© 2014, World of Researches Publication American Journal of Life Science Researches www.worldofresearches.com Am. J. Life. Sci. Res. Vol. 2, Issue 3, 360-366, 2014 ORIGINAL ARTICLE Received 1Jan. 2014 Accepted 27Jun. 2014 Assessment of Root Powder of Indigo Vine (Lonchocarpus cyanescens) for the Control of Maize Weevil (Sitophilus zeamais, Motschulsky) on Stored Maize Akunne C. E*1, Ozigbo J. I1, Mogbo, T.C 1, Ononye B. U1andNgenegbo, U2 1. 2. Department of Zoology, Nnamdi Azikiwe University Awka, Anambra State, Nigeria. Department of Parasitology and Entomology, Nnamdi Azikiwe University Awka, Anambra State, Nigeria. *Corresponding Author:chidiknne@yahoo.com Abstract: The laboratory assessment on the efficacy of the root powder of Indigo vine (Lonchocarpus cyanescens) was carried out against adult Sitophilus zeamais on stored maize grains. The result obtained shows that the root powder at various concentration, 0.5g, 2.5g and 5.0g per 50g of maize grains caused adult mortality of Sitophilus zeamais during the period of treatment. The highest mortality rate was obtained from the maize grains treated with 5.0g of the root powder at the 7th day after treatment while the lowest mortality rate was obtained on 28th day after treatment at 2.5g rate of the root powder application. Chemical analysis shows that rotenone was isolated as the active ingredient in the plant used. Key words: Assessment, Lonchocarpus cyanescens, Sitophilus zeamais, Maize INTRODUCTION Food security is a pressing concern for the world today especially in subSaharan Africa where it has been rapidly deteriorating 1. Diets in sub-Saharan Africa are based primarily on maize (Zea mays L.) which is an important food crop in many tropical, subtropical and temperate countries where it is grown and eaten 2. It is originally called mahiz by Native Americans and comes in several varieties, such as popcorn and dent corn usually ground and used for products such as corn chips. In developing countries, it is the main source of food for human consumption, supplying carbohydrate, protein, iron, vitamin B and C, fiber, potassium, and minerals 3. Maize is largely used as livestock feed and as industrial raw material in industrialized countries4. As a result of insect pest infestation, food situation has remained insecure and unpredictable in sub-Saharan Africa, leading to high levels of cyclic famine and poverty. The maize weevil, Sitophilus zeamais, a cosmopolitan pest of wholesome grains in both tropics and warm temperate regions of the world poses a serious threat to food security, particularly in developing countries. It is a serious primary pest of maize which attacks grains in the field and store and its infestation results in substantial losses in weight 5. Globally, post-harvest grain July, 2014 360 Assessment of Root Powder of Indigo Vine … losses caused by insect damage and other bioagents range from 10-40%. But grain loss in Africa due to insect pests’ damage in storage systems is estimated at 20 to 30%. Particularly, S. zeamais cause more than 20% grain loss for untreated maize worldwide. However Adedire and Oni observed the effects and damage pattern of S. zeamais on stored maize and noted that adult weevils and larvae feed on the undamaged grains and reduce them to a powdery form. Owing to the economic importance attached to grains especially maize in Nigerian agriculture, it became necessary to protect the crop against damage by the insect while in storage. The problem of protecting the surplus stocks of grains led to the search for chemical insecticides whose effects are long lasting and which ideally can be applied at the time when the grains are first put in storage5. The ancient man had deployed different methods of control, including prayers, magic spells, cultivation systems, mechanical practices as well as application of organic and inorganic substances to protect his crops from the attack of weeds, diseases and insect pests. In the modern times, inorganic substances such as chemical insecticides have been widely used in the control of insect pests of food crops. In Nigeria, the abuse and misuse of these chemical pesticides have several repercussions one of which is acute and chronic poisoning in man 6others include sudden deaths, blindness, skin irritation and pest resurgence in the ecosystem 7. As a result of the limitatons of synthetic pesticides in protecting our stored products (especially maize seeds), alternative methods of pest control that is environmentally friendly, inexpensive, repellents and antifeedants must be encouraged to guarantee the ever-increasing population in Nigeria with abundant food supply 8. However, studies on the effects of root powders of plant on the insect pest attacking maize grains have not been given much attention in Nigeria. This current study is aimed at using root powder of Lonchocarpus cyanescens to reduce grain damage caused by insect pests, particularly Sitophilus zeamais on maize grains. MATERIAL AND METHODS Preparation of the Plant Powder The roots of Lonchocarpus cyanescens were harvested using hoe and cutlass, washed with water to remove sand, chopped into small parts to allow proper drying. They were oven dried at 100◦C for 2 hours. The dried material was allowed to cool at room temperature and ground into powder in an electric hammer mill. The powder was kept in air tight container to prevent the suspected active ingredient from evaporating and as well not to absorb moisture. Experimental Protocol Infested and clean uninfested maize grains used in this study were obtained from Eke-Awka market in Awka. The uninfested maize grains were oven-dried for 15mins to rid them of insidious infestation and allowed to cool. Adults of Sitophilus zeamais used in this study were obtained from the infested maize and were cultured under ambient laboratory temperature. The root powder from Lonchocarpus cyanescens was applied at the following concentrations 0.5g, 2.5g Akunne et al., 2014 and 5.0g in containers containing 50g of uninfested maize grains of the same variety. The content of each container was shaken vigorously to have a thorough admixture of seeds and powder, the content was left for 1 hour to settle. Control treatment in which no plant powder was added was also set up. Then 20 adults of S. zeamais were introduced into each container and covered with Muslim cloth held tightly in place by a rubber band to prevent escape. Each treatment was replicated thrice. Extraction of Rotenone from Lonchocarpus cyanescens This rotenone extraction was done using Soxhlet extraction apparatus. 200g of powdered sample was accurately weighed and poured into 500ml beaker. 25g of Octyl stearate and 350g of chloroform was weighed and poured into the beaker containing the powdered sample. The mixture was agitated for 15 minutes at ordinary temperature (37◦C) using electric shaker. It was allowed to settle and then filtered using Watman No 1 filter paper and glass filter funnel. The residue was washed on the filter paper with 75g of chloroform. The filtrate was then poured into round-bottomed flask and fitted into Soxhlet extraction apparatus. Heat was applied and the chloroform was distilled off at 74◦C leaving behind the Rotenone-Octyl stearate solution which was treated with 60g of methyl alcohol with agitation and Rotenone precipitated out. Rotenone was separated by filtration and washed with 50g methyl alcohol. Qualitative Analysis of Lonchocarpus cyanescens Identification Tests: The substance extracted from the root powder of L. cyanescens was identified as Rotenone using the following physical/chemical properties of Rotenone. The substance when freshly extracted was colourless but turned scarlet when exposed to air. The melting point of the substance was determined using melting point apparatus with fitted thermometer. The melting point was observed to be 165◦C. One gram (1g) of the substance was weighed into a 50ml beaker and 10g of distilled water added. The substance observed was insoluble in water at ambient temperature. Solubility in Some Organic Solvents: One (1g) of the substance was distilled in 10g of acetone. The substance was totally soluble in acetone. Ethanol: 1g of substance was dissolved in 10g of ethanol . Chloroform: 1g of the substance was dissolved in 10g of chloroform. The substance was totally soluble in chloroform. Petroleum Ether: 1g of the substance was dissolved in 10g of petroleum ether. The substance was less soluble in petroleum. Data Collection and Analysis Mortality counts of adult Sitophilus zeamais were recorded at 7, 14, 21 and 28 days after treatment. The dead curculionids were discarded after each count. The data obtained was subjected to analysis of variance at the level of (0.05) significant level. July, 2014 362 Assessment of Root Powder of Indigo Vine … RESULTS The result in Table 1 shows the mean mortality count of adult weevils at 7days, 14days, 21days and 28days of post treatment. It indicates that the mean mortality count of adult S. zeamais caused by the application of Lonchocarpus cyanescens root powder (6.00) is highest in the maize grains treated with 5.0g concentration and lowest (4.00) in the maize grains treated with 2.5g concentration 7days after treatment. However the mean mortality count is higher (3.00) in the maize grains treated with 0.5g concentration of L. cyanescens root powder but lowest (1.00) in the maize grains treated with 2.5g concentration at 14 days after treatment. It also shows that the mean mortality count of S. zeamais is higher (3.00) in the maize grains treated with 5.0g concentration but those treated with 0.5g and 2.5g had equal mean mortality count (1.00) 21 days after treatment. Table 1 further shows that equal mean mortality count of S. zeamais was obtained in the maize grains treated with 0.5g and 5.0g concentration at 28 days after treatment with no mortality in those treated with 2.5g concentration. However, the result from the analysis of variance shows that no significant difference exists [Fcal (0.62) < Ftab (4.26)] between all treatments (0.5g, 2.5g, and 5.0g).This indicates that any of the powder concentrations could be effective in the control of S. zeamais per 50g of maize grains. The result in Table 2 shows the percentage mean mortality of adult weevils obtained at 7days, 14days, and 21days to 28days of post treatment applied. It indicates that the percentage mean mortality of adult S. zeamais caused by the application of Lonchocarpus cyanescens root powder (30%) is highest in the maize grains treated with 5.0g concentration and lowest (20%) in the maize grains treated with 2.5g concentration 7days after treatment. However the percentage means mortality count is higher (15%) in the maize grains treated with 0.5g concentration of L. cyanescens root powder but lowest (5%) in the maize grains treated with 2.5g concentration at 14 days after treatment. It also shows that the mean mortality count of S. zeamais is higher (15%) in the maize grains treated with 5.0g concentration but those treated with 0.5g and 2.5g had equal mean mortality count (5%) 21 days after treatment. Table 1 further shows that equal percentage mortality of S. zeamais was obtained in the maize grains treated with 0.5g and 5.0g concentration at 28 days after treatment with no percentage mortality in those treated with 2.5g concentration. In summary, the results of this study reveals that the highest mean mortality count and percentage mortality rate was obtained from the maize grains treated with 5.0g of the root powder at the 7th day after treatment while the lowest mortality rate was obtained on 28th day after treatment at 2.5g rate of the root powder application. Table 1. Mean Mortality Rate of S. zeamais at various concentration of Lonchocarpus cyanescens root Powder Concentration of Days Powder (g) 7 14 21 28 0.5 5.00 3.00 1.00 1.00 2.5 4.00 1.00 1.00 0 5.0 6.00 2.00 3.00 1.00 Akunne et al., 2014 Percentage mortality rate Table 2.Percentage Mean Mortality Rate of S. zeamais at various concentration of Lonchocarpus cyanescens root powder Concentration of Powder Days (g) 7 (%) 14 (%) 21 (%) 28 (%) 0.5 25.00 15.00 5.00 5.00 2.5 20.00 5.00 5.00 0.00 5.0 30.00 10.00 15.00 5.00 75 30 25 10 Number of days of Exposure Figure 1. Graph showing the percentage mortality of Sitophilus zeamais at various concentrations (in grams) per 50g of maize grains. Extraction of Active Ingredient in Lonchocarpus cyanescens The result from the chemical analysis done indicated that the active ingredient of L. cyanescens is rotenone. The Chemical formula of Rotenone is C23 H22 O6. Chemical Structure of Rotenone is shown below: July, 2014 364 Assessment of Root Powder of Indigo Vine … DISCUSSION From the overall results, it showed that Lonchocarpus cyanescens root powder is toxic on Sitophilus zeamais from the 7th day of post treatment. The ability of the powder to cause mortality of S. zeamais adults commencing from the 7th day of post treatment of maize grains is an indication of the presence of anti-feedant on the plant, which is in agreement with 9who reported that the powder from Lonchocarpus cyanescens and Derris elliptica have insecticidal value. Also the ability of L. cyanescens powder to cause adult mortality of S. zeamais increased with increase in concentration of the plant root powder, as 2.5g of powder/50g of maize grains caused 20% mortality from the 7th day post treatment while mortality increased to 30% on a higher concentration of 5.0g powder/50g of maize grains. 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