ABSTRACT

Olfaction in insects is mediated by elaborate olfactory appendages, antennae, and maxillary palps that carry a variety of structures, called sensilla. These sensilla house olfactory receptor neurons (ORNs) in which olfactory receptor (OR) proteins are embedded. A plethora of chemicals originating from skin, breath, plant/nectar, and oviposition sites are detected by these ORNs.1 Host detection in mosquitoes starts with interactions between odorants and distinct subpopulations of ORs present in the dendritic membrane of ORNs. There are two exciting aspects that make blood-feeding arthropods unique candidates to study olfaction. First, the numerically simple olfactory system (Figure 3.1) at the periphery comprises a handful of ORNs (ca. a hundred or so in bedbugs, ticks, and triatomines, to a few thousand in mosquitoes) housed in simple epicuticular structures termed sensilla. A majority of them are present on antennae and palps, and relatively lower numbers are present on other body parts. Second, distinct and limited range of volatiles that seem to be parsimoniously used in various contexts for releasing distinct behaviors such as attraction and repulsion exists.6 A recent addition to these advantages includes the availability of genomes of various hematophagous arthropods such as certain species of ticks, triatomines, sand ies, and mosquitoes (www.vectorbase.org). A highly divergent family of seven transmembrane proteins that are functionally and genetically distinct from those discovered in other taxa confers

CONTENTS

Introduction ...................................................................................................................................... 43 Peripheral Detection of Repellents ..................................................................................................44 Techniques Used for Identifying Novel Natural Ligands ................................................................46