Résumé
This thesis assesses plant factor impacts on host-plant selection and feeding behaviour in aphids. The applied context of this work is potato (Solanum tuberosum) resistance to the aphids, Macrosiphum euphorbiae and Myzus persicae (Hemiptera: Aphididae). Many wild Solanum species possess aphid resistance traits that can be introgressed into potato germplasm to increase the resistance level. The influence of accession and plant part on the resistance level of seven accessions of Solanum chomatophilum was assessed for two aphid developmental stages (nymph and adult) through clip cage and whole plant experiments. Fecundity and survival of both developmental stages, and population growth, but not the proportion of winged adults, were influenced by accession and plant part. The accession PI243340 was the most resistant to both aphid species, according to both methods. Using electrical penetration graph (EPG) and ethological visual observation, the aphid host-plant selection behaviour was examined on nine accessions belonging to eight different Solanum spp., including two accessions from S. chomatophilum . A multivariate statistical analysis was used to highlight host selection behavioural stages. Resistance mechanisms were inferred by comparing host selection behavioural stages on each accession to those when aphids were placed on the susceptible species, S. tuberosum. An increase in xylem sap consumption was observed on three resistant Solanum species, including S. chomatophilum. Previous studies have shown that winged aphids consume the nutrient poor xylem sap to rehydrate. In contrast, in the current study xylem sap consumption did not always occur as a consequence of dehydration but also varied inversely with fecundity in both winged and wingless morphs. Furthermore, it was demonstrated that aphids consume xylem sap to reduce the osmotic pressure of the diet present in their gut. The high osmotic pressure of phloem sap, which is primarily determined by sucrose concentration, is reduced by consuming xylem sap, which has a low osmotic pressure. This study can help breeding programs involved in improving potato resistance to aphids by providing information on candidate resistant parents and gathering information on the mode of resistance of eight resistant Solanum species. The demonstration that aphids use diet mixing for osmoregulation expanded our knowledge of aphid host-plant selection and feeding behaviour. This has implications for all phloem-sap feeding species, and improves our understanding of aphid physiology.