Faierstein, G. | Search bioRxiv

bioRxiv2019

A popular Indian clove-based mosquito repellent is a false economy

Insect repellents are important prophylactic tools for travelers to and populations living in endemic areas of malaria, dengue, encephalitis, and other vector-borne diseases, and the first line of defense against emerging arboviruses. However, the cost of daily applications of even the most affordable and the gold standard of insect repellents, DEET, is still high for low-income populations where repellents are needed the most. An Indian clove-based homemade recipe has been presented as a panacea. We analyzed this homemade repellent and confirmed by behavioral measurements and odorant receptor responses that eugenol is the active ingredient in this formulation. Prepared as advertised, this homemade repellent is ineffective, whereas 5X more concentrated extracts from the brand most enriched in eugenol showed moderate repellency activity against Culex quinquefasciatus and Aedes aegypti. DEET showed higher performance when compared to the 5X concentrated formulation and is available in the same market at a lower price than the cost of the ingredients to prepare the homemade formulation.

ecology↗

bioRxiv2019

Conspecific larval extracts along with biotoxin to attract-and-kill mosquitoes

One of the strategies of integrated vector management is to lure gravid mosquitoes for surveillance purposes or to entice them to lay eggs in water containing toxins that kill the offspring (attract-and-kill or trap-and-kill). Typically, the major challenge of this approach is the development of a lure that stimulates oviposition plus a toxin with no deterrent effect. Bacillus thuringiensis var. israelensis (Bti) satisfies the latter criterion, but lures for these autocidal gravid traps are sorely needed. We observed that gravid Aedes aegypti, Ae. albopictus, and Culex quinquefasciatus laid significantly more eggs in cups with extracts from 4th-stage larvae (4L) of the same or different species. No activity was found when 4L were extracted with hexane, diethyl ether, methanol, or butanol, but activity was observed with dimethyl sulfoxide extracts. Larval extracts contained both oviposition stimulant(s)/attractant(s) and deterrent(s), which partitioned in the water and hexane phases, respectively. Lyophilized larval extracts were active after a month, but activity was reduced by keeping the sample at 4{degrees}C. In the tested range of 0.1 to 1 larvae-equivalent per milliliter, oviposition activity increased in a dose-dependent manner. In field experiments, Ae. aegpti laid significantly more eggs in traps loaded with larval extracts plus Bti than in control traps with water plus Bti.

ecology↗