Computational insights of the molecular recognition between volatile molecules and odorant binding proteins from the red palm weevil Rhynchophorus ferrugineus

The red palm weevil Rhynchophorus ferrugineus (Coleoptera: Curculionidae) is one of the most harmful pests for palm trees, causing serious economic damage worldwide. The present work aims to model and study the 3D structures of highly expressed odorant binding proteins from R. ferrugineus (RferOBPs) and identify possible binding modes and ligand release mechanism by docking and molecular dynamics. Highly confident 3D structures of a total of 11 odorant binding proteins (OBPs) were obtained with AlphaFold2. All 3D RferOBPs modeled structures displayed six characteristic α-helices, except for RfeOBP7 and RfeOBP10, which had an extra terminal α-helix. Among the eleven modeled RferOBPs, RferOBP4 was highly expressed in the antennae and subsequently selected for further analyses. Molecular docking analyses demonstrated that ferruginol, α-pinene, DEET, and picaridin can favorably bind the RferOBP4 cavity with low affinity energies. Molecular dynamic simulations of RferOBP4 bound to ferruginol at different pH values showed that low pH environments dictate a structural change into an apo-state that modifies the number of tunnels where the ligand can coexist, further triggering ligand release by a pH-dependent mechanism. This is the first report concerning the modelling and study of ligand binding modes and release mechanism of R. ferrugineus OBPs.Communicated by Ramaswamy H. Sarma.

Insect repellents: An updated review for the clinician

Malaria, Zika virus, West Nile virus, Dengue fever, and Lyme disease are common causes of morbidity and mortality around the world. While arthropod bites may cause local inflammation and discomfort, a greater concern is the potential to develop deadly systemic infection. The use of insect repellents (IRs) to prevent systemic infections constitutes a fundamental public health effort. Cost effectiveness, availability, and high efficacy against arthropod vectors are key characteristics of an ideal IR. Currently, numerous IRs are available on the market, with N,N-diethyl-3-methylbenzamide (DEET) being the most widely used. DEET has an excellent safety profile and remarkable protection against mosquitoes and various other arthropods. Other Environmental Protection Agency-registered IR ingredients (eg, permethrin, picaridin, IR3535, oil of lemon eucalyptus, oil of citronella, catnip oil, and 2-undecanone) are alternative IRs of great interest because some of these ingredients have efficacies comparable to that of DEET. These alternative IRs possess low toxicity and favorable customer experiences in use (eg, cosmetically pleasant, naturally occurring). This review summarizes the currently available Environmental Protection Agency-registered IRs, including their origins, mechanisms of action, side effect profiles, and available formulations. This review will enable the clinician to select the best IR option to meet a patient's needs and provide the greatest protection from arthropod bites and their sequelae.

Evaluation of a Novel User-Friendly Arthropod Repellent Gel, Verdegen

Hand sanitizers are developed as alcohol-based liquid gel formulations, generally used to decrease the amount of infectious agents on human hands. Verdegen, LLC proposed to prepare an arthropod repellent gel for public use when the recent outbreaks of Zika infection vectored through Aedes mosquitoes in the American continents prompted multi-faceted emergency measures. Four different gel formulations were developed, comprising two of the most efficacious commercial arthropod repellent active ingredients, N,N-diethyl-3-methyl benzamide (deet) and 2-(2-hydroxyethyl)-1-piperidinecarboxylic acid 1-methylpropyl ester (picaridin), each at different concentrations (20 and 33% deet, or 20 and 33% picaridin). Compliance with the use of topical arthropod repellents remains an issue among military personnel. One of the most common complaints by Soldiers is that they do not like how the repellents applied on their skin leave behind an oily or greasy residue. These new gel formulations offer a user-friendly alternative for commonly used arthropod repellents formulations for the military and civilian personnel. We tested the efficacy and protection time of these new gel formulations in comparison with the commercially available cream formulations of deet and picaridin at similar concentrations. Our data show that gel formulations have better topical attributes, and offer equal or better biting protection for up to 48 h against host-seeking Aedes aegypti (L.) (Diptera: Culicidae) female mosquitoes.

Insecticidal and Behavioral Avoidance Responses of Anopheles minimus and Culex quinquefasciatus (Diptera: Culicidae) to Three Synthetic Repellents

Escape responses, knockdown (KD), and toxicity of laboratory strains of Anopheles minimus Theobald and Culex quinquefasciatus Say to three synthetic mosquito repellents, DEET (N, N-diethyl-3-methylbenzamide), IR3535, or picaridin, at 5% v/v concentrations, were evaluated using repellent-treated papers in standard WHO tube assays and an excito-repellency (ER) test chamber system. The tube assays recorded knockdown effects of each repellent immediately after 30-min exposure and the final morality following a 24-h holding period. DEET showed 100% KD at 30 min and complete toxicity at 24 h against both species. Both actions were either minimal or absent for IR3535 and picaridin, respectively. Culex quinquefasciatus showed significantly greater escape with DEET compared with the other compounds in both contact irritancy (excitation) and noncontact spatial repellency trials. Anopheles minimus showed much more pronounced irritancy and repellency flight escape to IR3535 than picaridin. DEET was the most active irritant and repellent compound against Cx. quinquefasciatus. When adjusting contact test responses based on paired noncontact repellency assays, DEET and IR3535 showed much stronger spatial repellent properties than irritancy with An. minimus. Picaridin performed poorly as an irritant or repellent against both species. We conclude that DEET, followed by IR3535, act as strong spatial repellents at 5% concentration. DEET also performs as a strong toxicant. Our findings show that different mosquitoes can respond contrastingly to repellents, thus the importance to test a wider range of species and populations to assess the full range of chemical action.

Mosquito odorant receptor for DEET and methyl jasmonate

Insect repellents are important prophylactic tools for travelers and populations living in endemic areas of malaria, dengue, encephalitis, and other vector-borne diseases. DEET (N,N-diethyl-3-methylbenzamide) is a 6-decade-old synthetic repellent, which is still considered the gold standard of mosquito repellents. Mosquitoes use their sense of smell to detect DEET, but there are currently two hypotheses regarding its mode of action: activation of ionotropic receptor IR40a vs. odorant receptor(s). Here, we demonstrate that DEET, picaridin, insect repellent 3535, and p-menthan-3,8-diol activate the odorant receptor CquiOR136 of the southern house mosquito, Culex quinquefasciatus. Electrophysiological and behavioral assays showed that CquiIR40a knockdown had no significant effect on DEET detection and repellency. By contrast, reduction of CquiOR136 transcript levels led to a significant decrease in electroantennographic responses to DEET and a complete lack of repellency. Thus, direct activation of an odorant receptor, not an ionotropic receptor, is necessary for DEET reception and repellency in Culex mosquitoes. Interestingly, methyl jasmonate, a repellent derived from the nonvolatile jasmonic acid in the signaling pathway of plant defenses, elicited robust responses in CquiOR136•CquiOrco-expressing Xenopus oocytes, thus suggesting a possible link between natural products with long insect-plant evolutionary history and synthetic repellents.