Assessment of A Simple Compound-Saving Method To Study Insecticidal Activity of Natural Extracts and Pure Compounds Against Mosquito Larvae

Abstract

Research on natural insecticides has intensified with the spread of resistance to chemicals among insects, particularly disease vectors. To evaluate compounds, the World Health Organization (WHO) has published standardized procedures. However, those may be excessively compound-consuming when it comes to assessing the activity of natural extracts and pure compounds isolated in limited amount. As part of our work on the discovery of new mosquito larvicides from Amazonian plants, we developed a compound-saving assay in 5-ml glass tubes instead of WHO larval 100-ml cups. Comparing activity of synthetic and natural chemicals validated the glass tube assay. Raw data, lethal doses that kill 50% (LD) and 90% (LD) at 24 and 48 h, were highly correlated (0.68 < R < 0.96, P < 0.001, Pearson test) between cups and tubes. It was also established that 10 tubes (N = 50 larvae) provided the same level of sensitivity as 20 tubes (N = 100). This method proved suitable for rapid screening of natural extracts and molecules, identifying active compounds using 10 times less material than in the WHO protocol.

Towards the optimization of botanical insecticides research: Aedes aegypti larvicidal natural products in French Guiana

“…We also highlighted during this project the strong larvicidal activity of these two compounds against Ae. aegypti, with respective LC 50 of 3.84 ± 0.02 and 0.60 ± 0.02 for rubrynolide and rubrenolide at 24 h, and 2.11 ± 0.04 and 0.30 ± 0.02 µg/mL at 48 h, alongside with a measured value of 3.15 ± 0.02 µg/mL for the crude wood extract at 24 h and 2.06 ± 0.02 µg/mL at 48 h (Falkowski et al 2016). Following a patent deposit concerning the bioactivity of the wood extract and its constituents, a further evaluation of the larvicidal activity and its mechanisms will be performed, alongside with the characterization of its ecotoxicity (Falkowski et al N° WO2016046489 A1).…”

“…(Fabaceae), of which leaves were previously described to contain the rotenoid compounds rotenone, tephrosin and deguelin, and to be toxic against Ae. aegypti mosquito larvae, was included in the screening to serve as a botanical positive control in order to validate the test protocol (Falkowski et al 2016;Nirma et al 2009). bbott"s formula was applied to mortalities if mortality in the control was between 5% and 20% (Abbott 1925).…”

The Effect of Secondary Metabolites Produced by Serratia marcescens on Aedes aegypti and Its Microbiota

“…Larvicidal assay in tubes was performed as described previously ( Falkowski et al, 2016 ). The crude extract was solubilized in 100% ethanol, adjusted to pH = 6 and a 1.5-fold dilution series of this extract was prepared.…”

Characterization, Diversity, and Structure-Activity Relationship Study of Lipoamino Acids from Pantoea sp. and Synthetic Analogues

“…Late third or early fourth-instar larvae were used in the tests. All crude extracts and fractions were investigated using the WHO procedure for testing mosquito larvicides [19,20]. The larvicidal activity of pure compounds was evaluated using a tube assay.…”