De verspreiding van <i>Ensis directus</i> (Conrad, 1843) in Noord-Frankrijk

The distribution of Ensis directus in the north of France was studied. After the first reports of Ensis directus on the beach of Bray-Dunes in January and February 1988 (KERCKHOF & DUMOULIN, 1988a), it bas moved very fast to the south. At present the species is very common between the Belgian-French border and Calais. It seems to be absent however between Sangatte and Bou1ogne-sur-Mer, as apparently also the other Ensis species as well as Solen marginatus ! It is not yet clear why Ensis directus would not live in the sandy environment of the beaches of Wissant and Wimereux. Collections on beaches south of Boulogne-sur-Mer show no evidence that the conclusion of an earlier report (SEVERIJNS & GILLES, 1993), namely that Berck-Plage is very probably the most southern European location where Ensis directus lives at this moment, does not have to be changed. Finally, the dataset seems to suggest that Ensis directus moves southward much faster when the coastline is directed north-south than when it is directed east-west. The reason for this is not yet clear .It might e.g. be related to the directions of the ocean currents. It is further probably that the rocky region around the Cap Griz-Nez has slowed down the spreading of Ensis directus to the south as well

Aphid and Plant Volatiles Induce Oviposition in an Aphidophagous Hoverfly

Episyrphus balteatus DeGeer (Diptera, Syrphidae) is an abundant and efficient aphid-specific predator. We tested the electroantennographic (EAG) response of this syrphid fly to the common aphid alarm pheromone, (E)-β-farnesene (EβF), and to several plant volatiles, including terpenoids (mono- and sesquiterpenes) and green leaf volatiles (C6 and C9 alcohols and aldehydes). Monoterpenes evoked significant EAG responses, whereas sesquiterpenes were inactive, except for the aphid alarm pheromone (EβF). The most pronounced antennal responses were elicited by six and nine carbon green leaf alcohols and aldehydes [i.e., (Z)-3-hexenol, (E)-2-hexenol, (E)-2-hexenal, and hexanal]. To investigate the behavioral activity of some of these EAG-active compounds, E. balteatus females were exposed to R-(+)-limonene (monoterpene), (Z)-3-hexenol (green leaf alcohol), and EβF (sesquiterpene, common aphid alarm pheromone). A single E. balteatus gravid female was exposed for 10 min to an aphid-free Vicia faba plant that was co-located with a semiochemical dispenser. Without additional semiochemical, hoverfly females were not attracted to this plant, and no oviposition was observed. The monoterpene R-(+)-limonene did not affect the females’ foraging behavior, whereas (Z)-3-hexenol and EβF increased the time of flight and acceptance of the host plant. Moreover, these two chemicals induced oviposition on aphid-free plants, suggesting that selection of the oviposition site by predatory hoverflies relies on the perception of a volatile blend composed of prey pheromone and typical plant green leaf volatiles

Herbivore-Mediated Effects of Glucosinolates on Different Natural Enemies of a Specialist Aphid

The cabbage aphid Brevicoryne brassicae is a specialist herbivore that sequesters glucosinolates from its host plant as a defense against its predators. It is unknown to what extent parasitoids are affected by this sequestration. We investigated herbivore-mediated effects of glucosinolates on the parasitoid wasp Diaeretiella rapae and the predator Episyrphus balteatus. We reared B. brassicae on three ecotypes of Arabidopsis thaliana that differ in glucosinolate content and on one genetically transformed line with modified concentrations of aliphatic glucosinolates. We tested aphid performance and the performance and behavior of both natural enemies. We correlated this with phloem and aphid glucosinolate concentrations and emission of volatiles. Brevicoryne brassicae performance correlated positively with concentrations of both aliphatic and indole glucosinolates in the phloem. Aphids selectively sequestered glucosinolates. Glucosinolate concentration in B. brassicae correlated negatively with performance of the predator, but positively with performance of the parasitoid, possibly because the aphids with the highest glucosinolate concentrations had a higher body weight. Both natural enemies showed a positive performance-preference correlation. The predator preferred the ecotype with the lowest emission of volatile glucosinolate breakdown products in each test combination, whereas the parasitoid wasp preferred the A. thaliana ecotype with the highest emission of these volatiles. The study shows that there are differential herbivore-mediated effects of glucosinolates on a predator and a parasitoid of a specialist aphid that selectively sequesters glucosinolates from its host plant

Iridoids and phenylethanoid glycosides from Plantago palmata Hook. f. s.

Quatre iridoïdes [aucubine (1), gardoside (2), acide 8-épi-loganique acid (3) et arborescoside (4)] et deux glycosides de phényléthanoïdes [plantamajoside (5) et actéoside (ou verbascoside, 6)] ont été isolés à partir de feuilles et/ou de racines de Plantago palmata par chromatographie liquide à moyenne pression. Les composés obtenus ont été identifiés par comparaison spectroscopique (RMN du proton) avec de standards authentiques et confirmés par chromatographie en phase gazeuse et sur couche mince. Les propriétés pharmacologiques bien connues de ces composés, notamment l'aucubine et l'actéoside permettent de justifier en partie les usages traditionnels et les activités biologiques de la plante.info:eu-repo/semantics/publishe