Western Flower Thrips Frankliniella Occidentalis Research Articles

Nitrogen Deficiency Enhances Eggplant Defense against Western Flower Thrips via the Induction of the Jasmonate Pathway.

Plant nutrition is connected to defense against insect herbivores, but the exact mechanism underlying the effect of the nitrogen (N) supply on the anti-herbivore capacity of eggplants (Solanum melongena) has not been studied in detail. Therefore, we examined the impact of low (LN, 0.5 mM) and high (HN, 5 mM) nitrate levels on eggplant resistance against the western flower thrips Frankliniella occidentalis (WFT), a major destructive eggplant pest. Our results showed that LN plants displayed enhanced defense responses to WFT compared to HN plants. This included increased transcript levels of key genes in the jasmonic acid (JA) pathway, the accumulation of JA-amido conjugates (jasmonoyl-isoleucine, jasmonoyl-phenylalanine, and jasmonoyl-valine), JA precursor (12-oxophytodienoic acid), and methyl jasmonate, higher transcript levels of defense marker genes (MPK3, MPK7, and WRKY53), and increased activities of polyphenol oxidase and peroxidase upon a WFT attack. Our findings suggest that N deficiency can prime JA-mediated defense responses in eggplants, resulting in increased anti-herbivore resistance.

Potential of a new phytoseiid species Neoseiulus setarius (Acari: Phytoseiidae) as a biocontrol agent: Biological and demographic parameters on prey and non-prey foods

Neoseiulus setarius Ma, Meng & Fan is a newly described phytoseiid species found in Inner Mongolia of China. To evaluate the potential of N. setarius as a biocontrol agent, we studied life table parameters of N. setarius reared on four food resources, including western flower thrips Frankliniella occidentalis Pergande, eriophyoid mite Aceria pallida Keifer, cattail pollen Typha latifolia L. and poplar pollen Populus alba L. Neoseiulus setarius fed on two prey species developed faster and produced more eggs than those fed with two kinds of pollen. Neoseiulus setarius had the shortest juvenile development time on A. pallida (5.38 days), and the highest daily fecundity on F. occidentalis (2.43 eggs/female/day). The juvenile development time of N. setarius was similar on cattail pollen and poplar pollen, but the fecundity of N. setarius was significantly higher on cattail pollen. There were significant differences in the demographic parameters of N. setarius reared on the four different diets. The highest intrinsic rate of increase (rm) was on F. occidentalis (0.178 day−1), followed by A. pallida (0.159 day−1), cattail pollen (0.127 day−1) and poplar pollen (0.092 day−1). Neoseiulus setarius showed higher fitness in development and reproduction on prey (F. occidentalis and A. pallida) and cattail pollen. These results suggest that N. setarius could be a promising biocontrol agent for the management of thrips and gall mites.

Effect of Volatile Organic Compounds of Entomopathogenic Fungi of the Genus Lecanicillium and Their Component, Acetic Acid, on Female Behavior in the Western Flower Thrips Frankliniella occidentalis (Pergande) (Thysanoptera, Thripidae)

Effect of Volatile Organic Compounds of Entomopathogenic Fungi of the Genus Lecanicillium and Their Component, Acetic Acid, on Female Behavior in the Western Flower Thrips Frankliniella occidentalis (Pergande) (Thysanoptera, Thripidae)

Insulin-like Peptides of the Western Flower Thrips Frankliniella occidentalis and Their Mediation of Immature Development.

Insulin-like peptides (ILPs) mediate various physiological processes in insects. Specifically, ILP expression is required for immature development in different insects. The western flower thrips, Frankliniella occidentalis, is polyphagous, but its occurrence and population density vary among different hosts. This study assesses the developmental variations in the thrips through quantitative analysis of their ILP expressions. Two types of ILPs (Fo-ILP1 and Fo-ILP2) were identified from the genome of F. occidentalis, and both ILPs were predicted to have the characteristics of signal peptides and B-C-A chains linked by cysteines. A phylogenetic analysis indicates that these two ILPs in the thrips are clustered with the ILP1 of Drosophila melanogaster, suggesting their physiological roles in growth. In addition, the two ILP genes were relatively highly expressed at all feeding stages, but their expression was reduced during the nonfeeding prepupal and pupal stages. Furthermore, RNA interference of each ILP expression led to significant developmental retardation. In validating the ILP expression in the thrips' development, five different varieties of host hot peppers were assessed in a choice test, along with the immature development of F. occidentalis. The expression levels of the two ILP genes were highly correlated with variations in the immature developmental rates of different hot pepper varieties. These suggest that Fo-ILP1 and Fo-ILP2 mediate the immature development of F. occidentalis by sensing different nutritional values of hot peppers. This study is the first report on ILPs in thysanopteran insects.

Increasing Frequency of G275E Mutation in the Nicotinic Acetylcholine Receptor α6 Subunit Conferring Spinetoram Resistance in Invading Populations of Western Flower Thrips in China.

Simple SummaryThe western flower thrips (WFT) Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae) is an important invasive pest in agriculture and forestry. It has developed resistance to a frequently used pesticide spinetoram world widely, including the invading area of China. However, the mechanism of resistance to spinetoram is unclear in China. In this study, we found the presence of the G275E mutation in the nicotinic acetylcholine receptor Foα6 in the early invading populations, which has now increased to a high frequency in China. There was a correlation between the frequency of the G275E mutation and resistance to spinetoram as characterized by median lethal concentration. Our results showed that G275E mutation is one of the mechanisms conferring spinetoram resistance in invading populations in China, as in many other countries. Our study highlights the rapid spread of the G275E mutation in China in the 2009–2021 period.The western flower thrips Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae) is an important invasive pest worldwide. Field-evolved resistance to the pesticide spinetoram is an increasing problem in the chemical control of this pest. Here, we examined changes in the frequency of a genetic mutation associated with spinetoram resistance, the G275E mutation in the acetylcholine receptor Foα6, in 62 field populations collected from 2009 to 2021 across areas of China invaded by this pest. We found a low frequency of the G275E mutation in populations collected at the early invasion stage, in contrast to a high frequency in native USA populations. However, the frequency of the G275E mutation has increased to a high level in recently collected populations, with the mutation becoming fixed in some populations. There was a correlation between the frequency of the G275E mutation and resistance to spinetoram as characterized by median lethal concentration, although two populations were outliers. These results showed that G275E mutation is one of the mechanisms conferring spinetoram resistance in many invading populations in China. Ongoing dispersal of the WFT may have facilitated a rapid increase in the G275E mutation across China. Our study highlights the rapid evolution of pesticide resistance in an invasive species and points to a useful marker for molecular diagnostics of spinetoram resistance.

Innate and learned responses of foraging predatory mites to polar and non-polar fractions of thrips’ chemical cues

Plant-inhabiting predatory mites (Acari, Phytoseiidae) are important natural enemies of herbivorous mites and insects and globally used in biological control in diverse agro-ecosystems. Foraging predatory mites predominantly use chemical cues to find plants harboring prey, to locate prey patches within plants and to detect prey individuals within patches. While a great deal of research has been dedicated to the response of predatory mites to herbivore-induced plant volatiles, comparatively little is known about close range chemosensory orientation such as the response to kairomones emanating from prey bodies. We addressed this issue in the interaction between the predatory mite Amblyseius swirskii Athias-Henriot and its prey Western flower thrips Frankliniella occidentalis Pergande. First, we assessed the predators’ innate response to polar and non-polar fractions of whole-body extracts of thrips, which were generated by four solvents, i.e. hexane (strongly non-polar), ethyl acetate (moderately non-polar), ethanol (moderately polar) and distilled water (strongly polar). The predators avoided the non-polar hexane extract, did not show a clear response to the ethyl acetate and ethanol extracts, and were strongly attracted by the polar water extract. Second, we evaluated the effects of early life experience with the aversive hexane and attractive water extracts on the foraging behavior of adult predators presented live thrips. The predators memorized which type of cue they had experienced early in life. Experience of the aversive hexane extract reduced, whereas experience of the attractive water extract enhanced, the attack likelihood and predation rate on thrips, relative to thrips extract-naïve predators. GC–MS analysis of the hexane extract revealed six major compounds, i.e. decyl acetate, dodecyl acetate, linolenic acid, pentacosan, heptacosane and an unidentified unsaturated acetate. Decyl acetate and dodecyl acetate are well known compounds released by thrips upon predation threat; whether the other four compounds convey any information to the predators is unknown. Our study provides evidence that polar and non-polar fractions of thrips’ chemical cues elicit opposite responses in foraging predatory mites. The finding that early learning of thrips chemical cues profoundly changes the predators’ foraging success later in life may be exploited to optimize biological control of thrips.

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.

Long-term storage stability of Beauveria bassiana ERL836 granules as fungal biopesticide

Abstract Beauveria bassiana (Balsamo) Vuillemin (Hypocreales: Cordycipitaceae) ERL836 has been commercialized under the name ChongchaeSak to control an agricultural insect pest, the western flower thrips Frankliniella occidentalis Pergande (Thysanoptera: Thripidae), in the Republic of Korea. As soon as it was launched in 2017, it became a popular product and has received a positive response. However, study of the storage stability of the fungus ERL836 has yet to be investigated. To determine the optimum conditions for long-term storage, we assessed conidial viability and insecticidal activity of B. bassiana ERL836 according to storage temperature and culture substrate. Viability of B. bassiana ERL836 conidia from mycotized grains (millet and rice) stored at low (4 °C) and moderate (25 and 30 °C) temperatures was maintained at >85% for 24 and 18 months, respectively, along with insecticidal activity. In contrast, the samples stored at 37 °C showed low germination rate (about 80% germination rate for only 5 months). This result suggests that low and moderate temperatures (4 to 30 °C) conserve B. bassiana ERL836 viability and virulence.

<b>Two new reports of thrips (Thysanoptera: Thripidae) from India</b>

Caliothrips punctipennis (Hood) and the male of Western Flower Thrips Frankliniella occidentalis (Pergande) have been recorded for the first time from India. F. occidentalis was collected on the leaves of Erythrina indica from Ooty in the Nilgiris, the Western Ghats, southern India, whereas C. punctipennis was collected from yellow pan traps laid at Great Nicobar, India. Considering the quarantine importance of the pest F. occidentalis, the report of the male for the first time in India needs attention and concern. Males are also known to be more effective vectors of tospoviruses than females. Xerochrysum bracteatum, the Common Golden Everlasting Daisy, is often taken out of Ooty by tourists to other parts of the country. This along with other planting materials carried by tourists and farmers could aid in the dispersal of F. occidentalis to the temperate regions of northern and southern India, where it is likely to thrive in the congenial climatic conditions prevalent there. Under these circumstances, it is imperative that quarantine mechanisms within the country are activated and strengthened, to prevent the spread of this notorious pest to the rest of India from the pockets of its occurrence in southern India - particularly the Nilgiris. The diagnostic characters of both species are discussed.

Pest Identification Guide: Western Flower Thrips Frankliniella occidentalis (Pergande)

Western flower thrips transmit the carmovirus Pelargonium flower break virus (PFBV), the ilarvirus Tobacco streak virus (TSV), the tospoviruses Chrysanthemum stem necrosis virus (CSNV), Groundnut ringspot virus (GRSV), Impatiens necrotic spot virus (INSV), Tomato chlorotic spot virus (TCSV), and Tomato spotted wilt virus (TSWV). This species is primarily a flower feeder, so most damage would be expected on the flower or fruit. Learn to identify the western flower thrips with this two-page illustrated guide written by Jeffrey D. Cluever and Hugh A. Smith, and published by the Department of Entomology and Nematology, May 2016. ENY-2034/IN1127: Pest Identification Guide: Western Flower Thrips Frankliniella occidentalis (Pergande) (ufl.edu)

Supplemental food that supports both predator and pest: a risk for biological control?

Supplemental food sources to support natural enemies in crops are increasingly being tested and used. This is particularly interesting for generalist predators that can reproduce on these food sources. However, a potential risk for pest control could occur when herbivores also benefit from supplemental food sources. In order to optimize biological control, it may be important to select food sources that support predator populations more than herbivore populations. In this study we evaluated the nutritional quality of four types of supplemental food for the generalist predatory mites Amblyseius swirskii Athias-Henriot and Amblydromalus (Typhlodromalus) limonicus (Garman and McGregor), both important thrips predators, and for the herbivore western flower thrips Frankliniella occidentalis Pergande, by assessing oviposition rates. These tests showed that application of corn pollen, cattail pollen or sterilized eggs of Ephestia kuehniella Zeller to chrysanthemum leaves resulted in three times higher oviposition rates of thrips compared to leaves without additional food. None of the tested food sources promoted predatory mites or western flower thrips exclusively. Decapsulated cysts of Artemia franciscana Kellogg were not suitable, whereas cattail pollen was very suitable for both predatory mites and western flower thrips. In addition, we found that the rate of thrips predation by A. swirskii can be reduced by 50 %, when pollen is present. Nevertheless, application of pollen or Ephestia eggs to a chrysanthemum crop still strongly enhanced the biological control of thrips with A. swirskii, both at low and high release densities of predatory mites through the strong numerical response of the predators. Despite these positive results, application in a crop should be approached with caution, as the results may strongly depend on the initial predator-prey ratio, the nutritional quality of the supplemental food source, the species of predatory mites, the distribution of the food in the crop and the type of crop.

Thiamethoxam resistance selected in the western flower thrips Frankliniella occidentalis (Thysanoptera: Thripidae): Cross-resistance patterns, possible biochemical mechanisms and fitness costs analysis

The western flower thrips (WFT) Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), an important pest of various crops in the world, has invaded China since 2003. To understand the risks and to determine possible mechanisms of resistance to thiamethoxam in WFT, a resistant strain was selected under the laboratory conditions. Cross-resistance and the possible biochemical resistance mechanisms were investigated in this study. A 15.1-fold thiamethoxam-resistant WFT strain (TH-R) was established after selection for 55 generations. Compared with the susceptible strain (TH-S), the selected TH-R strain showed extremely high level cross-resistance to imidaclothiz (392.1-fold) and low level cross-resistance to dinotefuran (5.7-fold), acetamiprid (2.9-fold) and emamectin benzoate (2.1-fold), respectively. No cross-resistance to other fourteen insecticides was detected. Synergism tests showed that piperonyl butoxide (PBO) and triphenyl phosphate (TPP) produced a high synergism of thiamethoxam effects in the TH-R strain (2.6- and 2.6-fold respectively). However, diethyl maleate (DEM) did not act synergistically with thiamethoxam. Biochemical assays showed that mixed function oxidase (MFO) activities and carboxylesterase (CarE) activity of the TH-R strain were 2.8- and 1.5-fold higher than that of the TH-S strain, respectively. When compared with the TH-S strain, the TH-R strain had a relative fitness of 0.64. The results show that WFT develops resistance to thiamethoxam after continuous application and thiamethoxam resistance had considerable fitness costs in the WFT. It appears that enhanced metabolism mediated by cytochrome P450 monooxygenases and CarE was a major mechanism for thiamethoxam resistance in the WFT. The use of cross-resistance insecticides, including imidaclothiz and dinotefuran, should be avoided for sustainable resistance management.

A Male-Predominant Cuticular Hydrocarbon, 7-Methyltricosane, is used as a Contact Pheromone in the Western Flower Thrips Frankliniella occidentalis

In a laboratory bioassay, adult female Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae) spent more time near filter paper disks that had been exposed to adult males than near unexposed disks; this effect was not observed on disks exposed to adult females. The response could only partly be explained by the known male-produced aggregation pheromone, neryl (S)-2-methylbutanoate, suggesting the presence of an unknown male-produced compound. In gas chromatography/mass spectrometry analyses, 7-methyltricosane was detected on disks exposed to males, but not on disks exposed to females. Extracts of cuticular lipids also showed relatively large amounts of 7-methyltricosane on males, whereas only trace amounts were found on females and none on larvae. Bioassays of synthetic 7-methyltricosane showed that adults responded only after contact. The response to this compound was clearly different from that to n-tricosane or hexane-only controls. Females that contacted 7-methyltricosane on glass beads stayed in the vicinity and frequently raised the abdomen, a behavior that rejects mating attempts by males. Males stayed in the vicinity and wagged the abdomen sideways, a behavior used in fighting between males. This is the first identification of a contact pheromone in the order Thysanoptera.

Developmental profile and hormonal regulation of the transcription factors broad and Krüppel homolog 1 in hemimetabolous thrips

In holometabolous insects, Krüppel homolog 1 ( Kr-h1) and broad ( br) are key players in the juvenile hormone (JH) regulation of metamorphosis: Kr-h1 is an early JH-response gene, while br is a transcription factor that directs pupal development. Thrips (Thysanoptera) are classified as hemimetabolous insects that develop directly from nymph to adult, but they have quiescent and non-feeding stages called propupa and pupa. We analyzed the developmental profiles of br and Kr-h1 in the western flower thrips Frankliniella occidentalis (Thripidae) that has one propupal instar and one pupal instar, and Haplothrips brevitubus (Phlaeothripidae) that has one propupal instar and two pupal instars, i.e. pupa I and pupa II. In F. occidentalis, the br mRNA levels were moderate in the embryonic stage, high at the larva-propupa transition, and low in the pre-final larval instar and the pupal stage, while Kr-h1 mRNA levels were high in the embryonic stage, remained at a moderate level in the larval and propupal stages, and low in the pupal stage. The expression profiles in H. brevitubus were very similar to those in F. occidentalis, except that the increase of br expression in the final larval stage occurs more slowly in H. brevitubus, and that the mRNA levels of br and Kr-h1 remained high in pupa I of H. brevitubus and then decreased. These profiles of br and Kr-h1 were comparable to those in holometabolous insects, although br expression found in thrips’ embryogenesis is reminiscent of several hemimetabolous species. Treatment with an exogenous JH mimic (JHM) in distinct developmental stages consistently resulted in lethality as pupa of F. occidentalis or pupa II of H. brevitubus. Treatment with JHM to newly molted propupae caused prolonged expression of Kr-h1 and br in both species, suggesting that Kr-h1 and br could be involved in mediating anti-metamorphic signals of JHM.

Identification of the cuticular lipid composition of the Western Flower Thrips Frankliniella occidentalis

The Western Flower Thrips Frankliniella occidentalis effectively resists many insecticides, but it can be controlled by the use of bioinsecticides such as entomopathogenic fungi. The epicuticular chemistry of these insects is therefore of great interest, and accordingly, the cuticular lipid composition of F. occidentalis was analysed. It was found that the cuticular lipids of both the adult and larval stages of F. occidentalis consist of two groups of compounds — hydrocarbons and free fatty acids. The same hydrocarbon pattern was found in both adults and larvae, with the exception of n-hentriacontane, which was detected only in adult insects. The following homologous series were identified: n-alkanes from C-25 to C-29 (31) with the marked dominance of odd numbers of carbon atoms, 3-methylalkanes with 26 and 28 carbon atoms, and branched monomethylalkanes (branched at C-9, -11, -13 and -15) with 26, 28 and 30 carbon atoms. The chemical composition of the free fatty acids consists of two homologous series: saturated (C 14:0, C 16:0, C 18:0) and unsaturated fatty acids (C 16:1 and C 18:1). This analysis confirmed the lack of potential inhibitors of entomopathogenic fungi in the cuticular lipids of this insect species.

Identification of a Male-produced Aggregation Pheromone in the Western Flower Thrips Frankliniella occidentalis

Two major components have been detected in the headspace volatiles of adult male Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae) that are not present in the headspace volatiles of adult females. The compounds were identified as (R)-lavandulyl acetate and neryl (S)-2-methylbutanoate by comparison with synthetic standards using gas chromatography (GC), GC mass spectrometry (MS), and chiral GC. Field trials were conducted with synthetic compounds in naturally infested crops of sweet pepper grown in large plastic greenhouses in Spain. The catch of adult females and males on blue sticky traps was increased by neryl (S)-2-methylbutanoate alone or by a 1:1 blend of (R)-lavandulyl acetate and neryl (S)-2-methylbutanoate, but (R)-lavandulyl acetate was not active alone. This is the first identification of an aggregation pheromone in the order Thysanoptera. The possible role of (R)-lavandulyl acetate is discussed.

Time and frequency of applications of entomopathogenic nematodes and their persistence for control of western flower thrips Frankliniella occidentalis

AbstractPost application persistence of two entomopathogenic nematode (EPN) species, Heterorhabditis bacteriophora strain HK3 and Steinernema carpocapsae strain DD136, was studied against soil-dwelling late second instar larvae (L2) of western flower thrips (WFT) Frankliniella occidentalis (Thysanoptera: Thripidae). The nematodes were applied at 200 and 400 infective juveniles (IJ) cm−2, and L2 WFT were introduced at 0 (same day), 3, 6, 9 or 12 days after nematode application (DANA). Heterorhabditis bacteriophora caused higher thrips mortality than S. carpocapsae in most of the tests and both species persisted for at least 6 days, causing WFT mortality of up to 76 and 37.8%, respectively. In a separate experiment, H. bacteriophora and S. feltiae (Filipjev) Sylt were applied at 200 and 400 IJ cm−2 once (10, 15, or 20 days) or twice (10 and 15, 10 and 20, or 15 and 20 days) after introduction of ten female and two male WFT adults onto bean plants (Phaseolus vulgaris). An early repeated application (10 and 15 days after adult WFT release) of H. bacteriophora at 200 IJ cm−2 resulted in significantly lower numbers WFT than a single applications at 400 IJ cm−2 indicating that better WFT control can be achieved if the same concentration is split over time. However, an early application (10 days after adult WFT release) of H. bacteriophora at 400 IJ cm−2 controlled WFT better than late applications, indicating that time of EPN application is additionally very crucial in WFT control. For S. feltiae, higher WFT mortality was recorded when nematodes were repeatedly applied on days 10 and 15 than in any other applications at a given concentration. Thus, an early application of an efficient and relatively more persistent nematode species, e.g., H. bacteriophora HK3, at a lower concentration but in a repeated manner, can result in higher thrips control than a single application at the higher concentration.

Ontogenetic shifts in intraguild predation on thrips by phytoseiid mites: the relevance of body size and diet specialization

In greenhouse agroecosystems, a guild of spider mite predators may consist of the oligophagous predatory mite Phytoseiulus persimilis Athias-Henriot, the polyphagous predatory mite Neoseiulus californicus McGregor (both Acari: Phytoseiidae) and the primarily herbivorous but facultatively predatory western flower thrips Frankliniella occidentalis Pergande (Thysanoptera: Thripidae). Diet-specialization and the predator body size relative to prey are crucial factors in predation on F. occidentalis by P. persimilis and N. californicus. Here, it was tested whether the relevance of these factors changes during predator ontogeny. First, the predator (protonymphs and adult females of P. persimilis and N. californicus): prey (F. occidentalis first instars) body size ratios were measured. Second, the aggressiveness of P. persimilis and N. californicus towards F. occidentalis was assessed. Third, survival, development and oviposition of P. persimilis and N. californicus with F. occidentalis prey was determined. The body size ranking was P. persimilis females > N. californicus females > P. persimilis protonymphs > N. californicus protonymphs. Neoseiulus californicus females were the most aggressive predators, followed by highly aggressive N. californicus protonymphs and moderately aggressive P. persimilis protonymphs. Phytoseiulus persimilis females did not attack thrips. Frankliniella occidentalis larvae are an alternative prey for juvenile N. californicus and P. persimilis, enabling them to reach adulthood. Females of N. californicus but not P. persimilis sustained egg production with thrips prey. Within the guild studied here, N. californicus females are the most harmful predators for F. occidentalis larvae, followed by N. californicus and P. persimilis juveniles. Phytoseiulus persimilis females are harmless to F. occidentalis.

Assessing the Attractiveness of Volatile Plant Compounds to Western Flower Thrips Frankliniella occidentalis

The responses of walking adult female western flower thrips, Frankliniella occidentalis, to plant volatiles at several concentrations were investigated in a Y-shaped glass tube olfactometer. The simple experimental design allowed comparing the effect of numerous volatiles and differentiated clearly between attractive and repellent compounds. Western flower thrips were attracted by the benzenoids benzaldehyde and pand o-anisaldehyde; the monoterpenes geraniol, nerol, linalool, and (+)-citronellol; the sesquiterpene (E)-β-farnesene, eugenol, and 3-phenylpropionaldehyde; two phenylpropanoids; and the nonfloral odor ethyl nicotinate. p-Anisaldehyde, nerol, ethyl nicotinate, and (E)-β-farnesene elicited positive responses at several concentrations; all other volatiles were attractive at a specific concentration. Salicylaldehyde, a benzenoid, elicited negative responses at two concentrations. Experimental series with several other volatiles belonging to the above mentioned chemical groups and the essential oils from rose and geranium did not result in either clearly positive or negative responses by tested thrips.

Variation in tospovirus transmission between populations of Frankliniella occidentalis (Thysanoptera: Thripidae)

AbstractFourteen populations of the western flower thrips Frankliniella occidentalis Pergande, originating from different hosts and countries in Asia, Europe, North America and New Zealand, were analysed for their competency and efficiency to transmit tomato spotted wilt virus (TSWV). All populations acquired and subsequently transmitted the virus, and were thus competent to transmit. They show marked differences in their efficiency, expressed as the percentage of transmitting adults. Efficiencies varied from 18% for a F. occidentalis population from the USA (US2) to 75% for a population from Israel (IS2). The differences between populations were not affected by the amount of virus ingested or by the host plant used. However, the tospovirus species studied and age at which the larvae acquired the virus affected the efficiency to transmit. First instar larvae of the NL3 population from The Netherlands were able to acquire tomato spotted wilt virus, whereas second instar larvae failed to do so. However, both instars of this population acquired impatiens necrotic spot virus (INSV), another tospovirus. This and tomato spotted wilt virus were both acquired by both larval stages of the populations IS2 and US2, although their ability to acquire virus decreased with their age. Hence, it is likely that, in general, both instar larvae of most F. occidentalis populations are competent to acquire both tospoviruses. These results show that large differences exist in the efficiency by which tomato spotted wilt is transmitted by the various F. occidentalis populations and that the ability to acquire tospovirus decreases with the age of the larvae