Synergism of three botanical termiticides as wood protectants against subterranean termites, Macrotermes subhyalinus (Rambur, 1842)

Abstract

Abstract Background The increased interest in the harmful effects of most chemical pesticides on the ecosystem has continually served as an impetus to search for safer and eco-friendly pesticides from plant origin. In this study, the termiticidal potentials of extract mixtures of Azadirachta indica (A. Juss.), Nicotiana tabacum (L.), and Jatropha curcas (L.) against Macrotermes subhyalinus (Rambur, 1842) infesting Triplochiton scleroxylon (K. Schum) wood blocks were investigated in the field (open and under shade) and laboratory conditions. Weight loss in wood blocks, level of wood damage, and termite mortality were used as indices of wood protection potential of the botanical mixtures. The level of repellent ability of the extracts mixture was also determined. For the laboratory bioassays, ten termites (worker/soldier) were used per treatment and each treatment was replicated thrice. Profile of components of the three mixtures was also obtained using head space–solid-phase micro-extraction, gas chromatography–mass spectrophotometry (HS-SPME, GC-MS) analysis. Results Extracts of A. indica plus N. tabacum achieved 100% mortality of worker within 4 h while those of N. tabacum plus J. curcas and A. indica plus N. tabacum plus J. curcas achieved 100% mortality of termites at 6 h post-treatment. Also, extract of A. indica plus N. tabacum and A. indica plus N. tabacum plus J. curcas evoked 100% mortality of soldier termites at 6 h. Termites exposed to N. tabacum plus J. curcas for 1, 2, 3, and 4 h were the most repelled at 73, 87, 73, and 73%, respectively. The extract of J. curcas plus A. indica plus N. tabacum offered the highest protection against termite damage in the open field (6.17%). The botanicals were ineffective under shade. Insecticidal compounds like (S)-3-(1-Methyl-2-pyrrolidinyl) pyridine; Methyl ester, Hexadecanoic acid; (Z, Z)-9, 12-Octadecadienoic acid; Anthracene; 2-Hydroxy-Cyclopentadecanone; and n-Hexadecanoic acid were found in the extracts. Conclusion These results suggest that the botanical mixtures could confer some protection against termites. Also, the knowledge about the components and varied level of potency under different conditions may be vital in developing biorationals against M. subhyalinus.