Rafts on the water, for mosquito vector control: hydrogel-based delivery systems and inhibition of insect defence mechanisms, to improve sustainable use of insecticides and counteract resistance development (RAFTING)

Vector-borne diseases are a global problem deeply affecting the health of humans and the economy. Insecticides remain, at present, the most effective way to control arthropod vectors and prevent the spread of diseases, particularly in the absence of effective vaccines. However, environmental pollution and resistance phenomena are great threats connected to the use or abuse of currently available insecticide products. This project has a practical/applied objective: the development of a product prototype that allows to reduce the amount of insecticides used for the control of arthropod vectors. Such reduction is a priority for the containment of environmental pollution, the protection of public health and the protection of non-target fauna. Our strategy will consist in a two-step approach: the development of molecules able to increase the susceptibility of the vectors, by inhibiting the cellular/immune defence of the target species towards insecticides, in conjunction with the development of delivery systems that will increase the amount of active insecticide molecules that reach mosquito larvae. The “product” will therefore increase the effectiveness of the insecticide and reduce the dosages, with consequent positive effects cascading on the environment and public health. The proposed research activity involves a combination of: transcriptomic analyses to discover defence genes that protect the arthropod from insecticides; RNAi technology to silence these genes; yeast engineered as biofactories, to produce dsRNAs interfering with the expression of defence genes; use of hydrogel matrices and technologies for micro-encapsulation, to develop an effective delivery system; bioassay experiments under different conditions, to test the efficacy of the developed prototype. The target species of the project is the mosquito Culex pipiens, a vector with worldwide distribution, and among the most common mosquitoes in urban areas in Europe. Members of the Cx. pipiens complex are the main vectors of several arboviruses and diseases, such as West Nile Virus, St. Louis encephalitis, Rift Valley fever and Japanese encephalitis, as well as primary vectors of various filariases. The insecticides we intend to investigate are diflubenzuron (DFB) and the bioinsecticide Bacillus thuringiensis subsp. israelensis (Bti). We expect to: i) uncover the details of the defence response of mosquito larvae to DFB and Bti, through comparative transcriptomic analyses; ii) design RNAi triggers to silence defence genes, to increase sensitivity to DFB and Bti in Cx. pipiens larvae; iii) develop economical and stable RNAi triggers, i.e. yeast engineered for the expression of dsRNAs (yeast biofactories); iv) develop floating hydrogel rafts, incorporating Bti (or micro-encapsulated DFB) and yeasts biofactories, for an effective delivery of insecticide and insecticide-defence inhibitors directly to feeding mosquito larvae. In conclusion, the project will lead to the creation of an effective, species-specific, ecologically sustainable and economical tool that can be considered in perspective for field applications. The project lays of solid foundations: the scientific results already obtained on this topic by the proposing groups, their experience in the research sector and the rigorously planned experimental system. The RNAi-based inhibitors of the defense genes of arthropods, as well as delivery systems based on microparticles and hydrogels that we aim to develop in this project, could become the objects of industrial research and subsequently of application in the field, not only for the control of the target species of this project, but more generally for the control of harmful insects/arthropods in the veterinary, agricultural and medical fields.