THE TERMITICIDAL ACTIVITIES OF THREE BOTANICALS ON SUBTERRANEAN TERMITES – Macrotermes subhyalinus (Rambur)

Abstract

Application of synthetic chemicals is an effective control measure to protect wood against insect pests. Continuous use of these chemicals is harmful to living organisms and the environment, hence the shift towards substitute means of control which includes the use of botanicals. Most previous reports on use of these botanicals were done using the botanicals singly in the control of termites. There is possibility of synergistic or antagonistic effect on potency of these botanicals against insect pests. This study screened mixtures of three botanicals: Azadirachta indica A. Juss., Nicotiana tabacum L. and Jatropha curcas L. for toxicity to, repellent and wood protection abilities against subterranean termites. Ten (10) g of the air-dried and ground sample of each plant were admixed together in dual combinations: A. indica + N. tabacum; A. indica + J. curcas; N. tabacum + J. curcas, and the three plants combined. The mixed plant powders soaked in distilled water for 24 h. The aqueous extracts were applied on cellulose sources in minimum of three replicates by dipping them into the water extracts of plant mixtures and spreading the slurry of the preparation on its entire surface, then exposed to termites invitro and invivo. Number of dead termites was recorded at 1 h interval for 6 h in toxicity test. The number of termites on treated and untreated filter paper was recorded at 4 h of exposure in repellent test. Signs of termite attack was observed and rated on weekly basis for 12 weeks in field experiment. Weight loss in wood blocks was used as index of termite consumption. Combinations of extracts that elicited some level of potency against termites were subjected to Gas Chromatography coupled with Mass spectrometry (GC-MS) analysis to reveal their biochemical components. The toxicity bio-assay revealed all the combinations used to elicit toxic effects on the termites. Combination of A. indica + N. tabacum achieved 100% mortality within 4 h of exposure. Combination of N. tabacum + J. curcas and combination of A. indica + N. tabacum + J. curcas achieved 80% and 83% mortality at 4 h respectively but both achieved 100% mortality at 6 h. In contrast, combination of J. curcas + A. indica caused the lowest mortality, 20% at 4 h and 40% at 6 h while control achieved mortality of 10% at 6 h. Similarly, when applied to soldier termites the combination of J. curcas + A. indica had the lowest mortality of 6% and 46% mortality at 6h. Combination of N. tabacum + J. curcas achieved 52% and 92% mortality at 2 and 6 h respectively; while, the combination of A. indica + N. tabacum and combination of A. indica + N. tabacum + J. curcas achieved 100% mortality of soldier termites at 6 h. Control elicited no mortality on the termites. A. indica + N. tabacum (33, 33, 47, and 47% at 1, 2, 3 and 4 exposure hours respectively), N. tabacum + J. curcas (73, 87, 73, and 73% termites repelled at 1, 2, 3 and 4 exposure hours respectively) and A. indica + N. tabacum + J. curcas (60, 20, 47 and 47% at 1, 2, 3 and 4 exposure hours respectively) effectively repelled termites while A. indica + J. curcas (-47, -20, -47, and -47% at 1, 2, 3 and 4 exposure hours respectively) was attractive to termites. The field assessment of the botanicals in the open field and under shade suggests increased termite activities on wood under shade than in the open field. Visual ratings of damage in both environments (open and shaded) revealed the combination of J. curcas + A. indica + N. tabacum to offer the highest protection against termite damage (35% damage under shade and no damage in the open), J. curcas + N. tabacum (33.3% damage under shade and 15% in the open), A. indica + N. tabacum (65% and 45% termite damage under shade and in the open respectively). Meanwhile, the combination of J. curcas and A. indica showed contrasting termite damage under shade and in the open with 70% and 5% damages respectively. Weight loss due to termite infestation revealed woods treated with combination of N. tabacum + J. curcas had the highest weight loss (50.35 and 17.92 under shade and in the open respectively). The weight loss in woods treated with the combination of A. indica + N. tabacum (43.05 and 43.81 under shade and in the open respectively), A. indica + J. curcas (43.80 and 13.10 under shade and in the open respectively) and N. tabacum + A. indica + J. curcas (36.42 and 6.17 under shade and in the open respectively) conferred considerable protection on wood. Interestingly, the control setup had the least weight loss (21.29 and 22.71 under shade and in the open respectively). Further research on reported potent biochemical components in the effective combinations should be carried out towards developing termite inhibiting agents.