Sextonia rubra (Mez.) van der Werff sawmills residues as a valuable resource for the production of larvicidal extracts against Ae. aegypti Linnaeus (Diptera: Culicidae)

In the development of botanical insecticides, the availability of a certifiable raw material and the guarantee of a stable biological efficacy over time are crucial factors. Sextonia rubra is one of the main tree species exploited by the Guianese forestry industry, and the valorization of the large volumes of sawmills residues available would represent an opportunity for the sustainable development of bioactive products in a biorefinery perspective. In this work, we studied the variability of the quality of S. rubra sawdust according to its origin and investigated the bioactivity of its extracts against Ae. aegypti mosquitoes. We evidenced homogeneous physico-chemical properties (particle size and NIRS profiles) of S. rubra sawdusts independently of the sawmill of origin, thus highlighting the consistency of the raw material before extraction. The amount of the gamma-lactones rubrenolide and rubrynolide was measured in 12 extracts of S. rubra by quantitative NMR (qNMR). GLM regression indicated significant correlation between these values and larval mortality (adj-R-2 0.93) for the extracts tested at 30 mu g/ml. Additionally, a 48-h DL50 of 18.6 mu g/ml was obtained for a S. rubra reference extract. While sawdust underwent chemical changes during the 10 months of storage, as shown by NIRS and qNMR analyses, we observed no significant impact on larval mortality for the extracts tested at 30 mu g/ml. A stability of 9-months was also observed for a crude extract stored at room temperature. Sawmill residues of S. rubra thus appear to be suitable raw material for the production of significant quantities of wood extracts containing larvicidal compounds against Ae. aegypti. Their stability over time also makes it possible to consider production routes that could be transferred to an industrial scale.