Modulation of Host Learning in Aedes aegypti Mosquitoes
How mosquitoes determine which individuals to bite has important epidemiological consequences. This choice is not random; most mosquitoes specialize in one or a few vertebrate host species, and some individuals in a host population are preferred over others. Mosquitoes will also blood feed from other hosts when their preferred is no longer abundant, but the mechanisms mediating these shifts between hosts, and preferences for certain individuals within a host species, remain unclear. Here, we show that olfactory learning may contribute to Aedes aegypti mosquito biting preferences and host shifts. Training and testing to scents of humans and other host species showed that mosquitoes can aversively learn the scent of specific humans and single odorants and learn to avoid the scent of rats (but not chickens). Using pharmacological interventions, RNAi, and CRISPR gene editing, we found that modification of the dopamine-1 receptor suppressed their learning abilities. We further show through combined electrophysiological and behavioral recordings from tethered flying mosquitoes that these odors evoke changes in both behavior and antennal lobe (AL) neuronal responses and that dopamine strongly modulates odor-evoked responses in AL neurons. Not only do these results provide direct experimental evidence that olfactory learning in mosquitoes can play an epidemiological role, but collectively, they also provide neuroanatomical and functional demonstration of the role of dopamine in mediating this learning-induced plasticity, for the first time in a disease vector insect.
© 2017 Elsevier Ltd. Published: January 25, 2018. Accepted: December 7, 2017. Received in revised form: November 7, 2017. Received: September 26, 2017. We thank B. Nguyen for mosquito colony maintenance, J. Joiner and K. Moosavi for assistance in olfactometer experiments, J. Stone for help with animal scent collections, and C. Bourgouin and M. Pereira for advice on the RNAi experiments. We thank P. Weir for comments and help with the arena experiments and B. Brunton for statistical advice. We are grateful to D. Dickens for the scanned electron microscope images of Ae. aegypti. We acknowledge the support of the Air Force Office of Sponsored Research under grant FA9550-14-1-0398 and FA9550-16-1-0167 , National Institutes of Health under grant NIH1RO1DCO13693-04 , National Science Foundation under grant IOS-1354159 , UC Riverside, MaxMind, an Endowed Professorship for Excellence in Biology (J.A.R.), the University of Washington Institute for Neuroengineering, and the Human Frontiers in Science Program under grant HFSP-RGP0022 . Author Contributions: C.V., C.L., and J.A.R. conceived the study. C.V. and C.L. participated in the execution and analysis of all aspects of the study. J.A.R. supervised and helped analyze the electrophysiology data presented in Figures 4 and 5. G.H.W. generated and processed the immunohistochemistry data and western blots presented in Figures 5 and S4. L.T.L. and J.E.L. helped carry out and analyze the behavioral assays presented in Figure 1, Figure 2, Figure 3, Figure 4. J.Z.P. helped design the RNAi assays. O.S.A. designed and generated the CRISPR mutant mosquitoes. M.H.D. designed the flight arena experiments presented in Figure 2. C.V., C.L., and J.A.R. wrote the paper, and all authors edited the manuscript. The authors declare no competing financial interests.
Submitted - 172726.full.pdf
Supplemental Material - mmc1.pdf
Accepted Version - nihms-1051413.pdf