Biomedical subjects

Michael A Birkett

Publications and source records attributed to Michael A Birkett.

13 recordsLinked to original sources

PubMed2006

Chemically mediated intraguild predator avoidance by aphid parasitoids: interspecific variability in sensitivity to semiochemical trails of ladybird predators.

The avoidance responses of aphid parasitoids with varying host ranges (Aphidius eadyi, Aphidius ervi, and Praon volucre) to chemical trails deposited by intraguild predatory ladybirds, Coccinella septempunctata and Adalia bipunctata, were investigated. Females of all three parasitoid species avoided leaves previously visited by C. septempunctata or A. bipunctata adults. The avoidance responses shown by the two Aphidius species were stronger to trails of C. septempunctata than to those of A. bipunctata. However, P. volucre avoided trails of both ladybird species to a similar degree. Dose responses of these three parasitoid species to the hydrocarbons n-tricosane (C23H48), n-pentacosane (C25H52), and n-heptacosane (C27H56), which are components of the trails of both C. septempunctata and A. bipunctata, were evaluated. Dual-choice bioassays indicated the following: (1) A. eadyi showed more sensitive avoidance responses to n-tricosane than did the other two parasitoid species, (2) all three species showed similar responses to n-pentacosane across a range of doses, and (3) only P. volucre showed avoidance responses to n-heptacosane. Quantitative analyses of each hydrocarbon in the trails of the two ladybird species showed that n-pentacosane and n-heptacosane occur in significantly greater amounts in C. septempunctata trails than in those of A. bipunctata. The trails of the two species also differ qualitatively in the other hydrocarbons present.

Alkanes↗

PubMed2006

Aphid alarm pheromone produced by transgenic plants affects aphid and parasitoid behavior.

The alarm pheromone for many species of aphids, which causes dispersion in response to attack by predators or parasitoids, consists of the sesquiterpene (E)-beta-farnesene (Ebetaf). We used high levels of expression in Arabidopsis thaliana plants of an Ebetaf synthase gene cloned from Mentha x piperita to cause emission of pure Ebetaf. These plants elicited potent effects on behavior of the aphid Myzus persicae (alarm and repellent responses) and its parasitoid Diaeretiella rapae (an arrestant response). Here, we report the transformation of a plant to produce an insect pheromone and demonstrate that the resulting emission affects behavioral responses at two trophic levels.

Animals↗

PubMed2005

Response of economically important aphids to components of Hemizygia petiolata essential oil.

The essential oil of Hemizygia petiolata Ashby (Lamiaceae) contains high levels (>70%) of the sesquiterpene (E)-beta-farnesene, the alarm pheromone for many economically important aphid species. In order to test the suitability of H. petiolata oil as a source of (E)-beta-farnesene for use in new integrated aphid control strategies, behavioural responses of pest aphid species were studied in laboratory and field experiments. In alarm pheromone assays the peach-potato aphid, Myzus persicae Sulzer, and the pea aphid, Acyrthosiphon pisum (Harr), showed a lower level of response to the oil than expected given the high levels of (E)-beta-farnesene. It was shown that minor components in the oil, (+)-bicyclogermacrene and (-)-germacrene D, caused inhibition of the alarm response for M. persicae and A. pisum respectively. Nevertheless, in olfactometer studies the oil was directly repellent to A. pisum and the grain aphid, Sitobion avenae F. Sitobion avenae was not only repelled by (E)-beta-farnesene but also by (-)-germacrene D. Furthermore, although it was not directly repellent to M. persicae, the oil interfered with its attraction to host plant stimuli. In field plot experiments, numbers of A. pisum were significantly reduced in plots treated with a slow release formulation of the oil, when compared with control plots.

Animals↗

PubMed2005

Antennal electrophysiological responses of three parasitic wasps to caterpillar-induced volatiles from maize (Zea mays mays), cotton (Gossypium herbaceum), and cowpea (Vigna unguiculata).

Many parasitic wasps are attracted to volatiles that are released by plants when attacked by potential hosts. The attractiveness of these semiochemicals from damaged plants has been demonstrated in many tritrophic systems, but the physiological mechanisms underlying the insect responses are poorly understood. We recorded the antennal perception by three parasitoids (Cotesia marginiventris, Microplitis rufiventris, and Campoletis sonorensis) to volatiles emitted by maize, cowpea, and cotton plants after attack by the common caterpillar pest Spodoptera littoralis. Gas chromatography-electroantennography (GC-EAG) recordings showed that wasps responded to many, but not all, of the compounds present at the physiologically relevant levels tested. Interestingly, some minor compounds, still unidentified, elicited strong responses from the wasps. These results indicate that wasps are able to detect many odorant compounds released by the plants. It remains to be determined how this information is processed and leads to the specific behavior of the parasitoids.

Animals↗

PubMed2004

Revisiting the odorant-binding protein LUSH of Drosophila melanogaster: evidence for odour recognition and discrimination.

LUSH is a soluble odorant-binding protein of the fruit fly Drosophila melanogaster. Mutants not expressing this protein have been reported to lack the avoidance behaviour, exhibited by wild type flies, to high concentrations of ethanol. Very recently, the three-dimensional structure of LUSH complexed with short-chain alcohols has been resolved supporting a role for this protein in binding and detecting small alcohols. Here we report that LUSH does not bind ethanol and that wild type flies are in fact attracted by high concentrations of ethanol. We also report that LUSH binds some phthalates and that flies are repelled by such compounds. Finally, our fluorescence data, interpreted in the light of the three-dimensional structure of LUSH, indicate that the protein undergoes a major conformational change, similar to that reported for the pheromone-binding protein of Bombyx mori, but triggered, in our case, by ligand.

Animals↗

PubMed2004

Antifeedant compounds from three species of Apiaceae active against the field slug, Deroceras reticulatum (Muller).

Extracts of volatiles from foliage of three plants in the Apiaceae, Conium maculatum L. (hemlock), Coriandrum sativum L. (coriander), and Petroselinum crispum Mill. (Nym.) (parsley), previously shown to exhibit antifeedant activity in assays with the field slug, Deroceras reticulatum (Muller) (Limacidae: Pulmonata), were studied further to identify the active components. Coupled gas chromatography-mass spectrometry (GC-MS) and neurophysiological assays using tentacle nerve preparations resulted in the identification of 11 active compounds from the three extracts. Wheat flour feeding bioassays were used to determine which of these compounds had the highest antifeedant activity. One of the most active compounds was the alkaloid gamma-coniceine, from C. maculatum. The role of potentially toxic alkaloids as semiochemicals and the potential for using such compounds as crop protection agents to prevent slug feeding damage is discussed.

Alkaloids↗

PubMed2004

Identification of two sex pheromone components of the potato aphid, Macrosiphum euphorbiae (Thomas).

Females of the potato aphid Macrosiphum euphorbiae exhibit typical calling behavior, with virgin female oviparae raising their back legs off the substrate to release sex pheromone from glands on the tibia. Airborne collections from calling oviparae were analyzed by GC and GC-MS to determine if, like the majority of aphids examined to date, they produced (1R,4aS,7S,7aR)-nepetalactol (1) and (4aS,7S,7aR)-nepetalactone (2). Both components were present and produced in ratios that varied with age from 4:1 to 2:1. The relative stereochemical configurations of these components were determined by GC-coinjection of the aphid-derived sample with synthetic standards on both HP-1 and DB-Wax GC columns. The absolute stereochemical configuration of the nepetalactol (determined from approximately 15 microg of material in an air entrainment sample) was determined as (1R,4aS,7S,7aR)-1 by derivatization of the aphid sample with (S)-(+)-alpha-methoxy-alpha-(trifluoromethyl)phenylacetyl chloride (Mosher's acid chloride) to generate a diastereoisomer that was compared to synthetic samples by NMR spectroscopy and GC. In bioassays in the wind tunnel, M. euphorbiae males responded to potato plants with oviparae but not to unattacked plants or those infested with parthenogenetically reproducing apterae. In no-choice laboratory bioassays, the same level of male response was observed to virgins and to the 3:1-5:1 synthetic blends of nepetalactol (1):nepetalactone (2). However, the time taken to reach the source was significantly less to virgin females than to the synthetic pheromone blends. In all cases, males walked rather than flew to the source. Males showed lower responses to a 1:1 synthetic mixture and did not respond to either of the components when presented alone. Under field conditions, few M. euphorbiae males were captured in traps baited with different ratios of the synthetic pheromone. Possible reasons for the different responses under laboratory and field conditions are discussed.

Animals↗

PubMed2004

Laboratory and field responses of the mosquito, Culex quinquefasciatus, to plant-derived Culex spp. oviposition pheromone and the oviposition cue skatole.

Laboratory and field studies were conducted on the oviposition behavior of the pathogen-vectoring mosquito, Culex quinquefasciatus, in response to the oviposition pheromone 6-acetoxy-5-hexadecanolide, produced from a renewable plant resource, Kochia scoparia (Chenopodiaceae) (plant-derived pheromone, PDP), and via an established synthetic route (synthetic oviposition pheromone, SOP). Responses to the oviposition cue skatole (3-methylindole), presented individually and in combination with the plant-derived and synthetic oviposition pheromone, were also studied. Both laboratory and field assays showed that PDP and SOP were equally attractive. Synergistic effects were observed with one combination of PDP and skatole combinations in laboratory assays. Synergy was also observed under field conditions. SOP and skatole combinations showed additive effects in laboratory assays, but were not tested in field bioassays. Although synergism has been previously demonstrated with combinations of SOP and polluted waters, the work presented here is the first example of synergy between a specific oviposition attractant and the oviposition pheromone. Furthermore, the efficacy of mosquito pheromone produced from a cheap, renewable botanical source has been demonstrated.

Animals↗

PubMed2004

The role of semiochemicals in the avoidance of the seven-spot ladybird, Coccinella septempunctata, by the aphid parasitoid, Aphidius ervi.

The role of semiochemicals in mediating intraguild interactions between the seven-spot ladybird, Coccinella septempunctata, and the aphid parasitoid, Aphidius ervi, was investigated. Female parasitoids avoided leaves visited by C. septempunctata adults and larvae during the previous 24 hr. Ethanol extracts of C. septempuntata adults and larvae also induced avoidance responses by A. ervi. Two of the hydrocarbons identified by gas chromatography (GC) and coupled GC-mass spectrometry (GC-MS), n-tricosane (C23H48), and n-pentacosane (C25H52), when tested individually at levels found in the adult extract, induced avoidance by A. ervi. Further investigation of the larvae extract, and footprint chemicals deposited by adults in glass Petri dishes, confirmed the presence of the hydrocarbons. Parasitism rates of the pea aphid, Acyrthosiphon pisum, on broad bean plants, Vicia faba, which had been sprayed with a mixture of the chemicals, were lower than those on control plants. The effect, however, was no longer evident if parasitoid foraging was delayed by 24 hr after the plants were treated. The ecological significance of intraguild avoidance behavior and implications for possible use of the semiochemicals involved in future biological control programs are discussed.

Alkanes↗

PubMed2004

Responses of female orange wheat Blossom midge, Sitodiplosis mosellana, to wheat panicle volatiles.

Air entrainment samples of volatiles from panicles of intact wheat, Triticum aestivum, cultivar 'Lynx' were collected at the ear emergence/early anthesis growth stage. In an olfactometer bioassay, both freshly cut panicles and an air entrainment sample were found to attract female orange wheat blossom midge adults, Sitodiplosis mosellana. Coupled gas chromatography-electroantennography (GC-EAG) analyses of panicle volatiles located six electrophysiologically active components. These were identified by coupled gas chromatography-mass spectrometry and coinjection with authentic standards, on polar and nonpolar GC columns, as acetophenone, (Z)-3-hexenyl acetate, 3-carene, 2-tridecanone, 2-ethyl-1-hexanol, and 1-octen-3-ol. Although none of these was active when presented individually at the levels present in the entrainment sample, acetophenone, (Z)-3-hexenyl acetate, and 3-carene were active in the olfactometer when presented at a higher dose of 100 ng on filter paper. However, the six-component blend and a blend of acetophenone, (Z)-3-hexenyl acetate, and 3-carene, in the same ratio and concentration as in a natural sample, was as attractive to female S. mosellana as the whole air entrainment sample.

Animals↗

PubMed2003

Aphid sex pheromones: from discovery to commercial production.

This review charts the progress made with aphid sex pheromone chemistry, from initial identification of cyclopentanoid nepetalactones, for example (4aS,7S,7aR)-nepetalactone (1). and (1R,4aS,7S,7aR)-nepetalactol (2). to commercial production from a renewable non-food crop, the catmint, Nepeta cataria (Lamiaceae). The availability of aphid sex pheromone components is now facilitating the development of new aphid pest control strategies, incorporating the use of other semiochemicals, particularly in the manipulation of populations of aphid parasitoids and aphid predators such as lacewings, which can utilise the nepetalactones and closely related molecules to locate their hosts and prey. This is the first example of a plant resource being developed as a feedstock for the production of a commercially valuable insect pheromone. The development of a plant-based production route highlights the tremendous potential that higher plants offer as cheap and renewable resources for the production of insect semiochemicals, through the wide array of secondary metabolites that they can generate.

Animals↗

PubMed2002

Semiochemical strategies for sea louse control: host location cues.

The development of behavioural bioassays and electrophysiological recording techniques has enabled the role of semiochemicals to be investigated for the first time in Lepeophtheirus salmonis (Krøyer). Adult male sea lice L salmonis were activated by, and attracted to, salmon-conditioned water (SCW) and SCW extract. Non-host fish odours, turbot-conditioned water (TCW) and turbot-conditioned water extract (TCW extract), elicited activation but no attraction in the lice. Solid-phase extraction techniques were developed to extract low molecular weight components of fish odours, and biological activity was shown to be confined to these. Electrophysiological activity from aesthetascs in the first antennae was found and neural responses to odours were recorded from the antennal nerves. Preliminary experiments on individual chemicals (isophorone, 1-octen-3-ol) linked to salmon revealed behavioural activation and electrophysiological responses in adult male L salmonis. Isophorone was shown to be significantly attractive to sea lice when placed in a slow-release system in a perfused tank of seawater in a choice situation. Proof of concept has been established for successfully extracting odour cues from seawater, analysing their biological activity and applying these to slow-release technologies for field trapping of lice. Future work involving linked GC-MS techniques using behaviour, electrophysiological responses, and organolepsis will establish further host location cues specific to Atlantic salmon.

Animals↗

PubMed2002

Role of semiochemicals in mate location by parasitic sea louse, Lepeophtheirus salmonis.

The role of olfaction and diffusible pheromones in mate location behavior of sea lice, Lepeophtheirus salmonis, was assessed with Y-tube behavioral bioassays. The pheromone "emitting" animals were located in a chamber in one arm of a Y-tube arena, with artificial seawater flowing through both arms. Adult male sea lice displayed both activation and directional responses to seawater conditioned with preadult II virgin females, but were only activated by mated adult female conditioned water. Further, when males were given the choice of preadult II virgin females or mated adult females, a significant number of males chose the arm with the preadult II virgin females. Adult males showed activation responses when presented with water conditioned with adult males but were not attracted to them. When presented with adult males, preadult II virgin females showed only directional responses, but not activation responses. Preadult II virgin female conditioned water was extracted using solid-phase extraction (SPE) protocols pioneered for semiochemical isolation. Adult male sea lice showed significant directional responses to the preadult II virgin female SPE extract. Distillation under vacuum was performed on the extract to give a distillate comprising components with a molecular weight range and physical properties comparable to those of compounds utilized as volatile semiochemicals by terrestrial organisms and a residue comprising components with higher molecular weight range comparable to those utilized as involatile semiochemicals. Adult males were found to be both significantly activated and attracted to the distillate, but not to the residue. This research provides evidence that small, lipophilic organic molecules are used by sea lice as sex pheromone signals to locate a member of the opposite sex.

Animals↗