Location: Arthropod-borne Animal Diseases Research
Project Number: 3020-32000-020-001-S
Project Type: Non-Assistance Cooperative Agreement
Start Date: Jul 1, 2022
End Date: Jun 30, 2025
1. To determine the impact of sublethal exposures of pesticides on bluetongue virus susceptibility in female Culicoides sonorensis midges. 2. To investigate whether bluetongue virus infection impacts the response of female Culicoides sonorensis midges to spatial repellents. 3. To determine the impact of sublethal exposures of larvicides on bluetongue virus susceptibility in female Culicoides sonorensis midges.
Identifying factors that contribute to midge susceptibility to control methods and vector competence for viruses, as well as the interaction of these processes, is paramount in preventing midge-transmitted diseases. In mosquitoes, sublethal pesticide exposure can cause changes in their susceptibility to infection by arboviruses, and therefore vector competence. Furthermore, there is evidence that arbovirus infection in Culicoides sonorensis, the primary North American vector of bluetongue virus, impacts their molecular phenotype (as shown through changes in gene expression), with potential impacts on how C. sonorensis midges respond to stimuli such as spatial repellents. This project has three main goals. The first goal will be to test the effects of sublethal doses of pesticides on C. sonorensis competence for Bluetongue virus (BTV). To accomplish this, sublethal dosages of common topical livestock insecticides (Coumaphos, Permethrin) will be determined and applied to female midges (3 replicates/pesticide). Midges that survive will then be infected with virus via an infectious blood meal. A control cohort will be used that is unexposed to pesticide (acetone only) but fed an infectious blood meal. Infection rates, dissemination rates, and titers of virus will be monitored in and compared between treated and control midges to determine whether previous sublethal exposures impact infection outcomes (vector competence). The second goal is to determine impacts of midge arbovirus infection on their susceptibility to spatial repellents (Permethrin, DEET). Female midges will be infected with BTV via an infectious blood meal and control midges will be fed clean blood. At five and ten days after feeding, infected and control midges will be provided a two-choice blood feeding assay in which one feeder will have a spatial repellent applied to the surface of the feeding membrane and the other will not. The effect of infection on response to the presence of spatial repellents will be determined by comparing the number of engorged females between the two groups (3 replicates/repellent). Midges will also be tested using a no-choice assay to determine the impact of infection on feeding persistence and blood feeding success. The third goal is to evaluate the impact of sublethal exposure of larval C. sonorensis to a larvicide (Temephos) on susceptibility of emerged adults to BTV. Sublethal dosages will be determined and applied to larval C. sonorensis. Surviving larvae will be reared to adults and infected with BTV via an infectious blood meal. A control cohort will be used in which larvae will not be exposed to the larvicide and fed an infectious blood meal as adults. Infection, dissemination, and transmission will be assessed between the treatment and control groups. To gain insight into the molecular underpinnings of the different responses in each experiment, treatments that produced significant results will be replicated by ABADRU scientists for transcriptome sequencing and comparative bioinformatic analyses.