Advances in mosquito repellents: effectiveness of citronellal derivatives in laboratory and field trials

Abstract

BACKGROUND: Several essential oils, including citronella (lemongrass, Cymbopogon sp., Poaceae), are well-known mosquito repellents. A drawback of such products is their limited protection time resulting from the high volatility of their active components. In particular, citronella oil protects for <2 h, although formulations with fixatives can increase this time.RESULTS: We synthesized hydroxylated cyclic acetals of citronellal, the main component of citronella, to obtain derivatives with lower volatility and weaker odour. The crude mixture of isomers obtained in the reaction was tested under laboratory conditions for its repellency against two mosquito species, the major malaria vector Anopheles gambiae and the arbovirus vector Aedes albopictus, and found to be endowed with longer protection time with respect to DEET (N,N-diethyl-meta-toluamide) at the same concentration. Formulated products were tested in a latin square human field trial, in an area at a high density of A. albopictus for 8 h from the application. We found that the performance of the citronellal derivatives mixture is comparable (95% protection for ≤3.5 h) with those of the most widespread synthetic repellents DEET and Icaridin, tested at a four-fold higher doses.CONCLUSIONS: Modifying the hydrophilicity and volatility of natural repellents is a valuable strategy to design insect repellents with a long-lasting effect.

Cyclic Acetals as Novel Long-Lasting Mosquito Repellents

“…The repellence of DEET, Icaridin (both supplied by Istituto Biochimico VEBI s.r.l. ), acetals, and the synthesized hydroxyacetals was evaluated againstAedes albopictususing the human-bait technique (to simulate the condition of human skin on which repellents will be applied) A.…”

“…The average time until protection which was higher than 95% protection time was considered for each compound. Moreover, for the compounds tested on at least three volunteers, the complete (100%) protection time was also estimated (SPSS 28.01.0) using the Kaplan–Meier survivor function procedure …”

“…), acetals, and the synthesized hydroxyacetals was evaluated againstAedes albopictususing the humanbait technique (to simulate the condition of human skin on which repellents will be applied). 22 A. albopictuswas reared and tested at 26 ± 2 °C, ≥60 ± 10% relative humidity (RH), and at 14:10 h light/dark photoperiod, within Plexiglas cylindrical laboratory cages (35 cm diameter, 60 cm length) with one end closed by a net. During the tests, cages contained ≈150 nulliparous, 4−7 day-old, nonblood-fed females.…”

“…Moreover, for the compounds tested on at least three volunteers, the complete (100%) protection time was also estimated (SPSS 28.01.0) using the Kaplan− Meier survivor function procedure. 22 2.6. Toxicity Profile of the New Derivatives.…”

“…In two previous papers, , we took a different approach to design mosquito repellents and modified the structure of two natural terpenoid repellents. Since most naturally occurring terpenoids endowed with an insect repellent activity show a short protection time against hematophagous insects, mainly because of their volatility, we hypothesized that derivatives of two well-known terpenoid repellents, menthone and citronellal, with lower volatility would have a longer protection time.…”