Relationship between levels of co-infection and relative fitness of WNV CP40-12 on mosquito cell culture. a. Individual points represent relative fitness values +/- standard error of duplicate competition assays carried out for 72 h at indicated MOIs. A significant negative correlation between MOI and relative fitness was measured (linear regression analysis, r2 = 0.68, p = 0.0035). b. Relationship between WNV titer and relative fitness during competition following infection at an MOI of 10. Individual points represent duplicate measurements of output virus following 24 (circles), 48(squares), or 72 (triangles) hours of competition. Results demonstrate a negative correlation between WNV titer and relative fitness (Pearson correlation, r = -0.88, p = 0.0195).