Significance of animal feces and its bacterial community in larval development and fitness of the biting midge, Culicoides sonorensis

Culicoides sonorensis is a biological vector of the epizootic hemorrhagic disease virus and the bluetongue virus that cause great economic losses in wildlife and animal agriculture worldwide. In this study, we investigated the significance of the type of animal feces and the associated bacterial community in the larval development and fitness of C. sonorensis. Larval development assays were conducted by placing surface sterilized 1^st instar larvae on the sterilized soil with fresh feces of cattle feedlot, dairy, sheep, goat, horse, deer or swine in a 3:1 ratio. Dairy feces at concentrations 100, 50, 25, 12.5, 6.3, and 3.1% were also tested. Bacterial diversity in dairy feces was analyzed by a culturing approach followed by sequencing of the 16S rRNA gene. Midge fitness was measured by the wing size of adults emerged from each substrate. Sheep feces supported the larval development significanly more than all other animal feces. Dairy feces at 25% concentration supported the larval development the best while 100, 6.3, and 3.1% did not support the larval development at all. Inoculation of the sterilized substrate (soil with 25% dairy feces) with the individual bacterial isolates (Comamonas, Shewanella, Sphingobacterium, Sinorhizobium, Xanthomonas, Stenotrophomonas, Leucobacter, Pseudochrobactrum, Salmonella, Enterococcus) or their mixture did not compensate for the lack of larval development in the sterile substrate. Culicoides sonorensis requires animal feces to complete its development and the larval development and adult fitness vary with different type and concentration of animal feces.