Stage-specific manipulation of a mosquito's host-seeking behavior by the malaria parasite Plasmodium gallinaceum

We present experimental evidence that different stages of the malaria parasite Plasmodium gallinaceum differentially affect the host-seeking behavior of its mosquito vector Aedes aegypti. In uninfected mosquitoes, host-seeking behavior is continued if mosquitoes have ingested less than a threshold volume of blood, whereas a larger blood meal inhibits host seeking. We investigated the parasite's effect on this behavior by feeding infected and uninfected mosquitoes for variable amounts of time and assaying 30-45 min later whether they continued their attempts at blood-feeding. Mosquitoes infected with oocysts (which cannot be transmitted) had a smaller threshold volume and were less likely to return for further probing, whereas individuals infected with transmissible sporozoites increased the threshold volume required to inhibit host-seeking behavior. We conclude that the stage-specific effect of the parasite on host-seeking behavior is likely to be an active manipulation by the parasite to increase its transmission success.