Y-tube Olfactometer Tests Research Articles

Infestation of Rice Striped Stem Borer (Chilo suppressalis) Larvae Induces Emission of Volatile Organic Compounds in Rice and Repels Female Adult Oviposition.

Plants regulate the biosynthesis and emission of metabolic compounds to manage herbivorous stresses. In this study, as a destructive pest, the pre-infestation of rice striped stem borer (SSB, Chilo suppressalis) larvae on rice (Oryza sativa) reduced the subsequent SSB female adult oviposition preference. Widely targeted volatilomics and transcriptome sequencing were used to identify released volatile metabolic profiles and differentially expressed genes in SSB-infested and uninfested rice plants. SSB infestation significantly altered the accumulation of 71 volatile organic compounds (VOCs), including 13 terpenoids. A total of 7897 significantly differentially expressed genes were identified, and genes involved in the terpenoid and phenylpropanoid metabolic pathways were highly enriched. Correlation analysis revealed that DEGs in terpenoid metabolism-related pathways were likely involved in the regulation of VOC biosynthesis in SSB-infested rice plants. Furthermore, two terpenoids, (-)-carvone and cedrol, were selected to analyse the behaviour of SSB and predators. Y-tube olfactometer tests demonstrated that both (-)-carvone and cedrol could repel SSB adults at higher concentrations; (-)-carvone could simultaneously attract the natural enemies of SSB, Cotesia chilonis and Trichogramma japonicum, and cedrol could only attract T. japonicum at lower concentrations. These findings provide a better understanding of the response of rice plants to SSB and contribute to the development of new strategies to control herbivorous pests.

Tomato yellow leaf curl virus manipulates Bemisia tabaci, MEAM1 both directly and indirectly through changes in visual and volatile cues.

The sweetpotato whitefly, Bemisia tabaci MEAM1, is one of the most devastating pests of row-crop vegetables worldwide, damaging crops directly through feeding and indirectly through the transmission of many different viruses, including the geminivirus Tomato yellow leaf curl virus (TYLCV). Y-tube olfactometer tests were conducted at different stages of TYLCV infection in tomatoes to understand how TYLCV affects B. tabaci behavior. We also recorded changes in tomato hosts' color and volatile profiles using color spectrophotometry and gas chromatography-mass spectrometry (GC-MS). We found that the infection status of B. tabaci and the infection stage of TYLCV influenced host selection, with uninfected whiteflies showing a preference for TYLCV-infected hosts, especially during the late stages of infection. Viruliferous B. tabaci attraction to visual targets significantly differed from non-viruliferous B. tabaci. Late-stage infected hosts had larger surface areas reflecting yellow-green wavelengths and higher emissions of methyl salicylate in their volatile profiles. These findings shed new light on several critical mechanisms involved in the viral manipulation of an insect vector and its economically important host.

Volatiles from essential oils of three Lamiaceae plants repel the winged cotton aphid, disturb its feeding behavior and reduce its fecundity.

Insects use odor detection to sense their surroundings. Use of volatile compounds, such as essential oils (EOs) of plants, to repel pests and disrupt their olfaction-driven behaviors has great practical potential for use in integrated pest management. Despite the available information on the repellent effects of EOs on herbivorous insects, the olfaction-based mechanisms remain unknown. Y-tube olfactometer tests showed that the EOs of three Lamiaceae plants - Mentha arvensis L., Mentha piperita L. and Lavandula angustifolia Mill. - were significantly repellent to winged cotton aphid, Aphis gossypii Glover. Electrical penetration graph (EPG) tests indicated the EOs reduced phloem feeding and increased the level of non-productive probing by the aphids. The EOs also reduced the fecundity of winged Aphis gossypii. Electrophysiological bioassays and gas chromatography-mass spectrometry (GC-MS) identified five physiologically active volatiles, that is menthone, isomenthone, neomenthol and menthol from Mentha piperita; menthone and menthol from Mentha arvensis; and linalool from L. angustifolia. Behavioral tests confirmed that all five compounds repelled winged Aphis gossypii. Under field conditions, the growth rate of aphid populations after 7 days was significantly lower in fields treated with these compounds than in the control fields. Our findings demonstrated that three EOs not only repelled winged Aphis gossypii but also interfered with the aphid's feeding behavior and reduced its fecundity. These EOs and their active constituents have great potential as eco-friendly control products for use against Aphis gossypii. The effects of these EOs also exceed other repellents that only keep pests away from host plants. © 2024 Society of Chemical Industry.

Plant volatiles mediate Aphis gossypii settling but not predator foraging in intercropped cotton.

The cotton aphid, Aphis gossypii Glover (Hemiptera: Aphididae) is an important pest of cotton and horticultural crops globally. In China, smallholder farmers regularly intercrop cotton with garlic or onion. Aside from higher farm-level revenue, cotton intercrops are typified by lower Aphis gossypii abundance than monocrops. So far, the mechanistic basis of this lowered pest pressure has not been empirically assessed. Field trials showed that Aphis gossypii abundance is lower and (relative) abundance of aphid predators higher in early-season cotton intercrops than in monocrops. Cage trials and Y-tube olfactometer tests further indicated that garlic and onion volatiles repel Aphis gossypii alates. Electrophysiological bioassays and gas chromatography-mass spectrometry (GC-MS) identified two physiologically active volatiles, that is, diallyl disulfide and propyl disulfide from garlic and onion respectively. Next, behavioral tests confirmed that both sulfur compounds exert a repellent effect on alate Aphis gossypii. Garlic and onion volatiles interfere with Aphis gossypii settling, but do not affect its main (ladybird) predators. Meanwhile, early-season cotton/onion intercrops bear higher numbers of Aphis gossypii predators and fewer aphids. By thus unveiling the ecological underpinnings of aphid biological control in diversified cropping systems, our work advances non-chemical management of a globally-important crop pest. © 2023 Society of Chemical Industry.

Exogenous Calcium Suppresses the Oviposition Choices of Frankliniella occidentalis (Thysanoptera: Thripidae) and Promotes the Attraction of Orius similis (Hemiptera: Anthocoridae) by Altering Volatile Blend Emissions in Kidney Bean Plants.

Frankliniella occidentalis is a destructive pest of horticultural plants, while Orius similis is a natural enemy of thrips. It has been demonstrated that exogenous calcium could induce plant defenses against herbivore attack. We examined whether CaCl2 supplementation altered the volatile emissions of kidney bean plants, which influence the oviposition preference of F. occidentalis. We also assessed the influence of volatile cues on O. similis. Using Y-tube olfactometer tests, we found that exogenous CaCl2 treatment inhibited the selectivity of F. occidentalis but attracted O. similis. In addition, CaCl2 treatment reduced the oviposition preference of F. occidentalis. Gas chromatography-mass spectrometry analyses revealed that CaCl2 treatment altered the number and relative abundance of the volatile compounds in kidney bean plants and that (E)-2-hexen-1-ol, 1-octen-3-ol, β-lonone, and (E,E)-2,4-hexadienal might be potential olfactory cues. Furthermore, the results of the six-arm olfactometer test indicated that 1-octen-3-ol (10-2 μL/μL), β-lonone (10-2 μL/μL), and (E,E)-2,4-hexadienal (10-3 μL/μL) repelled F. occidentalis but attracted O. similis. Overall, our results suggested that exogenous CaCl2 treatment induced defense responses in kidney bean plants, suggesting that CaCl2 supplementation may be a promising strategy to enhance the biological control of F. occidentalis.

Identification of Key Headspace Volatile Compounds Signaling Preference for Rice over Corn in Adult Females of the Rice Leaf Folder Cnaphalocrocis medinalis.

Volatile organic compounds are important for herbivorous insects in locating their host plants. The rice leaf folder, Cnaphalocrocis medinalis (Guenée), is a devastating migratory insect pest of rice in Asian countries. Although C. medinalis can develop even better on corn than on rice plants in insectaries, it rarely occurs on corn plants in the field. We hypothesized that plant volatile-mediated oviposition preference for rice over corn in adult females may be the reason for the observed rare field occurrence of the pest on corn plants. The present study was conducted to identify the olfactory active volatile compounds (OAVCs) that enable C. medinalis females to discriminate rice from corn plants. In cage tests, rice plants were highly preferred for oviposition over corn plants by C. medinalis females. From headspace, chemical analyses identified 15 rice unique, 8 corn unique, and 28 common volatile compounds. Fourteen OAVCs, including seven common, five rice unique, and two corn unique, were determined. In electroantennogram tests, the rice unique and common OAVCs activated the antennal responses in C. medinalis. In Y-tube olfactometer tests, (E)-2-hexenal and 3-hexanol(common OAVCs) and (Z)-3-hexenyl acetate and (E)-2-hexen-1-ol (rice unique OAVCs) attracted more C. medinalis females than the control, and only blends with both rice unique and common OAVCs were highly preferred over the control. Our results provide insights into the chemical cues used by C. medinalis adult females in host location, which may aid the development of novel crop protection strategies based on the manipulation of host-finding behaviors of C. medinalis.

Producing fluorescent plants to lure and trap insect pests.

Producing fluorescent plants to lure and trap insect pests.

Odor Perception in the Cotton Bollworm, Helicoverpa armigera, Exposed to Juglans regia, a Marginal Host Plant.

The cotton bollworm, Helicoverpa armigera, is one of the most destructive agricultural pests in the world, infesting cotton, maize, soybean, and many other crops. In recent years, H. armigera has been observed damaging walnuts, Juglans regia, in Xinjiang China. Here we examine the chemical perception by H. armigera of the marginal host J. regia. In Y-tube olfactometer tests, we found H. armigera females and males both showed significant behavioral responses to odors from walnut branches. Furthermore, nine electrophysiologically active volatiles (α-pinene, β-pinene, myrcene, limonene, eucalyptol, ocimene, β-caryophyllene, (E)-β-farnesene, and germacrene D) were identified from walnuts with gas chromatography coupled with electroantennography (GC-EAD) and gas chromatography-mass spectrometry (GC-MS). Among these volatiles, β-pinene and eucalyptol were released in relatively higher amounts. In electroantennogram (EAG) dose-dependent trials, all compounds evoked responses in H. armigera adults when tested at high concentrations, with germacrene D evoking the greatest response. In wind tunnel tests, H. armigera females preferred eight of the electrophysiologically active volatile dilutions compared with clean air, while males showed preference for only five compounds. As such we describe the chemical recognition of H. armigera for walnut, a marginal host. This study contributes to understanding the interaction between polyphagous pests and their host plants.

Electroantennographic and Behavioural Responses of European Cherry Fruit Fly, Rhagoletis cerasi, to the Volatile Organic Compounds from Sour Cherry, Prunus cerasus, Fruit.

Simple SummaryThe larvae of European cherry fruit flies are developing in sweet and sour cherry fruit. Non-insecticidal methods to control this pest are needed since most of the conventional insecticides used have been banned in Europe. Mass trapping is one of the environmentally friendly methods, however, it requires highly effective pest attractants. Three volatile compounds were identified as attractive to females of this species.European cherry fruit fly, Rhagoletis cerasi (Diptera: Tephritidae), is the most important pest of sweet and sour cherry fruit. This fly is difficult to control by insecticide application since most of the conventional insecticides used have been banned in Europe. Traps are used for both the pest’s mass trapping and the detection of the beginning of the flight period. Data on flies’ reactions to host-plant volatile organic compounds (VOCs) can be used to search for new attractants. VOCs were collected from the headspace of sour cherry, P. cerasus, fruit. Gas chromatography–mass spectrometry (GC–MS) resulted in the identification of 51 compounds. Terpenes and esters predominated in two aspects: in the highest diversity of the compounds, and the amount of the total VOC emissions (62.3%). Among the single VOCs, ethyl octanoate prevails, followed by (E)-4,8-dimethyl-1,3,7-nonatriene. GC–electroantennographic detection (GC–EAD) revealed 14 EAG-active compounds and those were identified. In Y-tube olfactometer tests, EAG-active compounds ((E)-β-ocimene, linalool, and (Z)-3-hexenyl 3-methylbutanoate) attracted R. cerasi females in a similar way to the odour of sour cherry fruit.

Attractiveness and toxicity of two insecticides to Tetragonula laeviceps (Apidae: Meliponinae)

Stingless bee, Tetragonula laeviceps, plays a primary role in ecosystem services as a pollinator for coffee, cocoa, and pepper. Attacks of insect pests cause low production of several plantation plants. Farmers commonly use synthetic insecticides to control insect pests. However, improper use of insecticides often adversely affects the ecosystem and human health, including pollinators. In Indonesia, research on the side effects of insecticides on non-target insects such as flower visitor insects (pollinators) is minimal. This study aimed to evaluate the attractiveness and toxicity of two insecticides to T. laeviceps. Stingless bees were obtained from beekeepers at Banten. Y-tube olfactometer test was used to determine the attractiveness of bees to insecticides, and a topical test was used to determine the mortality effect of insecticide on bees. The insecticides used were insecticide A (a.i. alpha-cypermethrin) and insecticide B (a.i. spinetoram) at 100 ppm and 60 ppm, respectively. The results showed that bees were more attracted to insecticide B by 73.3% than insecticide A (26.7%). Insecticide B caused 100% bee mortality after 48 hours after treatment (HAT), while Insecticide A caused 0% bee mortality after 48 HAT. The results indicate that insecticide B attracted stingless bees and has a high mortality level.

Olfactory Response of Plutella xylostella (Lepidoptera: Yponomeutidae) Adults to Refugia Plant

Selection of refugia plants is an important step when engineering the agroecological system. The refugia plants can be repellent or attractant to insect pests and in many species the role of each plant can be studied using the olfactory responses of the insect to volatile chemical cues emitted by the plant. The objective of this study was to determine the olfactory response of Plutella xylostella (Lepidoptera: Yponomeutidae) adults to several refugia plant candidates. Y-tube olfactometer tests were used to determine responses of P. xylostella to candidate plant species including: Ageratum conyzoides, Galinsoga parviflora, Synedrella nodiflora, Sphagneticola trilobata, Brassica rapa, Rorippa indica, Arachis pintoi, Ocimum basilicum, Apium graveolens, and Portulaca oleracea. Olfactory choice tests were conducted to compare preferences of insect. The results showed that R. indica, G. parviflora, and S. trilobata flowers attracted P. xylostella. R. indica and B. rapa leaves had high attractiveness for P. xylostella adults. At the same time, the A. graveolens, A. conyzoides, and O. basilicum leaves showed potential repellency. The conclusions of this study are R. indica and B. rapa have potential for use as trap crops, while A. graveolens, O. basilicum, and A. conyzoides have potential as repellent plants. Further study is necessary to test the olfactory response of P. xylostella’s natural enemies to these refugia plants.

Chemical signal is in the blend: bases of plant-pollinator encounter in a highly specialized interaction

In several highly specialized plant-insect interactions, scent-mediated specificity of pollinator attraction is directed by the emission and detection of volatile organic compounds (VOCs). Although some plants engaged in such interactions emit singular compounds, others emit mixtures of VOCs commonly emitted by plants. We investigated the chemical ecological bases of host plant recognition in the nursery pollination mutualism between the dioecious Ficus carica and its specific pollinator Blastophaga psenes. Using Y-tube olfactometer tests, we show that B. psenes females are attracted by VOCs of receptive figs of both sexes and do not exhibit preference for VOCs of either male or female figs. Electrophysiological tests and chemical analysis revealed that of all the VOCs emitted by receptive figs, only five were found to be active on female antennae. Behavioural tests show that, in contrast to VOCs presented alone, only a blend with a particular proportion of four of these VOCs is as attractive as the odour of receptive figs, and that if there is a very small change in this blend proportion, the pollinator is no longer attracted. This study revealed that in highly specialized mutualistic interactions specificity could be mediated by a particular blend of common compounds emitted by plants.

Three Host Plant Volatiles, Hexanal, Lauric Acid, and Tetradecane, are Detected by an Antenna-Biased Expressed Odorant Receptor 27 in the Dark Black Chafer Holotrichia parallela.

Insects rely on olfaction to locate their host plants by antennae in complex chemical environments. Odorant receptor (OR) genes are thought to play a crucial role in the process. ORs function together with odorant coreceptors to determine the specificity and sensitivity of olfactory reception. The dark black chafer, Holotrichia parallela Motschulsky (Coleoptera: Scarabaeidae), is a destructive underground pest. To understand the molecular basis of H. parallela olfactory reception, an olfactory-biased expressed odorant receptor HparOR27 and HparOrco (HparOR40) were identified from antennal transcriptome analysis and prediction of the sequence structure. Tissue expression analysis showed that HparOR27 was mainly expressed in adult antennae throughout developmental stages. The functions of HparOR27 were analyzed using the Xenopus laevis oocyte expression system. HparOR27 was broadly responsive to three host plant volatiles, including hexanal, lauric acid, and tetradecane. Electroantennogram tests confirmed that three ligands were electrophysiologically active in antennae of female adults. A Y-tube olfactometer test indicated that hexanal was a repellent for adults of both sexes. Taken together, our data support the identification of odorant receptors and provide a molecular basis for eco-friendly pest control.

Attraction of adult Harmonia axyridis to volatiles of the insectary plant Cnidium monnieri

Plant volatiles mediate the interactions within plant-insect communities and influence the distribution and behavior of insects. Natural enemies often utilize the volatiles that released from plants to locate the profitable patches for foraging. The lady beetle Harmonia axyridis (Pallas) is a dominant generalist predator of various pests in agriculture fields, yet little is known about the chemical cues which the predator employs to locate its prey. In this study, we tested the attractiveness of volatiles emanating from healthy and aphid-infested insectary plant Cnidium monnieri (L.) Cuss. to H. axyridis adults in a Y-tube olfactometer. Next, using coupled gas chromatography – electroantennogram detection (GC-EAD) and gas chromatography – mass spectrometry (GC–MS) identified the volatile components which elicited electrophysiological activity in H. axyridis adults. Lastly, Y-tube olfactometer tests in laboratory and field traps were used to verify the effectiveness of the volatile components. In olfactometer trials, H. axyridis adults preferred healthy and aphid-infested plants versus control. In GC–MS and GC-EAD trials, two antenna-active components (1,2-diethylbenzene and p-diethylbenzene) were detected among the volatile blends emanating from healthy and aphid-infested plants; and in ensuing behavioral assays, H. axyridis adults were attracted to two synthetic volatile compounds. Under field conditions, the number of H. axyridis adults as recorded in traps for two synthetic volatile components at three different concentrations (100 mg/ml, 10 mg/ml, and 1 mg/ml) were significantly higher than those for mineral oil (control). These findings could provide an effective means for the cultivation of insectary plants to develop natural enemy attractants and support the biological control in the field.

Tritrophic Interactions Between an Invasive Weed (Lepidium latifolium), an Insect Herbivore (Bagrada hilaris), and a Plant Pathogenic Fungus (Albugo lepidii).

Perennial pepperweed, Lepidium latifolium L. (Brassicales: Brassicaceae), is an invasive weed that can form dense stands and displace native species. Bagrada hilaris Burmeister (Hemiptera: Pentatomidae) is a serious economic pest of Brassicaceae vegetable crops. Bagrada bug also feeds on L. latifolium and may interact with the plant fungal pathogen Albugo lepidii S.I. (Peronosporales: Albuginaceae) to affect biological control of L. latifolium. A series of laboratory experiments, including Y-tube olfactometer and host-choice tests, were conducted to investigate B. hilaris host-preference behavior. Adults were attracted to the odor of healthy L. latifolium compared with A. lepidii-infected leaves. Bagrada hilaris consistently preferred to feed on healthy L. latifolium when offered both healthy and A. lepidii-infected plants. Experiments were conducted to determine the effects of A. lepidii-infected L. latifolium on B. hilaris survival and development. Survival of all B. hilaris immature stages and adults was markedly reduced for those reared on A. lepidii-infected leaves. Total development time and stage-specific development were faster on healthy L. latifolium leaves compared with A. lepidii-infected leaves. In addition, the ability of B. hilaris adults to passively transmit the rust was studied. Our data demonstrated that B. hilaris could acquire the rust spores while feeding, but it did not passively transmit the pathogen to healthy plants.

Screening of a potential leafhopper attractants and their applications in tea plantations

Pheromones can be used as leafhopper attractants. However, commercial pheromone products, such as the Ingle lure, have certain limitations, including poor persistence in the field. In this study, (E)-2-hexenal, (Z)-3-hexen-1-ol, (Z)-3-hexenyl acetate, (E)-ocimene, linalool, and geraniol were selected and behaviorally tested as potential leafhopper attractants. Y-tube olfactometer tests showed that the C2 formulation was more effective than other formulations. In tea field trials, the number of leafhoppers caught by sticky board traps baited with C2 lures was greater than that caught by treatment. The number of leafhoppers attracted by the C2 lures was greater than that attracted by the commercial Ingle lures. Additionally, the total amount of active C2 components on lures was greater than that of the active components on the lure after 14 days. Thus, the results indicated that the C2 formulation may attract leafhoppers and have a greater persistence than other formulations in tea field.

A Study on the Repellent Efficacy of Essential Oils Against Forcipomyia Taiwana

The majority of commercially available mosquito repellents contains N, N-diethyl-3-methylbenzamide compound (DETT). The long term uses of DETT have a negative influence on the nervous and *immune systems. Therefore, the development of mosquito repellents that are DETT-free is important. In this study, essential oils of lavandula angustifolia, Melaleuca Alternifolia, Mentha piperita, Eucalyptus globules, and Eucalyptus citriodora are evaluated in terms of the repellent efficacy against F. taiwana by using a Y-tube olfactometer test. Their repellent efficacy is then compared. The combination of 200 μl lavandula angustifolia and Eucalyptus citriodora attains a repellent efficacy of 70% and 65%, respectively. Conversely, using Melaleuca Alternifolia, Mentha piperita, and Eucalyptus globules does not result in any significant repellence against F. taiwana, which may be ascribed to the high concentration. When 1μl of these essential oils are added, they have a repellent efficacy of 61-65%. The repellent efficacy of different essential oils is ranked as Eucalyptus globules>Mentha piperita = Melaleuca Alternifolia> lavandula angustifolia> Eucalyptus citriodora.

Repellent Effects of Different Celery Varieties in Bemisia tabaci (Hemiptera: Aleyrodidae) Biotype Q.

Y-tube olfactometer and net cages experiments were used to investigate the repellent effects of different celery varieties in biotype Q of sweetpotato whitefly, Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae), on cucumber, Cucumis sativus L. (Cucurbitaceae). Y-tube olfactometer tests showed that whiteflies have strong repellent behavior to different celery varieties. Intercropping different celery varieties with cucumbers had significant repellent effects and oviposition deterrent effects in whiteflies. Results obtained demonstrated that the Western Europe celery varieties, Juventus and Ventura, and the Chinese celery variety, Jinnan, had good repellent efficacy against the whitefly. D-Limonene, β-myrcene, and (E)-β-ocimene might be the main active components in celery that affected the selection behavior of B. tabaci. In Western Europe celery varieties, D-limonene was the main volatile component for the repellent effects in B. tabaci; however, the two Chinese celery varieties that showed repellent effects had relatively higher volatilization quantities of β-myrcene than of D-limonene.

Queens of Bombus diversus tersatus (Hymenoptera: Apidae) are innately attracted to floral scents emitted by Cremastra appendiculata (Orchidaceae)

AbstractThe rewarding orchid, Cremastra appendiculata (Orchidaceae), has a strong floral scent and is pollinated by long-tongued bumble bee queens (Bombus diversus tersatus Smith; Hymenoptera: Apidae). The response of queens of B. diversus tersatus to the scent of C. appendiculata was investigated using a gas chromatography–electroantennographic detector system and Y-tube olfactometer. Gas chromatography–electroantennographic detector analysis of flower extracts showed that seven compounds (nerol, methyl decanoate, methyl dodecanoate, methyl tetradecanoate, methyl hexadecanoate, ethyl dodecanoate, and ethyl tetradecanoate) elicited antennal responses from B. diversus tersatus queens. Further, Y-tube olfactometer test results showed that queens significantly preferred both the flower extracts and synthetic mixture of seven EAD active compounds compared with pentane (a solvent control). These results suggest that floral scents play an important role in attracting queens and promote successful pollination.

Factors that affect the selection of tomato leaflets by two whiteflies, Trialeurodes vaporariorum and Bemisia tabaci (Homoptera: Aleyrodidae)

In Japan, although greenhouse whitefly, Trialeurodes vaporariorum (Westwood), and sweet potato whitefly, Bemisia tabaci (Gennadius), co-occur on tomato plants under greenhouse conditions, the two whiteflies are distributed differently with regard to leaf position. To elucidate the factors that determine the leaf position of these whiteflies, we investigated traits for leaflets collected from three positions on tomato plants. Furthermore, we examined leaflet selection by and fertility of the two whiteflies under choice and non-choice conditions. In addition, the effect on whitefly behavior of volatile compounds released from leaflets was evaluated by use of a Y-tube olfactometer test. Nitrogen and carbon content were highest for upper leaflets. In choice tests, more T. vaporariorum and B. tabaci adults selected upper and middle leaflets, respectively. Similarly, they oviposited more eggs on upper and middle leaflets. In non-choice tests, T. vaporariorum oviposited more eggs on upper leaflets, but B. tabaci oviposited equally on each leaflet. In Y-tube olfactometer tests, more T. vaporariorum adults moved to upper leaflets whereas more B. tabaci adults moved to middle leaflets. These results suggest that different leaflet selection by adults of these two whiteflies is likely to be associated with the different volatile compounds emitted by tomato leaflets at each position.