The spread of the western flower thrips Frankliniella occidentalis (Pergande)

Abstract 1 Since the late 1970s, the western flower thrips has spread from its original distribution in western North America to become a major worldwide crop pest. 2 A wide range of data sources have been used to map the original distribution in the U.S.A. and Canada, and the progress of the spread in the U.S.A., Canada, Europe, northern Africa and Australia. 3 The possible reasons for the start of the spread are discussed. The most likely reason is that intensive insecticide use in horticulture in the 1970s and 1980s selected an insecticide resistant strain or strains. These then established in glasshouses across North America and spread from there to Europe, Asia, Africa and Australia. 4 The international spread of the western flower thrips occurred predominantly by the movement of horticultural material, such as cuttings, seedlings and potted plants. Within Europe, an outward spread from the original outbreak in the Netherlands is discernible. The speed of spread was 229 ± 20 km/year. 5 The spread has not been restricted to glasshouses. The western flower thrips has established outdoors in areas with milder winters; for example, across the southern U.S.A., southern Europe and Australia. It also overwinters in some regions with colder winters. 6 Polyphagous phytophagous thrips have many factors predisposing them to become worldwide crop pests, particularly in glasshouses. Some other species that might spread in a similar way to the western flower thrips are listed.     

Optimization of dietary RNA interference delivery to western flower thrips Frankliniella occidentalis and onion thrips Thrips tabaci

In insect reverse genetics, dietary delivery of interfering RNAs is a practical approach in nonmodel species, such as thrips, whose small size, and feeding behavior restricts the use of other delivery methods. In a laboratory context, an unsuitable diet could confound the interpretation of an RNA interference (RNAi) phenotype, however well-formulated artificial diets can minimize experimental variability, reduce the need for insect handling, and can further be used for roles, such as delivering double-strand RNA (dsRNA)-expressing recombinant bacteria. In this study, artificial diets for oral delivery of dsRNA were developed for two important pest thrips species, western flower thrips (Frankliniella occidentalis) and onion thrips (Thrips tabaci), with the goal of (a) stimulating feeding behavior, (b) supporting optimal growth rates of dsRNA-expressing symbiotic bacteria, and (c) nutritionally supporting the thrips for sufficient periods to observe RNAi phenotypes. The efficacy of artificial diets for ingesting “naked” dsRNA or dsRNA-expressing symbionts and dsRNA delivery via host plant uptake was evaluated. Compared with previously published diet formulations, new combinations based on tryptone, yeast, and soy were superior for enhancing feeding and longevity. However, simply adding “naked” dsRNA to an artificial diet was an unreliable form of RNAi delivery in our hands due to dsRNA degradation. Delivery via host plants was more successful, and the new diet formulation was suitable for symbiont-mediated dsRNA delivery, which we believe is the most convenient approach for large-scale knockdown experiments. This study, therefore, provides alternative methodologies for thrips rearing, dietary RNAi delivery, and insights into the challenges of performing dietary RNAi in nonmodel insects.     

Rapid cold hardening in the western flower thrips Frankliniella occidentalis

A rapid cold hardening process is reported in first instar larvae of Frankliniella occidentalis. When larvae are transferred directly from 20 degrees C to -11.5 degrees C for 2h there is 78% mortality, whereas exposure to 0 degrees C for 4h prior to transfer to -11.5 degrees C reduces mortality to 10%. The response can also be induced by exposure to 5 degrees C for 4h or by gradual cooling at rates between 0.1 and 0.5 degrees C min(-1.) The acquired cold tolerance is transient and is rapidly lost (after 1h at 20 degrees C). Rapid cold hardening extends survival times at -11.5 degrees C and depresses lethal temperatures in short (2h) exposures. Rearing at 15 degrees C (12L:12D), (a cold acclimation regime for F. occidentalis), does not protect against the cold shock induced by direct transfer to -11.5 degrees C (which rapid cold hardening does) but does extend survival time at -5 degrees C (i.e. increased chill tolerance) whilst rapid cold hardening does not. The rapid and longer term cold hardening responses in F. occidentalis therefore appear to have different underlying mechanisms.     

Influence of tomato spotted wilt virus on performance and behaviour of western flower thrips (Frankliniella occidentalis)

The general principles in pathogen transmission by insects involve a complex and specific interplay, in this case between thrips, tospovirus and their shared host plant, which has led to outbreaks of crop disease epidemics of economic and social importance. The possible processes and factors driving their co‐evolution were partly studied by rearing Frankliniella occidentalis [western flower thrips (WFT)] on either tomato spotted wilt virus (TSWV)–infected or uninfected Capsicum annum leaflets throughout their larval stages. Later, pupae were transferred individually on healthy leaf discs for further studies of the influence of TSWV on WFT development and behavioural patterns. The exposure of WFT to TSWV was found to improve performance with regard to longevity and survival, with mean longevity being significantly higher in TSWV‐exposed WFT compared to unexposed ones (F_(3,403) = 22.44, P < 0.0001). The observed improvement in survival was as a result of significant reduction in mortality for the WFT individuals exposed to TSWV (F_(3,383) = 849.94, P < 0.0001) compared to the unexposed. However, the results showed a significant reduction in mean daily fecundity overtime (F_10,10) = 246.66, P < 0.0001) and across the four treatments (F_(3,30) = 6.62, P = 0.001), as well as lifetime fecundity (F_(3,23) = 21.23, P < 0.0001) of the WFT exposed to TSWV compared to the unexposed reared on uninfected leaf discs. For preferential test, C. annum leaf discs infected with TSWV were more attractive to WFT as compared to healthy leaf discs (χ²_{(4, 34)} = 112.35, P < 0.0001). These results are envisaged to contribute to a clear understanding into the plant–vector–virus interaction, which is essential for accurate diagnosis and control of the TSWV epidemic, as well as the control of F. occidentalis as crop pest.     

Inheritance genetics of the trait vector competence in Frankliniella occidentalis (Western flower thrips) in the transmission of Tomato spotted wilt virus

The complexity of tospovirus–vector–host plant interaction is linked to a range of factors influencing vector's efficacy in virus transmission, leading to high variability in the transmission efficiency within vector populations. Main shortcomings of most studies are the missing information on the intrinsic potential of individual insects to serve as efficient vectors, both at phenotypic and at genotypic levels. Moreover, detailed analysis of vector competence heredity and monitoring the splitting of both genotypes and phenotypes in filial generations has not been reported. In this study, using the model system Frankliniella occidentalis and Tomato spotted wilt virus, we evaluated the inheritance and stability of the trait vector competence in a population through basic crossings of individually characterized partners, as well as virgin reproduction. We hypothesized that the trait is heritable in F. occidentalis and is controlled by a recessive allele. From the results, 83% and 94% of competent and noncompetent males respectively, inherited their status from their mothers. The trait was only expressed when females were homozygous for the corresponding allele. Furthermore, the allele frequencies were different between males and females, and the competent allele had the highest frequency in the population. These suggest that the trait vector competence is inherited in single recessive gene in F. occidentalis, for which the phenotype is determined by the haplodiploid mechanism. These findings are fundamental for our understanding of the temporal and spatial variability within vector populations with respect to the trait vector competence and at the same time offer an essential basis for further molecular studies.     

Effect of elevated CO2 on interactions betwe en the western flower thrips, Frankliniella occidentalis (Thysanoptera: Thripidae) and the common milkweed, Asclepias syriaca

We measured the effect of elevated CO₂ on populations of the western flower thrips, Frankliniella occidentalis and on the amount of leaf damage inflicted by the thrips to one of its host plants, the common milkweed, Asclepias syriaca. Plants grown at elevated CO₂ had significantly greater aboveground biomass and C:N ratios, and significantly reduced percentage nitrogen. The number of thrips per plant was not affected by CO₂ treatment, but the density of thrips (numbers per gram aboveground biomass), was significantly reduced at high CO₂. Consumption by thrips, expressed as the amount of damaged leaf area per capita, was significantly greater at high CO₂, and the amount of leaf area damaged by thrips was increased by 33%. However overall leaf area at elevated CO₂ increased by 62%, more than compensating for the increase in thrips consumption. The net outcome was that plants at elevated CO₂ had 3.6 times more undamaged leaf area available for photosynthesis than plants at ambient CO₂, even though they had only 1.6 times the overall amount of leaf area. This study highlights the need for measuring the effects of herbivory at the whole-plant level and also the importance of taking herbivory into account when predicting plant responses to elevated CO₂. Received: 9 January 1996 /Accepted: 30 July 1996     

低温胁迫对西花蓟马抗氧化酶活性的影响

西花蓟马Frankliniella occidentalis(Pergande)是一种重要入侵害虫。温度是影响西花蓟马生长发育和繁殖的一个重要非生物因子,西花蓟马对温度的耐受性决定了它的越冬存活率和地理分布。本文研究了4种抗氧化酶在低温胁迫下的活力变化。结果表明,4种抗氧化酶对低温胁迫具有不同的响应模式。低温处理能显著提高SOD的活力,对POD的活力则具有明显的抑制作用;然而,CAT和GST的活力在低温胁迫处理表现为先降低,随后逐渐提高的趋势。本研究结果表明4种抗氧化酶在西花蓟马应对低温胁迫中具有重要作用。     

寄主植物接种番茄斑萎病毒对西花蓟马种群的影响

【目的】西花蓟马Frankliniella occidentalis (Pergande)是一种入侵我国的重要害虫, 而番茄斑萎病毒是以西花蓟马传播为主的一种极具危害性的世界性病毒, 通过研究西花蓟马与番茄斑萎病毒之间的互作将有助于进一步深入理解西花蓟马以及番茄斑萎病毒的发生与猖獗机制, 同时也将为制定合理、可持续的控制西花蓟马及其传播的植物病毒防控策略提供理论依据。【方法】利用应用特定年龄-龄期及两性生命表方法, 研究了西花蓟马在辣椒3种处理（健康CK、机械损伤MD、机械接种番茄斑萎病毒MI）叶片上的生长发育、存活及种群增长。【结果】健康、机械损伤和机械接毒叶片上的发育历期依次为12.45, 11.97和11.18 d。雌雄成虫寿命和雌虫产卵量在不同处理植株叶片上差异显著(P<0.05), 在机械接毒叶片上寿命最长(雌13.51 d, 雄12.69 d); 繁殖能力最强, 产子代数高达33.01头1龄若虫/雌。健康、机械损伤和机械接毒叶片上西花蓟马内禀增长率分别为-0.009, 0.153和0.190 d-1, 净生殖率依次为0.84, 14.54和21.79。【结论】番茄斑萎病毒诱导寄主植物辣椒反应使西花蓟马发育历期缩短, 成虫寿命延长, 繁殖能力提高, 种群增长加速。     

Effects of cysteine protease inhibitors on oviposition rate of the western flower thrips,Frankliniella occidentalis

Proteolytic activity in whole insect extracts of the western flower thrips, Frankliniella occidentalis, was found to belong predominantly to the class of cysteine proteases. The pH optimum of the general proteolytic activity was determined to be 3.5, which is low when compared to other insects using cysteine proteases for protein digestion. The proteinaceous cysteine protease inhibitors chicken cystatin, potato cystatin and sea anemone equistatin inhibited in vitro more than 90% of the protease activity. To test in vivo the biological effect of such inhibitors on the oviposition rate of western flower thrips, recombinant potato cystatin and equistatin were fed to adult females. A gradual reduction in oviposition rate to about 45% of control was observed when reared on these PIs for a period of 5 days, with no increase in mortality. These results are discussed in the light of the application of protease inhibitors in transgenic plants to control this insect pest.     

Prey suitability of western flower thrips,Frankliniella occidentalis,and onion thrips,Thrips tabaci,for the predatory mite Amblyseius swirskii

Western flower thrips, Frankliniella occidentalis, and onion thrips, Thrips tabaci, are both important polyphagous pests of vegetables and ornamentals in greenhouses. Difficulties in biological control of these pests have prompted a search for new natural enemies. Most recently, the predatory mite Amblyseius swirskii has been commercialised as biological control agent of whiteflies and thrips. However, little is known about the suitability of thrips as prey for A. swirskii. We therefore assessed prey acceptance and life history of A. swirskii when feeding on F. occidentalis and T. tabaci at 25±1°C. Amblyseius swirskii juveniles preyed upon first larval instars of both F. occidentalis and T. tabaci but suffered from high mortality (67 and 78%). Developmental time (egg to adult) of A. swirskii was 7.8 days with either prey species. Adult A. swirskii females readily accepted first larval instars of both thrips species, which were attacked in <20 min on a leaf and <10 min in an artificial cage. Oviposition rates (0.92 and 0.99 eggs/female/day) and offspring sex ratios (63 and 70% females) were similar with F. occidentalis and T. tabaci as prey. Less than one-third of juveniles reaching adulthood and oviposition rates below one egg/female per day resulted in relatively low intrinsic rates of increase (r _m) (0.056 and 0.024 per day with F. occidentalis and T. tabaci, respectively). Altogether, our study suggests that the recently reported superiority of A. swirskii to the widely used Neoseiulus cucumeris in suppression of thrips is due to other traits than its population growth capacity with thrips as prey.     

Increased damage by western flower thrips Frankliniella occidentalis in chrysanthemum intercropped with subterranean clover

Suppressive effects of intercropping on Frankliniella occidentalis (Pergande) infestations have been reported in several crops. However, this study demonstrates that in year-round chrysanthemum, Dendranthema grandiflora Tzvelev, undersowing with subterranean clover, Trifolium subterraneum L., results in an increased thrips feeding damage. In a pot experiment, performed with chrysanthemum plants (cultivars Reagan and Tiger) grown with or without subterranean clover, significantly more leaves with silver and growth damage were found in the chrysanthemum plants with subterranean clover in comparison with the monocropped chrysanthemum plants. Similarly, the degree of deformation of leaf perimeter and leaf surface was higher in the top leaves of the intercropped chrysanthemum plant. In the soil experiment (only performed with Tiger and plants were grown in the soil in the greenhouse) intercropped chrysanthemum plants suffered a higher feeding damage as well. Analysis of the relation between silver or growth damage and the thrips pressure demonstrates that at similar thrips pressure in the intercropped chrysanthemum plants suffered significantly more damage. The higher thrips pressure in the intercropped chrysanthemum only explains the differences in damage partly. Changes in the reaction of chrysanthemum plants to thrips feeding or in the behaviour of the thrips, mediated by the presence of the non-host crop, are discussed. Our explanation is that chrysanthemum plants grown with clover are more susceptible to thrips feeding than monocropped plants. We conclude that undersowing with clover does not contribute to reduce damage by F. occidentalis in year-round chrysanthemum. Also, the influence of crop diversification on a pest cannot be foreseen until the specific characteristics of each individual crop – pest system are studied.     

Obstructor,a Frankliniella occidentalis protein,promotes transmission of tomato spotted wilt orthotospovirus

Tomato spotted wilt orthotospovirus (TSWV) causes substantial economic losses to vegetables and other crops. TSWV is mainly transmitted by thrips in a persistent and proliferative manner, and its most efficient vector is the western flower thrips, Frankliniella occidentalis (Pergande). In moving from the thrips midgut to the salivary glands in preparation for transmission, the virions must overcome multiple barriers. Although several proteins that interact with TSWV in thrips have been characterized, we hypothesized that additional thrips proteins interact with TSWV and facilitate its transmission. In the current study, 67 F. occidentalis proteins that interact with G_N (a structural glycoprotein) were identified using a split-ubiquitin membrane-based yeast 2-hybrid (MbY2H) system. Three proteins, apolipoprotein-D (ApoD), orai-2-like (Orai), and obstructor-E-like isoform X2 (Obst), were selected for further study based on their high abundance and interaction strength; their interactions with G_N were confirmed by MbY2H, yeast β-galactosidase and luciferase complementation assays. The relative expressions of ApoD and Orai were significantly down-regulated but that of Obst was significantly up-regulated in viruliferous thrips. When interfering with Obst in larval stage, the TSWV acquisition rate in 3 independent experiments was significantly decreased by 26%, 40%, and 35%, respectively. In addition, when Obst was silenced in adults, the virus titer was significantly decreased, and the TSWV transmission rate decreased from 66.7% to 31.9% using the leaf disk method and from 86.67% to 43.33% using the living plant method. However, the TSWV acquisition and transmission rates were not affected by interference with the ApoD or Orai gene. The results indicate that Obst may play an important role in TSWV acquisition and transmission in Frankliniella occidentalis.     

Susceptibility of western flower thrips, Frankliniella occidentalis (Pergande) to fumigation with methyl bromide

All life stages of the western flower thrips (Frankliniella occidentalis Pergande) were tested for their response to the fumigant methyl bromide and dose response curves were established. Pseudo-pupae were the most tolerant stage with a calculated LD99 of 53.1 mg litre“¹ h at 15^oC with a gas concentration of 13.5 mg litre”¹, but no survivors were found in any test above a concentration time product of 40 mg litre“¹ h. Standard 4 h fumigations achieving a CTP of 54 mg litre”¹ h that are used to control other pests are therefore likely to give very high levels of control of western flower thrips.     

西花蓟马对多杀菌素的抗性汰选和遗传方式

在室内进行了西花蓟马Frankliniella occidentalis(Pergande)种群对多杀菌素的抗性筛选和抗性遗传方式分析。经过2年多的汰选,抗性水平相比较初始种群提高了30倍,与同时测定的敏感品系相比抗性达到80.8倍。抗性遗传方式分析结果表明,正、反交后代显性度分别为0.51和0.43,二者差异不显著,说明西花蓟马对多杀菌素的抗性为常染色体、不完全显性遗传;剂量对数死亡机率值曲线分析结果显示回交后代在死亡率50%处,自交后代在死亡率25%和75%处未出现明显平坡,回交和自交后代实测值卡方检验进一步证实抗性为多基因控制。     

Life-history parameters of the western flower thrips,Frankliniella occidentalis,are affected by host plant salinity stress

Salinization, as one of the foremost abiotic stresses, is an intensifying problem in many agroecosystems. Climatic changes, along with altering land use and also salinity of irrigation water all lead to enhanced soil salinity in agricultural lands. Changes in plant characteristics, as a result of raising soil salinity, may impose bottom-up impact on plant-feeding insects. We assessed the bottom-up impact of salinity stress on demographic traits of the western flower thrips (WFT), Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), on cherry tomato, Solanum lycopersicum L. var. cerasiforme (Solanaceae) plants under greenhouse conditions (27 ± 2 °C, 65 ± 5% r.h., and L16:D8 photoperiod). Our results indicated that salinity stress interfered with the immature development period, adult longevity, and sex ratio of WFT. Salinity stress biased the sex ratio in favor of males. Significant concentration-dependent differences were observed in the intrinsic (r) and finite (λ) increase rates and the net reproduction rate (R₀) of WFT at different salinity levels. Salinity adversely influenced WFT development; nonetheless, population projection forecasted an ascending WFT population growth under moderate salinity stress of 100 mM (2.8 dS m⁻¹ of NaCl), whereas severe salinity stress of 150 mM (4.7 dS m⁻¹ of NaCl) resulted in remarkable fitness costs in WFT. This study demonstrates that WFT has the potential to become problematic in regions with moderate salinity. Therefore, it might exacerbate the detrimental impact of salinity on tomato production. The current survey provides information on the abundance of WFT on saline-stressed tomato plants, thereby contributing to developing environmentally friendly measures to manage this notorious species in ecosystems under salinity stress.     

The potential of flower odours for use in population monitoring of Western flower thrips Frankliniella occidentalis Perg. (Thysanoptera: Thripidae)

Sticky blue traps are a suitable and important tool for Western Flower Thrips population monitoring in greenhouses. They can be used in vegetables and in ornamentals, and provide important information on the current status of the pest population. However, such traps cannot be used in some susceptible plant species when they are flowering because at that stage the plants are more attractive to Western Flower Thrips than the traps. We therefore tried to increase trap attractiveness by combining the colour cue with an attractive odour cue. In laboratory experiments, we found a significant additive effect on attractiveness for two odours in traps provided with both the visual and the olfactory cues as compared to traps with either cue alone. However, these results could not easily be reproduced in greenhouses. The main factors responsible for this failure seem to be (1) the only moderate, additive increase of trap attractiveness when using combined visual and olfactory cues, and (2) the problems associated with odour diffusion. Unless a more attractive odour is found and a suitable odour dispenser is available, the use of odours to enhance sticky blue trap attractiveness for Western Flower Thrips cannot be recommended and, given the added cost for the trap, may not be affordable for growers.     

北京地区西花蓟马田间种群的抗药性监测

采用叶管药膜法在室内测定了2009—2010年北京海淀地区和昌平地区西花蓟马Frankliniella occidentalis(Pergande)田间种群对12种杀虫剂敏感性的年度变化。结果表明,北京昌平和海淀地区的西花蓟马对多数的药剂仍处于敏感状态,但对氯氟氰菊酯已产生近40倍的抗性,昌平种群对多杀菌素具有产生低水平抗性的趋势(抗性倍数为4倍)。推荐药剂包括多杀菌素、阿维菌素、甲氨基阿维菌素苯甲酸盐(甲维盐)、毒死蜱和溴虫腈,应注意与其它药剂的轮换使用,灭多威对西花蓟马的毒力水平最低,不推荐使用。     

不同温度下双尾新小绥螨对西花蓟马的捕食功能反应

为明确双尾新小绥螨Neoseiulus bicaudus各螨态对西花蓟马Frankliniella occidentalis不同龄期若虫的捕食量及不同温度对其捕食量的影响。本研究通过测定不同温度下24 h内双尾新小绥螨各螨态对不同密度西花蓟马若虫的捕食情况(西花蓟马猎物密度分别为5、10、15、20和25头/室,温度分别设置为23、26、29、32和35℃)。研究结果表明,双尾新小绥螨各螨态对猎物的捕食量随猎物密度的升高而增加。当温度为29℃,雌成螨对西花蓟马1龄若虫捕食量最高,在猎物数为25头/室时,可达4.4头/日。23~32℃内,双尾新小绥螨的雌成螨的捕食量随温度的上升而增加,到达35℃时开始降低。29~32℃双尾新小绥螨的雌成螨对西花蓟马1龄若虫的捕食量最高,可达6.7头/日,最适于其捕食。结果表明双尾新小绥螨对西花蓟马若虫的捕食功能反应类型符合Holling II模型,其对西花蓟马有较好的捕食能力,可利用于西花蓟马的生物防治。     

Apple pollen as a supplemental food for the western flower thrips, Frankliniella occidentalis: response of individuals and populations

Experiments were performed to investigate the influence of apple pollen, plant diet, and relative humidity on the individual life‐history traits and on the population growth of the western flower thrips, Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae). In experiments with individual thrips, availability of bean pods plus a mixture of apple pollen and lycopodium shortened larval development time, and hence time from egg to adult, compared to bean pods alone. Similarly, the total number of eggs laid and the mean number of eggs laid per female per day were greater in the presence of pollen plus bean pods than on bean pods alone. Diet did not affect survival or length of the pre‐oviposition and oviposition periods. A diet including bean pods plus pollen shortened the generation time and population‐doubling time, and increased the net reproductive rate and the intrinsic rate of increase, compared to bean pods alone. In experiments on populations, growth was measured with different amounts of pollen on bean pods under two relative humidities, ca. 38% and 66%, and separately on two bean substrates, pods or leaves, at ca. 45% r.h. The presence or amount of pollen had no effect on population growth regardless of the other variables. Greater population growth occurred under the higher relative humidity regardless of substrate. Population growth was greater on bean pods than on bean leaves. Despite reports on the nutritional benefit of pollen for F. occidentalis, this benefit may be affected by pollen type, host plant, and other factors. In situations in which pollen has little influence on the growth of F. occidentalis populations, pollen that benefits a thrips predator could be used in an integrated management plan for controlling thrips.