Efficacy of Biopesticides from the Leaves of Dioscorea bulbifera L. in the Control of Drywood Termites (Cryptotermes cynocephalus Light)

Damage to building wood due to termite infestation, especially the dry wood termite (Cryptotermes cynocephalus Light) leads to considerable economic losses. Among the potential biopesticides considered for termite control is the yam Dioscorea bulbifera; the leaves contain bioactive compounds such as alkaloids, flavonoids, saponins, tannins, steroids, and terpenoids, which are thought to have potential as biopesticides. The goal of this study was to determine the effectiveness of D. bulbifera leaves as a biopesticide in the control of C. cynocephalus. The experimental approach was based on a completely randomized factorial design, with factor A being the type of solvent (n-hexane, ethyl acetate, and methanol) and factor B the concentration of the extract (1%, 1.5%, 2%, 2.5%, and 3%). Contact toxicity tests were performed (five replicates). The observed parameters included wood retention, termite mortality, wood weight loss, degree of damage, and qualitative and quantitative phytochemical tests (through gas chromatography-mass spectrometry). The most effective D. bulbifera leaf extract was that prepared with methanol, with the following results: wood retention, 0.33 kg/m3; termite mortality, 76%; test weight reduction, 2.88 g; and degree of damage, 56.55%. The phytochemical test results showed that the secondary metabolites in the methanol extract of D. bulbifera leaves contained alkaloids, flavonoids, phenols, steroids, terpenoids, tannins, and saponins. The methanol extract also contained 11 compounds with potential biopesticide activity. Further studies are required to determine the appropriate concentration for application as a biopesticide.