Evaluation of the nematodes Steinernema feltiae and Thripinema nicklewoodi as biological control agents of western flower thrips Frankliniella occidentalis infesting chrysanthemum

In greenhouse studies, we evaluated a commercial formulation of the entomopathogenic nematode Steinernema feltiae and the inoculative release of the thrips-parasitic nematode Thripinema nicklewoodi against western flower thrips (WFT), Frankliniella occidentalis Pergande infesting potted chrysanthemums. Foliar sprays of S. feltiae applied at 1.25-2.5×10³ IJ mL^-1 and 1000 - 2000 L ha^-1 at 3-day intervals alone (targeting feeding stages) or in combination with soil applications (simultaneously treating non-feeding stages in the soil at the same rates) decreased but did not provide adequate control of thrips in flowering plants artificially infested with a dense population. Similar nematode treatments applied for four to five applications at 6-day intervals in two batches of initially clean chrysanthemums failed to prevent unacceptable damage to flowers and leaves from a dense natural infestation within the greenhouse. Although some IJ survived up to 48 h within flowers and flower buds, few nematode-infected thrips (larvae and adults) were recovered. In studies with T. nicklewoodi (which is not amenable for mass production), the inoculative releases of two parasitized hosts per plant enabled the nematode to become established within existing WFT populations under greenhouse conditions. However, relatively poor transmission and slow speed of kill (nematode primarily suppresses populations through host sterilization) prevented low level inoculations being effective over a single crop cycle. Further studies showed that transmission of T. nicklewoodi persisted for nine host generations, infected up to 83% of adult thrips and provided long-term suppression of discrete caged populations, but only after uneconomically high thrips densities had been reached.     

海南岛芒果蓟马种类调查研究

芒果是海南仅次于香蕉的重要热带水果。近年来,由于农药的滥用,蓟马已从过去的次要害虫上升为主要害虫。蓟马以若虫、成虫锉吸为害芒果花、叶、芽、幼果,严重影响芒果生长和果实质量。研究调查了海南岛儋州,昌江等7个主要芒果种植区,共采集蓟马成虫标本1241头。经鉴定,得出害虫种类9种,即茶黄硬蓟马Scirtothrips dorsalis Hood、黄胸蓟马Thrips hawaiiensis(Morgan)、褐蓟马Thrips physapus Linnaeus、威岛蓟马Stenchaetothrips victoriensis(Moulton)、红带滑胸针蓟马Selenothrips rubrocinctus(Giard)、温室蓟马Heliothrips haemorrhoidalis(Bouché)、腹突皱针蓟马Rhipiphorothrips cruentatus Hood、丽色皱针蓟马Rhipiphorothrips pulchellus Morgan和华简管蓟马Haplothrips chinensis Priesner:天敌1种,即横纹蓟马Aeolothrips fasciatus(Linnaeus)。茶黄硬蓟马是芒果蓟马的优势种,在调查的所有种植地均有分布,占所采集鉴定蓟马总数的75.51%。     

Plant odours with potential for a push–pull strategy to control the onion thrips, Thrips tabaci

We compared the efficacy of four plant essential oils to repel onion thrips, Thrips tabaci (Lindeman) (Thysanoptera: Thripidae), in the presence of an attractive odour, ethyl iso‐nicotinate in a pasture field. Four horizontal white sticky plates were placed adjacent to (directions: N, S, E, W) a central horizontal white plate (C). After 24 h, in the treatment combination where the four plates were sprayed with essential oil surrounding a central sticky plate sprayed with ethyl iso‐nicotinate, fewer onion thrips were found on the plates treated with sweet marjoram [Origanum majorana L. (Labiatae)] or clove basil [Ocimum gratissimum L. (Labiatae)] (87 and 71% less, respectively) compared to the control treatment of four water‐sprayed plates surrounding a central plate with ethyl iso‐nicotinate. We also compared the distribution of onion thrips on the plates. Relative thrips numbers on each plate were compared with similar (N, S, E, W, and C) plates in the control treatment. There were relatively lower thrips numbers on the south (23% reduction) and west (26% reduction) O. majorana‐treated plates and higher numbers (37% increase) on the central attractant‐treated plate indicating a short‐distance push–pull effect. When four plates were sprayed with the thrips attractant surrounding a central sticky plate sprayed with an essential oil or water (control), only O. majorana reduced the number of thrips on the attractant‐sprayed plates (62% reduction). The distribution of thrips on the different plates within this treatment combination did not change substantially when compared to the distribution in the water‐control treatment. Other essential oils tested (wormwood [Artemisia arborescens L. (Compositae)]) and tea tree [Melaleuca alternifolia (Maiden. & Betche.) Cheel. (Myrtaceae)]) were not effective in any of the treatments. It appears that O. majorana is a promising thrips repellent which could be used for further testing in a push–pull system with the attractant ethyl iso‐nicotinate. The field setup used also proved to be a valuable tool for evaluating the potential of repellents to control onion thrips.     

Sequential sampling of Aphis gossypii Glover (Hemiptera: Aphididae) and Frankliniella schultzei Trybom (Thysanoptera: Thripidae) on cotton crop

The goal of this research was to use the sequential probability ratio test to establish a sequential sampling plan for Aphis gossypii Glover and Frankliniella schultzei Trybom infesting cotton. Field work was conducted at the agricultural experimental station of the Universidade Federal da Grande Dourados during the 2003/2004 and 2004/2005 agricultural years. Aphid colonies and individual thrips in the sampling area were counted and their numbers were recorded. The spatial distribution pattern of A. gossypii and F. schultzei in the cotton culture was aggregated. Sequential sampling plans were developed for aphids and thrips with type I and type II errors set at 0.1, common Kc = 0.6081 (aphids) and = 0. 9449 (thrips), and safety and management levels of 20% (aphids) and 40% (thrips) of infested plants. The sampling plans resulted in two decision boundaries for each species, as follows: the upper boundary, indicating when management (population control) is recommended: S1 = 4.6546 + 0.2849n (aphids), and S1 = 3.6514 + 0.1435n (thrips); and the lower boundary, indicating when population control is not necessary: S0 = -4.6546 + 0.2849n (aphids) and S0 = - 3.6514 + 0.1435n (thrips). The highest probability of error when making a decision was 3% for aphids and 2% for thrips, respectively. The maximum number of samples required to reach a decision was 63 for aphids and 95 for thrips.     

Effect of maize plants on colonisation of cowpea plants by bean flower thrips,Megalurothrips sjostedti

The effect of non-host maize plants on colonisation of cowpea byMegalurothrips sjostedti (Trybom) (Thysanoptera; Thripidae) was investigated. There were no differences in population density and activity ofM. sjostedti on sole cowpea crop and mixed cowpea/maize crop during the colonisation phase (i.e. 10–30 days after emergence of the plants. However, subsequentlyM. sjostedti numbers were lower in the mixed than in the sole crop, suggesting that maize did not interfere with colonisation of cowpea crop by thrips. In a choice situation, higher numbers ofM. sjostedti oriented towards, and settled on, sole cowpea plants than on those mixed with maize. Olfactory tests indicated that fewer thrips oriented towards a cowpea/maize mixed odour source. When equal numbers of thrips were introduced into the centre of sole- and mixed-cropped cowpea plots, the thrips became randomly distributed in each plot. Fewer thrips were recovered from the mixture than from the sole crop. It is concluded that, although non-host plant odours do not reduce thrips colonisation they interfere with host plant utilisation.     

Host-plant-mediated interaction between populations of a true omnivore and its herbivorous prey

Western flower thrips, Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), are competitors with twospotted spider mites, Tetranychus urticae Koch (Acari: Tetranychidae), for plant resources and potential predators on spider mites when the opportunity arises. Which interaction predominates may depend on relative population densities and individual species’ responses to the plants on which they co‐occur. We examined interactions between populations of thrips and spider mites on several cultivars of two bedding plants: impatiens (Impatiens wallerana Hook.f) cultivars ‘Impulse Orange’ and ‘Cajun Carmine’, and ivy geranium [Pelargonium peltatum (L.) L’Her ex Aiton] cultivars ‘Sybil Holmes’ and ‘Amethyst 96’. Four combinations of thrips and mite numbers were studied: thrips alone, mites alone, and two densities of thrips and mites together. We compared population numbers after 4 weeks. Overall, mite numbers increased more rapidly than thrips did, but both species increased more rapidly on impatiens than on ivy geraniums. Between impatiens cultivars, thrips and mites increased more slowly on ‘Cajun Carmine’ (i.e., it was more resistant) than on ‘Impulse Orange’. On ivy geraniums, spider mites increased more slowly on ‘Sybil Holmes’ than on ‘Amethyst 96’ but the reverse was the case for thrips. Regardless of plant species or cultivar, thrips had a strong negative effect on spider mites whenever they co‐occurred, suppressing mite population growth by around 50% compared to when mites were alone. However, the effect of spider mites on western flower thrips depended on the quality of the plant species. On impatiens, thrips co‐occurring with spider mites increased slightly more than thrips alone did, while on ivy geranium mites had a small negative effect on thrips. Contrary to expectations, thrips had a larger negative impact on spider mites on plants that were more susceptible to thrips than they did on plants more resistant to thrips. We suggest that host plants mediate the interaction between an omnivore and its herbivorous prey not only by altering individual diet choice but by changing the relative population dynamics of each species.     

施氮水平影响蚯蚓介导的番茄生长及抗虫性

过量施用氮肥不仅导致严重的生态环境问题, 还会限制土壤生物驱动的生态系统服务功能。蚯蚓的取食和掘穴等活动可以促进土壤肥力和植物生长, 进而影响植物与病虫害的关系。了解氮肥与害虫作用下蚯蚓对植物抗虫性的影响, 有助于揭示土壤动物的生态功能调控机制。采用蚯蚓(威廉腔环蚓Metaphire guillelmi)、西花蓟马(Frankliniella occidentalis)和氮肥用量的三因子完全交互设计, 利用番茄(Lycopersicon esculentum)盆栽实验探索了不同氮水平下蚯蚓对番茄生长及对植食者抗性的影响。结果表明, 在低氮条件下蚯蚓显著降低了番茄茎叶干生物量、根系干生物量及茎叶可溶性糖含量, 而茎叶的茉莉酸和水杨酸含量分别是无蚯蚓对照的6倍和3倍, 且伴随着西花蓟马数量下降了58%。在高氮水平时, 蚯蚓未影响番茄茎叶茉莉酸、茎叶水杨酸含量及西花蓟马数量。蚯蚓介导的番茄营养物质(茎叶可溶性糖和茎叶全氮)和防御信号物质(茎叶茉莉酸和茎叶水杨酸)含量分别与西花蓟马数量呈显著的正相关和负相关。总之, 氮肥施用改变的土壤氮有效性通过改变植物资源和防御物质含量转变了蚯蚓介导的植物抗虫性响应; 全面了解土壤生物对植物生长的影响需要综合考虑土壤管理-土壤动物-植物病原物三者之间的关系。     

Odour-baited traps influence thrips capture in proximal unbaited traps in the field

Two field experiments examined the distance over which an attractant odour of a volatile chemical could influence thrips capture in proximal traps that were without the odour. In each experiment a star‐shaped array of water traps consisted of a centre trap with or without an odour surrounded by odourless traps at 0.5, 1, 2, 5, and 10 m in eight equally spaced radial arms 45° apart. Experiments ran for 47 h (centre trap: ethyl nicotinate) or 7 h (centre trap: ethyl isonicotinate). Each had four replicates. With ethyl nicotinate, more thrips were trapped in the centre‐baited traps than in the unbaited centre traps (63×, 7×, 98× and 200× for total thrips, Thrips tabaci Lindeman ♀, and Thrips obscuratus Crawford ♀and ♂, respectively) (Thysanoptera: Thripidae). More total thrips and T. tabaci♀ were trapped in the centre traps baited with ethyl isonicotinate than in unbaited centre traps (21× for both). For ethyl nicotinate, numbers of T. obscuratus in unbaited traps downwind from the baited centre trap declined by 50% within 0.4 m (♀) and 2 m (♂) and by 95% within 3 m (both ♀ and ♂) based on model predictions. For ethyl isonicotinate, numbers of T. tabaci in unbaited traps downwind from the baited centre trap declined by 50% within 1.3 m and by 95% within 10 m based on model predictions. Wind direction was an important factor in the degree and direction of thrips capture with the highest thrips capture downwind from the centre trap with odour. There was no increase in numbers of T. tabaci in any traps without odour in the ethyl nicotinate‐centred array. Differences in trapping patterns between thrips species and odours indicated that there were thrips species–odour specific interactions. Experiments examining differences between traps with and without a thrips attractant odour need to be designed very carefully to ensure meaningful results especially in enclosed and/or low‐wind indoor situations.     

Evaluation of efficacy of Neoseiulus cucumeris for control of western flower thrips in spring bedding crops

Western flower thrips, Frankliniella occidentalis (Pergande), is the principal insect pest of spring flower crops grown in the northeastern United States for use as bedding plants. Neoseiulus (=Amblyseius) cucumeris (Oudemans) is a predacious mite reared commercially that is recommended for control of western flower thrips in various vegetable and flower crops at a rate of ca 53 mites/m²/week. Efficacy on spring flower crops, however, is not well demonstrated, reports being either from other crops or extension demonstration trials. In two trials (each replicated), we compared suppression of western flower thrips in spring bedding plants provided by (1) N. cucumeris at the recommended rate, (2) spinosad (at the labeled rate), the most widely used thrips-control pesticide, and (3) both combined. Trial No. 1 was run in mixed bedding plants in commercial greenhouses and Trial No. 2 in impatiens monocultures in University greenhouses. We found that in commercial greenhouses, variation in species composition of crops and movement of plants during crop production made it difficult to detect any significant effects. In an impatiens monoculture (Trial No. 2), we found better evidence of partial suppression of thrips larvae and adults by treatments. Spinosad alone provided the best control, with mites alone usually providing control intermediate to that of spinosad alone and the untreated control. Control from spinosad plus mites was not significantly different from that of spinosad alone (all treatments evaluated as counts of thrips per plant, in flowers). In another University-based trial (Trial No. 3), we compared the commercially recommended rate of N. cucumeris (53 mites/m²/week) to a 3- to 4-fold higher rate (190 mites/m²/week) in impatiens monocultures. This trial was replicated twice in the fall of 2004 and once in spring of 2005 in Amherst, Massachusetts. We found that the higher release rate, while not resulting in statistically significantly more mites per plant (in flowers) than the standard rate, did suppress thrips larvae per plant (in flowers) by 50–75%, a higher level than that achieved by the recommended standard rate. No reductions, however, were found in counts of adult thrips, either as numbers per plant (in flowers) or as numbers caught per yellow sticky card, except for one replication in which thrips counts were lowered compared to controls by mites (at both release rates). We conclude that N. cucumeris, especially at the higher rate, provides partial control of western flower thrips in impatiens bedding plants, but that control from spinosad is better. Biological control of western flower thrips with this predator is not a complete thrips IPM program, but may be used together with spinosad or other materials to prevent development of pesticide resistance. This approach is most likely to be of value in crops grown as continuous relay plantings or a series of different, but thrips-susceptible, crop species.     

Comparison of greenhouse screening materials for excluding whitefly (Homoptera: Aleyrodidae) and thrips (Thysanoptera: Thripidae)

Twenty-eight greenhouse screening materials, with predetermined airflow resistance values, were evaluated for exclusion of the silverleaf whitefly Bemisia argentifolii Perring & Bellows and thrips from a mixed-species population. Screens differed in exclusion efficacy, expressed as a percentage of the fiberglass window screen control and at an approach velocity of 92 m/min, from -35 to 94% for silverleaf whitefly and from -13 to 95% for thrips. Seventeen screens excluded more silverleaf whitefly than did the window screen control, whereas only seven excluded more thrips. One material differentially excluded whitefly over thrips; many more differentially excluded thrips over whitefly. Airflow resistance, indicative of mesh hole size, did not necessarily correspond with degree of exclusion. Not all materials characterized as highly resistant to airflow provided significant exclusion. Exclusion of both types of pests was attained with several moderate- and one low-resistance screen. Another low-resistance screen excluded silverleaf whitefly only.     

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

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.     

Development of a novel bioassay for estimation of median lethal concentrations (LC50) and doses (LD50) of the entomopathogenic fungus Beauveria bassiana, against western flower thrips, Frankliniella occidentalis

To conduct laboratory experiments aimed at quantifying secondary acquisition of fungal conidia by western flower thrips (Frankliniella occidentalis), an efficient assay technique using Beauveria bassiana as the model fungus was developed. Various application protocols were tested and it was determined that the percent mortality did not vary among protocols. Peak mortality of second-instar nymphs, under constant exposure to conidia, occurred 5 days post-inoculation. Second-instar thrips that were exposed to conidia within 24 h of the molt to second instar were more susceptible to Beauveria bassiana than thrips exposed after times greater than 24 h post-molt. Conidia efficacy, which was monitored at 24 h intervals, did not differ significantly within 72 h. A test of the final bioassay system was conducted in a series of assays aimed at determining the LD50 of B. bassiana technical powder against second-instar western flower thrips. It was determined that B. bassiana (strain GHA) is highly effective at very low doses (LD50 of 33-66 conidia/insect).     

Jasmonate-dependent plant defenses mediate soybean thrips and soybean aphid performance on soybean

Insect herbivores from different feeding guilds induce different signaling pathways in plants. In this study, we examined the effects of salicylic acid (SA)- and jasmonic acid (JA)-mediated defenses on performance of insect herbivores from two different feeding guilds: cell-content feeders, soybean thrips and phloem feeders, soybean aphids. We used a combination of RT-qPCR analysis and elicitor-induced plant resistance to determine induction of SA and JA signaling pathways and the impact on herbivore performance. In the early interaction between the host plant and the two herbivores, SA and JA signaling seems to occur simultaneously. But overall, soybean thrips induced JA-related marker genes, whereas soybean aphids increased SA and ABA-related marker genes over a 24-h period. Populations of both soybean thrips and soybean aphids were reduced (47 and 25 %, respectively) in methyl jasmonate (MeJA)-pretreated soybean plants. SA treatment has no effect on either herbivore performance. A combination pretreatment of SA and MeJA did not impact soybean thrips population but reduced soybean aphid numbers which was comparable with MeJA treatment. Our data suggest that SA–JA antagonism could be responsible for the effect of hormone pretreatment on thrips performance, but not on aphid performance. By linking plant defense gene expression and elicitor-induced resistance, we were able to pinpoint the role for JA signaling pathway in resistance to two herbivores from different feeding guilds.     

Decreased preference and reproduction, and increased mortality of Frankliniella occidentalis on thrips-resistant pepper plants

The effect of thrips resistance in pepper (Capsicum annuum L.) – previously shown to result in impeded thrips population development (Maris PC, Joosten NN, Goldbach RW & Peters D (2003a) Restricted spread of Tomato spotted wilt virus in thrips‐resistant pepper. Phytopathology 93: 1223–1227. Maris PC, Joosten NN, Goldbach RW & Peters D (2003b) Spread of Tomato spotted wilt virus and population development of Frankliniella occidentalis in pepper resistant to thrips. Proceedings of the Section Experimental and Applied Entomology Netherlands Entomological Society (NEV) Amsterdam 14: 95–101.) – on thrips’[Frankliniella occidentalis Pergande (Thysanoptera: Thripidae)] reproduction, mortality, host preference, and behaviour was investigated. Reproduction, studied by oviposition and larval survival, was negatively affected by the thrips‐resistant (TR) phenotype, whereas the offspring's developmental rate did not differ on TR and the thrips‐susceptible (TS) phenotype. While thrips’ behaviour was hardly affected by thrips resistance, a significant preference for TS plants over the TR plants was found in different tests. When released on either a TR or a TS plant, thrips dispersed at significantly higher rates from the TR plants, demonstrating that not only an impeded reproduction, but also a reduced residence time adds to the reported lower thrips numbers on TR plants.     

Cover crop, rye residue and in-furrow treatment effects on thrips

Abstract:  Thrips and thrips damage to cotton and peanut plants were compared in plots with in-furrow treatments of aldicarb, phorate and diammonium phosphate (DAP) fertilizer under two tillage regimes with a winter cover of crimson clover and under different levels of rye residue ground cover. Adult and larval thrips numbers were significantly lower in cotton plots following winter crimson clover cultivation compared with no-cover plots in all 3 years. Thrips numbers did not differ with respect to the in-furrow treatments in the clover plots, but in the no-cover plots, they were significantly higher in the untreated control and DAP treatments compared with the aldicarb treatment. Thrips damage was higher in the no-cover than the clover plots except in the aldicarb treatments. Within the cover crop plots, thrips damage was highest in the control and phorate treatments and similar in the DAP and aldicarb treatments. There was an inverse relationship between the amount of rye residue ground cover and thrips density and thrips damage in cotton and peanuts. There was also an inverse relationship between the density of rye residue and damage to peanuts from Bunyaviridae tospovirus. Cotton yield was reduced in the cover crop plots and was not measured in the rye residue and peanut plots. These results suggest that ground cover alone decreases thrips numbers and thrips damage in both cotton and peanuts and that a winter crimson clover cover and an in-furrow treatment of DAP enhanced plant protection from thrips in cotton.     

Euseius addoensis addoensis,an effective predator of citrus thrips,Scirtothrips aurantii,in the eastern Cape Province of South Africa

The predacious mite,Euseius addoensis addoensis (McMurtry) (Acari: Phytoseiidae), significantly (P<0.05) reduced scarring on Palmer Navel oranges,Citrus sinensis (L.) Osbeck, caused by the citrus thrips,Scirtothrips aurantii Faure (Thysanoptera: Thripidae). A chemical exclusion method employing dicofol was used to determine the effect of the predator and numbers ofS. aurantii were monitored on sticky yellow traps. At two sites where numbers of citrus thrips and predacious mites were high, the percentage fruit culled from export quality due to damage byS. aurantii was reduced from 25.5 to 15.5% and from 32.7 to 18.7% by predacious mite activity.Euseius a. addoensis sometimes prevented damage from exceeding 1% cull and was most effective when mean numbers exceeded one mite per inside leaf at petal fall. The best correlation between numbers of mites and the percentage fruit culled at harvest was –0.96 at the location with the highest number of citrus thrips. Tartar emetic (0.398% a.i.) plus sugar (0.4% a.i.) treatments for citrus thrips were slightly detrimental toE. a. addoensis populations but their numbers soon recovered. An alternative treatment, methiocarb 0.016% a.i. plus sugar (0.4% a.i.), almost eliminated the predacious mites and resulted in more citrus thrips damage (10.7% cull) than in the adjacent untreated control (0.2% cull) which contained predacious mites.     

Starvation period and age affect the response of female Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae) to odor and visual cues

The effects of starvation or age on the walking or flying response of female Frankliniella occidentalis to visual and/or odor cues in two types of olfactometer were examined in the laboratory. The response of walking thrips starved for 0, 1, 4, or 24h to an odor cue (1microl of 10% p-anisaldehyde) was examined in a Y-tube olfactometer. The take-off and landing response of thrips (unknown age) starved for 0, 1, 4, 24, 48 or 72h, or of thrips of different ages (2-3 days or 10-13 days post-adult emergence) starved for 24h, to a visual cue (98 cm(2) yellow sticky trap) and/or an odor cue (0.5 or 1.0 ml p-anisaldehyde) was examined in a wind tunnel. More thrips walked up the odor-laden arm in the Y-tube when starved for at least 4h (76%) than satiated thrips (58.7%) or those starved for 1h (62.7%, P<0.05). In the wind tunnel experiments the percentage of thrips to fly or land on the sticky trap increased between satiated thrips (7.3% to fly, 3.3% on trap) and those starved for 4h (81.2% to fly, 29% on trap) and decreased between thrips starved for 48 (74.5% to fly, 23% on trap) and 72 h (56.5% to fly, 15.5% on trap, P<0.05). Fewer younger thrips (38.8%) landed on a sticky trap containing a yellow visual cue of, those that flew, than older thrips (70.4%, P<0.05), although a similar percentage of thrips flew regardless of age or type of cue present in the wind tunnel (average 44%, P>0.05).     

Integrated management tactics for Frankliniella thrips (Thysanoptera: Thripidae) in field-grown pepper

In a 2-yr study, the impacts of different plastic soil mulches, insecticides, and predator releases on Frankliniella thrips and their natural enemies were investigated in field-grown peppers. Ultraviolet light (UV)-reflective mulch significantly reduced early season abundance of adult thrips compared with standard black plastic mulch. This difference diminished as the growing seasons progressed. Late season abundance of thrips larvae was higher in UV reflective mulch compared with black mulch plots. The abundance of the predator Orius insidiosus (Say) was significantly lower in UV-reflective mulch compared with black mulch treatments. Infection of plants with tomato spotted wilt virus, a pathogen vectored by Frankliniella occidentalis (Pergande), was <6%. In the year with the higher disease incidence (2000), UV-reflective mulch plots had significantly less disease (1.9%) compared with black mulch plots (4.4%). Yield was significantly higher in UV-reflective mulch (24,529 kg/ha) compared with black mulch (15,315 kg/ha) during this year. Effects of insecticides varied with species of thrips. Spinosad reduced abundance of F. occidentalis, but not Frankliniella tritici. In contrast, esfenvalerate and acephate reduced numbers of F. tritici and Frankliniella bispinosa, but resulted in higher populations of F. occidentalis. Spinosad was the least disruptive insecticide to populations of O. insidiosus. Releases of O. insidiosus and Geocoris punctipes (Say) reduced populations of thrips immediately after releases; naturally occurring predators probably provided late season control of thrips. Our results suggest that UV-reflective mulch, combined with early season applications of spinosad, can effectively reduce abundance of thrips in field-grown pepper.     

The effect of undersowing cabbage with white clover on thrips infestation and flight activity

In 2001-2003, the levels of infestation of thrips in cabbage monocrops and cabbage/white clover intercrops were compared. The flight activity of thrips was monitored using blue sticky traps and white water traps to obtain a better understanding of population dynamics of thrips. Plant samples were taken to record the number of thrips on cabbage. Over the years of observations, the highest number of thrips was collected in blue sticky traps on cabbage undersown with white clover. In the period from 15th June to 5th July 2001, the number of thrips collected in blue sticky traps in the monocropped cultivation and intercrops with white clover was on similar low levels. Next, the number suddenly increased to 372 thrips/trap in monocropped cultivation and 509 thrips/trap in the intercropped cultivation. During the period of the highest peak of thrips activity, which was on 17th July, there were 650 thrips/trap and nearly the same number was noticed for both types of cultivations. After this period, until the end of vegetation, the greater number of thrips was noticed for the traps placed in the intercrops. Additionally, in 2001 the thrips were collected in white water traps. Using this type of traps, 480 total thrips/trap were collected in the monocropped cultivation and 819/thrips/trap in the intercrops during the whole vegetation season. The percentage participation of Thrips tabaci Lind. caught in white water traps was 24.4% in the monocropped cultivation and 15.4% in the intercrops. In 2002, during the period from the middle of June to the third decade of July, significantly higher number of thrips was collected in blue sticky traps placed in the cabbage with white clover. The number of thrips collected during the period of the mass flights, which means in the first decade of July was over twice as many thrips in the traps placed in the intercropped cultivation (1316 thrips/trap) as in the monocropped cultivation (589 thrips/trap). In 2003, during the whole vegetation period, the number of thrips collected in blue sticky traps placed on the plots where cabbage was cultivated with white clover was evidently higher. In this year two peaks of the thrips flight activity were recorded: the first on 16th July and the second on 5th August. On both occassions, the number of thrips collected in blue sticky traps placed in the intercropped cultivations was about twice as high as in the monoculture cultivation. In 2001-2003, the thrips feeding on cabbage in the monocropped and intercropped cultivations were observed mainly in July and once again in August. The number of thrips on cabbage was low, only in 2002 this number was higher. In 2001, the number of thrips on cabbage in both types of cultivations was on similar level. The highest number of thrips was observed during the peak of thrips flight activity, which was in the middle of July. In years 2002-2003, despite the higher number of thrips collected in blue sticky traps placed in the intercropped cultivations, the number of pests collected from the cabbage undersown with white clover was lower than in the monocropped cultivation. In 2002, the period of the most intensive occurrence of thrips on cabbage was overlapping with the period of mass flight activity of thrips. During this period, a little higher number of thrips was noticed on cabbage in the intercropped cultivation (3.4 thrips/plant) than in the monocropped cultivation (3.2 thrips/plant). In 2003, the highest number of thrips on cabbage in both types of cultivations was noticed before the first significant peak of thrips flight activity. Whereas in the first decade of August, when the same high number of thrips collected in blue sticky traps was again noticed, no increase in the number of thrips feeding on cabbage was observed in both type of cultivations. Over all years of observations, despite the higher number of thrips collected in blue sticky traps in the intercropped cultivation, this number was always lower on the cabbage undersown with white clover. The most dominant species in both cultivations was Thrips tabaci Lind. Its percentage participation in the collected material was 83.1% in the monocropped cultivation and 76.6% in the intercropped cultivation.     

模拟增温对青藏高原多年冻土区小嵩草和藏嵩草生长与抗氧化特征的影响

采用开顶式增温小室(OTCs)方法模拟气候变暖,分别选取青藏高原腹地风火山地区高寒小嵩草草甸和高寒藏嵩草沼泽草甸优势物种小嵩草和藏嵩草为研究对象,对比分析增温处理下两种优势物种叶片的形态与生理特征变化,从而探索高寒植物对气候变暖的内在响应机理.结果表明: 增温显著增加了小嵩草叶片长度(40.0%)和叶片数量(72.7%),也显著增加了藏嵩草株高(11.9%)和叶片长度(19.3%),促进了两种优势植物的形态生长和地上生物量增加.增温处理下小嵩草和藏嵩草叶片的膜透性(电导率),活性氧(过氧化氢和超氧阴离子自由基),超氧化物歧化酶、过氧化物酶、抗坏血酸过氧化物酶和过氧化氢酶活性,丙二醛含量均没有显著变化.但抗坏血酸和游离脯氨酸含量在藏嵩草叶片内分别显著增加了29.8%和53.8%,而在小嵩草叶片内没有明显变化.可见,增温下小嵩草和藏嵩草均能够维持正常的抗氧化水平,以维持该区域优势植物生长;但藏嵩草生理过程对增温更加敏感.