Reverse chemical ecology approach for the identification of an oviposition attractant for Culex quinquefasciatus

Abstract

Pheromones and other semiochemicals play a crucial role in today's integrated pest and vector management strategies. These semiochemicals are typically discovered by bioassay-guided approaches. Here, we applied a reverse chemical ecology approach; that is, we used olfactory proteins to lead us to putative semiochemicals. Specifically, we used 7 of the top 10 odorant receptors (ORs) most expressed in the antennae of the southern house mosquito, Culex quinquefasciatus, and which are yet to be deorphanized. We expressed these receptors in the Xenopus oocyte recording system and challenged them with a panel of 230 odorants, including physiologically and behaviorally active compounds. Six of the ORs were silent either because they are not functional or a key odorant was missing. CquiOR36, which showed the highest transcript levels of all OR genes in female antennae, was also silent to all odorants in the tested panel, but yielded robust responses when it was accidentally challenged with an old sample of nonanal in ethanol. After confirming that fresh samples were inactive and through a careful investigation of all possible "contaminants" in the old nonanal samples, we identified the active ligand as acetaldehyde. That acetaldehyde is activating CquiOR36 was further confirmed by electroantennogram recordings from antennae of fruit flies engineered to carry CquiOR36. Antennae of female mosquitoes also responded to acetaldehyde. Cage oviposition and dual-choice assays demonstrated that acetaldehyde is an oviposition attractant in a wide range of concentrations and thus of potential practical applications.southern house mosquito | CquiOR36 | acetaldehyde | odorant receptors | EAG

Deorphanization of an odorant receptor revealed new bioactive components for green mirid bug Apolygus lucorum (Hemiptera: Miridae)

“…Reverse chemical ecology approach, a new concept in the field of insect chemical ecology and similar to ‘receptor‐based drug discovery’, was firstly proposed by Professor Walter S. Leal in 2005 and recently is gaining more attention for the management of agricultural and medical pests . This method has been developed based on understanding the molecular basis of the insect's olfactory system and binding ability of two major types of olfactory proteins‐OBPs and ORs‐ to behaviorally active compounds . In comparison with conventional chemical ecology, reverse chemical ecology strategy is a quick and cost‐effective approach for screening of potential semiochemicals with putative behavioral effects which could be used as attractants or repellents.…”

“…Therefore, it seems necessary to look for environmentally‐friendly and alternative approaches for managing this destructive pest. Since the identification of the first sex pheromone in silkworm, almost six decades ago, chemical ecologists have been focusing on exploring of the semiochemicals and their application in integrated pest management (IPM) …”

“…Insect ORs are highly divergent seven‐transmembrane ligand‐specific proteins which have been described as heteromeric ligand‐gated ion channels and work as complexes together with a highly conserved OR called OR co‐receptor (Orco) . Since the first report of ORs in Drosophila , several methods have been developed for functional studies of ORs, of which heterologous expression in Xenopus oocyte and two‐electrode voltage‐clamp system (TEVC) have been adopted for several years . Recently, based on transcriptome and genome sequencing, a large number of insect OR repertoires have been identified .…”

“…Since the identification of the first sex pheromone in silkworm, almost six decades ago, chemical ecologists have been focusing on exploring of the semiochemicals and their application in integrated pest management (IPM). 8 Generally, insects sense semiochemicals through their olfactory systems and the olfaction relies on interactions between semiochemicals and various olfactory receptors. [9][10][11] Vital behaviors such as foraging, predation and pathogen avoidance, mate recognition, and oviposition site selection are primarily dependent on the detection of blends of airborne molecules from the environment.…”

“…13,16 Since the first report of ORs in Drosophila, several methods have been developed for functional studies of ORs, of which heterologous expression in Xenopus oocyte and two-electrode voltage-clamp system (TEVC) have been adopted for several years. 8,13,14,16,17 Recently, based on transcriptome and genome sequencing, a large number of insect OR repertoires have been identified. [17][18][19] A total of 109 ORs has been annotated in A. lucorum 20 .…”