Field assessment of 4-hydroxycoumarin as an attractant for anthropophilic Anopheles spp. vectors of malaria in Madagascar

A review of Musca sorbens (Diptera: Muscidae) and Musca domestica behavior and responses to chemical and visual cues

Musca flies (Diptera: Muscidae) have been found culpable in the mechanical transmission of several infectious agents, including viruses, bacteria, protozoans, and helminths, particularly in low-income settings in tropical regions. In large numbers, these flies can negatively impact the health of communities and their livestock through the transmission of pathogens. In some parts of the world, Musca sorbens is of particular importance because it has been linked with the transmission of trachoma, a leading cause of preventable and irreversible blindness or visual impairment caused by Chlamydia trachomatis, but the contribution these flies make to trachoma transmission has not been quantified and even less is known for other pathogens. Current tools for control and monitoring of house flies remain fairly rudimentary and have focused on the use of environmental management, insecticides, traps, and sticky papers. Given that the behaviors of flies are triggered by chemical cues from their environment, monitoring approaches may be improved by focusing on those activities that are associated with nuisance behaviors or with potential pathogen transmission, and there are opportunities to improve fly control by exploiting behaviors toward semiochemicals that act as attractants or repellents. We review current knowledge on the odor and visual cues that affect the behavior of M. sorbens and Musca domestica, with the aim of better understanding how these can be exploited to support disease monitoring and guide the development of more effective control strategies.

Chirality Effects on Repellent Properties of 4-Alkoxycoumarins Against Asian Tiger Mosquito (Diptera: Culicidae)

The use of semiochemicals as repellents and attractants has been proposed to complement insecticides used for the control of vector mosquito populations. In several studies, the optical purities of the molecules tested have been described as having little or no effect on repellent activity. However, these observations seem difficult to explain because of the chirality effect of molecules on the olfactory system of insects and humans. Thus, the purpose of this study is to assess the effects of chirality on the repellent properties of 4-alcoxycoumarins against Aedes albopictus Skuse, mosquito vector of arboviruses. We report here that the racemic (R/S)-4-sec-butoxycoumarin had the highest repellent effect (Repellent Index = 49.9%) followed by (R) enantiomer (Repellent Index = 24.2%) for the dose of 5 mg/mL. Contrary, no significant repellent activity was recorded for S-(+)-4-sec-butoxycoumarin. This experiment demonstrates the close relationship between the molecules' optical purities and the behavioral response of mosquitoes.

Development of Sustainable Chemistry in Madagascar: Example of the Valuation of CNSL and the Use of Chromones as an Attractant for Mosquitoes

This article describes a part of the results obtained from the cooperation between the University of Lyon1 (France) and the University of Antananarivo (Madagascar). It shows (among others) that useful research can be carried out in developing countries of the tropics if their social, technical, and economic conditions are taken into account. The concepts and methods associated with so-called “green chemistry” are particularly appropriated for this purpose. To illustrate this approach, two examples are shown. The first deals with industrial ecology and concerns waste transformation from the production of cashew nut into an amphiphilic product, oxyacetic derivatives. This product was obtained with a high yield and in a single step reaction. It exhibited an important surfactant property similar to those of the main fossil-based ones but with a much lower ecological impact. The second talks about chemical ecology as an alternative to insecticides and used to control dangerous mosquito populations. New substituted chromones were synthesized and showed biological activities toward Aedes albopictus mosquito species. Strong repellent properties were recorded for some alkoxylated products if others had a significant attractant effect (Kairomone) depending on their stereochemistry and the length of the alkyl chain.

Effect of the Stereoselectivity of para-Menthane-3,8-diol Isomers on Repulsion toward Aedes albopictus

Vector-borne diseases cause around 700,000 deaths every year. Insect repellents are one of the strategies to limit them. Para-menthane-3,8-diol (PMD), a natural compound, is one of the most promising alternatives to conventional synthetic repellents. This work describes a diastereodivergent method to synthesize each diastereoisomer of PMD from enantiopure citronellal and studies their repellence activity against Aedes albopictus. We found that cis-PMD is the kinetic control product of the cyclization of citronellal, while trans-PMD is the thermodynamic control product. X-ray diffraction analysis of crystals highlighted some differences in hydrogen-bond patterns between cis or trans isomers. The present paper demonstrates that (1R)-(+)-cis-PMD has the highest repellency index using a new evaluation system for 24 h. (1S)-(-)-cis-PMD has somewhat lower and (1S)-(+)-trans-PMD and (1R)-(-)-trans-PMD have a slight effect. Volunteer tests show that (1R)-(+)-cis-PMD is the most efficient. This effect could be ascribed to the interaction of PMD/insect odorant receptors and their physical properties, that is, the evaporation rate.

Mosquito Attractants

Vector control and personal protection against anthropophilic mosquitoes mainly rely on the use of insecticides and repellents. The search for mosquito-attractive semiochemicals has been the subject of intense studies for decades, and new compounds or odor blends are regularly proposed as lures for odor-baited traps. We present a comprehensive and up-to-date review of all the studies that have evaluated the attractiveness of volatiles to mosquitoes, including individual chemical compounds, synthetic blends of compounds, or natural host or plant odors. A total of 388 studies were analysed, and our survey highlights the existence of 105 attractants (77 volatile compounds, 17 organism odors, and 11 synthetic blends) that have been proved effective in attracting one or several mosquito species. The exhaustive list of these attractants is presented in various tables, while the most common mosquito attractants - for which effective attractiveness has been demonstrated in numerous studies - are discussed throughout the text. The increasing knowledge on compounds attractive to mosquitoes may now serve as the basis for complementary vector control strategies, such as those involving lure-and-kill traps, or the development of mass trapping. This review also points out the necessity of further improving the search for new volatile attractants, such as new compound blends in specific ratios, considering that mosquito attraction to odors may vary over the life of the mosquito or among species. Finally, the use of mosquito attractants will undoubtedly have an increasingly important role to play in future integrated vector management programs.