Abstract
Botanical insecticides are preferred for their environment and user-friendly nature. Eugenol is a plant-based monoterpene having multifarious biocidal activities. To understand whether eugenol would persistently work against Aedes aegypti, we performed larvicidal bioassays on thirty successive generations and determined median lethal concentration (LC50) on each generation. Results showed no apparent differences between LC50 at F0 (63.48 ppm) and F30 (64.50 ppm) indicating no alteration of susceptibility toward eugenol. To analyze, if eugenol has any effect on metabolic detoxification-associated enzymes, we measured esterases (alpha and beta), cytochrome P450, and GST activities from the survived larvae exposed to LC50 concentration from F0–F30. Results revealed a decrease of esterases, GST, and cytochrome P450 activities at the initial 4–8 generations and then a gradual increase as the generations progressed. GST activity remained significantly below the control groups. Synergists (TPP, DEM, and PBO) were applied along with eugenol at F30 and LC50 concentration, and the said enzyme activities were recorded. Results showed a noticeable decrease in LC50 and enzyme activities indicating effective inhibitions of the respective enzymes. Overall, present results inferred that eugenol would effectively work as a larvicide for a longer period in successive generations without initiating rapid resistance and therefore could be advocated for controlling A. aegypti.
Highlights
Botanical insecticides are preferred for their environment and user-friendly nature
There were fluctuations between generations, over 30 generations of exposure, the mosquitos showed no obvious changes in susceptibility to eugenol in terms of median lethal concentration
In cytochrome p450, the pattern of an initial decrease and subsequent increase in enzyme activity was observed in the studied generation
Summary
Botanical insecticides are preferred for their environment and user-friendly nature. Eugenol is a plant-based monoterpene having multifarious biocidal activities. Present results inferred that eugenol would effectively work as a larvicide for a longer period in successive generations without initiating rapid resistance and could be advocated for controlling A. aegypti. As an alternative, plant secondary metabolites (essential oils, extracts, and their phytochemical components) are increasingly being claimed to be effective as promising insecticides[6] Among these metabolites, terpene compounds are extensively studied owing to their broad-spectrum applications[7]. All terpene compounds have a common precursor- isopentyl pyrophosphate These compounds can be categorized into several groups based on the number of carbon atoms present; hemiterpene (5C), monoterpene (C10), sesquiterpene (C15), diterpene (C20), sesterpene (C25), triterpene (C30), tetraterpene (C40) and polyterpenes ( C40 and above carbon units)[8]. We selected eugenol, a monoterpene, the main constituent of basil and clove essential oil It has been proven effective in controlling a wide range of pests, including m osquitoes[15–17]. To evaluate the persistent toxicity of eugenol, the study was performed to determine LC50 concentration in each generation, from F0 to F30, and to spectrophotometrically estimate the said enzymes, using suitable substrates, to examine the effect of eugenol on these detoxifying enzymes
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