Synergistic terpene combinations as larvicides against the dengue vector Aedes aegypti Linn.

Abstract

Most of the essential oils (EO) known for mosquitocidal activity contain terpenes as part of their chemical constituents. In this study, four monoterpenes namely γ‐terpinene (T), R‐(+)‐limonene (L), carvacrol (C), and trans‐anethole (A) were screened against late third instar Aedes aegypti Linn. larvae singly and in combination to find out the synergistic interaction. The monoterpenes γ‐terpinene, R‐(+)‐limonene, trans‐anethole, and carvacrol showed larvicidal activity with LC50 values of 9.76, 11.88, 50.19, 48.57 ppm and LC90 values of 16.99, 17.78, 65.21, 75.02 ppm, respectively for Ae. aegypti when tested individually. Prepared binary combinations at LC20 values and studied the synergistic interactions based on cotoxicity factor (CTF) and found that all the binary combinations showed synergistic interactions (CTF > 20). Further, the binary (1:1), ternary (1:1:1), and quaternary (1:1:1:1) terpene combinations on equal weight basis were prepared, evaluated against Ae. aegypti larvae and synergistic interactions were studied by Wadley's method. Among the eight combinations two combinations viz. LC (LC5010.42 ppm) and LA (LC5011.86 ppm) were showing synergistic interactions (R > 1.5) and others were exhibiting additive effect (1.5 ≥ R > 0.5) and none of the combinations showed antagonism (R < 0.5). Among the two methods used the Wadley's method found suitable when combinations were made on an equal weight basis. The two binary combinations found in this study are promising synergistic mixtures which has scope in designing mosquito larvicidal EOs by enriching the EOs with terpenes or by producing EO combinations with these terpenes as chemical constituents in the correct proportions.

Combinations of plant essential oils and their major compositions inducing mortality and morphological abnormality of Aedes aegypti and Aedes albopictus

“…The same synergistic effect against Ae . aegypti was reported in a paper by Dhinakaran et al. (2019) .…”

“…Therefore, this study was not designed to test d-limonene and trans-anethole at concentrations higher than 5% because they had already been shown to provide a full 100% mortality rate against Ae . aegypti at 3% ( Dhinakaran et al., 2019 ). Both d-limonene and trans-anethole have been reported to provide high efficacy against several insect pests.…”

The Mosquito Larvicidal Activity of Essential Oils from Cymbopogon and Eucalyptus Species in Vietnam

“…Regarding the mode of action, several mechanisms through which essential oils produce neurotoxic effects have been proposed, such as EOs acting on GABA receptors, octopamine receptors, or acetylcholinesterase [30]. Further, the synergistic effect of the essential oil constituents likely increases their larvicidal activity [31][32][33]. Scalerandi et al proposed an interesting mode for synergistic effects using the metabolic model [34].…”

Plant-Based Bioinsecticides for Mosquito Control: Impact on Insecticide Resistance and Disease Transmission

“…The synergistic effect is also observed with mixture of oils. The synergistic action of the major compounds in essential oils results in higher repellent and larvicidal activity and toxicity to insects [140,[143][144][145]. A combination of blends assayed on An.…”