Viruses affecting transmission capability of mosquitoes
There have been some studies looking at this, but not many. One is this study which reported an interaction between Aedes densovirus (AeDNV) and dengue virus (DENV) in Aedes albopictus: mosquitoes already infected with AeDNV were more resistant to infection with DENV, although DENV infection appeared to accelerate the replication of the existing AeDNV infection. A similar interaction was not seen with chikungunya virus (CHIKV).

In addition there are indirect interactions between pathogens of all kinds - viruses such as AeDNV which kill a high proportion of the mosquitoes they infect reduce the average survival and population density of the vector and therefore the ability of the local population to transmit disease (ref).