Charles Descoins

Male-produced aggregation pheromone of the american palm weevil,Rhynchophorus palmarum (L.) (Coleoptera, Curculionidae): Collection, identification, electrophysiogical activity, and laboratory bioassay

Male American palm weevils (APWs),Rhynchophorus palmarum (L.) produced two sex-specific compounds, which were disclosed by volatile collections on Supelpak-2 and gas chromatography. One was a minor compound, not always detected. The major male-produced volatile was identified as (2E)-6-methyl-2-hepten-4-ol through coupled gas chromatography-mass spectrometry and gas chromatography-Fourier transform infrared spectrometry, proton nuclear magnetic resonance spectrometry, and rational synthesis. We propose the trivial name rhynchophorol for this new molecule, which proved to be the essential component of the APW aggregation pheromone by electroantennography, coupled gas chromatography-electroantennography and behavioral bioassays.

Control of sex pheromone biosynthesis in the moth Mamestra brassicae by the pheromone biosynthesis activating neuropeptide

The physiological route for the action of the pheromone biosynthesis activating neuropeptide (PBAN) was determined in Mamestra brassicae (L.) (Lepidoptera:Noctuidae). Removal of the ventral nerve cord including the terminal abdominal ganglia did not affect PBAN stimulation of pheromone production and the biogenic amine octopamine did not stimulate pheromone production in isolated abdomens. PBAN-like activity was found in the hemolymph of intact females in scotophase and not in the hemolymph of decapitated females or females in photophase. Our results suggest that PBAN follows a humoral route to its site of action rather than a neural one after being released from the brain. The hormonal control of the pheromone biosynthetic pathway was investigated using labeled precursors. Our results suggest that PBAN regulates an early step in the pheromone biosynthetic pathway, contrary to a previous report that it stimulates the Δ11-desaturase.

Purification and characterization of multiple forms of odorant/pheromone binding proteins in the antennae of mamestra brassicae (noctuidae)

Proteins extracted form the antennae of Mamestra brassicae (L.) (Lepidoptera: Noctuidae) adults were biochemically characterized as pheromone-binding proteins (PBP) and general odorant-binding proteins (GOBP). PBP and GOBP were purified by two successive and different HPLC (high performance liquid chromatography) systems and native polyacrylamide gel electrophoresis (native-PAGE). Their N-terminal sequence was determined by Edman microsequencing. The combined results showed evidence for three different PBPs in males, and two different PBPs in females. In addition, one GOBP was characterized in both males than in females antennae. In the males, two isoforms of PBP have the same N-terminal sequence, but different apparent mobilities and hydrophobicities: they could be separated by electrophoresis and reverse phase-HPLC (RP-HPLC). The other PBP sequence (SQEIM) showed particularly high homology (88%) with the PBP of Heliothis virescens, another noctuid moth. The existence of several forms of PBP in the same animal strongly supports the hypothesis of the specificity of binding between the proteins and their odorant ligands, the pheromonal compounds. The observed microdiversity at the soluble proteins level could provide a good model for studying their involvement in the initial stages of odor discrimination.

Taste detection of phytoecdysteroids in larvae of Bombyx mori, Spodoptera littoralis and Ostrinia nubilalis.

A number of plants produce significant amounts of phytoecdysteroids that can disrupt the hormonal levels of insects feeding upon them. Insects equipped with taste receptors sensitive to phytoecdysteroids are able to avoid such plants. How common is this strategy? By recording from the lateral and medial sensilla styloconica in two polyphagous species (Ostrinia nubilalis and Spodoptera littoralis) and in a monophagous species (Bombyx mori), we tested whether the receptors could detect three commonly occurring phytoecdysteroids 20-hydroxyecdysone (20E), ponasterone A (ponA) and ecdysone (E). In B. mori, 20E and ponA elicited dose-dependent responses with a threshold of 1 &mgr;M only in the medial sensilla. In O. nubilalis, 20E, E and ponA elicited responses at threshold of 1 &mgr;M in both sensilla. In S. littoralis, 20E elicited responses with a threshold of 10 &mgr;M in both sensilla. By means of behavioural choice tests, we show that 20E is an effective feeding deterrent for O. nubilalis and S. littoralis first instar larvae. This suggests that the perception of phytoecdysteroids is more common among phytophagous lepidoptera than previously thought, although their toxicity or antifeedancy varies between species.

Which Chemical Constituents from Dog Feces are Involved in its Food Repellent Effect in Sheep

This study is an attempt to identity the active chemicals (signal) of the odor of dog feces that suppress feeding in domestic sheep. The repellent effects of the odors of dog, wolf, pig, and sheep feces (potential predator and nonpredator species) were assessed on sheep, using a food-choice situation. The odors of wolf and dog feces had the highest repellent effect. A total pentane extract of dog feces was split by micropreparative gas chromatography and the fractions obtained were analyzed and presented to sheep in a food-choice situation. The quantitatively major constituents of the pentane extract, identified by gas chromatography–mass spectrometry, are indole and fatty acids. In food repellency tests, indole had no repellent effect. The active odorous signal contained in dog feces appears to consist of fatty acids mixed with neutral compounds acting synergically. These experiments underline the complexity of this biological signal and constitute a first step in the development of a practical repellent for ungulates.

Electrophysiological responses of gustatory sensilla of Mamestra brassicae (Lepidoptera, Noctuidae) larvae to three ecdysteroids: ecdysone, 20-hydroxyecdysone and ponasterone A.

Specialised phytophagous Lepidoptera such as Bombyx mori and Pieris brassicae have contact chemoreceptors that perceive ecdysteroids at very low concentrations. This sensory perception allows them to feed on substrates with a high content of phytoecdysteroids. We have evaluated if a polyphagous insect like Mamestra brassicae does possess contact chemoreceptor cells that are sensitive to these molecules. Electrophysiological recordings were performed from contact chemoreceptors located on the maxilla. These receptors were stimulated with some sugars, amino acids and salts and with three ecdysteroids. Our results demonstrate that a specific cell within the lateral sensilla responds to 20-hydroxyecdysone and ponasterone A but not to ecdysone.

Dorsal abdominal glands in nymphs of southern green stink bug,Nezara viridula (L.) (heteroptera: Pentatomidae): Chemistry of secretions of five instars and role of (E)-4-oxo-2-decenal, compound specific to first instars

We investigated the exocrine secretions from the five nymphal instars in the southern green stink bug,Nezara viridula, by analyzing separately the contents of the three dorsal abdominal reservoirs. All DAGs 1 produced a mixture of five alkanes with 12, 13, 14, 15, and 16 carbons. No differences were found between DAGs 2 and DAGs 3, for the five instars: the glands of first instars produce the same alkanes as DAGs 1,n-tridecane, traces of (E)-2-decenal, and a specific compound: (E)-4-oxo-2-decenal. In the other instars (second to fifth), (E)-4-oxo-2-decenal is absent from the secretion but another compound is present: (E)-4-oxo-2-hexenal. The kinetics of production of the different compounds were studied, the maximum amounts produced occurring 36 hr after hatching. The biological function of (E)-4-oxo-2-decenal was investigated. Using olfactometry, we showed that this compound acts as an attractant and an arrestant on second instars, at physiological doses. Moreover, this semiochemical was shown to be repellent to the fire-antSolenopsis geminata, a potential predator ofN. viridula and we established the dose-response curve for the repellent activity.

Stereospecific synthesis of (Z,E)-9,11,13-tetradecatrien-1-yl acetate and aldehyde sex pheromone components of stenoma cecropia and ectomyelois ceratoniae

Abstract a stereospecific synthesis of (Z,E)-9,11,13-tetradecatrien-1-yl acetate and aldehyde is described. The key steps are two sequential palladium-catalyzed cross-coupling reactions between adequate organo-zinc reagents and 1,2-dibromo ethylene with stereoselective semi-hydrogenation of a dienynic intermediate.

Identification of PBAN-like peptides in the brain-subesophageal ganglion complex of lepidoptera using western-blotting

An immunoblotting technique used to visualize pheromone-biosynthesis-activating-neuropeptide (PBAN)-like peptides in insect tissues is described. This technique involves a tricine-SDS-PAGE system and a chemiluminescent revelation of the antigens. Using this technique, PBAN-like immunoreactive peptides were found in the brain-subesophageal ganglion complex of various lepidopteran species, including moths: Heliothis zea, Mamestra brassicae, Spodoptera littoralis, S. latifascia and S. descoinsi (Noctuidae), Eldana saccharina (Pyralidae), and a butterfly: Pieris brassicae (Pieridae). PBAN-like peptides were detected in both sexes of the species studied, and even in a butterfly species that does not use pheromone to mate. This suggests that those peptides are widely distributed among Lepidoptera and confirms that they could be involved in functions other than regulation of sex pheromone production.

Electrophysiological and field activity of halogenated analogs of (E,E)-8,10-dodecadien-1-ol, the main pheromone component, in codling moth (Cydia pomonella L.)

Pest monitoring and control of the codling moth,Cydia pomonella L., have been developed using the main pheromone component of this species, (E,E)-8,10-dodecadienol (codlemone). However, the activity of codlemone is not satisfactory for pest control by mating disruption. Thus, we have synthesized halogenated analogs of codlemone to see if they could be used as new agents for pest control of the codling moth. Their biological activity was measured by electrophysiological techniques. In EAG screening, codlemone was the most active compound. F(10,11)-codlemone [(E,E)-10,11-difluoro-8,10-dodecadienol] and Cl-codlemone [(E,E)-11-chloro-8,10-undecadienol] elicited significant EAG responses, F(10,11)-codlemone triggering responses not significantly different from responses to codlemone. EAG cross-adaptation experiments and single sensillum recordings revealed that these compounds were detected by the same receptor neuron type as codlemone. No competitive inhibition with codlemone was observed from nonactive compounds. In field trapping, F(10,11)-codlemone and Cl-codlemone were more attractive to male codling moths than codlemone itself. Possible explanations of this activity are discussed.