Efficacy of some selected botanical extracts against the Efficacy of some selected botanical extracts against the Efficacy of some selected botanical extracts against the Efficacy of some selected botanical extracts against the Efficacy of some selected botanical extracts against the Efficacy of some selected botanical extracts against the Efficacy of some selected botanical extracts against the Efficacy of some selected botanical extracts against the Efficacy of some selected botanical extracts against the Efficacy of some selected botanical extracts against the Efficacy of some selected botanical extracts against the Efficacy of some selected botanical extracts against the Efficacy of some selected botanical extracts against the Efficacy of some selected botanical extracts against the Efficacy of some selected botanical extracts against the Cotton mealybug Cotton mealybug Cotton mealybug Cotton mealybug Phenacoccus solenopsis Phenacoccus solenopsisPhenacoccus solenopsis Phenacoccus solenopsis Phenacoccus solenopsis (Tinsley) (Tinsley) (Tinsley) (Hemiptera: Pseudococcidae) (Hemiptera: Pseudococcidae) (Hemiptera: Pseudococcidae) (Hemiptera: Pseudococcidae) (Hemiptera: Pseudococcidae) (Hemiptera: Pseudococcidae)M.Prishanthini and M.VinobabaDepartment of Zoology, Faculty of Science,Eastern University, Sri LankaAbstract- Laboratory studies were carried out to evaluate the efficacy of some locally available botanicals against cotton mealy bug Phenacoccus solenopsis on shoe flower plants Hibiscus rosa-sinensis. Plants extracts obtained from Azadirachta indica, Ocimum sanctum, Calotropis gigantea, Nicotina tabacum and Alium sativum using standard methods. Among all these botanicals, extracts were prepared and dilutions were obtained at 0.2, 0.4, 0.6, 0.8, 1.0,1.2,1.5, 2.0 percentage concentrations with the addition of soap solution. Among the treated botanicals, O.sanctum was effective significantly (p<0.05) at lower concentrations and has the 0.6% concentration as LC50. O.sanctum solution of this particular strength was applied in a field trial and was resulted lower adult mortality (39%) and a higher nymphal mortality (72%). Neem, Tobacco, Calotropis and Garlic solutions have LC50 values as 0.82, 0.89, 0.95 and 1.15 percentages respectively.Index Terms- Botanicals, Efficacy, Extracts, Phenacoccus solenopsis
I. INTRODUCTION
T he mealybug species are widespread throughout the world. The cotton mealybug Phenacoccus solenopsis Tinsley (Hemiptera: Pseudococcidae) has been described as a serious and invasive polyphagous pest with a vast host range by several authors. It has a wide geographical distribution with its origin in Central America (Fuchs et al, 1991) followed by reports of the Caribbean and Ecuador (Ben-Dov, 1994), Chile (Larrain, 2002), Argentina (Granara de Willink, 2003), Brazil (Mark and Gullan 2005). P. solenopsis has been described as a serious and invasive pest of shoe flower in Pakistan and India (Hodgson et al. 2008) on Hibiscus rosa-sinensis in Nigeria (Akintola and Ande, 2008) Latest report by the authors on the invasiveness of P. solenopsis has been from the Eastern region of Sri Lanka (Prishanthini and Vinobaba, 2009) on ornamentals, vegetable crops, and weeds, and in China (Wang et al. 2009; Wu and Zhang, 2009) on shoe flower. P.solenopsis is identified as one of the major damage causing and fastly spreading invasive mealybugs of Sri Lanka next to Papaya mealybug Paracoccus marginatus. Being a polyphagous pest, the P. solenopsis has been recorded to feed on a number of cultivated crops including weeds (Patel et al. 2009). According to the recent information provided by the authors (Prishanthini and Vinobaba, 2011) P.solenopsis has been reported from 28 host plant species comprising 10 families in Sri Lanka. This includes the major field crops of family Malavaceae, Solanaceae and Amaranthaceae. Farmers are currently using some toxic chemical insecticides against cotton mealy on large and small scale cultivations of Okra, Brinjal, Tomato and Amaranthus.
Reliance on synthetic chemicals to control pests has also given rise to a number of problems such as destruction of beneficial non-target organisms (parasitoids and predators) thereby affecting the food chain and impacting on biological diversity. The injudicious use of synthetic pesticides can lead to secondary outbreaks of pests that are normally under natural control resulting in their rapid proliferation. There have also been cases of pests becoming tolerant to insecticides, resulting in the use of double and triple application rates (Stoll, 2000). In addition, due to other problems such as health hazards, undesirable side effects and environmental pollution caused by the continuous use of synthetic chemical pesticides (Nas, 2004), there is renewed interest in the application of botanical pesticides for crop protection. Botanical pesticides are biodegradable (Devlin and Zettel, 1999) and their use in crop protection is a practical sustainable alternative. It maintains biological diversity of predators (Grange and Ahmed, 1988), and reduces environmental contamination and human health hazards. Botanicals are safe for homegardens and green houses. Therefore the present study attempts to evaluate the efficacies of some native botanicals against cotton mealybugs.
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ISSN 2250-3153
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II. MATERIALS AND METHODS
The study was conducted under laboratory conditions of Department of Zoology, Eastern University, Sri Lanka during the period from June 2012 to May 2013.
Culture of mealybugs
The laboratory culture of P.solenopsis was established from individuals collected from shoe flower plants in home gardens those do not have any previous exposure to pesticides. P.solenopsis were reared in on potato sprouts and on potted shoe flower plants under laboratory conditions.
Collection of botanicals
The botanicals used in this experiment were, Ocimum sanctum L. (Lamiaceae), Azadirachta indica A. Juss. (Meliaceae),Calotropis gigantea R. Br. (Asclepidaceae), Nicotina tabacum Linn. (Solanaceae ) and Alium sativum Linn. (Amaryllidaceae). Leaves of Ocimum sanctum (Tulasi) and Azadiracta indica (Neem) and Calotropis sp. were collected from the home gardens of Batticaloa. The dried leaves of Tobacco (Nicotina tabacum) and Garlic cloves were bought from local market.
The leaves collected were washed with sterile distilled water until the dirt was completely removed and allowed to shade dry for one week. Then the dried materials were finely ground using motor and pestle until the powdered form was obtained. The powders were stored separately in dark bottles for extraction.
Preparation of extracts
A. Extracts of Neem, Tulsi, Calotropis and Tobacco leaves
50 g of powdered botanicals from each was weighed and transferred to a cellulose extraction thimble (Whatman, UK). These materials were extracted using 250 ml ethanol (78 oc) for 5 hours in a Soxhlet apparatus (250 ml) and the extracts were decanted from the flask separately. Then the volume of each abstract was measured and each was made to a final volume of 200 ml and transferred separately into round bottom flasks. The flasks were fitted with the Rotatory evaporator (Buchi; R-114; Switzerland) individually and evaporated to dryness at a temperature not exceeding 85 oc. Then the flasks with dried materials were removed and weighed. The weight of the dried extract was calculated by subtracting the weight of the empty flask. Thereafter few milliliters of ethanol were added to each flask to aid the dissolution of the extract with water. Finally 50 ml of distilled water was added to the extract to get 1gml-1 (100% w/v) concentration. Further dilutions were made for further experiments.
B. Extract of Garlic
50 g Garlic cloves were taken and ground well using mortar and pestle to obtain a paste form. Then 25 ml of distilled water is added to the paste and shaken well. The mixture was kept for three days; strained using a clean muslin cloth and the volume was made to 50ml by adding further 25 ml of water, shaken well and stored in a dark bottle.
10 ml solution from each of the initially prepared botanical extracts (1gml-1) was transferred into 500ml volumetric flask using a pipette and the final volume was made to 500ml to obtain a solution with a concentration 20 mg/ml (2% w/v). From these solutions different dilutions were obtained by adding certain volume of botanical solution, certain volume of distilled water and 1ml of 1% (w/v) soap solution.
Evaluation of efficacy of different botanicals against P.solenopsis
Laboratory studies
Approximately 10-12 cm length terminal portions of the Shoe flower stems (Hibiscus rosa-sinensis) infected with the P.solenopsis were cut off using a sharp knife. The cut end of each was wrapped with wet paper towel and collected in polythene bags. Then they were brought to the laboratory by keeping them inside a regiform container to prevent from heat and mechanical damages during transport. Then yoghurt cups were taken and filled with tap water. A hole was made on each lid to tightly fix the stem portion. The
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number of leaves on each plant terminal was reduced to 4 (only the upper terminal leaves were allowed to remain) and all the nymphal stages including crawlers, and egg masses except twenty adult females were removed from the stem by using a hand lens and a camel hair brush. Then the stem portions were fixed with the lid by allowing the cut end to contact with the water inside the yoghurt cup to keep the stem cutting fresh throughout the study. The stem portion fitted with the cup was placed inside a rectangular cubic glass container measuring 10cm x 10cm x 20 cm. Then prepared solution of a particular concentration from each botanical was sprayed over the mealy bu
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