Influence of salicylaldehyde and methyl salicylate on post-landing behaviour of Frankliniella occidentalis Pergande

This study investigates behavioural responses of adult western flower thrips (Frankliniella occidentalis Pergande; Thysan., Thripidae) females to direct contact with repellent phenylpropanoid plant compounds (salicylaldehyde and methyl salicylate) applied on bean and cucumber leaves. The residence time of F. occidentalis females until take off was significantly shorter on bean or cucumber leaf discs treated with salicylaldehyde at 1% concentration compared with control leaf discs. A methyl salicylate (1%) treatment of cucumber resulted in shorter time periods until thrips took off the treated leaf discs compared with the control leaf discs. In a choice experiment thrips avoided to settle on a 1% salicylaldehyde treatment of bean and cucumber leaf discs for a maximum of 3 h, on a 1% methyl salicylate treatment for a 5‐h period. Within a 24‐h period neither the egg‐laying nor the feeding activity of F. occidentalis was affected after salicylaldehyde application (0.1%, 1%) on bean or cucumber. In contrast, methyl salicylate (1%) applied on bean and cucumber significantly prevented thrips females from oviposition and reduced the percentage of damaged area caused by their feeding activity for 24 h. As olfactory repellent plant volatiles applied on crop plants may elicit diverse post‐landing responses of F. occidentalis, short‐ and long‐term effects should be considered when evaluating the factual applicability of secondary plant compounds in a successful thrips management strategy.     

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

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

Continuous exposure to the deterrents cis‐jasmone and methyl jasmonate does not alter the behavioural responses of Frankliniella occidentalis

Behavioural responses of Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), a generalist, cell sap‐feeding insect species with piercing‐sucking mouthparts, after continuous exposure to two deterrent secondary plant compounds are investigated. We compared in choice assays on bean leaf discs, the settling, feeding, and oviposition preferences of F. occidentalis females that had no experience with the two fatty acid derivatives methyl jasmonate and cis‐jasmone before testing (naïve thrips) vs. females that had been exposed to the deterrent compounds before testing (experienced thrips). The thrips were exposed to the deterrents at low or high concentrations for varied time periods and subsequently tested on bean leaf discs treated with the respective deterrent at either a low or a high concentration. Frankliniella occidentalis females avoided settling on the deterrent‐treated bean leaf discs for an observation period of 6 h, independent of their previous experience. Our results demonstrate that feeding and oviposition deterrence of the jasmonates to the thrips were not altered by continuous exposure of the thrips to the jasmonates. Habituation was not induced, neither by exposure to the low concentration of the deterrents nor by exposure to the high concentration. These results indicate that the risk of habituation to two volatile deterrent compounds after repeated exposure is not evident in F. occidentalis. This makes the two compounds potential candidates to be integrated in pest management strategies.     

Olfactory response towards its prey Frankliniella occidentalis of wild and laboratory‐reared Orius insidiosus and Orius laevigatus

Orius species are important biological control agents of thrips in protected crops. Rearing conditions in mass production facilities may affect their performance in the crop when searching for the target prey. The aim of this study was to evaluate and compare the search behaviour and orientation towards prey of two Orius species, O. laevigatus (Fieber) and O. insidiosus (Say) that have been reared in the laboratory under different conditions, with wild (field‐collected) individuals. Adult predator females were placed in a Y‐tube olfactometer and offered a choice between the odours released by plants of different species (cotton, common bean, sweet pepper and cucumber), which were either non‐infested or infested with Frankliniella occidentalis (Pergande) adults.O. laevigatus and O. insidiosus responded to odours from thrips‐infested plants and these responses were influenced by the origin of the colonies. A larger percentage of laboratory‐reared O. laevigatus females (42%) did not made a choice between thrips‐infested or clean plants, compared with wild individuals (17%). Of those females that did respond to plant odours, a smaller percentage of laboratory‐reared O. laevigatus females (34%) responded to the odours from thrips‐infested plants compared with wild insects (76%). No significant differences were found inO. insidiosus females that did not make a choice between thrips‐infested or clean plants (14% for wild vs. 17% for lab individuals). Also, no significant differences were found between O. insidiosus females that selected thrips‐infested plants at the corresponding proportion of wild (75%) and laboratory‐reared (70%) individuals. We propose that the olfactometer test could be a complementary evaluation aspect to the already developed quality criteria for performance of mass‐reared Orius predators.     

Reducing fertilization: a management tactic against western flower thrips on roses

Fertilization reduction could be a useful pest management tactic for floriculture crops if it reduced pest populations with minimal impact on crop yield and quality. We evaluated the response of the western flower thrips, Frankliniella occidentalis Pergande (Thysanoptera: Thripidae), to different fertilization levels for cut roses, Rosa hybrida L. cv. ‘Tropicana’, and quantified fertilization effects on (i) abundance of F. occidentalis on cut roses, (ii) biological control of F. occidentalis on cut roses and (iii) nutritional quality of the cut flower crop. We tested a commercially available fertilizer (Peters Excel 15‐5‐15 Cal‐Mag; The Scotts Company, Marysville, OH) at 100% and 33% of the recommended nitrogen level (150 ppm N) for rose production using liquid‐feeding and two control measures: no thrips control measure; release of a predatory mite, Amblyseius swirskii (Athias‐Henriot). To maintain equivalent ratios of macro‐ and micronutrients for all our fertilizer treatments, we varied only the concentration of the fertilizer to the levels specified in our experiments. Lowering fertilization rate from 100% to 33% of the recommended level reduced mean F. occidentalis abundance on cut roses by 30%. Combinations of both bottom‐up (fertilization) and top‐down (biological control) tactics provided better F. occidentalis control than either tactic alone. Flower production was not compromised on plants fertilized with 33% of the recommended level. Nitrogen, phosphorous and potassium content of the leaf tissue decreased at 33% of the recommended fertilization level, but all values were within optimal ranges for cut roses. We propose that fertility management may be an effective means of reducing thrips numbers on cut roses.     

Resistance to three thrips species in Capsicum spp. depends on site conditions and geographic regions

Capsicum species are commercially grown for pepper production. This crop suffers severely from thrips damage and the identification of natural sources of thrips resistance is essential for the development of resistant cultivars. It is unclear whether resistance to Frankliniella occidentalis as assessed in a specific environment holds under different conditions. Additionally, other thrips species may respond differently to the plant genotypes. Screening for robust and general resistance to thrips encompasses testing different Capsicum accessions under various conditions and with different thrips species. We screened 11 Capsicum accessions (C. annuum and C. chinense) for resistance to F. occidentalis at three different locations in the Netherlands. Next, the same 11 accessions were screened for resistance to Thrips palmi and Scirtothrips dorsalis at two locations in Asia. This resulted in a unique analysis of thrips resistance in Capsicum at five different locations around the world. Finally, all accessions were also screened for resistance to F. occidentalis in the Netherlands using a leaf disc choice assay, allowing direct comparison of whole plant and leaf disc assays. Resistance to F. occidentalis was only partially consistent among the three sites in the Netherlands. The most susceptible accessions were consistently susceptible, but which accession was the most resistant differed among sites. In Asia, one C. chinense accession was particularly resistant to S. dorsalis and T. palmi, but this was not the most resistant accession to F. occidentalis. Overall, resistance to F. occidentalis correlated with S. dorsalis but not with T. palmi resistance in the C. annuum accessions. Damage inflicted on leaf discs reflected damage on the whole plant level. Our study showed that identifying broad spectrum resistance to thrips in Capsicum may prove to be challenging. Breeding programmes should focus on developing cultivars suitable for growing in defined geographic regions with specific thrips species and abiotic conditions.     

Preference of the vector thrips Frankliniella occidentalis for plants infected with thrips‐non‐transmissible Tomato spotted wilt virus

The effect of a thrips‐non‐transmissible Tomato spotted wilt virus (TSWV) on insect–host interactions between thrips and Arabidopsis thaliana was analysed. A wild‐type TSWV virulent isolate and a TSWV isolate that induces mild symptoms on inoculated plants (TSWV‐Mo) were used in this study, and TSWV‐Mo isolate was obtained by single local lesion isolation using Petunia x hybrid after several passages on Nicotiana rustica plants. In transmission test, although wild‐type TSWV (TSWV‐wt) was transmitted by two thrips species (transmission ratio; Frankliniella occidentalis, 25%; Thrips tabaci, 10%; and T. palmi, 0%), none of the thrips transmitted TSWV‐Mo. Feeding damage by F. occidentalis in A. thaliana plants was more extensive on TSWV‐wt‐infected plants than on TSWV‐Mo‐infected plants, despite comparable preference. Among the markers of plant defences, salicylic acid‐regulated genes were upregulated threefold to sixfold by TSWV‐wt or TSWV‐Mo infection. In contrast, jasmonate‐regulated genes and jasmonate/ethylene‐regulated genes were not affected by the infections. Pull assays showed that adjacent TSWV‐Mo‐infected plants were preferred over uninfected plants. In conclusion, our results showed that the transmissibility by thrips of TSWV is not related to preference of vector thrips and suggested that TSWV‐Mo‐infected plants may be used as attractants for behaviour control of thrips.     

Effects of plant volatiles on electrophysiological and behavioral responses of Cryptorrhynchus lapathi

Electroantennogram (EAG), Y‐tube olfactometer, and wind tunnel bioassays were conducted to test the electrophysiological and behavioral responses of Cryptorrhynchus lapathi L. (Coleoptera: Curculionidae) to six individual volatiles and seven essential oils (compounded volatiles). The aim of this study was to select effective plant compounds that can be used in the development of semiochemical‐based push–pull methods for the control of this harmful insect. Male and female C. lapathi displayed strong EAG responses to linoleic acid, α‐pinene, (Z)‐3‐hexen‐1‐ol, geraniol, turpentine oil, and salicylaldehyde. Y‐tube olfactometer assays indicated that salicylaldehyde and α‐pinene elicited strong repellent effects on female C. lapathi. Linoleic acid and (Z)‐3‐hexen‐1‐ol showed greater luring effects on male and female C. lapathi compared with the control. Turpentine oil was stronger repellent, and geraniol showed stronger luring effects on male C. lapathi than the control. Wind tunnel assays with both male and female C. lapathi indicated that salicylaldehyde, α‐pinene, and turpentine oil elicited repellent effects compared with the control. Linoleic acid, (Z)‐3‐hexen‐1‐ol, and geraniol were stronger lures of both male and female C. lapathi than the control. These results provide a basis for the further development of C. lapathi luring and repellent agents.     

Use of spinosad and predatory mites for the management of Frankliniella occidentalis in low tunnel‐grown strawberry

Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae) is a major pest of strawberry. The efficacy of three species of predatory mites, Typhlodromips montdorensis (Schicha), Neoseiulus cucumeris (Oudemans) (both: Acari: Phytoseiidae), and Hypoaspis miles (Berlese) (Acari: Laelapidae), and their compatibility with spinosad for the control of this thrips was evaluated in commercial strawberry in spring. Low tunnel‐grown strawberry was treated with ‘water then mites’, ‘spinosad then mites’, or ‘mites then spinosad’. Predatory mites were released as single‐, two‐ and three‐species combinations. Overall, spinosad‐treated plants had fewer thrips than water‐treated plants (control). In all treatment regimes, each species of predatory mite reduced the number of thrips relative to those plants that received no mites. Predatory mites were most effective in reducing thrips when released after spinosad was applied. Any multiple‐species combination of predatory mites reduced thrips numbers more than single‐species releases. The two‐species combination of T. montdorensis (foliage inhabiting) and H. miles (soil dwelling) was the most effective in suppressing thrips. The next most effective combination was a three‐species release. Of multiple‐species combinations, the two‐species combination of T. montdorensis and N. cucumeris was the least effective in suppressing thrips numbers. The spinosad and mites only temporarily reduced the numbers of F. occidentalis. This suggests that further application of predatory mites, spinosad, or both is required to maintain F. occidentalis populations below an economically damaging level.     

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

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

Trap colour and aggregation pheromone dose affect the catch of western flower thrips in blackberry crops

Frankliniella occidentalis causes significant damage to berry crops in Mexico. Traps may be used for monitoring or mass-trapping thrips populations. Generally, colour traps are used for monitoring thrips, but sometimes a chemical stimulus can be added to the traps. However, there is conflicting information about what colour is the most attractive and efficient for capturing F. occidentalis. In this study, we first evaluated six colours of adhesive traps for catching F. occidentalis in blackberries grown in tunnels or in an open field. Subsequently, using the most attractive trap colour, we assessed the biological activity of neryl (S)-2-methylbutanoate and (R)-lavandulyl acetate, components of the pheromone aggregation of F. occidentalis. Finally, we examined the effect of neryl (S)-2-methylbutanoate dosage rates on the number of captured thrips. We found that blue (tunnel) and yellow (open field) followed by violet traps captured a significantly greater number of F. occidentalis compared with the white, black and green traps. Our results confirm that neryl (S)-2-methylbutanoate is the only component necessary for enhancing the performance of coloured traps. Blue and yellow traps baited with 200–400 µg of neryl (S)-2-methylbutanoate increased the capture 2.5–3 times compared to unbaited traps. In all experiments, traps captured more females than males in blackberries grown in tunnels, whereas the opposite was found in blackberries cultivated in the open field. These results constitute the first step in the development of a monitoring system for F. occidentalis in soft fruit crops in Mexico.     

Attraction of a generalist predator towards herbivore-infested plants

The occurrence and strength of interactions among natural enemies and herbivores depend on their foraging decisions, and several of these decisions are based on odours. To investigate interactions among arthropods in a greenhouse cropping system, we studied the behavioural response of the predatory bug Orius laevigatus (Fieber) (Hemiptera: Anthocoridae) towards cucumber plants infested either with thrips (Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae)) or with spider mites (Tetranychus urticae Koch (Acari: Tetranychidae)). In greenhouse release-recapture experiments, the predatory bug showed a significant preference for both thrips-infested plants and spider mite-infested plants over clean plants. Predatory bugs preferred plants infested with spider mites to plants with thrips. Experience with spider mites on cucumber leaves prior to their release in the greenhouse had no effect on the preference of the predatory bugs. However, this experience did increase the percentage of predators recaptured. Y-tube olfactometer experiments showed that O. laevigatus was more attracted to odours from plants infested with spider mites than to odours from clean plants. Thus, O. laevigatus is able to perceive odours and may use them to find plants with prey in more natural conditions. The consequences of the searching behaviour for pest control are discussed.     

Does natural deposition of pine pollen affect the ovipositional behavior of Frankliniella occidentalis and Frankliniella fusca?

Tree pollen, especially Pinus spp. (Pinaceae), is shed in large quantities every spring in North America. Pine pollen deposition onto leaves was found to significantly influence the ovipositional behaviors of certain thrips species (Thysanoptera: Thripidae) in peanut and tomato leaf choice and no‐choice tests. Pine pollen (Pinus elliottii Engelm.) increased the oviposition rate 2.9‐fold for Frankliniella occidentalis (Pergande) (western flower thrips) and 1.6‐fold for Frankliniella fusca (Hinds) (tobacco thrips) in choice tests averaged over both plant species. These results support the idea that pollen has a greater impact on F. occidentalis behavior than on F. fusca behavior. The most dramatic increase was in peanut, where F. occidentalis only oviposited on leaves dusted with pollen, suggesting that the addition of pollen stimulated this flower thrips to lay eggs on a poor host‐plant part. The impact of pollen on the rate of oviposition by thrips is important because it is the early‐instar nymphs that acquire tomato spotted wilt virus (TSWV), which these two thrips species vector. In a laboratory bioassay, the addition of pine pollen to TSWV‐infected peanut foliage increased the percentage of infected F. fusca after one generation.     

Behavioral responses of <Emphasis Type="Italic">Frankliniella occidentalis</Emphasis> to floral volatiles combined with different background visual cues

The Western flower thrips, Frankliniella occidentalis (Thysanoptera: Thripidae), is one of the most destructive sucking pests of flowering plants. We examined behavioral responses of F. occidentalis adults to the floral volatiles of Rosa chinensis, Gardenia jasminoides, and Tagetes erecta in a Y-tube olfactometer with background visual cues (green, red, white, yellow, and blue backgrounds). The results show that F. occidentalis adults had similar responses under all the different background colors, but the responses by sex varied significantly when offered floral volatile or clean air. In pairings of floral volatiles, female F. occidentalis adults presented significant preferences (R. chinensis > G. jasminoides > T. erecta) in each treatment, while male F. occidentalis adults had no significant preference. Furthermore, the responses of female F. occidentalis adults to the three different floral volatiles compared with each other were greater under green and blue backgrounds than red, white, or yellow backgrounds. However, the responses of male F. occidentalis adults to floral volatiles were similar to all five backgrounds. These results indicate that female thrips could discriminate different floral volatiles, while male thrips could not. Both male and female thrips performed steady preferences of floral volatiles under all the five visual backgrounds, and the behavioral responses of female thrips to the floral volatiles could be enhanced under the green and blue backgrounds. These findings could hopefully aid in the development of effective trapping and monitoring strategies for this pest.     

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.     

Control of <Emphasis Type="Italic">Bemisia tabaci</Emphasis> and <Emphasis Type="Italic">Frankliniella occidentalis</Emphasis> in cucumber by <Emphasis Type="Italic">Amblyseius swirskii</Emphasis>

Bemisia tabaci Genn. (Hemiptera: Aleyrodidae) and Frankliniella occidentalis (Thysanoptera: Thripidae) are major pests in greenhouse grown cucumber crops. Recently, Amblyseius swirskii Athias-Henriot (Acari: Phytoseiidae) was shown an effective biological control agent of both pests. Hence, perhaps both pests can be controlled simultaneously by this predator. However, with simultaneous infestation of both pests, synergistic effects, or interference could affect biological control and perhaps require changes in release rates of the predator. Thus, the aim of the present study was to evaluate different release rates of A. swirskii to control both pests under a worst case scenario of rapid immigration into a cucumber greenhouse. Two experiments were conducted, one simulating the influx of whiteflies alone (whitefly experiment) and the other immigration of whiteflies and thrips together (whitefly plus thrips experiment). Three treatments were compared in the whitefly experiment: (1) B. tabaci alone, (2) B. tabaci + 25 A. swirskii m⁻² and (3) B. tabaci + 75 A. swirskii m⁻². The high release rate was more effective than the low rate in controlling B. tabaci alone. The high rate was subsequently tested against B. tabaci and F. occidentalis for the whitefly and thrips experiment in which five treatments were compared: (1) B. tabaci alone, (2) F. occidentalis alone, (3) B. tabaci + 75 A. swirskii m⁻², (4) F. occidentalis + 75 A. swirskii m⁻² and (5) B. tabaci + F. occidentalis + 75 A. swirskii m⁻². This rate of A. swirskii controlled whiteflies and thrips either alone or together. Therefore, 75 A. swirskii m⁻² should be an adequate rate for controlling both pests either alone or simultaneously in cucumber greenhouses.     

Odour-mediated responses of phytophagous mites to conspecific and heterospecific competitors

Plants under herbivore attack produce volatiles, thus attracting natural enemies of the herbivores. However, in doing so, the plant becomes more conspicuous to other herbivores. Herbivores may use the odours as a cue to refrain from visiting plants that are already infested, thereby avoiding competition for food, or, alternatively, to visit plants with defences weakened by earlier attacks. We investigated the response of one species of herbivore (the spider mite Tetranychus urticae) to odours emanating from cucumber plants infested by conspecific or heterospecific (the western flower thrips, Frankliniella occidentalis) herbivores. Olfactometer experiments in the laboratory showed that spider mites have a slight, but significant, preference for plants infested with conspecifics, but strongly avoid plants with thrips. These results were substantiated with greenhouse experiments. We released spider mites on the soil in the centre of a circle of six plants, half of which were infested with either conspecifics or heterospecifics (thrips), whereas the other half were uninfested. It was found that 60–70% of the mites were recaptured on the plants within 5 h after release. Results of these experiments were in agreement with results of the olfactometer experiments: (1) significantly fewer spider mites were found on plants infested with thrips than on uninfested plants and (2) more mites were found on plants with conspecifics than on clean plants (although this difference was not significant). From a functional point of view it makes sense that spider mites prefer clean plants over thrips-infested plants, since thrips are not only competitors, but are also known as intraguild predators of spider mites. Possible reasons for the slight attraction of spider mites to plants infested with conspecifics are discussed. Received: 22 June 1996 / Accepted: 29 September 1996     

嗜食植物与非嗜食植物对西花蓟马成虫寄主选择性的影响

【目的】西花蓟马是世界性害虫,利用西花蓟马对寄主植物嗜食性的差异,通过驱避作用防控西花蓟马,能够为绿色治理提供依据。【方法】在西花蓟马嗜食的甘蓝和非嗜食的大蒜上互喷汁液,采用黄瓜+甘蓝、黄瓜+大蒜2种相间种植方式,研究它们对西花蓟马寄主选择性的影响。【结果】在甘蓝上喷洒大蒜汁液后,甘蓝叶片上西花蓟马的虫量和产卵量均明显减少。大蒜汁液浓度越高,减少得越多;在大蒜上喷洒甘蓝汁液后,大蒜植株上西花蓟马的虫量和产卵量明显增加,且增加程度与甘蓝汁液的浓度呈正相关。黄瓜和甘蓝相间排列时,西花蓟马在黄瓜叶片上的数量与单作黄瓜叶片上无明显差异;但黄瓜和大蒜相间排列时,西花蓟马在黄瓜上的数量明显高于单作黄瓜上的虫数,多52.4%。【结论】在嗜食寄主植物上喷洒非嗜食植物汁液或间作非嗜食的寄主可以明显减少西花蓟马的选择性。研究结果为利用非嗜食植物挥发物防控西花蓟马提供了理论依据和新的方法。     

Behavioural and chemical evidence of a male‐produced aggregation pheromone in the flower thrips Frankliniella intonsa

The response of adult flower thrips Frankliniella intonsa (Trybom) (Thysanoptera: Thripidae) to conspecifics is investigated in Y‐tube olfactometer bioassays. The results show that both males and females are attracted to the odours of adult males, which indicates a male‐produced aggregation pheromone in this species. Gas chromatography‐mass spectroscopy analyses of headspace volatiles collected on solid‐phase microextraction fibres show that two major components and six minor components are present in volatiles from males but not in females. Further gas chromatography‐mass spectroscopy analyses reveal that the two major components in head‐space volatiles produced by F. intonsa males are the same compounds that are reported in volatiles of Frankliniella occidentalis males: (R)‐lavandulyl acetate and neryl (S)‐2‐methylbutanoate. However, the quantity of these two compounds in the volatiles differs between the species.     

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.