BIOPESTICIDAL POTENTIAL OF EXTRACTS OF TWO PLANTS AGAINST SUBTERRANEAN TERMITES, MACROTERMES BELLICOSUS (SMEATHMAN) (BLATTODEA: TERMITIDAE).

Abstract

Termites are important because their activities impact positively or negatively on the environment. Synthetic insecticides offer reasonable protection against termites and their uses are however not without problems. This has led to an increasing interest in the development of alternative termite control methods and plants with pesticidal properties are one of such alternatives. The bioactivity of Milicia excelsa (Welm) C. Berg (heart wood) and Khaya senegalensis (Desr) (leaves) were tested in protecting Triplochiton scleroxylon (Schum) against subterranean termites. The extracts were analyzed using Head Space – Solid Phase Micro Extraction (HS-SPME) coupled with Gas Chromatography – Mass Spectrometry (GC-MS) to reveal their profiles of compounds, which were evaluated for termiticidal effects against Macrotermes bellicosus (Smearthman) in wood protection. The pulverized plants were used for laboratory test. Toxicity and repellency tests were carried out in laboratory while assessment of wood damage (visual rating and weight loss) was conducted in the field. The laboratory results showed that, highest mortality of termites, 98%, was recorded in M. excelsa treated substrate at 72 h. Student t-Test revealed significant differences between termite mortality obtained with the powder of K. senegalensis and M. excelsa at the four levels of exposure periods (12, 24, 48 and 72hrs). Correlation coefficient showed that M. excelsa had a greater potency (r = 0.94) on termites mortality than K. senegalensis with r = 0.86. M. excelsa had 100% repellent effect on the termites exposed at all levels. The highest repellency (100%) was observed at 1 h exposure to K. senegalensis treatment while the lowest percentage repellency (88) was recorded at 5 and 8 h of exposure. Treated wood blocks in open field were less infested compared to those under shade. Generally, there were significant differences between the two conditions for all extracts tested using Student t – test. Of all the extracts tested, wood treated with n-hexane extract of the mixture of K. senegalensis and M. excelsa in open field was found to have lasting protective potential on wood blocks with lowest damaged (21%) compared to those treated with other single and mixture extracts. Treated wood blocks in open fields had lower percentage weight loss to termite when compared to those under shade. Wood blocks in open field treated with n-hexane extract of the mixture (M. excelsa + K. senegalensis) had the lowest weight loss (21.14%) while those treated with water extract of M. excelsa under shade had lowest weight loss (70.73%). GC-MS analysis showed quantitative and qualitative differences between the extracts. Thirty-seven (37) chemical compounds were identified in heartwood of M. excelsa. Major compounds identified are Tridecane <n-> (11.61%), 1, 2-Benzenedicarboxylic acid (8.30%) among others. The lowest revealed compound was 2, 5-di-tert-Butyl-1,4-benzoquinone (0.55%). Only five (5) out of the thirty-seven (37) chemical compounds revealed were found to have pesticidal properties. These compounds are; Butylated Hydroxyl toluene (BHT) (7.90%), Docosane <n-> (1.36%), Tridecane (11.61%), Cyclohexane (0.78%) and Citral (1.22%). Fourty-seven (47) chemical compounds were identified in leaves of K. senegalensis. Major compounds identified are Ylangene (14.93%), Cadinene <gamma-> (10.14%) among others. The lowest revealed Decanedioic acid was least in quantity (0.04%). Only two (2) out of the fourty-seven (47) chemical compounds revealed in K. senegalensis were found to have pesticidal properties. These compounds are Cyclohexane (5.52%) and Cucubene <alpha> (0.55%). The revealed compounds with insecticidal properties in this study could be of importance in developing ecologically tolerable agents for managing subterranean termites.