acylsugars, appears to correlate with whitefly resistance. For type VI-trichomes, however, it seems resistance is determined by the specific content of the glands. There is a strong qualitative and quantitative variation in the metabolite profiles between different accessions, even when they are from the same species. Out of 76 acylsugars found, the random forest algorithm linked two acylsugars (S3:15 and S3:21) to whitefly resistance, but none to thrips resistance. Out of 86 volatiles detected, the sesquiterpene α-humulene was linked to whitefly susceptible accessions instead. The algorithm did not link any specific metabolite to resistance against thrips, but monoterpenes α-phellandrene, α-terpinene and β-phellandrene/D-limonene were significantly associated with susceptible tomato accessions.

CONCLUSIONS

Whiteflies and thrips are distinctly targeted by certain specialised metabolites found in wild tomatoes. The machine learning approach presented helped to identify features with efficacy toward the insect species studied. These acylsugar metabolites can be targets for breeding efforts towards the selection of insect-resistant cultivars.

Species Composition of Thrips (Thysanoptera: Thripidae) in Strawberry High Tunnels in Denmark

Simple Summary

One of the main insect pests in protected strawberry production are thrips, but little is known about which species of thrips are present in the production system. In this study, we identified the thrips species of adults and larvae present in two strawberry cultivars at a commercial strawberry farm in Denmark. The most abundant species found were Frankliniella intonsa, followed by Thrips tabaci. The abundance of thrips peaked in July (temperature range 18–23 °C, mean humidity 65%, mean precipitation 5 mm). More thrips were found in the earlier flowering cultivar. In order to optimize control of thrips, a fundamental first step is knowing which species are present on the target crop.

Abstract

Thrips are a major pest in protected strawberry production. Knowledge of thrips species composition could be instrumental for improved thrips management, but very little is known about which species are present in strawberries grown in high-tunnels in Denmark. Thrips (adults and larvae) were sampled in two strawberry tunnels of the cultivars Murano and Furore from May to August 2018, in the middle and in the edges of the tunnels. The most abundant thrips species found in the tunnels were Frankliniella intonsa and Thrips tabaci adults. Frankliniella intonsa were also the most frequently found species of the immatures sampled, followed by T. tabaci larvae, and other species. The number of thrips differed between the two cultivars, sampling times and location in the tunnel. Frankliniella intonsa was more abundant in the middle of the tunnels, while T. tabaci was more abundant in the edge of the tunnels adjacent to the field margins. The number of thrips peaked by the end of July. Both chemical and biological control should consider species composition and occurrence; hence, a fundamental first step for thrips management is to identify the species present on the target crop.

(Lamiales: Lamiaceae), a Promising Repellent Plant for Thrips Management

A number of thrips species are among the most significant agricultural pests globally. Use of repellent intercrop plants is one of the key components in plant-based 'push-pull' strategies to manage pest populations. In this study, the behavioral responses of three thrips species, Frankliniella occidentalis (Pergande), Frankliniella intonsa (Trybom), and Thrips palmi Karny (Thysanoptera: Thripidae) to Rosmarinus officinalis were investigated in Y-tube olfactometer bioassays and cage experiments. In addition, the major volatile compounds from rosemary were identified and the effect of the individual compounds on thrips behavior was evaluated. Females and males of the three thrips species were significantly repelled by the volatiles from cut rosemary leaves. The presence of rosemary plants significantly reduced settlement of females of the three thrips species and eggs laid by F. occidentalis females on target host plants. In total, 47 compounds were identified in the volatiles collected from the cut leaves of rosemary plants. The responses of the three thrips species to 10 major volatile compounds showed significant differences. However, α-pinene, the most abundant volatile, was repellent to F. occidentalis and F. intonsa. Eucalyptol, the second most abundant volatile, showed significant repellent activity to all the three thrips species. Our findings showed that rosemary is a promising repellent plant against the three thrips pests we tested, which could be a good candidate for 'push' plants in plant-based 'push-pull' strategies. The identified volatile compounds that accounted for the repellent activity could be developed as repellents for sustainable thrips management.

High Concentrations of Very Long Chain Leaf Wax Alkanes of Thrips Susceptible Pepper Accessions (Capsicum spp)

The cuticular wax layer can be important for plant resistance to insects. Thrips (Frankliniella occidentalis) damage was assessed on 11 pepper accessions of Capsicum annuum and C. chinense in leaf disc and whole plant assays. Thrips damage differed among the accessions. We analyzed the composition of leaf cuticular waxes of these accessions by GC-MS. The leaf wax composition was different between the two Capsicum species. In C. annuum, 1-octacosanol (C28 alcohol) was the most abundant component, whereas in C. chinense 1-triacotanol (C30 alcohol) was the prominent. Thrips susceptible accessions had significantly higher concentrations of C25-C29 n-alkanes and iso-alkanes compared to relatively resistant pepper accessions. The triterpenoids α- and ß-amyrin tended to be more abundant in resistant accessions. Our study suggests a role for very long chain wax alkanes in thrips susceptibility of pepper.

Comparison of the phytoseiid mites Amblyseius swirskii and Amblydromalus limonicus for biological control of chilli thrips, Scirtothrips dorsalis (Thysanoptera: Thripidae)

The chilli thrips, Scirtothrips dorsalis Hood, is a recently established pest in the USA and poses a serious risk to many economically important ornamental and food crops. In this study the biological control potential of the phytoseiid mites Amblydromalus limonicus (Garman and McGregor) and Amblyseius swirskii (Athias-Henriot) was compared by examining their predation and oviposition rates when fed different developmental stages of S. dorsalis. Gravid females were offered 10 individuals of either first instar, second instar, or adult S. dorsalis using a no-choice leaf disc bioassay and oviposition and predation rates were assessed daily for 2 and 3 days, respectively. There was no significant difference in predation and oviposition rates between mite species fed specific S. dorsalis life stages. There was, however, a significant effect of S. dorsalis life stage on the oviposition and predation rates observed for each mite species. The larval stage was the most preferred stage for both mite species, with A. swirskii consuming 4.6-6.3 and A. limonicus 4.8-6.4 individuals/day compared to only 1.6-1.7 adults/day consumed by both species. Female A. swirskii and A. limonicus laid 0.55-0.75 and 0.73 eggs/day on the two larval stages, respectively, compared to only 0.25-0.30 eggs/day observed for individuals feeding on adults. Although the results showed that the biological control potential of both mite species was similar, having an additional predator available that may be as effective as A. swirskii, a proven control agent against S. dorsalis in the field, warrants additional research into its potential utility.

Epidemiology of tomato spotted wilt virus in Chrysanthemum morifolium in South Korea and its management using a soil-dwelling predatory mite (Stratiolaelaps scimitus) and essential oils

Tomato spotted wilt virus (TSWV) is one of most destructive viruses in vegetable and ornamental crop production worldwide. A greenhouse survey to determine the incidence of TSWV in Chrysanthemummorifolium Ramat. was conducted during the 2018 and 2019 growing seasons in South Korea. TSWV was detected using a double antibody sandwich-enzyme-linked immunosorbent assay, and positive results were confirmed using reverse transcription-polymerase chain reaction (RT-PCR). A total of 1569 chrysanthemum plants (70.77 %) tested positive for TSWV among 2217 symptomatic chrysanthemum plants collected from 16 greenhouses. In addition, 116 thrips (72.96 %; Frankliniella occidentalis Pergande) that contained TSWV were identified using RT-PCR from a total of 159 thrips collected from the greenhouses during the survey. A high incidence of viruliferous thrips may have played a role in TSWV occurrence in the chrysanthemum greenhouse. To develop a novel approach for thrips management, the effectiveness of a soil-dwelling predatory mite (Stratiolaelaps scimitus Berlese) and 45 essential oils (as bio-insecticides applied via foliar treatment) was assayed. Four essential oils (cinnamon oil, cinnamon bark oil, oregano oil, and thyme oil) were shown to be significantly toxic to eggs, larvae, and adults of F. occidentalis. For the combined treatment, individuals of S. scimitus (60/m²) were placed on the soil in the chrysanthemum greenhouses. Then, a mixture of the four essential oils was applied as foliar treatment at 4-day intervals. A very low incidence of thrips emerged as adults from the soil (1.2-8.5 %) in the combined treatment in the chrysanthemum greenhouses when surveyed twice per month, compared with the non-treated control or when conventional insecticide sprays were applied. The incidence of TSWV (0.93 %) in chrysanthemum treated with S. scimitus in conjunction with the mixture of four essential oils decreased significantly compared with that treated with chemical insecticides (32.05 %) and in the non-treated controls (84.85 %). Our findings contribute to the development of novel strategies to control TSWV disease in chrysanthemum plants; notably, the control of F. occidentalis using eco-friendly insecticides appears promising.

Spectral sensitivity of L2 biotype in the Thrips tabaci cryptic species complex

The onion thrips, Thrips tabaci (Lindeman, 1889), is a cosmopolitan pest of economic importance on a wide range of crops. Despite being one of the most studied thrips species, there is very limited knowledge available about its ability to perceive light. The T. tabaci cryptic species complex consists of a tobacco-associated (T) and two leek-associated (L1, L2) biotypes. We made electroretinogram recordings on the most widespread thelytokous (where unfertilized eggs produce females) T. tabaci L2 biotype and measured attraction to light sources in this biotype as a function of wavelength in behavioural experiments. The spectral sensitivity of the T. tabaci L2 biotype shows a unimodal curve peaking at λ_max = 521 nm. Contrary to this spectral sensitivity curve, L2 biotype attraction in an arena is bimodal with local maxima at 368 nm (UV) and 506-520 nm (green) being practically of the same magnitude. Although being similar to the arrhenotokous (where unfertilized eggs produce males) L1 biotype in phototaxis, significant differences regarding photoreceptor cell responses emerged. This study contributes to our understanding of light perception in Thysanoptera as well as to the development of more effective monitoring tools for this economically important pest species.

Bioassays to Evaluate the Resistance of Whole Plants to the Herbivorous Insect Thrips

Thrips are tiny, cell-content-feeding insects that are a major pest on crops and ornamentals. Besides causing direct feeding damage, thrips may also cause indirect damage by vectoring tospoviruses. Novel resistance mechanisms to thrips need to be discovered and validated. Induction of jasmonic acid-dependent defenses has been demonstrated to be essential for resistance to thrips, but underlying mechanisms still need to be discovered. For this, it is vital to use robust plant-thrips assays to analyze plant defense responses and thrips performance. In recently developed high-throughput phenotyping platforms, the feeding damage that is visible as silver spots, and the preference of thrips in a two-choice setup is assessed, using leaf discs. Here, we describe whole-plant thrips assays that are essential for (1) validation of findings obtained by the leaf disc assays, (2) assessment of longer-term effects on thrips feeding success and fecundity, (3) determination of spatial-temporal effects induced by primary thrips infestation on a secondary attack by thrips or other insects or pathogens, and (4) assessment of gene expression and metabolite changes. We present detailed methods and tips and tricks for (a) rearing and selection of thrips at different developmental stages, (b) treatment of the whole plant or an individual leaf with thrips, and (c) determination of feeding damage and visualization of thrips oviposition success in leaves.

Fumigant effect of essential oils on mortality and fertility of thrips Frankliniella occidentalis Perg

The western flower thrips (Frankliniella occidentalis Perg.) is one of the most economically important insect pests of greenhouse plants. Plant protection against this pest is based predominantly on synthetic insecticides; however, this form of protection poses problems in terms of thrip resistance to the active substances, along with health risks associated with insecticide residues on the treated plants. Therefore, new active substances need to be sought. Essential oils could be a new, appropriate, and safe alternative for greenhouse culture protection. As greenhouses are enclosed areas, fumigation application of EOs is possible. This paper presents acute toxicity results for 15 commercial EOs applied by fumigation, as well as the effect of sublethal concentrations on fertility of F. occidentalis females. The most efficient EOs were obtained from Mentha pulegium and Thymus mastichina, with LC₅₀₍₉₀₎ estimated as 3.1(3.8) and 3.6 (4.6) mg L^-1 air, respectively. As found for the very first time, sublethal concentrations of EOs could result in a significant reduction in the fertility of surviving T. occidentalis females. Among the tested EOs, the EO from Nepeta cataria provided the highest inhibition of fertility, with EC₅₀₍₉₀₎ estimated as 0.18 (0.36) mg L^-1 air. Chemical composition of the most efficient EOs and possible applications of the results in practice are discussed. In conclusion, in light of the newly determined facts, EOs can be recommended as active substances for botanical insecticides to be applied against Thysanopteran pests by fumigation.

Entry of bunyaviruses into plants and vectors

The majority of plant-infecting viruses are transmitted by arthropod vectors that deliver them directly into a living plant cell. There are diverse mechanisms of transmission ranging from direct binding to the insect stylet (non-persistent transmission) to persistent-propagative transmission in which the virus replicates in the insect vector. Despite this diversity in interactions, most arthropods that serve as efficient vectors have feeding strategies that enable them to deliver the virus into the plant cell without extensive damage to the plant and thus effectively inoculate the plant. As such, the primary virus entry mechanism for plant viruses is mediated by the biological vector. Remarkably, viruses that are transmitted in a propagative manner (bunyaviruses, rhabdoviruses, and reoviruses) have developed an ability to replicate in hosts from two kingdoms. Viruses in the order Bunyavirales are of emerging importance and with the advent of new sequencing technologies, we are getting unprecedented glimpses into the diversity of these viruses. Plant-infecting bunyaviruses are transmitted in a persistent, propagative manner must enter two unique types of host cells, plant and insect. In the insect phase of the virus life cycle, the propagative viruses likely use typical cellular entry strategies to traverse cell membranes. In this review, we highlight the transmission and entry strategies of three genera of plant-infecting bunyaviruses: orthotospoviruses, tenuiviruses, and emaraviruses.

Metabolomics of Thrips Resistance in Pepper (Capsicum spp.) Reveals Monomer and Dimer Acyclic Diterpene Glycosides as Potential Chemical Defenses

The development of pesticide resistance in insects and recent bans on pesticides call for the identification of natural sources of resistance in crops. Here, we used natural variation in pepper (Capsicum spp.) resistance combined with an untargeted metabolomics approach to detect secondary metabolites related to thrips (Frankliniella occidentalis) resistance. Using leaf disc choice assays, we tested 11 Capsicum accessions of C. annuum and C. chinense in both vegetative and flowering stages for thrips resistance. Metabolites in the leaves of these 11 accessions were analyzed using LC-MS based untargeted metabolomics. The choice assays showed significant differences among the accessions in thrips feeding damage. The level of resistance depended on plant developmental stage. Metabolomics analyses showed differences in metabolomes among the Capsicum species and plant developmental stages. Moreover, metabolomic profiles of resistant and susceptible accessions differed. Monomer and dimer acyclic diterpene glycosides (capsianosides) were pinpointed as metabolites that were related to thrips resistance. Sucrose and malonylated flavone glycosides were related to susceptibility. To our knowledge, this is the first time that dimer capsianosides of pepper have been linked to insect resistance. Our results show the potential of untargeted metabolomics as a tool for discovering metabolites that are important in plant - insect interactions.

Species Identification in the Thrips Genus-Group in Brazil

The Thrips genus-group is a monophyletic taxon composed of 17 genera, whose representatives exhibit three main synapomorphies: absence of ocellar setae I, presence of ctenidia on tergites V-VIII, and ctenidia on tergite VIII positioned posteromesad to the spiracles. The group is native to and more diverse in the Old World, especially in Southeast Asia, but several species are widely distributed, including some pests of cultivated plants. Here, we provide an identification key to the species of the Thrips genus-group currently recorded in Brazil, including three new records of Bolacothrips striatopennatus (Schmutz), Thrips florum Schmutz, and Thrips orientalis (Bagnall), and present notes on their morphology and biology. Stenchaetothrips biformis Bagnall is excluded from the list of thrips recorded in Brazil.

Molecular footprint of Frankliniella occidentalis from India: a vector of Tospoviruses

The western flower thrips, F. occidentalis is a vector of Tospoviruses and native to Western North America and Mexico. The present study is based on collected F. occidentalis specimens from Karnataka state in southern India and morphologically identified through available keys. The generated DNA barcode data show 99–100% similarity with the database sequences of F. occidentalis. The phylogenetic analysis (NJ, ML, and BA) shows three distinct clades of F. occidentalis in the present dataset with high bootstrap supports and posterior probabilities. The K2P genetic distances further depicted high similarity of the generated sequences from India and Netherlands. The Clade-1 (India + Netherlands) also shows a close relationship with Clade-2 (Kenya) rather than Clade-3 (Canada + USA). This study recorded the first genetic footprint of F. occidentalis in India and indicated the gene flow from the Netherlands to India. The similar molecular techniques may help to detect the invasion of many alien species in the near future and assists the quarantine regulations to protect the native ecosystem.

Broad spectrum insect resistance and metabolites in close relatives of the cultivated tomato

Wild relatives of tomato possess effective means to deal with several pests, among which are a variety of insects. Here we studied the presence of resistance components against Trialeurodes vaporariorum, Myzus persicae, Frankliniella occidentalis, and Spodoptera exigua in the Lycopersicon group of Solanum section Lycopersicon by means of bioassays and comprehensive metabolite profiling. Broad spectrum resistance was found in Solanum galapagense and a few accessions of S. pimpinellifolium. Resistance to the sap sucking insects may be based on the same mechanism, but different from the caterpillar resistance. Large and highly significant differences in the leaf metabolomes were found between S. galapagense, containing type IV trichomes, and its closest relative S. cheesmaniae, which lacks type IV trichomes. The most evident differences were the relatively high levels of different methylated forms of the flavonoid myricetin and many acyl sucrose structures in S. galapagense. Possible candidate genes regulating the production of these compounds were identified in the Wf-1 QTL region of S. galapagense, which was previously shown to confer resistance to the whitefly B. tabaci. The broad spectrum insect resistance identified in S. galapagense will be very useful to increase resistance in cultivated tomato.

Three decades of managing Tomato spotted wilt virus in peanut in southeastern United States

Southeastern states namely Georgia, Florida, and Alabama produce two-thirds of the peanuts in the United States. Thrips-transmitted Tomato spotted wilt virus (TSWV), which causes spotted wilt disease, has been a major impediment to peanut production for the past three decades. The cultivars grown in the 1980s were extremely susceptible to TSWV. Early yield losses extended to tens of millions of dollars each year (up to 100% loss in many fields). This situation led to the creation of an interdisciplinary team known as "SWAT: Spotted Wilt Action Team". Initial efforts focused on risk mitigation using a combination of chemical and cultural management practices along with a strong investment in breeding programs. Beginning in the mid 1990s, cultivars with field resistance were developed and integrated with cultural and chemical management options. A Risk Mitigation Index (Peanut Rx) was made available to growers to assess risks, and provide options for mitigating risks such as planting field resistant cultivars with in-furrow insecticides, planting after peak thrips incidence, planting in twin rows, and increasing seeding rates. These efforts helped curtail losses due to spotted wilt. The Peanut Rx continues to be refined every year based on new research findings. Breeding efforts, predominantly in Georgia and Florida, continue to develop cultivars with incremental field resistance. The present-day cultivars (third-generation TSWV-resistant cultivars released after 2010) possess substantially greater field resistance than second-generation (cultivars released from 2000 to 2010) and first-generation (cultivars released from 1994 to 2000) TSWV resistant cultivars. Despite increased field resistance, these cultivars are not immune to TSWV and succumb under high thrips and TSWV pressure. Therefore, field resistant cultivars cannot serve as a 'stand-alone' option and have to be integrated with other management options. The mechanism of resistance is also unknown in field resistant cultivars. Recent research in our laboratory evaluated field resistant cultivars against thrips and TSWV. Results revealed that some resistant cultivars suppressed thrips feeding and development, and they accumulated fewer viral copies than susceptible cultivars. Transcriptomes developed with the aid of Next Generation Sequencing revealed differential gene expression patterns following TSWV infection in susceptible than field resistant cultivars. Results revealed that the upregulation of transcripts pertaining to constitutive and induced plant defense proteins in TSWV resistant cultivars was more robust over susceptible cultivars. On the flipside, the long-term effects of using such resistant cultivars on TSWV were assessed by virus population genetics studies. Initial results suggest lack of positive selection pressure on TSWV, and that the sustainable use of resistant cultivars is not threatened. Follow up research is being conducted. Improvements in TSWV management have enhanced sustainability and contributed to increased yields from <2800kg/ha before 1995 to ∼5000kg/ha in 2015.

Predatory interactions between prey affect patch selection by predators

Abstract

When predators can use several prey species as food sources, they are known to select prey according to foraging efficiency and food quality. However, interactions between the prey species may also affect prey choice, and this has received limited attention. The effect of one such interaction, intraguild predation between prey, on patch selection by predators was studied here. The predatory mite Neoseiulus californicus preys on young larvae of the western flower thrips Frankliniella occidentalis and on all stages of the two-spotted spider mite Tetranychus urticae. The two prey species co-occur on several plant species, on which they compete for resources, and western flower thrips feed on eggs of the spider mites. A further complicating factor is that the thrips can also feed on the eggs of the predator. We found that performance of the predatory mite was highest on patches with spider mites, intermediate on patches with spider mites plus thrips larvae and lowest on patches with thrips larvae alone. Patch selection and oviposition preference of predators matched performance: predators preferred patches with spider mites over patches with spider mites plus thrips. Patches with thrips only were not significantly more attractive than empty patches. We also investigated the cues involved in patch selection and found that the attractiveness of patches with spider mites was significantly reduced by the presence of cues associated with killed spider mite eggs. This explains the reduced attractiveness of patches with both prey. Our results point at the importance of predatory interactions among prey species for patch selection by predators.

Significance statement

Patch selection by predators is known to be affected by factors such as prey quality, the presence of competitors and predators, but little is known on the effects of interactions among prey species present on patch selection. In this paper, we show that patch selection by a predator is affected by such interactions, specifically by the feeding of one prey species on eggs of the other.

Transgenerational loss and recovery of early learning ability in foraging predatory mites

The ability to learn is ubiquitous in animals but highly variable within and between species, populations and individuals. Diet-related circumstances, such as diet quantity and quality can influence both long-term constitutive (genetic; by selection) and short-term operational (non-genetic; by the immediate circumstances) learning performance. Here, we scrutinized the causes of loss of learning ability, following multi-generational feeding on pollen, in a line of the predatory mite Amblyseius swirskii, which was previously well able to learn prey during early life, enhancing foraging later in life. We investigated whether, and, if so, how quickly, a transgenerational diet switch to live prey restores the early learning ability of foraging predatory mites. The first experiment shows that the early learning ability was restored after switching the diet of the pollen-fed predator line to live spider mites for two generations before conducting the behavioral assay. The second experiment reveals that offspring regained their learning ability if the diet of their mothers was switched from pollen to spider mites for 3 or 10 days before offspring production. Both experiments in concert suggest transgenerational, pollen-induced operational loss of learning ability in the predatory mite A. swirskii. Maternally-transmitted nutrient deficiency and/or maternally-induced epigenetic changes are the most plausible explanations for the pollen diet-induced loss of learning ability. Our study represents a key example for maternal diet-induced variation in learning ability.

Induction of Jasmonic Acid-Associated Defenses by Thrips Alters Host Suitability for Conspecifics and Correlates with Increased Trichome Densities in Tomato

Plant defenses inducible by herbivorous arthropods can determine performance of subsequent feeding herbivores. We investigated how infestation of tomato (Solanum lycopersicum) plants with the Western flower thrips (Frankliniella occidentalis) alters host plant suitability and foraging decisions of their conspecifics. We explored the role of delayed-induced jasmonic acid (JA)-mediated plant defense responses in thrips preference by using the tomato mutant def-1, impaired in JA biosynthesis. In particular, we investigated the effect of thrips infestation on trichome-associated tomato defenses. The results showed that when offered a choice, thrips preferred non-infested plants over infested wild-type plants, while no differences were observed in def-1. Exogenous application of methyl jasmonate restored the repellency effect in def-1. Gene expression analysis showed induction of the JA defense signaling pathway in wild-type plants, while activating the ethylene signaling pathway in both genotypes. Activation of JA defenses led to increases in type-VI leaf glandular trichome densities in the wild type, augmenting the production of trichome-associated volatiles, i.e. terpenes. Our study revealed that plant-mediated intraspecific interactions between thrips are determined by JA-mediated defenses in tomato. We report that insects can alter not only trichome densities but also the allelochemicals produced therein, and that this response might depend on the magnitude and/or type of the induction.

Non-associative versus associative learning by foraging predatory mites

BACKGROUND

Learning processes can be broadly categorized into associative and non-associative. Associative learning occurs through the pairing of two previously unrelated stimuli, whereas non-associative learning occurs in response to a single stimulus. How these two principal processes compare in the same learning task and how they contribute to the overall behavioural changes brought about by experience is poorly understood. We tackled this issue by scrutinizing associative and non-associative learning of prey, Western flower thrips Frankliniella occidentalis, by the predatory mite, Neoseiulus californicus. We compared the behaviour of thrips-experienced and -naïve predators, which, early in life, were exposed to either thrips with feeding (associative learning), thrips without feeding (non-associative learning), thrips traces on the surface (non-associative learning), spider mites with feeding (thrips-naïve) or spider mite traces on the surface (thrips-naïve).

RESULTS

Thrips experience in early life, no matter whether associative or not, resulted in higher predation rates on thrips by adult females. In the no-choice experiment, associative thrips experience increased the predation rate on the first day, but shortened the longevity of food-stressed predators, a cost of learning. In the choice experiment, thrips experience, no matter whether associative or not, increased egg production, an adaptive benefit of learning.

CONCLUSIONS

Our study shows that both non-associative and associative learning forms operate in foraging predatory mites, N. californicus. The non-rewarded thrips prey experience produced a slightly weaker, but less costly, learning effect than the rewarded experience. We argue that in foraging predatory mites non-associative learning is an inevitable component of associative learning, rather than a separate process.

The anatomy of the thrips Heliothrips haemorrhoidalis (Thysanoptera, Thripidae) and its specific features caused by miniaturization

A new set of data on the internal and external structure of the adult and larva of the thrips Heliothrips haemorrhoidalis (Bouché, 1833) is presented. The structure of the internal systems of this thrips was revealed using modern methods of 3D computer modelling. The changes in shape and relative size are discussed as an outcome of miniaturization in comparison to the supposed ancestor of this species. The layout of the internal systems of thrips is compared to those of other insects similar in size: beetles of the families Ptiliidae and Corylophidae and wasps of the families Mymaridae and Trichogrammatidae.

Salivary gland morphology, tissue tropism and the progression of tospovirus infection in Frankliniella occidentalis

Tomato spotted wilt virus (TSWV) is transmitted by thrips in a propagative manner; however, progression of virus infection in the insect is not fully understood. The goal of this work was to study the morphology and infection of thrips salivary glands. The primary salivary glands (PSG) are complex, with three distinct regions that may have unique functions. Analysis of TSWV progression in thrips revealed the presence of viral proteins in the foregut, midgut, ligaments, tubular salivary glands (TSG), and efferent duct and filament structures connecting the TSG and PSG of first and second instar larvae. The primary site of virus infection shifted from the midgut and TSG in the larvae to the PSG in adults, suggesting that tissue tropism changes with insect development. TSG infection was detected in advance of PSG infection. These findings support the hypothesis that the TSG are involved in trafficking of TSWV to the PSG.

Life History Characteristics of Frankliniella occidentalis and Frankliniella intonsa (Thysanoptera: Thripidae) in Constant and Fluctuating Temperatures

Frankliniella occidentalis (Pergande) and Frankliniella intonsa (Trybom) are sympatric pests of many greenhouse and field crops in Korea. We compared the influence of constant (27.3°C) and fluctuating temperatures (23.8-31.5°C, with an average of 27.3°C) on the life table characteristics of F. occidentalis and F. intonsa held at a photoperiod of 16:8 (L:D) h and 45±5% relative humidity. The development times of both F. occidentalis and F. intonsa were significantly affected by temperature fluctuation, species, and sex. The development time from egg to adult of F. intonsa was shorter than that for F. occidentalis at both constant and fluctuating temperatures. Survival of immature life stages was higher under fluctuating than constant temperature for both thrips species. The total and daily production of first instars was higher in F. intonsa (90.4 and 4.2 at constant temperature, and 95.7 and 3.9 at fluctuating temperatures) than that of F. occidentalis (58.7 and 3.3 at constant temperature, and 60.5 and 3.1 at fluctuating temperatures) under both constant and fluctuating temperatures. The percentage of female offspring was greater in F. intonsa (72.1-75.7%) than in F. occidentalis (57.4-58.7%) under both temperature regimes. The intrinsic rate of natural increase (rm) was higher at constant temperature than at fluctuating temperature for both thrips species. F. intonsa had a higher rm value (0.2146 and 0.2004) than did F. occidentalis (0.1808 and 0.1733), under both constant and fluctuating temperatures, respectively. The biological response of F. occidentalis and F. intonsa to constant and fluctuating temperature was found to be interspecifically different, and F. intonsa may have higher pest potential than F. occidentalis based on the life table parameters we are reporting first here.

RNA interference tools for the western flower thrips, Frankliniella occidentalis

The insect order Thysanoptera is exclusively comprised of small insects commonly known as thrips. The western flower thrips, Frankliniella occidentalis, is an economically important pest amongst thysanopterans due to extensive feeding damage and tospovirus transmission to hundreds of plant species worldwide. Geographically-distinct populations of F. occidentalis have developed resistance against many types of traditional chemical insecticides, and as such, management of thrips and tospoviruses are a persistent challenge in agriculture. Molecular methods for defining the role(s) of specific genes in thrips-tospovirus interactions and for assessing their potential as gene targets in thrips management strategies is currently lacking. The goal of this work was to develop an RNA interference (RNAi) tool that enables functional genomic assays and to evaluate RNAi for its potential as a biologically-based approach for controlling F. occidentalis. Using a microinjection system, we delivered double-stranded RNA (dsRNA) directly to the hemocoel of female thrips to target the vacuolar ATP synthase subunit B (V-ATPase-B) gene of F. occidentalis. Gene expression analysis using real-time quantitative reverse transcriptase-PCR (qRT-PCR) revealed significant reductions of V-ATPase-B transcripts at 2 and 3 days post-injection (dpi) with dsRNA of V-ATPase-B compared to injection with dsRNA of GFP. Furthermore, the effect of knockdown of the V-ATPase-B gene in females at these two time points was mirrored by the decreased abundance of V-ATPase-B protein as determined by quantitative analysis of Western blots. Reduction in V-ATPase-B expression in thrips resulted in increased female mortality and reduced fertility, i.e., number of viable offspring produced. Survivorship decreased significantly by six dpi compared to the dsRNA-GFP control group, which continued decreasing significantly until the end of the bioassay. Surviving female thrips injected with dsRNA-V-ATPase-B produced significantly fewer offspring compared to those in the dsRNA-GFP control group. Our findings indicate that an RNAi-based strategy to study gene function in thrips is feasible, can result in quantifiable phenotypes, and provides a much-needed tool for investigating the molecular mechanisms of thrips-tospovirus interactions. To our knowledge, this represents the first report of RNAi for any member of the insect order Thysanoptera and demonstrates the potential for translational research in the area of thrips pest control.

Size does matter: the life cycle of Steinernema spp. in micro-insect hosts

The life cycle of four Steinernema species was observed in 4 insect micro-insect host species (less than 5mm long). Several parameters were measured: sex ratio of invading nematodes, percentages of host infection and offspring production, penetration rate of infective juveniles per insect and number of new generation of infective juveniles. All parameters varied among nematode species, micro-host species and application rates. All Steinernema species were capable to invade micro-insect hosts, however, invasion decreased as insect size decreased and as nematode species size increased. None of the nematode species achieved 100% mortality in the micro-hosts. Due to size differences in the nematode species, Steinernema glaseri was less capable of completing its life cycle and unable to invade smaller hosts whereas S. riobrave completed its life cycle in smaller hosts more frequently. The number of invading nematodes and the number of offspring produced had the same levels regardless of the nematode application rates, those results showed a maximum top in the number of individuals per micro-insect host. The offspring production in thrips species was only possible by endotokia matricida in S. riobrave. The sex of the invader nematodes also impeded the life cycle of S. affine because males colonized the entire body of the micro-insect host leaving no room for female invasion. The size of the host plays an irrefutable role in limiting the development of nematodes and it appears improbable that an entomopathogenic nematode population can persist in the soil without the presence of bigger insects.

Genomic analyses of sodium channel α-subunit genes from strains of melon thrips, Thrips palmi, with different sensitivities to cypermethrin

We examined the genomic organization of the sodium channel α-subunit gene in two strains of melon thrips, Thrips palmi, having differing sensitivity to cypermethrin. The nucleotide sequences of the strains included 18 or 16 putative exons which covered the entire coding region of the gene producing 2039 amino acid residues. Deduced amino acid sequences of both strains showed 80% homology with those of Periplaneta americana and Cimex lectularius. Comparison of deduced amino acid sequences of both strains showed no consistent amino acid difference. In addition to the previously reported resistant amino acid (Ile) at the T929I site, both strains encoded another resistant amino acids at two positions which are involved in pyrethroid resistance in other arthropods. These amino acids might also involve in the basal levels of resistance to pyrethroids of both strains.

Behavioural responses of Frankliniella occidentalis Pergande larvae to methyl jasmonate and cis-jasmone

The larval stages of Frankliniella occidentalis Pergande (Thysanoptera: Thripidae) cause more direct feeding damage to plants than the adults. We, therefore, investigated the behaviour-modifying effects on second instar larvae of two jasmonic acid derivatives. The artificial application of methyl jasmonate and cis-jasmone, both at 1 % concentration, deterred the larvae from settling in a dual choice bean leaf disc assay. We observed a dose-dependent feeding deterrence of both jasmonates and calculated the concentration required to reduce the feeding damage by 50 % relative to the control treatment (FDC₅₀) for each jasmonate. The feeding damage was reduced by the application of cis-jasmone at 1 % concentration, but not by the jasmonates at the respective FDC₅₀ in no-choice leaf disc bioassays. However, significantly more larvae left jasmonate-treated whole potted bean plants by migrating to the soil compared with control plants. Our results may be exploited extending behavioural manipulation by using plant compounds in thrips control programmes to the full lifecycle of the pest. Plant compounds could be used in integrated and biological pest management strategies against F. occidentalis in combination with the application of various above and below ground control measures.

A simple, novel and high efficiency sap inoculation method to screen for tobacco streak virus

A rapid and efficient sap inoculation method for tobacco streak virus (TSV) was developed in sunflower. Sap from TSV-infected sunflower plants was freshly extracted in phosphate buffer and diluted serially from 10(-1) to 10(-8). Two-day old seedlings of sunflower were injured at the meristem and immersed in the sap for 10 min, maintained at 20 °C for 2-3 days and shifted to greenhouse. The surviving seedlings in the respective sap dilution were scored for symptoms of sunflower necrosis disease (SND). SND symptoms were seen in 80 % of the seedlings inoculated with a sap dilution of 10(-5). ELISA and RT-PCR analysis of coat protein and movement protein of TSV confirmed SND symptoms. The methodology was also found to be reproducible when the sap from the infected plants was inoculated onto healthy plants. The main aim of the study was to develop a primary screening strategy for the selection of transgenics developed for SND resistance. This methodology can also be extended for the analysis of resistance against other viruses.

The species composition of thrips (insecta: thysanoptera) inhabiting mango orchards in pulau pinang, malaysia

A field study was conducted at two localities on Pulau Pinang, Malaysia, during two consecutive mango flowering seasons in 2009 to identify variations in the species composition of thrips infesting treated and untreated mango (Mangifera indica L.) orchards. The CO2 immobilisation technique and the cutting method were used to recover different thrips species from mango panicles and weed host plants, respectively. The mango panicles and various weed species within the treated orchard were found to harbour four thrips species from the family Thripidae. These species were identified as Thrips hawaiiensis (Morgan), Scirtothrips dorsalis (Hood), Frankliniella schultzei (Trybom) and Megalurothrips usitatus (Bagnall). The weed species Mimosa pudica, Cleome rutidosperma, Echinochloa colonum, Borreria laevicaulis, Veronia cinerea and Asystasia coromandeliana served as additional hosts to these thrips. Six thrips species were found in the untreated orchard. These species included Thrips palmi (Karny), Haplothrips sp. (Amyot and Serville) and the four thrips species found in the treated orchard. A brief description of the larvae for each genus is provided.