RESUMO
Complex landscapes including semi-natural habitats are expected to favour natural enemies thereby enhancing natural pest biocontrol in crops. However, when considering a large number of situations, the response of natural biocontrol to landscape properties is globally inconsistent, a possible explanation being that local agricultural practices counteract landscape effects. In this study, along a crossed gradient of pesticide use intensity and landscape simplification, we analysed the interactive effects of landscape characteristics and local pesticide use intensity on natural biocontrol. During 3 years, using a set of sentinel prey (weed seeds, aphids and Lepidoptera eggs), biocontrol was estimated in 80 commercial fields located in four contrasted regions in France. For all types of prey excepted weed seeds, the predation rate was influenced by interactions between landscape characteristics and local pesticide use intensity. Proportion of meadow and length of interface between woods and crops had a positive effect on biocontrol of aphids where local pesticide use intensity was low but had a negative effect elsewhere. Moreover, the landscape proportion of suitable habitats for crop pests decreased the predation of sentinel prey, irrespectively of the local pesticide use intensity for weed seeds, but only in fields with low pesticide use for Lepidoptera eggs. These results show that high local pesticide use can counteract the positive expected effects of semi-natural habitats, but also that the necessary pesticide use reduction should be associated with semi-natural habitat enhancement to guarantee an effective natural biocontrol.
Assuntos
Agricultura/métodos , Ecossistema , Controle Biológico de Vetores , Praguicidas , Animais , Afídeos , Produtos Agrícolas , França , Plantas Daninhas , Comportamento Predatório , SementesRESUMO
We investigated the bioactivity of new chitosan-based multi-membrane hydrogel (MMH) architectures towards chondrocyte-like cells. The microstructure of the hydrogels constituting the membranes precludes any living cell penetration, whereas their lower scale architecture allows the protein diffusion. The biological behavior of chondrocytes implanted within the MMH inter-membrane spaces was studied for 45 days in culture. Chondrocytes formed cell aggregates and proliferated without loosing their chondrogenic phenotype as illustrated by collagen II and aggrecan expressions at the mRNA and protein levels. Cells produced neo-formed alcyan blue matrix proteins filling MMH interspaces. The HiF-2α/SOX9 pattern of expression suggested that the elevated chondrocytic phenotype in MMH could be related to a better hypoxic local environment than in classical culture conditions. Pro-inflammatory markers were not expressed during the period of culture. The low level of nitric oxide accumulation within the inter-membrane spaces and in the incubation medium implied that chitosan consumed nitrites produced by entrapped chondrocytes, in relation with the decrease of its molecular weight of 50%. Our data suggest that MMH structures may be considered as complex chondrocytic cell bioreactors; "active decoys of biological media", potentially promising for various biomedical applications like the inter-vertebral disk replacement.
Assuntos
Reatores Biológicos , Quitosana/química , Condrócitos/citologia , Hidrogéis/química , Engenharia Tecidual/métodos , Agrecanas/genética , Animais , Fatores de Transcrição Hélice-Alça-Hélice Básicos/genética , Contagem de Células , Técnicas de Cultura de Células/métodos , Sobrevivência Celular , Células Cultivadas , Quitosana/metabolismo , Condrócitos/metabolismo , Colágeno Tipo I/genética , Expressão Gênica/genética , Hidrogéis/metabolismo , Subunidade alfa do Fator 1 Induzível por Hipóxia/genética , Microscopia Eletrônica de Varredura , Microscopia de Contraste de Fase , Nitratos/metabolismo , Óxido Nítrico Sintase Tipo II/genética , Óxido Nítrico Sintase Tipo II/metabolismo , Coelhos , Fatores de Transcrição SOX9/genética , Propriedades de SuperfícieRESUMO
West Nile Virus infection is an arbovirosis accidentally transmitted to humans from an aviary reservoir via an infected mosquito. Though a French surveillance network set up in 2001 reports low circulation in France, the virus is endemic in other territories. Approximately 80% of infected children remain asymptomatic, fever is seen in 20%, and very few develop a severe neurological disease in the patient's blood or spinal fluid. Treatment remains essentially symptomatic though new specific antiviral treatments and human immunization are currently being developed.
