(How) does vector species richness increase parasite transmission?

midgesThis is a question we got interested in through hemorrhagic disease, a vector-borne viral disease affecting white-tailed deer. We observed that disease reporting rate was positively associated with vector species richness (VSR: where species of midge belong to the large genus Culicoides). We thought this could be because high VSR:

  1. is associated with high vector abundance
  2. increases the likelihood that the vector community contains a highly competent subset
  3. is associated with long seasonal transmission if vector species in a community exhibit distinct phenologies

We found no support for 1 and 2 in our system, but strong support for 3. This means that VSR can manifest as functional diversity, facilitating parasite transmission. It remains to be seen if this operates more widely in vector borne diseases.