Aphids, like whiteflies, leafhoppers and planthoppers, are hemipteran sap-feeding insects of plants. Aphid feeding results in induction of plant defences, which during successful aphid infestation become suppressed. Several studies showed that aphid salivary gland proteins can suppress host defences and are important for aphid survival. Aphid salivary glands are complex consisting of multiple lobes with distinct cell types, each of which secrete distinct sets of proteins that could manipulate plant processes. If true, the salivary gland is a key organ that ensures delivery of effector proteins into plants via the insect stylet. Despite the importance of sap-feeding insects in agriculture, few researchers study the role of salivary gland proteins in plant infestation. Recently, genomics resources have become available, offering unprecedented opportunities for investigating the perturbations aphids cause in plants. The aim is to identify and characterize salivary gland proteins of two aphid species, Myzus persicae (green peach aphid), and Acyrthosiphon pisum (pea aphid) and to elucidate how these proteins enhance feeding and affect host range specificity. We hypothesize that aphids produce and secrete salivary gland proteins during plant infestation that 1) enable the insects to feed and survive by modulating host cell processes and 2) determine host range. We will apply a proteomics-based approach to identify and compare secreted proteins produced by M. persicae and A. pisum salivary glands and generate catalogues of salivary gland proteins with potential roles in plant infestation and host range specificity. In addition, we will functionally characterize M. persicae and A. pisum salivary gland proteins with regards to their ability to modulate host cell responses to enable plant infestation. This research will facilitate the development of aphid resistant plant varieties, which in turn, will decrease the use of insecticides and improve the environment globally.