If you consider only the mosquito factors in Macdonald's equation, you obtain a quantitative index of a mosquito population's capacity to transmit malaria. This is called vectorial capacity, C.
C is defined as 'the number of secondary cases arising per day from one infective case in a susceptible population'.
So, R0 is the total number of secondary cases, C is the daily rate at which they arise.
The interactive version of this session includes an interactive version of the vectorial capacity equation.