Lethal Concentration–Based Evaluation of Dioscorea bulbifera L. Leaf Extracts as a Botanical Termiticide

This study evaluated the potential of Dioscorea bulbifera L. leaf extract as a natural termiticide against the drywood termite Cryptotermes cynocephalus and as an environmentally friendly alternative to synthetic chemicals. The leaves were macerated in methanol and fractionated into polar (methanol), semi-polar (ethyl acetate), and non-polar (n-hexane) extracts. Toxicity was assessed using a filter-paper contact bioassay over 30 days. Lethal concentration (LC) assays for the semi-polar fraction were prepared across a 1.17%–7.35% gradient corresponding to LC10–LC90. The semi-polar ethyl acetate fraction exhibited the strongest activity; the LC90 dose (7.35%) produced the highest mortality (48%), compared with 24% in the control. This fraction also showed the greatest protective potential, as indicated by reduced feeding-related substrate loss (1.35 ± 5.01%) and surface damage (7.28 ± 25.53%), which are commonly used as proxies for potential wood protection. In comparison, the control treatment exhibited 18.57 ± 5.01% substrate loss and 100 ± 25.53% surface damage. Scanning electron microscopy-energy-dispersive X-ray analysis revealed differences in the surface elemental composition of filter papers treated with different fractions, with the semi-polar fraction showing a more homogeneous distribution of carbon and oxygen than the other fractions. Penetration, transport, and mechanistic interactions were not experimentally confirmed in this study; therefore, these observations are correlative and describe only surface characteristics. These results support the potential of the semi-polar fraction of D. bulbifera leaves as a biodegradable botanical termiticide, as demonstrated by measurable termiticidal activity and reduced feeding-related damage under laboratory conditions.