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Mosquito-borne diseases such as malaria, Zika virus, and dengue virus are a menace to the human population. Although many mosquito species are not attracted to humans and do not feed on blood, human-biting female mosquitoes are strongly attracted to people and use chemosensory cues to identify a suitable host for a blood meal. Mosquitoes need blood components to reproduce, rendering them excellent vectors for blood-borne diseases. The three genera (Culex,Anopheles, andAedes) responsible for most of these diseases find hosts by using their peripheral sensory organs. These organs include the antennae, maxillary palps, and proboscis. All three contain diverse populations of highly sensitive neurons that express sensory receptors that can detect odorants, temperature, chemicals, and tastants. Although these organs are essential to the host-seeking behavior that results in biting, their small size and thick outer cuticle can hinder typical histochemical analyses. Here, we briefly review the role the peripheral sensory organs play in mosquito behavior. Then, we introduce how to investigate their gene expression profiles using immunohistochemical and RNA in situ approaches for both whole-mount and frozen-section preparations.

Immunohistochemistry analysis of mosquitoes is complicated by the outer cuticle that prevents reagents from penetrating peripheral tissues. This protocol incorporates a cryosectioning method that provides a higher resolution of the internal architecture of mosquito peripheral sensory tissues and enables the visualization of protein expression. This eliminates the need for enzymatic steps to digest the outer cuticle that encases these tissues. This protocol can also be adapted for other tissues, such as the brain and the legs, as chitin exoskeleton thickness does not affect antibody penetration once the sample is sectioned.