Reverse and Conventional Chemical Ecology Approaches for the Development of Oviposition Attractants for Culex Mosquitoes

Abstract

Synthetic mosquito oviposition attractants are sorely needed for surveillance and control programs for Culex species, which are major vectors of pathogens causing various human diseases, including filariasis, encephalitis, and West Nile encephalomyelitis. We employed novel and conventional chemical ecology approaches to identify potential attractants, which were demonstrated in field tests to be effective for monitoring populations of Cx. p. quinquefasciatus in human dwellings. Immunohistochemistry studies showed that an odorant-binding protein from this species, CquiOBP1, is expressed in trichoid sensilla on the antennae, including short, sharp-tipped trichoid sensilla type, which house an olfactory receptor neuron sensitive to a previously identified mosquito oviposition pheromone (MOP), 6-acetoxy-5-hexadecanolide. CquiOBP1 exists in monomeric and dimeric forms. Monomeric CquiOBP1 bound MOP in a pH-dependent manner, with a change in secondary structure apparently related to the loss of binding at low pH. The pheromone antipode showed higher affinity than the natural stereoisomer. By using both CquiOBP1 as a molecular target in binding assays and gas chromatography-electroantennographic detection (GC-EAD), we identified nonanal, trimethylamine (TMA), and skatole as test compounds. Extensive field evaluations in Recife, Brazil, a region with high populations of Cx. p. quinquefasciatus, showed that a combination of TMA (0.9 µg/l) and nonanal (0.15 ng/µl) is equivalent in attraction to the currently used infusion-based lure, and superior in that the offensive smell of infusions was eliminated in the newly developed synthetic mixture.

Acute olfactory response of Culex mosquitoes to a human- and bird-derived attractant

“…In addition to these sensilla responding to plant and human compounds, we recorded also from two functionally distinct classes of A1 sensilla. One houses ORNs sensitive to the insect repellent DEET, whereas the other type responded to a mosquito oviposition pheromone (MOP) (10,18).…”

“…Several OBPs have been isolated and cloned from Culex spp. (7)(8)(9), and CquiOBP1 has been mapped to a specific sensilla type on antenna, and functional studies showed binding of this OBP to semiochemicals involved in the chemical ecology of this mosquito species (10).…”

Crystal and solution structures of an odorant-binding protein from the southern house mosquito complexed with an oviposition pheromone

“…Effective management of Culex mosquito populations may be achieved with oviposition attractants and other kairomones (3,4), because larval development is a particularly vulnerable point in their life cycle. These semiochemicals are detected by the antennae of female adults with sensilla housing odorant receptors (ORs) (5,6) and odorant-binding proteins (OBPs) (7)(8)(9), and these molecular targets can be used in reverse chemical ecology approaches (10) for the development of green chemistry-based strategies for insect vector management (8). Previously, we have isolated an OBP from the antennae of C. quinquefasciatus, CquiOBP1, which is highly expressed in trichoid sensilla involved in the detection of a mosquito oviposition pheromone (8), (5R,6S)-6-acetoxy-5-hexadecanolide (11) (hereafter referred to as MOP).…”

“…Previously, we have isolated an OBP from the antennae of C. quinquefasciatus, CquiOBP1, which is highly expressed in trichoid sensilla involved in the detection of a mosquito oviposition pheromone (8), (5R,6S)-6-acetoxy-5-hexadecanolide (11) (hereafter referred to as MOP). CquiOBP1 bound MOP with high affinity at high pH but showed no affinity at low pH (8). OBPs essential role for odorant reception in C. quinquefasciatus has been demonstrated by RNA interference experiments in which reduction of CquiOBP1 expression led to lower sensitivity for the detection of oviposition attractants, including MOP (12).…”

“…OBPs essential role for odorant reception in C. quinquefasciatus has been demonstrated by RNA interference experiments in which reduction of CquiOBP1 expression led to lower sensitivity for the detection of oviposition attractants, including MOP (12). Using CquiOBP1 as a molecular target in a reverse chemical ecology approach (10), we identified C. quinquefasciatus oviposition attractants (8), which are now commercially available for monitoring and surveillance.…”