ASSESSMENT OF THE EFFECT OF CRUDE EXTRACTS OF ANARCARDIUM OCCIDENTALE AND SYZIGIUM AROMATICUM USED AS WOOD PRESERVATIVES ON EARTHWORM

Abstract

The application of synthetic chemicals is an effective control measure to protect wood against insect pests. Continuous use of these chemicals is harmful to humans, environment, and destruction of non-target organisms, hence the shift towards alternative means of control is now the focus which includes the use of botanicals, but the study on the toxicity of these botanicals on non-target organisms is not well to understand. This study investigated the toxicity of the extract of Anacardium occidentale (L.) shell and Syzygium aromaticum on non-target soil fauna using (earthworm) as an indicator organism and also the bioactivity of the individual and mixtures of the two plants were also tested in protecting wood using Triplochiton scleroxylon, a highly susceptible wood to termite infestation. Toxicity of the plants to earthworm were carried out in the laboratory bioassay while the assessment on the wood samples against termite was carried out in the field. The methanol extract of the two plants were tested on earthworm to know their effect on non-target soil fauna. Toxicity of the plant extract was tested at the water for ( Negative control), 0.2, 0.5, 1.0, 1.5, and 2.0% concentration of each extract, and each treatment were replicated three times while positive control were treated with solignum according to manufacturer's specification. 5ml of the extracts solutions were applied on 20gram of soil in the petri dish and thoroughly mixed with spatula and earthworm were introduced into it, mortality and time of death were recorded at an interval for 1hour. Individual and mixtures of the plant's extracts were also assessed as a wood protectant against termite infestation, four concentrations: 5, 10, 25, and 50% of each extract were tested singly while mixtures were also assessed in ratios 30:70, 70:30 and 50:50% (v/v) to test the possible synergistic or antagonistic effect of the extracts. Negative control was left untreated while positive control were treated with solignum and each treatment having eight (8) replicate. Experiments were set-up on termite-infested soil and assessed weekly for visual signs of termite attack. The damage was rated as a measure of resistance to termite destruction using a damage rating system. Weight loss in wood samples were used as an index of the protectant-ability of the two plant extracts. The experiment was laid down in a complete randomized design, Data obtained were subjected to analysis of variance (ANOVA) and means were separated using Tukey's HSD (Honest Significant Difference) at 5% level of significance. The results of toxicity bioassay obtained revealed that all the concentration used elicits toxic effects on an earthworm. A. occidentale extracts at 1.5% achieved 50% mortality of the earthworm within 3 mins while 2.0% of the extract gave 100% mortality within 5mins of exposure. Two percent (2.0%) extract of S. aromaticum achieved 100% mortality at 5 mins. The mortality was significantly different (P<0.05) from the control (0%). The effect of the extracts as evaluated by lethal concentration gave LC50 and LC90 of A. occidentale are 0.19 and 0.60 mL-1 while that of S. aromaticum 0.16 and LC90 0.50 mL-1 reflected that low concentration of these extracts were required to achieve 50 and 90% mortality of earthworm within 1h respectively and this showed that A. occidentale was the most toxic of the extracts. The result of weight loss in treated wood samples with the extracts ranged from, 7.08% - 0.69% of A. occidentale, and 22.09% - 3.07% of S. aromaticum respectively, while the weight loss in mixtures of the extracts ranged from A. occidentale : S. aromaticum (70:30) is (4.94%), (30:70) is (19.57%) and (50:50) is (1.79%). Every single extract significantly (P<0.05) protected the wood but the degree of effectiveness varied with increased concentration of every single extract. A. occidentale was more potent in suppressing wood damage than S. aromaticum. The weight loss recorded at all treatment levels of A. occidentale was lowered compared to the result obtained in the treatment of S. aromaticum. The weight loss in wood samples treated with mixtures of the extracts was lower (1.79-19.57%) than that of the samples treated with single plants of the extracts (0.69-22.09%) which signals the possibility of synergistic activity while the control setup had the least weight loss (64.51%). This research reveals that the two plants extract are potential wood protectants and are less toxic to soil fauna.