Olfactory responses of western flower thrips (Frankliniella occidentalis) populations to a non‐pheromone lure

Western flower thrips (WFT), Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), is a major pest of horticultural crops worldwide. The search for alternative pest management techniques has resulted in increasing interest in the use of kairomones and other behaviour‐modifying chemicals to mitigate the impact of this pest. In this study, we determined whether the origin of populations, feeding history, and/or genotype influence the response of WFT to the thrips kairomone lure methyl isonicotinate (MI) in a Y‐tube olfactometer study. Four New Zealand thrips populations were tested: (1) from a commercial glasshouse capsicum crop, (2) from a long‐established laboratory colony (>222 generations) kept on chrysanthemums, (3) from a laboratory colony (6–9 generations) kept on French dwarf beans, and (4) thought to be a separate cryptic non‐pest species from outdoor yellow tree lupins, Lupinus arboreus Sims (Fabaceae). In the laboratory tests, significantly more WFT from all four populations chose the MI‐laden arm of a Y‐tube olfactometer when it contained 1 μl methyl isonicotinate (61.3–73.2%) compared with the blank no‐odour arm. No differences in response to MI were found between the two laboratory and the one glasshouse WFT populations. Both laboratory populations and the greenhouse population belonged to the ‘glasshouse pest’ genotype of WFT. However, the cryptic non‐pest WFT genotype responded more strongly to MI than any of the other populations, although the response was only significantly stronger than that of the long‐established laboratory population. Significant differences were also found among populations in the average time taken for thrips to make a choice to enter either arm of the Y‐tube olfactometer, with the cryptic non‐pest lupin genotype taking the shortest time, followed by thrips from the capsicum glasshouse. The results are discussed with respect to the variability in olfactory perception and olfactory behaviour within a species and the relevance to the use of such a kairomone lure in pest management programmes.     

Biotic resistance limits the invasiveness of the western flower thrips,Frankliniella occidentalis (Thysanoptera: Thripidae), in Florida

The spread of the western flower thrips, Frankliniella occidentalis (Pergande), has resulted in the world‐wide destabilization of established integrated pest management programs for many crops. It is hypothesized that frequent exposure to insecticides in intensive agriculture selected for resistant populations, which allowed invasive populations in the eastern USA to overcome biotic resistance from the native community of species. Research conducted in Florida to understand the role of biotic factors in limiting the abundance of the western flower thrips is reviewed. Orius spp. (Hemiptera: Anthocoridae) are effective predators that suppress populations of thrips on crop and non‐crop hosts in southern and northern Florida. Orius are more effective predators of the western flower thrips than the native flower thrips, F. tritici (Fitch) and F. bispinosa (Morgan). The native species are competitors of the western flower thrips. Excessive fertilization and the use of broad‐spectrum insecticides in crop fields further enhances populations of the western flower thrips. Interactions with native species clearly limit the abundance of western flower thrips in Florida, but populations are abundant in fertilized crop fields where application of insecticides excludes predators and competitor species.     

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 effect of photoperiod on walking, feeding, and oviposition in the western flower thrips

The western flower thrips, Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), is a major pest in glasshouses, where light and photoperiod are often manipulated to grow crops. The effect of five photoperiods (L0:D24, L6:D18, L12:D12, L18:D6, and L24:D0) on the behaviour of adult females was investigated in the laboratory at 25 °C. The amount of walking, pollen consumption, and oviposition all increased with increasing photophase. The three behaviours occurred at a low rate in continuous darkness, and are therefore not exclusively diurnal. Three out of 16 thrips (19%) showed weakly rhythmic walking activity in continuous darkness, with an average circadian period of 25.3 ± 1.5 h. It is proposed that the length of the photophase determines the amount of nutrient intake, which in turn determines oviposition rate and thus affects population increase.     

Dehydration yields distinct transcriptional shifts associated with glycogen metabolism and increases feeding in the western flower thrips,Frankliniella occidentalis

We examined water balance characteristics and the influence of desiccating conditions on the physiology and behavior of adult western flower thrips, Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae). Western flower thrips are globally invasive and likely to contend with shifts in water availability across their expansive geographic range. Basic water balance characteristics, including water mass and dry mass, were established for adult males and females, revealing a distinct sexual dimorphism wherein females are larger, and males retain a larger percentage of their body mass as water. Males lose relative water mass more quickly and their survival times are shorter compared to females. RNA-seq analysis identified significant enrichment of a multitude of factors including carbohydrate transport and metabolism in dehydrated males and females. This was validated by altered glycogen levels, suggesting a rapid depletion in glycogen during dehydration. The probability of thrips feeding significantly increases when desiccation occurs, potentially to replenish water content and nutrient reserves. Our results establish the fundamental water balance characteristics of adult thrips and indicate that dehydration significantly influences the survivorship and feeding behavior of thrips; all of which being crucial factors that contribute to their capacity as vectors for plant pathogens.     

Effects of post-application irrigation and substrate moisture on the efficacy of entomopathogenic nematodes against western flower thrips, Frankliniella occidentalis

The efficacy of entomomatogenic nematodes (Steinernema bicornutum Tallosi, Peters and Ehlers and/or Heterorhabditis indica LN2 Poinar, Karunakar and David) against the soil‐dwelling life stages of western flower thrips Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae) was assessed under different moisture conditions in a commercial plant‐growing substrate in laboratory experiments. In the first experiment, both nematode species were tested at substrate moisture ranges of 67, 78, 88, or 95% relative moisture content, that were maintained before applying the nematodes at 100 or 400 infective juveniles (IJs) cm^?2. In the second experiment, 10, 25, 50, 100, or 120 ml irrigation water, resulting in relative moisture contents of 72, 81, 90, 99%, or more than the saturation level of the substrate, respectively, was applied to the substrate. Heterorhabditis indica LN2 was applied either in 3 ml water and followed by irrigation, or by suspending the infective juveniles in the water amounts indicated above to apply the nematodes in higher volume. Results indicated that at the higher application rate, initial moisture content did not significantly affect the efficacy of H. indica LN2. On the other hand, increasing moisture content resulted in an improved efficacy of H. indica LN2 and S. bicornutum at lower and higher application rates, respectively. Similar thrips control levels of 44 and 60% at the lower and higher application rate of H. indica LN2, respectively, were obtained at 88% relative moisture content. In the second experiment, higher and statistically similar thrips mortality of 40 and 50% at lower and higher application rates of H. indica LN2, respectively, were obtained when the infective juveniles were applied in a high volume suspension of 100 ml, or when followed by irrigation with 25 ml water, resulting in both cases in 81% relative moisture content. Generally, efficacies of the nematodes for thrips control can be improved by using an appropriate moisture content and/or post‐application irrigation. Thus, the high nematode application rates required for successful F. occidentalis control can be partly attributed to substrate moisture content and/or post‐application irrigation.     

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.     

Patterns of change in secondary and tertiary sex ratios of the Terebrantian thrips,Frankliniella occidentalis

Adult sex ratios (tertiary sex ratios) of the haplo-diploid Terebrantian thrips species, Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae) were examined from several native and introduced hosts in an apple (Malus spp.) ecosystem. The ratios were variable and most were female-biased, ranging from 0 to 61% males. Populations in apple bud clusters during early bloom were female-biased (0–10% males). At later bloom states, populations were less female-biased in open blossom clusters (up to 33% males) compared with those in either unopened buds or older petalless blossoms (<11% males). Changes in tertiary sex ratio in all hosts were associated with changes in resource quality, suggesting a possible effect of host quality on sex allocation. In contrast, larval (secondary) sex ratios within apples were slightly male-biased (57%) with little change across apple bud reproductive stages or over time, indicating little to no differential sex allocation. Sex ratios of populations in flight were less female-biased than those found on plants in 62 of 65 comparisons, which suggests that males are more likely to be in flight relative to females. The evidence supports that differential dispersal and distribution of sexes toward various host qualities together with a shorter longevity of adult males determines the pattern of adult sex ratios rather than any significant differential sex allocation.     

Potential of a strain of the entomopathogenic fungus Beauveria bassiana (Hypocreales: Cordycipitaceae) as a biological control agent against western flower thrips,Frankliniella occidentalis (Thysanoptera: Thripidae)

Five Beauveria bassiana strains were evaluated for control of western flower thrips. Strain RSB was the most virulent, causing 69–96% mortality at concentrations of 1×10⁴–1×10⁷ conidia mL^?1, 10 days after inoculation of first instars. In greenhouse trials, RSB applied to broccoli foliage significantly reduced adult and larval populations.     

入侵害虫西花蓟马及其他8种常见蓟马的分子鉴定

用PCR产物直接测序法对入侵害虫西花蓟马和其他8种蓟马的线粒体 COⅠ基因433 bp片段测序，获得62个个体的序列。分子数据分析显示： 种内个体间平均遗传距离在0～0.005之间，2003年在北京发现的西花蓟马与欧洲等地区报导的西花蓟马不存在明显的遗传差异； 9种蓟马种间平均遗传距离为0.213。构建的NJ树可以很好的显示蓟马的聚类，物种各单元型最初分支自展值均达到100%。结果表明，基于PCR及直接测序技术的分子鉴定可以达到准确鉴定蓟马物种之目的。     

Light spectra blocking films reduce numbers of western flower thrips,Frankliniella occidentalis (Thysanoptera: Thripidae) in strawberry,Fragaria x ananassa

1. Frankliniella occidentalis is a pest of horticultural crops, including commercial strawberry (Fragaria x ananassa). Control is challenging because certain populations are resistant to insecticides and, in strawberry, now relies on the application of biocontrols. However, this approach is not always successful if F. occidentalis populations overwhelm biocontrols. We investigated whether targeted spectral modifications to cladding materials could reduce numbers of F. occidentalis, in strawberry flowers.
2. Five UV-attenuating plastic-film materials were tested in three, 6-week, semi-field tunnel experiments containing strawberry plants. F. occidentalis were introduced into tunnels from a laboratory culture and subsequent numbers that developed in strawberry flowers were recorded.
3. Limiting UV-A radiation to the crop significantly reduced the numbers of adult and larval F. occidentalis in strawberry flowers. The numbers of adult (and larvae) in flowers were reduced by 42 (47)%, 54 (41)%, 70 (73)%, and 82 (73)% in UV350, UV370, UV400, and UV430-attenuating films, respectively, compared with the UVopen (control) film. However, no damage to strawberry fruits was observed regardless of the film treatment.
4. Incorporating UV-attenuating films as tunnel cladding can suppress F. occidentalis numbers in strawberry. Reducing populations of F. occidentalis in crops is likely to enable the more successful use of other non-chemical control strategies.

     

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.     

Rapid diagnosis of the invasive species,Frankliniella occidentalis (Pergande): a species‐specific COI marker

The western flower thrips, Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), is an invasive species and currently occurs in only a few areas in China. An easy, accurate and developmental‐stage independent method to identify F. occidentalis would be a valuable tool to facilitate pest management decision making and, more importantly, to provide an early warning so actions can be taken to prevent its introduction into non‐infested areas. Morphological identification of thrips adults and, to a lesser extent, of second‐stage larvae is the main method currently available to identify F. occidentalis. Molecular identification, however, can be easily carried out by a non‐thrips‐specialist with a little training. In this study, DNA sequence data [within the mitochondrial cytochrome oxidase I gene (COI)] and polymerase chain reaction (PCR) were utilized to develop a molecular diagnostic marker for F. occidentalis. A primer set and PCR cycling parameters were designed for the amplification of a single marker fragment (340 bp) of F. occidentalis COI mtDNA. Specificity tests performed on 28 thrips species, efficacy tests performed on five immature developmental stages as well as on male and female adults and tests on primer sensitivity all demonstrated the diagnostic utility of this marker. Furthermore, the primer set was tested on seventeen F. occidentalis populations from different countries and invaded areas in China and proved to be applicable for all geographic populations. It was used successfully to clarify the distribution of F. occidentalis in the Beijing metro area. These results suggested that this diagnostic PCR assay provides a quick, simple and reliable molecular technique for the identification of F. occidentalis.     

Combined releases of entomopathogenic nematodes and the predatory mite Hypoaspis aculeifer to control soil-dwelling stages of western flower thrips Frankliniella occidentalis

The effect of the predatory miteHypoaspis aculeifer Canestrini (Acarina:Laelapidae) on soil-dwelling stages of thewestern flower thrips (WFT) Frankliniellaoccidentalis Pergande (Thysanoptera: Thripidae)and the influence of combined releases of H.aculeifer and two entomopathogenic nematodes(EPNs) Heterorhabditis bacteriophora Poinar(Rhabditida: Heterorhabditidae) (strain HK3,HK3) and Steinernema feltiae Filipjev(Rhabditida: Steinernematidae) (Nemaplus®,SFN) were investigated in pot trials usingseedlings of green beans (Phaseolus vulgarisL.). Ten H. aculeifer adults per pot and 400infective juveniles (IJs) cm^–2 soil, of the twoEPN strains were used. In comparison withuntreated control, H. aculeifer reduced theproportion of adult F. occidentalis emergenceby 46%, while SFN and HK3 led to a reductionin adult thrips emergence by 46% and 61%,respectively. Significant differences in adultWFT emergence were found between combinedtreatments of EPNs and H. aculeifer, andindividual applications of EPNs and/or H.aculeifer, with significantly lower adultthrips emergence in the combined treatments.These findings highlight the potential for acombined use of EPNs with H. aculeifer for thecontrol of soil-dwelling stages of thrips.     

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。     

Isolation and characterization of six polymorphic microsatellite loci in the western flower thrips Frankliniella occidentalis (Insecta,Thysanoptera)

Highly polymorphic microsatellite markers can provide important demographic information on founder events and range expansion following initial introduction of invasive insect species. Six microsatellite loci were isolated from an enriched DNA library in order to study the invasion patterns of the western flower thrips, Frankliniella occidentalis. All loci tested were found to be polymorphic and successfully amplified in all individuals. The number of alleles per locus ranged from five to nine and heterozygosity ranged from 45 to 73%. Some of the loci were also successfully amplified in other thrips species.     

Potential use of the fungus Beauveria bassiana against the western flower thrips Frankliniella occidentalis without reducing the effectiveness of its natural predator Orius sauteri (Hemiptera: Anthocoridae)

Orius sauteri (Poppius; Hemiptera: Anthocoridae) is an important predator of western flower thrips, Frankliniella occidentalis (Pergande; Thysanoptera: Thripidae). O. sauteri would be directly exposed to the entomopathogenic fungus Beauveria bassiana (Bals.) Vuillemin in the field should the fungus be used as a biopesticide. If the fungus were to negatively affect O. sauteri in agro-ecosystems, predation of F. occidentalis by O. sauteri may be limited. The present study was undertaken to evaluate the insecticidal activity of strain B.bassiana-RSB of B. bassiana, which is highly virulent to F. occidentalis, on the predator under laboratory conditions. Results showed that, regardless of the concentration applied to first instars, Bb-RSB was not insecticidal against O. sauteri, nor did direct applications affect the developmental rate of the predator. Significant differences in developmental rates and adult longevity were observed between O. sauteri that fed on Bb-RSB-infected F. occidentalis cadavers and those that fed on untreated thrips. Developmental time (from first instar to adult) increased from 0.3 to 0.7 days and adult longevity decreased by 0.8 to 1.2 days for predators fed thrips treated with low and high concentrations of strain Bb-RSB, respectively, compared with predators fed on untreated thrips. However, these differences were only 3–13% of mean values for the controls, suggesting that the effects of Bb-RSB on O. sauteri are relatively minor. These findings highlight the potential use of O. sauteri in combination with B. bassiana for the biocontrol of F. occidentalis, but field tests must be performed to confirm their compatible use.     

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。