We demonstrate that B. bassiana can significantly shorten the life span of A. aegypti mosquitoes at infection with as low as 103 conidia/ml. Furthermore, we have for the first time we have shown that fungal treatment can significantly suppress the dengue virus in the mosquitoes' midgut, at least partly through the immune activation of the Toll and JAK-STAT pathway-controlled effector genes. We also show for the first time that the JAK-STAT pathway plays a role in the Aedes mosquito's anti-fungal defense. The fact that both these events can influence the dynamics of dengue transmission renders B. bassiana a potentially promising agent for the development of dengue control strategies. B. bassiana has previously been used for the bio-control of agricultural pests, is commercially available, and is harmless to humans (reviewed in Kanzok and Jacobs-Lorena, 2006). A field study carried out in Tanzania suggests that application of M. anisopliae-impregnated black cotton sheets to mosquito's resting places could lead to a reduction of 75% in malaria transmission (Scholte et al., 2005). Considering that A. aegypti, like A. gambiae, is highly anthropophilic and endophilic (Harrington et al., 2001), the use of entomopathogenic fungus to infect field populations of A. aegypti appears to be a promising approach for reducing dengue transmission and therefore deserves further investigation.