Virulence is expected to be linked to parasite fitness via transmission. However, it is not clear whether this relationship is genetically determined, nor if it differs when transmission occurs continuously during, or only at the end of, the infection period. Here, we used inbred lines of the macro-parasitic spider mite Tetranychus urticae to disentangle genetic vs non-genetic correlations among traits, while varying parasite density and opportunities for transmission. A positive genetic correlation between virulence and...