Interannual population dynamics of the green spruce aphid Elatobium abietinum (Walker) in France

The hypothesis that similar processes govern interannual dynamics of green spruce aphid in the UK and France, is generally supported by the application of a general discrete model. A simple model based on relatively few parameters was able to closely characterise interannual population dynamics from completely independent aerial and arboreal samples of aphids. Long term field population estimates of the green spruce aphid Elatobium abietinum (Walker) in France have provided the opportunity to select and evaluate the generality of a model which was developed in the UK to explain the year‐to‐year variations in peak abundance of the aphid. Aims The objective was to observe the influence of the local climates and disturbing climate factors on the population densities of the insect in two regions of France. Methods The model uses climate variables and aphid population data from regular samples in the two regions that were investigated. A general discrete model was used to predict aphid population densities. Results The model performed well in tracking the interannual patterns of population but was less likely to predict absolute population density. Conclusion To improve predictions, further account would need to be taken of additional site‐specific climate variables and the strength of overcompensating density dependence. Nevertheless it is clear that broadly similar processes are at work in the population dynamics of this insect across its biogeographical range

Nature des effets d'un traitement au Carbosulfan sur des plants de résineux

One cytotrope insecticide with Carbosulfan and progressive liberation is used to protect conifer seedlings against attacks of Hylobius abietis. One experiment with different doses of the product, and different species of trees is realized in order to compareeffects of treatment, like repulsive and insecticide. Resuts prove a good efficiency of the product by quick mortality of the insect and strong repulsion. So the Marshal Suxon treatment protects tree as much it controls Hylobius abietis. / Un insecticide à base de Carbosulfan et à relargage progressif est utilisé pour protéger les jeunes plants de conifères contre les morsures de Hylobius abietis. Une expérience avec différentes doses de produit, et avec des plants de différentes natures, est réalisée pour confronter les effets du traitement, d'une part en tant que répulsif, d'autre part en tant qu'insecticide. Si la mortalité rapide des insectes consommateurs prouve une bonne efficacité du produit, les résultats montrent également un fort effet de répulsion. Le traitement au Marshal Suxon se révèle ainsi avoir plus un rôle de protection de l'arbre qu'un rôle de contrôle de Hylobius abietis

Effects of climate on radial growth of Norway spruce and interactions with attacks by the bark beetle Dendroctonus micans (Kug., Coleoptera : Scolytidae): a dendroecological study in the French Massif Central

International audienceSamples of Norway spruce (Picea abies [L.] Karst) were dendrochronologically investigated in order to detect infestations by Dendroctonus micans (Kug.), the great spruce bark beetle (Col. Scolytidae), a relatively recent introduction to France. Uninfested natural forests located in the north-eastern French Alps and heavily infested plantations in the Ardeche region (Massif Central) were compared. The penetration holes bored in trunks by the bark beetle induced visible marks on wood, such as extreme ring width reductions, locally missing rings and crescent-shaped resin patches between consecutive rings that make possible a post-infestation dating. The outbreak began in 1979, 5 years prior to first insect visual detection by foresters. In the infested forest, tree basal area growth was not as sustained as in uninfested natural stands, but showed an inflection point at an unusually young tree age (from 30 to 40 years). Ring widths showing extreme synchronous radial growth reductions were caused either by excessively cold periods (e.g. in 1948, 1980, 1984, 1992) or by summer drought (as in 1986). Most of these weak growth years were shared with uninfested sites. In healthy forests, the consequences of extremely cold years were usually recorded only in high elevation stands, especially near the timberline, whereas summer drought effects were mostly visible in low altitude forests. By contrast, both phenomena were recorded in the infected Ardeche plantation. An analysis of tree-rings and monthly climate confirmed that Norway spruce growth in Ardeche plantations was reduced by excessively low minimum temperature during most parts of the year prior to ring formation, by higher than average maximum temperature during current spring and summer, and by drought in winter, spring and summer. Thus, the regional Ardeche climate with both cold winters and dry summers (especially in July) seems to weaken spruce trees planted there. Moreover, tree sensitivity to climate was found to be greatly enhanced by insect infestation. Such interactions between climatic stress and insect outbreak led to forest dieback in a 15-20-year period, when trees were still young (less than 70 years), and without any tree recovery. Therefore, in that region spruce plantations should be replaced by non-host species of Dendroctonus micans, especially where soil conditions may exacerbate drought effects. (C) 2004 Elsevier B.V. All rights reserved

Do herbicide treatments reduce the sensitivity of mosquito larvae to insecticides?

International audienceInvasive mosquitoes are economic and sanitary concerns especially in Europe and America. Most work has emphasized the role of resistance [Berrada, S., Fournier, D., Cuany, A., Nguyen, TX, 1994. Identification of resistance mechanisms in a selected laboratory strain of Cacopsylla pyri (Homoptera: Psyllidae): altered acetylcholinesterases and detoxifying oxidases. Pesticide Biochemistry and Physiology 48, 41-47; Hemingway, J., Hawkes, N.J., McCarroll, L., Ranson, H., 2004. The molecular basis of insecticide resistance in mosquitoes. Insect Biochemistry and Molecular Biology 34, 653-665] to insecticides. Compounds acting on larval sensitivity to insecticides are not well studied and their action remains poorly understood. Among several residual chemicals in ecosystems, particularly in wetlands, we identified a possible interaction of an herbicide on larval resistance to an insecticide. Our work contributes to the global control of mosquito populations by identifying possible pathways of resistance to insecticides of these vectors. Resistance or tolerance to insecticide treatments might contribute to successful invasion by mosquitoes. Here we report an ecotoxicological approach to test the hypothesis of an indirect effect of atrazine on mortality of an invasive vector. A brief contact (48 h) between Aedes aegypti mosquito larvae and atrazine led to a modification of larval sensitivity to an insecticide: using atrazine as an inducer led to a decrease in the mortality of larvae treated with Bacillus thuringiensis var. israelensis (Bti). (c) 2006 Elsevier Ltd. All rights reserved

Response of Aedes aegypti (Diptera : Culicidae) larvae to three xenobiotic exposures: Larval tolerance and detoxifying enzyme activities

The ability of mosquito larvae to tolerate toxic compounds (temephos, Bacillus thuringiensis var. israelensis, toxic vegetable leaf litter) was examined on a laboratory larval strain of Aedes aegypti L. Bioassays and detoxifying enzyme activity measurements were performed to compare tolerance/resistance capacities. The possibility of a functional plasticity of detoxifying equipment was investigated through experimental determination of the inductive effect of each xenobiotic within a given generation. In the same way, the selective effect of a toxic leaf litter was also investigated along successive generations. Results revealed that differential cytochrome P450 monooxygenase, esterase, and glutathione S-transferase activity levels correlated with the bioassay results. Both induction and selection increased larval tolerance to the xenobiotics used and increased the levels of larval detoxifying enzyme activities