Female Thrips Research Articles

Impatiens necrotic spot virus infection and feeding behavior of nematode-parasitized western flower thrips

Abstract The effects of parasitism by the nematode Thripinema nicklewoodi Siddiqi (Tylenchida: Allantonematidae) on tospovirus infection and feeding behavior of Frankliniella occidentalis Pergande (Thysanoptera: Thripidae) were studied in the laboratory. In an initial experiment, nematode parasitism reduced the numbers of adult thrips that were positive to Impatiens necrotic spot virus (INSV) by enzyme-linked immunosorbent assay (ELISA) compared to controls. Three hypotheses on possible mechanisms causing this reduction were tested. H1: nematodes have a tendency to penetrate healthy thrips rather than INSV-infected thrips; H2: parasitized first instar thrips are less able to acquire virus during feeding; or H3: INSV replication is suppressed in parasitized thrips. H1 and H2 were proven false as we found no difference in nematode attack rate between healthy thrips and thrips that have taken up INSV and no difference in virus uptake or feeding activity between parasitized and non-parasitized larval thrips. H3 was not supported by data from our tests (P=0.07) but remains the explanation most worthy of future investigation. Interestingly, INSV transmission was not affected by nematode parasitism even though it reduced feeding activity of adult female thrips by 81% on leaves, 38% on pollen, and 22% on honey. However, despite lowered total feeding, probing by parasitized thrips (in honey) was not reduced, and this may explain why lowered feeding did not result in lowered virus transmission.

Population dynamics of nematode transmission in western flower thrips on caged impatiens

Abstract To evaluate potential of Thripinema nicklewoodi (Tylenchida: Allantonematidae) as a biological control agent of western flower thrips, Frankliniella occidentalis (Thysanoptera: Thripidae), dynamics of nematode transmission were studied in two experimental thrips populations with different initial parasitism rates in caged impatiens plants. The initial parasitism rates of adult female thrips were set at 50% in a ‘Low nematode’ treatment and at 70% in a ‘High nematode’ treatment and were compared to a control population. Transmission of T. nicklewoodi persisted for seven host generations in both nematode treatments. There was convergence in both number of parasitized thrips and percent parasitism among all the subpopulations of the western flower thrips, and no differences were found between the two treatments. The highest parasitism rates were in adult female thrips, reaching 52% in the second generation of the ‘Low nematode’ treatment and 48% in the fifth generation of ‘High nematode’ treatment. Populations of healthy (i.e., not parasitized) female thrips declined 50–79% in the ‘Low nematode’ treatment and 39–73% in ‘High nematode’ treatment compared to the control thrips population between the fourth and seventh generations. However, no significant reductions were found in numbers of larval thrips in either treatment, compared to controls, and the numbers of larval thrips were not different between the two treatments. Higher proportion of male in thrips populations with nematode was observed during the last four sampling dates when adult female thrips declined significantly in both treatments compared to control population.

Labiate essential oils affecting host selection and acceptance of Thrips tabaci lindeman

Essential oils from plants within the Lamiaceae family at several concentrations were evaluated for their repellent and deterrent properties against Thrips tabaci Lindeman (Thysanoptera: Thripidae), the onion thrips. Rosemary ( Rosmarinus officinalis L.) essential oil repelled onion thrips females at 10% concentration in olfactometer bioassays. In leaf disc bioassays on leek ( Allium porrum L .), 1% concentration of rosemary oil inhibited settling within a 4-h period. In dual-choice experiments marjoram ( Origanum majorana L.) and mint ( Mentha arvensis L.) oil both at 0.1% and 1% concentrations significantly deterred the egg-laying activity of thrips females on treated leaf discs. Lavender ( Lavandula angustifolia L.) oil at 1% and sage ( Salvia officinalis L.) oil at 0.1% concentration affected oviposition. In no-choice assays, thrips oviposition rate was significantly reduced by about 45–60% compared to the untreated control after application of marjoram and lavender oil at 1% or 0.1% concentration. With mint oil, oviposition deterrence was found only at 1% concentration. Repellent and/or deterrent essential oils combined with other control measures against T. tabaci may contribute to the enhancement of biological or integrated pest management strategies.

Effects of a juvenile hormone analog, pyriproxyfen, on Thrips tabaci (Thysanoptera: Thripidae).

Effects of a juvenile hormone analog, pyriproxyfen, on various developmental stadia of the onion thrips, Thrips tabaci Lindeman, were determined on cabbage leaves in the laboratory. Pyriproxyfen was applied at 0.064 or 0.128 g AI liter(-1) on leaves (residual contact-ingestion), thrips (direct contact) and leaf-thrips (residue contact-ingestion-direct contact). Pyriproxyfen did not have any significant lethal effects on thrips pupae in any treatment. Lethal effects on thrips larvae varied depending on application method and dosage. In the leaf and the leaf-thrips treatments, few larvae and pre-pupae molted to the next stage, and none developed to adults. In contrast, in the thrips-only treatment, pyriproxyfen did not show any significant lethal effects. The developmental times of larvae and pre-pupae were prolonged when larvae were treated with pyriproxyfen, and those of pre-pupae and pupae were shortened when pre-pupae and pupae were treated. The longevity and survival rates of thrips adults were generally shorter when they contacted and ingested pyriproxyfen-treated leaves than those in water control. Significantly fewer progeny (0.22-1.15 larvae per female) were produced by females that had fed on and been in contact with the pyriproxyfen-treated leaves than by those in the water control (11.94 larvae per female). However, the number of progeny produced by the thrips females increased significantly (3.32-7.28 larvae per female) when the females were transferred to untreated leaves after feeding on treated leaves for 5 days; the daily larval hatching pattern was similar to those in water control, indicating that female adults were able to produce viable eggs when untreated food was offered.

Insecticide resistance in onion thrips (Thrips tabaci) (Thysanoptera: Thripidae)

Onion thrips from onion (Allium cepa) crops were tested for resistance to four insecticides (deltamethrin, diazinon, dichlorvos, and endosulfan) following reports of failure of insecticides to control onion thrips in the field. Bioassays to determine baseline concentration‐mortality responses used thrips from two insecticide susceptible populations. Leaf discs (24 mm diam.) cut from leek (Allium porrum) were dipped in insecticide solutions and placed, when dry, in Petri dishes (50 mm diam.) with ventilated lids. Ten adult female thrips were added, and mortality was recorded after 24 h at 25°C. Five or six concentrations of each insecticide were tested and bioassays were usually repeated 3 times. The lowest concentration, which consistently killed over 90% thrips, was used as a diagnostic concentration to screen thrips populations collected from four onion crops and compared with both susceptible populations using the same bioassay. Each test population was also exposed to leaves dipped in water. One Canterbury and three Auckland populations were resistant to deltamethrin, whereas only the three Auckland populations were resistant to diazinon and dichlorvos. No population was resistant to endosulfan. Concentration‐mortality responses were determined for deltamethrin and diazinon. Based on the LC50s, one Auckland population was 40 times more resistant to diazinon and the Canterbury population was 550 times more resistant to deltamethrin than susceptible populations. The New Zealand onion industry responded to the initial failure of insecticides by developing and implementing an insecticide resistance management strategy and research to improve onion thrips control.

Behavioural responses of western flower thrips (Frankliniella occidentalis (pergande)) to extract from meadow-sweet (filipendula ulmaria maxim.): Laboratory and field bioassays

The behavioural responses of adult female western flower thrips (Frankliniella occidentalis (Pergande)) to fresh flowers and extracts from meadowsweet (Filipendula ulmaria Maxim.) were investigated in laboratory bioassays using three different techniques (a modified Pettersson 'star' olfactometer, dual-choice, and tunnel olfactometers). F. occidentalis was significantly attracted to the original extract and most fractions tested. Increasing the dosages resulted in an increase of insects attracted and taking off. One fraction showed repellent properties. Attractant activity of the extract was also confirmed in field tests (greenhouses with roses and pinks).

Insecticide resistance in field populations of Frankliniella occidentalis (Pergande) in Murcia (south-east Spain).

Thirty-nine field populations of Frankliniella occidentalis (Pergande) were collected from different crops (sweet pepper, tomato, lettuce, artichoke, melon, cucumber, carnation, broad bean, peach and plum) in Murcia (south-east Spain). All populations were reared separately in the laboratory to obtain enough individuals for bioassays. Female thrips were bioassayed, using a standard topical application method, against methiocarb, methamidophos, acrinathrin, endosulfan, deltamethrin and formetanate. Methiocarb was the only insecticide that showed a high efficacy against F occidentalis at field dose rates. Acrinathrin and methamidophos were moderately effective, while endosulfan and deltamethrin were ineffective. Only moderate levels of resistance (Resistance Ratios at LC50 of 10-30) were detected for the selective insecticides methiocarb, formetanate and acrinathrin used against F occidentalis in crops where these insecticides are used intensively. This generalized and low level of resistance to these insecticides, coupled with a lack of efficacy for the three broad-spectrum insecticides, was observed even in intensively managed vegetable crops. Implementation of IPM strategies in Murcia has contributed to more successful insecticide anti-resistance management.

Infection ofFrankliniella fusca(Thysanoptera: Thripidae) in Peanut by the Parasitic NematodeThripinema fuscum(Tylenchidae: Allantonematidae)

Frankliniella fusca (Hinds) is a species of thrips that is a pest of peanuts and an important vector of tomato spotted wilt virus. In previous research, populations of thrips declined in peanut during midseason for unexplained reasons. Nematodes in the genus Thripinema are parasites of thrips that render infected females sterile. A new species, T. fuscum Tipping & Nguyen, was recently described as a parasite of F. fusca in peanut. In 1997 and 1998, the temporal changes in percent parasitism of F. fusca in plots of peanuts were determined. Parasitism of adult female thrips increased from an estimated 1% on seedling peanut each year to a maximum of 68% later in the 1997 growing season and 38% in the 1998 growing season. Treatments of several insecticides for control of thrips reduced percent parasitism of the females on most sample dates in 1997, but parasitism was not significantly affected in 1998. Estimates of the numbers of F. fusca in the flowers and terminal buds of peanuts declined each year as parasitism increased. The very high levels of parasitism in 1997 were associated with near extinction of larval populations of thrips during midseason. As a result, the spread of tomato spotted wilt virus by this vector species was reduced. Thus, T. fuscum may be an important natural enemy of F. fusca responsible for suppression of populations of thrips in peanut.

Enhanced fumigant toxicity of p-cymene against Frankliniella occidentalis by simultaneous application of elevated levels of carbon dioxide.

The fumigant toxicity of the essential oil component p-cymene was assessed against Western Flower Thrips, Frankliniella occidentalis. F occidentalis adult females, first- and second-instar larvae and eggs were exposed for 2, 24 and 48 h to combinations of three p-cymene doses and two carbon dioxide levels (ambient, 10%). Additional experiments were conducted on F occidentalis adult females with lower carbon dioxide levels (ambient, 2%, 4%, 6%) applied in combination with p-cymene. Combined applications of p-cymene and carbon dioxide were found to increase significantly the fumigant toxicity of p-cymene against both adult female and larval thrips, but not thrips eggs. An increase in exposure time also led to an increase in adult and larval mortalities in both the p-cymene alone and combined treatments. These results indicate that by combining applications of the essential oil component, p-cymene, with increased carbon dioxide, it may be possible to achieve toxicity levels similar to those of standard chemical fumigants.

Biological Attributes of the Nematode, Thripinema nicklewoodi, a Potential Biological Control Agent of Western Flower Thrips

Abstract Western flower thrips (WFT), Frankliniella occidentalis (Thysanoptera: Thripidae), is the most important insect pest for greenhouse flower crops, but chemical control is often difficult because of the thrips' location in flowers and buds. Thripinema nicklewoodi (Tylenchida: Allantonematidae) is an entomoparasitic nematode that attacks and sterilizes WFT, but its biology and impact on WFT are poorly understood. Methods to propagate and study T. nicklewoodi with a microscope slide arena for observation and a rolled bean leaf arena for rearing were developed. On average, 21.4 nematodes were excreted per day by a parasitized female WFT. The sex ratio of the excreted nematodes was 6.0/1.0 (female/male). After dissection of adult WFT, a maximum of 11 ovoid-shaped first-generation nematodes in a female thrips and 6 in a male thrips were found. There were more second-generation nematodes in the adult female WFT (192.6) than in the adult male WFT (93.7). When 50 healthy first instar WFT were exposed to 4 parasitized female WFT in a rolled bean leaf, a 75.3% mean parasitization rate in the adult stage of the thrips was obtained. In contrast to previous reports, male WFT can be parasitized as readily as females. Parasitism reduced the longevity of both adult female and adult male WFT, and the degree of reduction was higher in adult male WFT. T. nicklewoodi, when presented with various WFT life stages (first instar, second instar, prepupa, pupa, adult female, and adult male), achieved the highest attack rate in first and second instars and prepupa. The free-living nematodes excreted by the hosts actively migrated to a trichome on leaf disks in the observation arena and moved up this structure. Then, the nematode actively waved the anterior part of its body while attaching itself to the trichome with the posterior part of its body. After a nematode contacted the leg of a thrips, the nematode immediately moved up along the leg toward the abdomen of the host. Increased understanding of the biology of T. nicklewoodi is important to better assess its potential for biological control of WFT.

Influence of plant volatiles on feeding damage caused by the onion thrips Thrips tabaci

Leaf disc bioassays were conducted to determine the effects of essential oils and their volatile constituents from plant species ( Lamiaceae family) at three concentrations ranging from 0.01% to 1% on the feeding activity of adult female onion thrips ( Thrips tabaci Lindeman; Thysanoptera: Thripidae). The percentage of feeding damage area on leek ( Allium porrum L .) leaf discs and the adult survival was assessed after 24 h. Onion thrips were significantly deterred by the essential oils of marjoram ( Origanum majorana L.), lavender ( Lavandula angustifolia L.) and mint ( Mentha arvensis L.) at several concentrations, and by the oil of rosemary ( Rosmarinus officinalis L.) at 1% concentration. Furthermore, thrips feeding damage was reduced as a result of linalool and eugenol application at three concentrations. Adult survival on the leaf disc surface was significantly decreased by application of terpinen-4-ol at 1% concentration. Evaluation of the potential of biologically active plant volatiles against T. tabaci may provide a new approach to the development of antifeedants and/or natural insecticides for use in both biological and integrated pest management strategies.

Host Range, Release, and Establishment of Sericothrips staphylinus Haliday (Thysanoptera: Thripidae) as a Biological Control Agent for Gorse, Ulex europaeus L. (Fabaceae), in New Zealand and Hawaii

This paper presents the results of tests to determine the host range of Sericothrips staphylinus Haliday (Thysanoptera: Thripidae), an agent selected for control of Ulex europaeus (Fabaceae). It also describes the biology of the thrips and its release and establishment in New Zealand and Hawaii. Eighty-three plant species were tested. Research was conducted in several institutions by use of five testing methods. Adult thrips survived for up to 15 days without food or longer on nonhost plants (causing small feeding scars). Female thrips laid eggs on several species of the Fabaceae other than U. europaeus, but with one exception, larvae died. Chamaecytisus palmensis (Christ) Bisby et K. Nichols supported the development of one adult in nine laboratory tests. Thrips produced adults on this plant in field cage tests, but in small numbers compared to controls. S. staphylinus appears to be narrowly oligophagous, but might establish on C. palmensis. At 19°C, females laid 1 egg per day on seedlings, for up to 8 weeks. Lifetime fecundity averaged 76 eggs per female. Development from egg to adult took 42 days. Thrips originating from the United Kingdom were released at 129 sites in New Zealand and have established at 59% of sites to date. Thrips originating from the United Kingdom, Portugal, and France were released in Hawaii, and all established. Thrips have caused heavy foliar damage at some field sites, and growth of the target weed has been significantly reduced in laboratory experiments. However, the impact of S. staphylinus on the gorse problem in New Zealand and Hawaii remains to be seen.

Behavioural Responses of Western Flower Thrips, Frankliniella occidentalis (Pergande), to Volatiles from Three Aromatic Plants

The behavioural responses of adult female western flower thrips, Frankliniella occidentalis (Pergande) to volatiles from meadow-sweet (Filipendula ulmaria), bay laurel (Laurus nobilis) and sage (Salvia officinalis) were investigated in laboratory bioassays. Volatiles collected by entrainment of a solvent extract of F. ulmaria were more attractive than was the original extract. Frankliniella occidentalis was also significantly attracted to volatiles from L. nobilis and S. officinalis. Analysis by gas chromatography and mass spectrometry identified 1,8-cineole (eucalyptol) as one of the main volatile components of all three plant species. In coupled gas chromatography-electroantennography studies with F. ulmaria, both 1,8-cineole and methyl salicylate elicited responses from F. occidentalis. Eucarvone was identified as the major component of F. ulmaria volatiles, but showed no electrophysiological activity. Behavioural responses of thrips to a range of concentrations of 1,8-cineole and methyl salicylate were tested using a modified Pettersson ’star’ olfactometer. 1,8-Cineole showed some attractant activity for the thrips at 0.01 mg, but methyl salicylate was repellent at all the concentrations tested.

Damage to nectarines by the western flower thrips (Thysanoptera: Thripidae) in the interior of British Columbia, Canada.

The phenology of damage by the western flower thrips, Frankliniella occidentalis (Pergande), on nectarines was investigated using sticky cards and direct sampling of buds between 1993 and 1995 in the interior of British Columbia, the most susceptible period for damage by western flower thrips to nectarines. The life stage responsible for damage and variation in susceptibility to damage of 11 different nectarine varieties were determined. To evaluate the predictive ability of 2 sampling methods, thrips were counted from both buds and sticky cards before petal fall and correlated to damage levels at husk drop. Damage to nectarines was caused almost entirely by larval feeding at petal fall. No predictive relationships between adult or larval densities of western flower thrips and subsequent damage to fruit were apparent. Varieties did not differ in terms of larval densities at petal fall or the subsequent damage to fruit. Female western flower thrips oviposit in nectarine buds from dormant through bloom stages primarily in sepal tissues in the early buds, and in filaments and petals as these become available.

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.

Assessing the susceptibility of chrysanthemum cultivars to tomato spotted wilt virus

Three methods were compared to assess the susceptibility of vegetatively propagated chrysanthemum to tomato spotted wilt tospovirus (TSWV): mechanical and thrips‐mediated inoculation of whole plants, and a leaf‐disc assay. As symptom expression was often poor or even absent, TSWV infections and subsequent susceptibility to TSWV were determined by ELISA. All 15 chrysanthemum cultivars tested were susceptible to TSWV, irrespective of their degree of vector resistance (based on feeding‐scar damage rates). Thrips‐mediated inoculation using different numbers of thrips revealed that 100% infection was obtained when plants were challenged by six thrips per plant, whereas 80 and over 50%, respectively, of the plants became infected when inoculated by a single male or female thrips. However, false negatives were scored even after intensive sampling because of erratic, cultivar‐specific and time‐dependent virus distribution after inoculation in the plants. Labour‐intensive samplings and long incubation periods could be overcome by a readily applicable leaf‐disc assay. This assay was as reliable as thrips‐mediated inoculation of whole plants, and its use is therefore favoured to assess chrysanthemum cultivars for TSWV susceptibility.

Colour and odour responses of flying western flower thrips: wind tunnel and greenhouse experiments

AbstractThe behavioural responses of flying western flower thrips (Frankliniella occidentalis Pergande) (Thysanoptera: Thripidae) to the colour yellow and the odour anisaldehyde were examined. In a wind tunnel, upwind flight by female thrips was common in an airflow of 0.11 m s−1 but was impeded at 0.22 m s−1. In the absence of anisaldehyde, flying female thrips exhibited an oriented response towards a yellow cue in the wind tunnel at a wind speed of 0.11 m s−1. The main response of females to anisaldehyde in the wind tunnel was flight inhibition. There was no evidence of an odour‐induced visual response, an odour‐induced anemotactic response or chemotaxis by female thrips to anisaldehyde in wind tunnel bioassays, but chemokinesis was implicated. With a matrix of yellow or black water traps with and without anisaldehyde in a greenhouse sweet pepper crop, yellow traps with anisaldehyde caught more thrips adults than yellow traps without anisaldehyde, black traps with anisaldehyde and black traps without anisaldehyde (1.3, 28 and 721 times for males respectively and 2.4, 9 and 117 times for females, respectively). Differences between respective traps were statistically significant in almost all cases. Trapping experiments using a centre‐baited trap design to reduce the interaction of anisaldehyde between baited and unbaited traps were undertaken in tomato and sweet pepper greenhouse crops. When the spatial distribution of the thrips adult population within the greenhouse was taken into account, yellow water traps with anisaldehyde caught between 11 and 15 times more female and 3 and 20 times more male F. occidentalis adults than yellow traps without anisaldehyde.

Citrus Thrips (Thysanoptera: Thripidae) Resistance Monitoring in California

Tolerance of adult female citrus thrips, Scirtothrips citri (Moulton), to chlorfenapyr, cyfluthrin, and spinosad was monitored at 10 sites in California in 1996. Chlorfenapyr and spinosad have yet to be used commercially in California and baseline LC90s were estimated to assist in future resistance monitoring efforts. The LC90s for chlorfenapyr ranged from 0.505 to 4.13 mg (AI) /Iiter and for spinosad from 2.09 to 5.37 mg (AI) /liter. On California citrus, cyfluthrin usc, 1991-1996, has been restricted to the San Joaquin Valley and to a single application per year on navel oranges. Compared with the LC90 from the most susceptible site outside the San Joaquin Valley, resistance ratios ranged from 6.2 to 56.6 at 4 sites within the valley. The 56.6-fold resistance observed at the site in Kern County is a cause for concern and may be the result of citrus thrips exposure to pyrethroids applied to nearby cotton and vegetables. Strategies for slowing further escalation of pyrethroid resistance are discussed.

ダイズウスイロアザミウマ雌における生殖休眠の温度と日長による制御

Female Thrips setosus were reared under various combinations of temperatures (23°C, 18°C and 5°C) and photoperiods (15L-9D and 10L-14D) at diffferent stages and ages. Preoviposition period was examined to identify the presence of reproductive diapause and the conditions controlling induction and termination of diapause. Short-day photoperiod induced and maintained reproductive diapause, and both high temperature (23°C) and long-day inhibited diapause induction and maintenance. Reproductive diapause was never terminated under moderate temperature (18°C) and short-day, but it was terminated under the same photothermic conditions after low temperature (5°C) incubation for a certain period.

Effects of sub‐lethal cold stress on the Western Flower Thrips, Frankliniella occidentalis

SummaryIn order to establish in a new geographical area, introduced insects must be able to survive any period of adverse conditions such as a temperate winter and be capable of subsequent development to adulthood and/or reproduction. However, this aspect of insect overwintering and cold tolerance has been poorly studied. At high latitudes, Frankliniella occidentalis is typically associated with artificially heated glasshouses, but has some ability to tolerate low temperatures and may survive winter field conditions for short periods, or for longer periods of time during mild winters. The effects of overwintering on the viability of survivors are, however, unknown. In this study, acute and chronic cold exposure regimes were imposed on first instar larvae and adult female Western Flower Thrips, after which the longevity, development and reproductive capacity of the survivors were monitored and compared to those of non‐stressed individuals. Survival of cold exposure did not affect subsequent survivorship of immature or adult insects, though cold treated larvae took approximately two days longer to reach adulthood than untreated individuals (at 20°C, 18L:6D). Chill treatment of adult females significantly reduced their rate of reproduction (from 1.45 to 0.93 larvae day‐1), reproductive lifespan (from 13.3 to 9.2 days) and as a result, total reproductive output (from 20.4 to 10.8 larvae), compared to control females. Acute exposure resulted in non‐significant decreases of the same parameters. The relevance of the above effects to overwintering of F. occidentalis is discussed.