Identification and ecology of alternative insect vectors of ‘Candidatus Phytoplasma solani’ to grapevine

Bois noir, a disease of the grapevine yellows complex, is associated with 'Candidatus Phytoplasma solani' and transmitted to grapevines in open fields by the cixiids Hyalesthes obsoletus and Reptalus panzeri. In vine-growing areas where the population density of these vectors is low within the vineyard, the occurrence of bois noir implies the existence of alternative vectors. The aim of this study was to identify alternative vectors through screening of the Auchenorrhyncha community, phytoplasma typing by stamp gene sequence analyses, and transmission trials. During field activities, conducted in Northern Italy in a vineyard where the bois noir incidence was extremely high, nine potential alternative insect vectors were identified according to high abundance in the vineyard agro-ecosystem, high infection rate, and harbouring phytoplasma strains characterized by stamp gene sequence variants found also in symptomatic grapevines. Transmission trials coupled with molecular analyses showed that at least eight species (Aphrodes makarovi, Dicranotropis hamata, Dictyophara europaea, Euscelis incisus, Euscelidius variegatus, Laodelphax striatella, Philaenus spumarius, and Psammotettix alienus/confinis) are alternative vectors of 'Candidatus Phytoplasma solani' to grapevines. These novel findings highlight that bois noir epidemiology in vineyard agro-ecosystems is more complex than previously known, opening up new perspectives in the disease management

Cold winter temperatures condition the egg-hatching dynamics of a grape disease vector

The leafhopper Scaphoideus titanus is the vector of a major phytoplasma grapevine disease, Flavescence dorée. The vector’s distribution is in Eastern and Northern Europe, and its population dynamics varies as a function of vineyard latitude. We tested the hypothesis that hatching dynamics are cued by cold temperatures observed in winter. We exposed eggs from a natural population to simulated “cold” and “mild” winters and varied the exposure time at 5 °C from 0 to 63 days. We show that temperature cooling mainly affected the onset of hatching and is negatively correlated to the cold time exposure. The majority of hatchings occurred more quickly in cold rather than in mild winter simulated conditions, but there was no significant difference between the duration of hatching of eggs whatever the cold time exposure. In agreement with the Northern American origin of the vector, the diapause termination and thus the timing regulation of egg hatching require cold winters

Do Scaphoideus titanus (Hemiptera: Cicadellidae) nymphs use vibrational communication?

Small Auchenorrhyncha use substrate-borne vibrations to communicate. Although this behaviour is well known in adult leafhoppers, so far no studies have been published on nymphs. Here we checked the occurrence of vibrational communication in Scaphoideus titanus (Hemiptera: Cicadellidae) nymphs as a possible explanation of their aggregative distributions on host plants. We studied possible vibratory emissions of isolated and grouped nymphs, as well as their behavioural responses to vibration stimuli that simulated presence of conspecifics, to disturbance noise, white noise and predator spiders. None of our synthetic stimuli or prerecorded substrate vibrations from nymphs elicited specific vibration responses and only those due to grooming or mechanical contacts of the insect with the leaf were recorded. Thus, S. titanus nymphs showed to not use species-specific vibrations neither for intra- nor interspecific communication and also did not produce alarm vibrations when facing potential predators. We conclude that their aggregative behaviour is independent from a vibrational communication

Pi-Facial Diastereoselection in [4+2]-Cycloadditions of 3,4-Epoxy-2-Methyleneoxolanes with Oxadienes - a Short Synthesis of Spiroketals

Hetero Diels-Alder reaction of oxadienes with 3,4-epoxy-2-methyleneoxolanes gave the corresponding 3,4-epoxy-1,6-dioxaspiro[4,5]-dec-7-enes with high stereoselectivity. Good yields of adducts were obtained in the presence of mild Lewis acis, such as zinc or stannous chloride. The spiroketal adducts have been transformed chemio- and stereospecifically by either hydrogenation, hydride reduction or acid catalyzed isomerization. The stereochemical outcome of the cycloadditions has been investigated. The spiroketal adducts always result from an oxadiene addition anti relative to the allylic epoxy substituent. When the oxadiene is substituted suitably as in crotonaldehyde, we demonstrated that the cycloaddition is totally endo selective relative to the enol ether function. Ab initio calculations suggested that 3,4-epoxy-2-methyleneoxolane and 3,4-epoxy-3-methyl-2-methyleneoxolane adopt envelopw conformations with the oxygen atom of the oxolane moiety pointing toward the epoxide ring. No significant distortion from planarity was calculated for the exocyclic double bond of these dienophiles

Pi-facial diastereoselection in [4+2]-cycloadditions of 3,4-epoxy-2-methyleneoxolanes with oxadienes : a short synthesis of spiroketals

Hetero Diels-Alder reaction of oxadienes with 3,4-epoxy-2-methyleneoxolanes gave the corresponding 3,4-epoxy-1,6-dioxaspiro[4,5]-dec-7-enes with high stereoselectivity. Good yields of adducts were obtained in the presence of mild Lewis acis, such as zinc or stannous chloride. The spiroketal adducts have been transformed chemio- and stereospecifically by either hydrogenation, hydride reduction or acid catalyzed isomerization. The stereochemical outcome of the cycloadditions has been investigated. The spiroketal adducts always result from an oxadiene addition anti relative to the allylic epoxy substituent. When the oxadiene is substituted suitably as in crotonaldehyde, we demonstrated that the cycloaddition is totally endo selective relative to the enol ether function. Ab initio calculations suggested that 3,4-epoxy-2-methyleneoxolane and 3,4-epoxy-3-methyl-2-methyleneoxolane adopt envelopw conformations with the oxygen atom of the oxolane moiety pointing toward the epoxide ring. No significant distortion from planarity was calculated for the exocyclic double bond of these dienophile

Reactivity of [(alkylthio)methylene]ketenes in the gas phase and photoelectron spectra of thiophen-3(2H)-ones

International audienceno abstrac

SYNTHESIS OF ALPHA-CYANO CARBONYL-COMPOUNDS BY FLASH VACUUM THERMOLYSIS OF (ALKYLAMINO)METHYLENE DERIVATIVES OF MELDRUMS ACID - EVIDENCE FOR FACILE 1,3-SHIFTS OF ALKYLAMINO AND ALKYLTHIO GROUPS IN IMIDOYLKETENE INTERMEDIATES

The syntheses and flash vacuum thermolyses of 5-[(alkylamino)methylene]-2,2-dimethyl-1,3-dioxane-4,6-diones (Meldrum's acid derivatives) 13a-i are described. Thermolysis of 13a as well as of ethyl 3-(tert-butylamino)acrylate (22) gives a tautomeric mixture of cyanoacetaldehyde (14) and 3-hydroxypropenenitrile (15). Thermolysis of 13b gives iminoacrolein 26 and not cyanoacetone (29). Thermolysis of 13c,d gives S-methyl cyanothioacetate (30), and 13f-h give cyanoacetamides 31 in high yields. 2-Cyanopent-4-enoic acid derivatives 32 are obtained from Meldrum's acids 13e,i. The results are discussed in terms of facile 1,3-shifts of methylthio and alkylamino groups in imidoylketenes, interconverting imidoylketenes and acylketene imines