Research progress on the function of Toll pathway in heteropteran insects: A review

As an important component of innate immunity in insects, the Toll pathway is a conserved signaling cascade that activates humoral immunity through NF-κB-related pathways, contributing to the production of antimicrobial peptides (AMPs) and effectors in response to fungal, bacterial and viral infections. Although extensive advances have been made in the identification and function of the Toll pathway in insects, knowledge of the regulatory mechanisms of this pathway in heteropteran insects, for which the available knowledge is rare, is essential for exploring their developmental and immune functions to exploit species-specific and environmentally friendly bioinsecticides for control of heteropteran pests. In addition, increasing attention has been given to the activation, signal transduction and regulation of the Toll pathway in response to various stimuli in heteropteran insects because of the absence of some components of the immune deficiency (IMD) pathway and interaction with gut symbionts. In this review, we outline the current research progress on the functional roles of the Toll pathway in several heteropteran insects, such as Riptortus pedestris, Rhodnius prolixus, Triatoma pallidipennis, Cimex lectularius, Plautia stali, and others, which are involved in the responses to changes in feeding conditions, pathogenic infection, embryogenesis and wing polyphenism, as well as interactions with gut symbionts. Ultimately, we propose a framework for future research on the identification and functional characterization of the Toll pathway to expand the current data and address potential limitations on the investigation and application of this pathway in the design of pioneering pest control strategies for heteropteran pests.