E. Thibout

Origin and identification of bacteria which produce kairomones in the frass of Acrolepiopsis assectella (Lep., Hyponomeutoidea).

The volatiles used by the parasitoidDiadromus pulchellus to find its host, the leek moth, are produced by the bacteria developing in the frass of the host larvae. The origin and the nature of these bacteria were investigated. Samples were taken from healthy leeks and from infested leeks in the field, as well as from the frass of larvae reared in the laboratory either on the host plant or on an artificial diet. The various species of bacteria identified were cultured in the presence of precursors of leek sulphur volatiles and their volatile emissions were analysed.Klebsiella oxytoca and variousBacillus, common decomposers of plant matter, were the principal species producing active volatiles which were alkyl disulphides.

Direct Analysis of Odors Emitted by Freshly Cut Allium Using Combined High‐performance Liquid Chromatography and Mass Spectrometry

Allium odors were re-examined to determine whether or not they contain degradation compounds of thiosulfinates. Garlic (Allium sativum), leek (Allium porrum) and onion (Allium cepa) were investigated using cryotrapping and direct injection of aqueous solutions of the samples into a high-performance liquid chromatograph (HPLC), with a diode-array detector, coupled to a mass spectrometer (MS). Various commercial systems which couple HPLC to tandem MS, but using different ionization systems, were compared. Best results were obtained with atmospheric pressure chemical ionization although degradation of certain thiosulfinates was observed. Depending on the HPLC/MS interface, thiosulfinates formed dimers in variable quantity and this reaction could be used to differentiate isomeric 1-propenyl and 2-propenyl thiosulfinates. Some unresolved isomers were identified by their fragment ions. No disulfides or other rearrangement products were observed and it was concluded that Allium odors contain only thiopropanal S-oxide and thiosulfinates as sulfur volatiles.

Gustatory sensilla sensitive to protein kairomones trigger host acceptance by an endoparasitoid.

Proteins isolated from the host cocoon of Acrolepiopsis assectella (Lepidoptera: Yponomeutoidea) act as kairomones for host acceptance by the endoparasitoid wasp Diadromus pulchellus Wesmael (Hymenoptera: Ichneumonidae). In this study, morphological, ultrastructural and electrophysiological studies were carried out in order to identify the contact chemoreceptive sensilla on the parasitoid antennae that perceive the protein kairomones. Three types of sensillum on the antennae of the females were found to have a chemosensory function. The receptor cell(s) of one sensillar type were shown to give a positive electrophysiological response to protein kairomones. This sensillar type is apically multiporous and female specific. Consequently, this sensillum could be the one implicated in the perception of the protein kairomone that triggers the host–acceptance behaviour of D. pulchellus females.

Nature and role of sexual pheromones emitted by males ofAcrolepiopsis assectella (LEP.)

Seven compounds that do not exist in the extracts from legs of males have been isolated in the hair-pencil extracts of maleAcrolepiopsis assectella. By combining techniques of GC-MS and GC-FT-IR, six of these compounds have been identified. They are sixn-alkanes: hexadecane (C16), heptadecane (C17), octadecane (C18), nonadecane (C19), eicosane (C20), and heneicosane (C21). Twelven-alkanes of the homologous series, from the C14–C25 compounds were presented to virgin females, mated females, and males. At the end of the scotophase, four of then-alkanes (C16, C17, C19, C21) present in the hair-pencil extract induced the virgin females to adopt the acceptance posture after having induced the virgin females to remain stationary. The two othern-alkanes (C18 and C20) present in the extract have less effect on the females similar to then-alkanes not present in the males. The blends tested do not seem to indicate any synergy between the most active compounds. The threen-alkanes with an odd number of carbons and the C16 compound would thus be the principle components of the male pheromone ofA. assectella. As well as their role of female aphrodisiac, they tend to make males and fertilized females flee.

Defensive role ofAllium sulfur compounds for leek mothAcrolepiopsis assectella Z. (Lepidoptera) against generalist predators

It has been shown previously that sulfur volatiles produced byAllium plants affect the behavior of their specialist phytophages and of their specialist entomophages. The action of these compounds in protecting the leek mothAcrolepiopsis assectella against generalist entomophages was studied in comparison to the proposed original defensive role of these compounds against generalist herbivorous insects. Two ants species,Formica selysi andF. fusca, were used as generalist predators. Six behavioral criteria of the predatory behavior of the ants were studied in presence of the last-instar caterpillars (C5). C5 reared on artificial diets with or without leek components were tested, as well as C5 soaked in frass of leek-reared caterpillars or disulfide solutions. In addition, the response of the ants to pure chemicals found in leek was studied using honey solutions with or without sulfur compounds. The sulfur allelochemicals ofAllium plants have a negative action on predatory ants. Interestingly, the nonvolatile precursors of sulfur volatiles ofAllium plants seem to have a protective role for their phytophagous insects against generalist entomophages.

Polypeptides of Acrolepiopsis assectella cocoon (Lepidoptera: Yponomeutoidea): an external host-acceptance kairomone for the parasitoid Diadromus pulchellus (Hymenoptera: Ichneumonidae).

Contact kairomones are essential for host-acceptance behaviour by female parasitoids. In the solitary endoparasitoid wasp, Diadromus pulchellus, this behaviour depends mainly on compound(s) in the cocoon of their host, Acrolepiopsis assectella pupae. Extracts of empty cocoons and polypeptides extracted from cocoons were tested in acceptance behaviour assays using cotton fibre lures bearing extracts. Extractions with solvents of increasing polarity indicated that the active compounds were polar, while SDS-PAGE showed that four glycopolypeptides contained enough information to trigger host-acceptance behaviour in female wasps. This kairomonal activity was found to be due to the protein moieties, and was independent of any glycosylation. These four glycopolypeptides might be two variants of two soluble sericin-like polypeptides differing in their degree of glycosylation.

Food Experience on the Predatory Behavior of the Ant Myrmica rubra Towards a Specialist Moth, Acrolepiopsis assectella

Entomophagous insects are often repelled by the secondary compounds of the plants eaten by their prey. These compounds, therefore, take on a defensive role for the phytophagous species that sequester them. Given that numerous entomophagous species are capable of learning, the effects on the foraging behavior of a repeated experience were investigated in the predatory ant Myrmica rubra. The sulfur amino acids methyl-cysteine sulfoxide (MCSO) and propyl-cysteine sulfoxide (PCSO) produced by Allium plants were identified in caterpillars of the leek moth Acrolepiopsis assectella. Three behavioral studies were carried out, with or without prior familiarization with caterpillars reared either on leek or on an artificial diet containing no Allium compounds. In choice tests with the two types of caterpillars, unfamiliarized ants displayed a preference for caterpillars reared on the artificial diet, but this preference disappeared or was reversed in both young and old ants after familiarization.

Role of Caterpillar Silk Thread in Location of Host Pupae by the Parasitoid Diadromus pulchellus

Diadromus pulchellus is a solitary ichneumonid parasitoid. Its only known host is the pupa of Acrolepiopsis assectella, a specialist herbivore of Allium species. D. pulchellus females parasitize A. assectella pupae within 48 h after the caterpillars spin their cocoon and begin to pupate. Having observed that the cocoon produced by the leek moth caterpillar stimulates parasitoid egg-laying and that caterpillar leaves a silk thread, we studied the hypothesis that silk thread might be involved in host-finding by the parasitoid. Behavioral tests showed that when D. pulchellus females encounter a host silk thread, they change directions, follow the thread, and quickly locate the host. These findings show that pupal parasitoids can use signals produced by their hosts at the developmental instar preceding the one that they parasitize.

Characterization of a Behaviorally Active, Gender-Specific Volatile Compound from the Male Asparagus Fly Plioreocepta poeciloptera

Adult male asparagus flies exhibit typical calling behaviors (suggestive of pheromone production) during which they emit a single volatile compound that was identified as isopropyl (S)-5-hydroxyhexanoate. In laboratory bioassays, synthetic samples elicited an arrestant response in females, but did not appear to attract females. On the other hand, the synthetic material attracted conspecific males in olfactometer bioassays.

Composés soufrés bes Allium et lutte contre les insectes

Summary Sulfur volatiles emitted by Allium plants attract the insects which develop in contact with these plants. But the sulfur volatiles can be perceived by other organism living in the vicinity or far from this biocenose and can have negative effects on them. Several works have shown that Allium or extracts were active on many insects. The present knowledges on odour emission of Allium were then summarized to search the active compounds. Two kinds of actions were shown. The first one was the behavioural consequences like repulsion and anti- appetence. The second one was the physiological consequences like the effects on development and the insecticidal effects. Many insect species were concerned among predators, parasitoids, hematophages, specialist and generalist phytophages, follivores and seminivores. The properties of the sulfur volatiles can be used to control insect populations friendly to the environment.