Resistance to common organophosphate and carbamate insecticides in Aphis pomi (Hemiptera: Aphididae)

Introduction. Aphis pomi (De Geer) has developed resistance to organophosphate and carbamate insecticides, as a result of long-term application of these insecticides in conventional apple orchards. For many years, the only mechanism of resistance identified in aphids was overproduction of insecticide-detoxifying esterases. Materials and methods. Insecticide resistance of A. pomi, collected from two conventional apple orchards (localities of Radmilovac-RA and Bela Crkva-BC) and one organic apple orchard (locality of Surcin-SU), was tested by bioassays and biochemical assays. Results and discussion. Compared with LC50 values for the susceptible population (organic orchard), both populations from the conventional orchards were highly resistant to pirimicarb (234.5 and 52.9 times) and moderately resistant to dimethoate (10.7 and 9.0 times). Increased esterase activity was determined in these two resistant aphid populations. Each of them also produced one esterase isoform more than the susceptible population, when 1-naphthyl acetate was used as a substrate for zymographic detection; when 2-naphthyl acetate was used as a substrate, only one resistant population produced two new esterase isoforms. In one of the resistant populations acetylcholinesterase (AChE) was significantly less inhibited by pirimicarb than in the other resistant population and the susceptible population, which indicates that this population developed another resistance mechanism-Modification of AChE (MACE). Conclusion. Detoxification of insecticides by the metabolic resistance mechanism of esterase enzymes and mechanism of modification of AChE was proven in one aphid population (RA). The other population (BC) has developed only metabolic resistance (enhanced metabolism by esterases), without modification of the insecticide target site (AChE). Development of insecticide resistance was caused by long-term application of acetylcholinesterase inhibitors (organophosphates and carbamates) in these conventional orchards

Host plant range of a fruit fly community (Diptera: Tephritidae): Does fruit composition influence larval performance?

Background: Phytophagous insects differ in their degree of specialisation on host plants, and range from strictly monophagous species that can develop on only one host plant to extremely polyphagous species that can develop on hundreds of plant species in many families. Nutritional compounds in host fruits affect several larval traits that may be related to adult fitness. In this study, we determined the relationship between fruit nutrient composition and the degree of host specialisation of seven of the eight tephritid species present in La Réunion; these species are known to have very different host ranges in natura. In the laboratory, larval survival, larval developmental time, and pupal weight were assessed on 22 fruit species occurring in La Réunion. In addition, data on fruit nutritional composition were obtained from existing databases. Results: For each tephritid, the three larval traits were significantly affected by fruit species and the effects of fruits on larval traits differed among tephritids. As expected, the polyphagous species Bactrocera zonata, Ceratitis catoirii, C. rosa, and C. capitata were able to survive on a larger range of fruits than the oligophagous species Zeugodacus cucurbitae, Dacus demmerezi, and Neoceratitis cyanescens. Pupal weight was positively correlated with larval survival and was negatively correlated with developmental time for polyphagous species. Canonical correspondence analysis of the relationship between fruit nutrient composition and tephritid survival showed that polyphagous species survived better than oligophagous ones in fruits containing higher concentrations of carbohydrate, fibre, and lipid. Conclusion: Nutrient composition of host fruit at least partly explains the suitability of host fruits for larvae. Completed with female preferences experiments these results will increase our understanding of factors affecting tephritid host range. (Résumé d'auteur

The endoplasmic reticulum through proteomics- Identifying the links between morphology and function

The eukaryotic cell is organized into several membranous subcellular compartments that contribute to the spatial segregation of the many cell physiological functions. One of these organelles, the endoplasmic reticulum (ER), is a continuous compartment, emanating from the nuclear envelope, through the rough ER, and ending with the reticulated smooth ER network. Each domain of the organelle is distinct for its morphology, as well as the many diverse functions that it performs. In this thesis, a survey of a proteomics resource for both the rough and smooth domains of the ER reveals that the organelle is further divided into spatial and functional subdomains. Furthermore, the assignment of novel proteins that were uncovered by proteomics to these various functional clusters can provide insight into their functions and guide future functional studies. Lastly, this thesis demonstrates the importance of the distinct morphology of the smooth ER network in maintaining basic physiological processes. Taken together, these data demonstrate that while the ER is a single, continuous, subcellular compartment, it is highly complex in its spatial, functional, and morphological organization.La cellule eucaryote est constituée de plusieurs structures spécialisées dénommées organites qui contribuent à la démarcation des fonctions physiologiques de la cellule. L'un de ces organites, le réticulum endoplasmique (RE), est une structure continue qui provient de l'enveloppe nucléaire, devient le RE rugueux, et se termine avec le réseau réticulé RE lisse. Chaque division de l'organite est unique pour sa morphologie, ainsi que ses fonctions nombreuses et diverses. Dans cette thèse, une analyse d'une ressource protéomique révèle que les deux domaines du RE sont encore divisés en de nouvelles sections régionales et fonctionnelles. De plus, l'attribution de nouvelles protéines découvertes par la protéomique à ces divisions fonctionnelles peut donner un aperçu de leurs fonctions et guider de nouvelles études. Enfin, cette thèse démontre l'importance de la morphologie distincte du réseau RE lisse pour le maintient de certains processus physiologiques de base. Le tout démontre que même si le RE est en effet un compartiment continu, son organisation régionale, fonctionnelle et morphologique est très complexe