Around 20% of insects rely on long-term relationships with heritable nutritional intracellular bacteria (endosymbionts). Endosymbionts provide their hosts with nutrients restricted in their diet allowing insects to thrive on poor or unbalanced habitats, which often results in the colonization of new empty ecological niches, including crops and agricultural products, therefore posing an important economic and ecological challenge. With the rise of insecticide resistance and the changing distribution patterns of pests due to globalization and climate change, there is a growing need for ecologically friendly pest control solutions. Understanding the dynamics of the host-endosymbiont interactions is therefore crucial for developing innovative pest management strategies. This project focuses on true weevils (Coleoptera: Curculionidae) and their diverse interactions with endosymbiotic bacteria. Weevil species within the Sitophilus genus exhibit drastic variations in their ecological niches and host-endosymbiont interactions. By comparing these closely related Sitophilus species, this project aims to uncover the genetic underpinnings of their phenotypic diversification. First, we will identify the genomic differences in both weevil hosts and endosymbionts that underlie their diverse phenotypes. Then, the project will explore the diversity of intricate molecular interactions between weevils and their endosymbionts by performing dual RNA-seq throughout the weevils’ lifecycle. Finally, the project will assess the roles of key genes through functional genomic strategies including RNA interference and the impact on insect biology, endosymbiont load, and host immunity will be thoroughly examined. Overall, this project will identify the molecular hallmarks of the drastic diversification of cereal weevils, offering fundamental knowledge regarding endosymbiont co-evolution and will serve as a foundation for innovative strategies to manage weevil pests more sustainably.