TABLE 1.

Proportions of infected and uninfected eggs and sperm

Gametes	Equation
Infected eggs	$I_{♀}=\frac{P_{i}C{t}_{♀}}{w_{♀}}$
Uninfected eggs	$U_{♀}=\frac{(1-P_i)+P_{i}C(1-t_{♀})}{w_{♀}}$
Infected sperm	$I_{♂}=\frac{P_i{s}_{i}C{t}_{♂}}{w_{♂}}$
Uninfected sperm	$U_{♂}=\frac{(1-P_i)+P_i(1-s_i)C+P_i{s}_{i}C(1-t_{♂})}{w_{♂}}$

P_i is the proportion of adults infected in generation i, which we assume to be equal for males and females. The virus is transmitted from mother to offspring at a rate t_♀ and from father to offspring at rate t_♂. We assume that both female and male fertility are changed by a factor C in infected flies relative to uninfected flies. We split the infected population in generation i into a fraction s_i that inherited the virus from their mother and a fraction (1 – s_i) that inherited the virus from their father. Male D. obscura that inherit the virus from their father do not transmit it to the next generation (i.e., they produce uninfected sperm). To obtain proportions, we divide by w_♀, the sum of the numerators of I_♀ and U_♀, and w_♂, the sum of the numerators of I_♂ and U_♂.