Olfactometer Studies Research Articles

Methyl isonicotinate – a non-pheromone thrips semiochemical – and its potential for pest management

AbstractMethyl isonicotinate is one of several patented 4-pyridyl carbonyl compounds being investigated for a variety of uses in thrips pest management. It is probably the most extensively studied thrips non-pheromone semiochemical, with field and glasshouse trapping experiments, and wind tunnel and Y-tube olfactometer studies in several countries demonstrating a behavioural response that results in increased trap capture of at least 12 thrips species, including the cosmopolitan virus vectors such as western flower thrips and onion thrips. Methyl isonicotinate has several of the characteristics that are required for an effective semiochemical tool and is being mainly used as a lure in combination with coloured sticky traps for enhanced monitoring of thrips in greenhouses. Research indicates that this non-pheromone semiochemical has the potential to be used for other thrips management strategies such as mass trapping, lure and kill, lure and infect, and as a behavioural synergist in conjunction with insecticides, in a range of indoor and outdoor crops.

Chemically Mediated Arrestment of the Bed Bug, Cimex lectularius, by Volatiles Associated with Exuviae of Conspecifics.

Extracts of the exuviae (cast skins) of nymphal bed bugs (Cimex lectularius) were analyzed for volatile compounds that might contribute to arrestment of adult bed bugs. Four volatile aldehydes, (E)-2-hexenal, 4-oxo-(E)-2-hexenal, (E)-2-octenal, and 4-oxo-(E)-2-octenal were consistently detected in the headspace of freshly shed exuviae regardless of the developmental stages from which the exuviae were obtained. Quantification of the aldehydes in the solvent extracts of homogenized fresh, 45- or 99-d aged 5th instar exuviae indicated that the aldehydes are present in the exuviae and dissipate over time, through evaporation or degradation. Microscopic observation of the fifth instar exuviae indicated that the dorsal abdominal glands on the exuviae maintained their pocket-like structures with gland reservoirs, within which the aldehydes might be retained. Two-choice olfactometer studies with the volatiles from exuviae or a synthetic blend mimicking the volatiles indicated that adult bed bugs tend to settle close to sources of the aldehydes. Our results imply that the presence and accumulation of bed bug exuviae and the aldehydes volatilizing from the exuviae might mediate bed bugs’ interaction with their microhabitats.

Bt rice does not disrupt the host-searching behavior of the parasitoid Cotesia chilonis.

We determined whether plant volatiles help explain why Cotesia chilonis (a parasitoid of the target pest Chilo suppressalis) is less abundant in Bt than in non-Bt rice fields. Olfactometer studies revealed that C. chilonis females responded similarly to undamaged Bt and non-Bt rice plants. Parasitoids preferred rice plants damaged by 3rd-instar larvae of C. suppressalis, but did not differentiate between caterpillar-infested Bt and non-Bt plants. According to GC-MS analyses of rice plant volatiles, undamaged Bt and non-Bt rice plants emitted the same number of volatile compounds and there were no significant differences in the quantity of each volatile compound between the treatments. When plants were infested with and damaged by C. suppressalis larvae, both Bt and non-Bt rice plants emitted higher numbers and larger amounts of volatile compounds than undamaged plants, but there were no significant differences between Bt and non-Bt plants. These results demonstrate that the volatile-mediated interactions of rice plants with the parasitoid C. chilonis were not disrupted by the genetic engineering of the plants. We infer that parasitoid numbers are lower in Bt than in non-Bt fields because damage and volatile induction by C. suppressalis larvae are greatly reduced in Bt fields.

Baculovirus-Induced Climbing Behavior Favors Intraspecific Necrophagy and Efficient Disease Transmission in Spodoptera exigua.

Shortly prior to death, many species of Lepidoptera infected with nucleopolyhedrovirus climb upwards on the host plant. This results in improved dissemination of viral occlusion bodies over plant foliage and an increased probability of transmission to healthy conspecific larvae. Following applications of Spodoptera exigua multiple nucleopolyhedrovirus for control of Spodoptera exigua on greenhouse-grown sweet pepper crops, necrophagy was observed by healthy S. exigua larvae that fed on virus-killed conspecifics. We examined whether this risky behavior was induced by olfactory or phagostimulant compounds associated with infected cadavers. Laboratory choice tests and olfactometer studies, involving infected and non-infected cadavers placed on spinach leaf discs, revealed no evidence for greater attraction of healthy larvae to virus-killed over non-infected cadavers. Physical contact or feeding on infected cadavers resulted in a very high incidence of transmission (82–93% lethal disease). Observations on the behavior of S. exigua larvae on pepper plants revealed that infected insects died on the uppermost 10% of foliage and closer to the plant stem than healthy conspecifics of the same stage, which we considered clear evidence of baculovirus-induced climbing behavior. Healthy larvae that subsequently foraged on the plant were more frequently observed closer to the infected than the non-infected cadaver. Healthy larvae also encountered and fed on infected cadavers significantly more frequently and more rapidly than larvae that fed on non-infected cadavers. Intraspecific necrophagy on infected cadavers invariably resulted in virus transmission and death of the necrophagous insect. We conclude that, in addition to improving the dissemination of virus particles over plant foliage, baculovirus-induced climbing behavior increases the incidence of intraspecific necrophagy in S. exigua, which is the most efficient mechanism of transmission of this lethal pathogen.

Differential parasitism by a generalist parasitoid is mediated by volatile organic chemicals of the herbivore’s host

A native parasitoid, Apanteles polychrosidis, shifted hosts to exploit the invasive leaf miner, Caloptilia fraxinella, on horticultural ash, Fraxinus spp. in Edmonton, AB, Canada. A. polychrosidis has the potential to control populations of the invasive leaf miner, and parasitism rates are studied on two host plants, black ash, F. nigra, and green ash, F. pennsylvanica. Parasitism by A. polychrosidis of C. fraxinella differs on the two ash species. Parasitism is independent of leaf miner density on black ash, but is negatively density dependent on green ash. On green but not black ash, the host plant appears to mediate the numerical response of the parasitoid. Parasitoids are less effective at high host densities on green ash which may be because foraging behavior is not enhanced by leaf miner activity on green ash. Thirteen volatile organic chemicals (VOCs) released by green ash are detected by the antennae of A. polychrosidis, and eleven are identified here. The potential for host location mediated by VOCs is examined with olfactometer studies. Parasitoid females are differentially attracted to volatile cues of each ash species. Undamaged and mechanically damaged green ash leaflets attract female parasitoids, but in black ash, only leaflets mined by host larvae are attractive to parasitoids in olfactometer tests. These results suggest that A. polychrosidis uses host location cues induced by feeding damage on black ash but not on green ash. This differential attraction to VOCs from each ash species may mediate the differential parasitism observed in field studies.

English

Behaviour-modifying chemicals like pheromones and kairomones hold a great potential in pest management. Evidences from mating behaviour studies of the banana weevil, and from the weevil’s responses to their freeze-killed conspecifics, body washes/extracts, live conspecifics (olfactometer studies), and trapped volatiles of mature and immature adults clearly suggest that two types of pheromones are produced in this insect: a female produced sex pheromone and a male produced aggregation pheromone. Both are perceived by olfactory means. The latter has already been isolated by earlier workers and is in use in control programs. Greater successes may however, be recorded with the control of this pest (e.g. in mating disruptions, mass trappings, pest monitoring) if the female-sex pheromone also gets finally isolated, and used in conjunction with good cultural practices. Key words: Cosmopolites sordidus, sex pheromone, mating disruptions, bioassays, olfactometer studies, gas chromatographic profiles, electroantennogram studies.

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.

Behavioral and Antennal Responses of Drosophila suzukii (Diptera: Drosophilidae) to Volatiles From Fruit Extracts.

Native to Southeast Asia, the spotted wing drosophila, Drosophila suzukii Matsumura (Diptera: Drosophilidae), has become a serious pest of soft-skinned fruit crops since its introduction into North America and Europe in 2008. Current monitoring strategies use baits based on fermentation products; however, to date, no fruit-based volatile blends attractive to this fly have been identified. This is particularly important because females are able to cut into the epicarp of ripening fruit for oviposition. Thus, we conducted studies to: 1) investigate the behavioral responses of adult D. suzukii to volatiles from blueberry, cherry, raspberry, and strawberry fruit extracts; 2) identify the antennally active compounds from the most attractive among the tested extracts (raspberry) using gas chromatography (GC)-mass spectrometry and coupled gas chromatography -electroantennographic detection (GC-EAD); and 3) test a synthetic blend containing the EAD-active compounds identified from raspberry extract on adult attraction. In olfactometer studies, both female and male D. suzukii were attracted to all four fruit extracts. The attractiveness of the fruit extracts ranks as: raspberry ≥ strawberry > blueberry ≥ cherry. GC analyses showed that the fruit extracts emit distinct volatile compounds. In GC-EAD experiments, 11 raspberry extract volatiles consistently elicited antennal responses in D. suzukii. In choice test bioassays, a synthetic EAD-active blend attracted more D. suzukii than a blank control, but was not as attractive as the raspberry extract. To our knowledge, this is the first report of a behaviorally and antennally active blend of host fruit volatiles attractive to D. suzukii, offering promising opportunities for the development of improved monitoring and behaviourally based management tools.

Importance of the experimental setup in research on attractiveness of odours in moths: an example with Busseola fusca

AbstractWind tunnel and Y‐tube olfactometer studies are useful for demonstrating the responsiveness of male moths to sex pheromones. However, in the cereal stem borer, Busseola fusca (Fuller) (Lepidoptera: Noctuidae), wind tunnel bioassays yielded poor results when the behavioural responses of females to plant odours were tested. We demonstrated that for B. fusca females, the Y‐tube olfactometer was better suited for measuring the attractiveness of plant odours, compared with the wind tunnel. In particular, we showed B. fusca preference for odours of a host over a non‐host plant species using this apparatus. Behavioural responses for B. fusca after host finding are also discussed.

Identification of Sex Pheromone Components of Blueberry Spanworm Itame argillacearia (Lepidoptera: Geometridae)

Blueberry spanworm, Itame argillacearia (Packard), is an important defoliator of lowbush (syn. 'wild') blueberry, Vaccinium angustifolium Aiton, in north-eastern North America. The goal of the present study was to identify the female I. argillacearia sex pheromone, which could be used in traps for monitoring or mass-trapping this pest. Gas chromatography/mass spectrometry (GC/MS) and electroantennogram (EAG) recordings of sex pheromone gland extracts, in combination with chemical synthesis, a Y-tube olfactometer study and field experiments confirmed (2R,3S)-2-ethyl-3-((Z,Z)-tridecadi-2,5-enyl) oxirane (hereafter (Z,Z)-(3R,4S)-3,4-epoxy-6,9-heptadecadiene) and (Z,Z,Z)-3,6,9-heptadecatriene as female-produced sex pheromone components. (Z,Z)-(3R,4S)-3,4-Epoxy-6,9-heptadecadiene elicited a response from male I. argillacearia antennae during EAG recording, and in the Y-tube olfactometer tests males did not discriminate between a live female and (Z,Z)-(3R,4S)-3,4-epoxy-6,9-heptadecadiene. Field-trapping experiments showed that a blend of (Z,Z)-(3R,4S)-3,4-epoxy-6,9-heptadecadiene and (Z,Z,Z)-3,6,9-heptadecatriene was more attractive to male moths than (Z,Z)-(3R,4S)-3,4-epoxy-6,9-heptadecadiene alone.

Influence of cornicle droplet secretions of the cabbage aphid, Brevicoryne brassicae, on parasitism behavior of naïve and experienced Diaeretiella rapae

Insects have evolved amazing methods of defense to ward off enemies. Many aphids release cornicle secretions when attacked by predators and parasitoids. These secretions contain an alarm pheromone that alerts other colony members of danger, thereby providing indirect fitness benefits to the releaser. In addition, contact with cornicle secretions could also threaten an attacker and could provide direct fitness to the releaser. However, cornicle secretions may also be recruited as a kairomonal cue by aphid natural enemies. In this study, we investigated the effect of the cornicle droplet volatiles of the cabbage aphid, Brevicoryne brassicae (L.), on the host-searching behavior of naïve and experienced female Diaeretiella rapae (M(') Intosh) parasitoids in olfactometer studies. In addition, we evaluated the role of B. brassicae cornicle droplets on the oviposition preference of the parasitoid in a two-choice bioassay. Naïve females did not exhibit any preference between volatiles from aphids secreting cornicle droplets over non-secreting aphids, while experienced parasitoids exploited the secretions in their host location. Experienced females were also able to choose volatiles from both secreting and non-secreting aphids over clean air, while this ability was not observed in naïve females. Although secretion of cornicle droplets did not influence the percentage of first attack in either naïve or experienced females, the success of attack (i.e. resulting in a larva) was significantly different between secreting and non-secreting aphids in the case of experienced parasitoids.

Red oilseed rape? The potential for manipulation of petal colour in control strategies for the pollen beetle (Meligethes aeneus)

The pollen beetle (Meligethes aeneus) is a major pest of oilseed rape (Brassica napus) at the inflorescence stage and is well known to prefer colours called yellow by human observers over many other colours. While commercial cultivars of oilseed rape have yellow flowers, little is known about the potential to manipulate host plant location and reduce subsequent infestation by this pest through variation in flower colour. We investigated the responses of pollen beetles to flowers of a white-petalled oilseed rape variety that had been dyed different colours in semi-field arena and field experiments. Flowers dyed blue or red were less heavily infested than those dyed yellow or the white flowers, indicating that blue and red flowers were less attractive than yellow and white ones. This response was most likely due to differences in petal colour because olfactometer studies showed that beetle responses to the odours of the coloured treatments did not differ. The comparatively high infestation of untreated white flowers is interpreted as a consequence of their high UV reflectance; the presence of a UV receptor in M. aeneus is suggested, and its role in visually guided insect–plant interactions in this species described. The potential for manipulation of petal colour in control strategies for the pollen beetle is discussed.

Why eat extrafloral nectar? Understanding food selection by Coleomegilla maculata (Coleoptera: Coccinellidae)

Methods of increasing predator abundance within a habitat include the incorporation of non-prey food items, yet the influence of this on predation intensity toward herbivores remains unknown. In order to gain an understanding of nectar feeding in the predaceous beetle, Coleomegilla maculata (DeGeer), laboratory studies were conducted evaluating prey consumption in the presence of extrafloral nectaries. The physiology of beetles with access to prey only and a mixed diet were compared. To elucidate results of beetle physiology, Y-tube olfactometer studies were conducted and preferences between food types evaluated. Coleomegilla maculata females consumed 9 % fewer aphids when nectar was available. Lipid and glycogen content, as well as oocyte volume were not increased upon consumption of a mixed diet. Evaluation of predator behavior when offered both food resources together and separately demonstrated that extrafloral nectaries are attractive.

Monitoring aroma changes during human milk storage at − 19 °C by quantification experiments

In previous human-sensory and gas chromatographic–olfactometric studies we observed major changes in the overall aroma profile of human milk during frozen storage at −19°C. The data indicated that the changes were predominantly due to lipid degradation processes, most specifically oxidative decomposition of (poly) unsaturated fatty acids. In the present study, characteristic odorants from degradation and oxidation of fat were quantified by means of stable isotope dilution assays in samples stored at −19°C for 2 and 6months, and were compared with fresh human milk control samples. In total 20 odorants were determined, amongst which several highly potent odor substances showed drastic increases in concentration after storage for 6months, some even by two orders of magnitude. However, even after storage for 2months several major changes in the aroma profiles of human milk were observed. Our investigations support our previous assumption that storage recommendations for breast milk require reconsideration.

1134 Upwind responses of Anopheles stephensi to carbon dioxide and L-lactic acid: an olfactometer study

Excretion of carbon dioxide and L-lactic acid through exhalation and perspiration provides olfactory signals to mosquitoes which allow them to find and bite humans; however, mosquito species differ in this regard. This study investigated upwind responses of Anopheles stephensi, mysorensis form, an important malaria vector in Asia, to carbon dioxide and L-lactic acid under laboratory conditions. While a minimal dose of carbon dioxide (90 ppm) activated the mosquitoes, 10 times this amount suppressed them. L-lactic acid alone did not produce a significant effect by itself, but addition of 6 microg/min of L-lactic acid to a range of 90 to 410 ppm carbon dioxide resulted in attraction. The results provide further support for the hypothesis that CO2 plays an important role in the host-seeking behaviour of zoophilic mosquitoes, and suggests that L-lactic acid might play a more critical role than CO2 in the attraction of An. stephensi.

The Role of Volatile Organic Compounds in the Indirect Defense of Plants Against Insect Herbivores Above- and Belowground

Plants respond to attacks by herbivorous insects by releasing specific blends of volatile organic compounds (VOCs). These herbivore-induced VOCs are known to play a major role in the interaction between plants and insects and may directly protect the plant by being toxic or deterrent, but may also benefit the plant indirectly by attracting natural enemies of the herbivores. The chemical composition of herbivore-induced VOC blends is known for many plant–herbivore systems. Some VOCs are taxon-specific, whereas other VOCs appear to be common to many different plant families. These common compounds mainly include ‘green leaf volatiles’ (C6 aldehydes, alcohols and derivatives), cyclic and acyclic terpenes, phenolic compounds and nitrogenous compounds. Our model plant is maize, which shows a rapid reaction to an attack by caterpillars and root feeding beetle larvae. Belowground, maize roots respond within hours to feeding of larvae by releasing the sesquiterpene (E)-beta-caryophyllene. The emission of this compound results in increased recruitment of entomopathogenic nematodes (tiny worms that parasitize and kill insect larvae). Similarly, after being attacked by caterpillars aboveground, maize leaves emit a complex blend of volatiles that is attractive to parasitic wasps, which use the volatiles to find and kill the caterpillars. It remains largely unclear which VOCs within the blend are the key compounds mediating this parasitoid attraction. To study the importance of individual volatiles we combine different methods to generate and modify herbivore-induced VOC blends by manipulating the plant genotype, the plant phenotype and the headspace of volatiles produced by the plant. We focus on ‘subtractive’ approaches used to obtain blends differing in only few known VOCs and ‘additive’ approaches to generate blends of known composition. All blends are analyzed with gas chromatography/mass spectrometry and tested for attraction to the wasps in olfactometer studies. By combining the above approaches, we aim to provide new insights into the relevance of individual VOCs involved in indirect defenses, which might help to develop ecologically sound methods to control pest insects.

Density-dependent processes in leaf beetles feeding on purple loosestrife: aggregative behaviour affecting individual growth rates

Aggregative responses are commonly observed in insects, including chrysomelids, affecting both individual and population growth rates. In two closely related chrysomelid beetles (Galerucella calmariensis and G. pusilla) feeding on purple loosestrife (Lythrum salicaria), recent studies suggest that male-produced pheromones may cause both inter- and intraspecific attraction. This paper further examines the causes and consequences of feeding aggregations in these species. Olfactometer studies confirm previous findings, showing cross-species attraction to damaged plants, but suggest that also damaged induced plant volatiles may be involved. In addition, the studies suggest that the cross-species attraction observed in previous studies have asymmetric effects on the two beetles. Galerucella pusilla was more attracted to damage by G. calmariensis than to damage by conspecifics. Laboratory and field data suggest that feeding aggregations in these species increase pupal mass, at least at low to intermediate larval densities. This positive feedback may have important consequences for the spatiotemporal dynamics and as a consequence on the role of the two chrysomelid beetles on biological control of purple loosestrife.

Responses of Ceutorhynchus obstrictus (Marsham) (Coleoptera: Curculionidae) to olfactory cues associated with novel genotypes developed by Sinapis alba L. × Brassica napus L.

Many herbivorous insects use olfactory cues for host location. Extracts from Brassica napus L. have been shown to elicit electrophysiological and behavioural responses in the cabbage seedpod weevil, Ceutorhynchus obstrictus (Marsham) (syn. C. assimilis (Paykull)) (Coleoptera: Curculionidae). These include volatile products of the hydrolysis of glucosinolates. Here we present results of a laboratory olfactometer study examining the attractiveness of odours from flowering racemes and foliage of Sinapis alba L. (an inappropriate host for larval development), B. napus (an excellent host for larval development) and lines derived from S. alba × B. napus selected from colonization studies to demonstrate resistance or susceptibility. Results of this study indicate differential attraction of C. obstrictus to the odours of resistant and susceptible lines and suggest the role of hydrolysis products of glucosinolates, particularly the attractive effects of 2-phenylethyl isothiocyanate.

Development of a synthetic plant volatile‐based attracticide for female noctuid moths. II. Bioassays of synthetic plant volatiles as attractants for the adults of the cotton bollworm, Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae)

AbstractThis paper reports olfactometer studies to determine the attractiveness of synthetic equivalents of plant volatiles to Helicoverpa armigera (Hübner) moths. Synthetic volatiles identified from host plants and other volatiles reported in literature as attractants to various noctuid species were tested in a two‐choice olfactometer. Of 34 single chemicals tested, only seven were significantly attractive, and six were significantly repellent. However, when presented as blends of two or more volatiles, 21 of 31 blends tested were significantly attractive, and only one was significantly repellent. The most attractive blends were those containing four to six components, including aromatic volatiles primarily found in flowers, especially 2‐phenylethanol and phenylacetaldehyde and volatiles found primarily in leaves, including green leaf volatiles and terpenoids. Some general principles in blending volatiles for developing attracticides for H. armigera are presented, including the need for blend complexity, the combination of volatiles from leaves and flowers, and early consideration of pragmatic factors such as price and toxicological profile.

Behavioral response of femaleHelicoverpa armigera(Hübner) to different plant part extracts of African marigoldTagetes erecta(L.)

The flowering stage of African marigold Tagetes erecta (L.) was the most preferred for oviposition by Helicoverpa armigera (Hübner). The lower sides of leaf margins received more eggs compared to buds, stem tip and flowers. Olfactometer studies revealed that more female moths were attracted towards the flower extracts, followed by leaf, bud and stem tip extracts of African marigold. The thin layer chromatography analysis of these extracts showed a blend of compounds including careen, ocimene, methyl benzoate, phenyl acetaldehyde and phenyl ethanol. Attempts have been made to correlate insect behavior with the presence of these compounds.