First report on the termiticidal activity of extracts of Annona squamosa (Annonaceae) seeds and on its active constituent squamocins
T S Djenontin, N Amusant, P H Ducrot, D C K Sohounhloué, D Pioch
Termites inflict severe damage on wood commodities and impede usage of several forest species. The biological metabolites could potentially replace synthetic termiticidal products which are becoming more restricted to use. Annona squamosa is well known for its edible fruits - tropical custard apple. Annonaceous tetrahydrofuran acetogenins have attracted much interest due to their broad range of biological activities, and seeds containing them are reported to show insecticidal and abortifacient properties. Under the course our exploratory investigation of non food valuable products from less known forest species (here from Benin), the fractions obtained from cake of Annona squamosa with solvents covering a broad range of polarity, revealed a significant termiticidal activity, when applied at 5 - 10 mg/cm² (non-polar solvent) and 1.2 - 5 mg/cm² (case of a more polar solvent). Based on the result (0: no attack) from the standard procedure EN 118, these extracts could be used for preserving wood used hazard class. A derivatization step with Kedde reagents A and B, elemental analysis C,H,O, HPLC/MS and proton NMR showed the presence of squamocin type acetogenins (MW 594 and 622 g/mole: C35H62O7 and C37H66O7) as main components of the most active fraction by no-choice test (FR-13 : 100% mortality within 7 days for a sample applied at 2 mg/cm²). Additional work will be undertaken to confirm the structure of most active compounds in the extracts, and to check whether some Annona squamosa seed extracts (non timber products of sustainable management of native forest) could show even higher activity to protect wood and be alternative active natural products to synthetic compounds.