The study was done to find out the effect of four plant products and a chemical insecticide such as neem leaf powder, datura leaf powder, nishinda leaf powder, garlic tablet powder and Sevin 85SP against maize weevil, Sitophilus zeamais Motschulsky in the laboratory of the Department of Seed Science and Technology, Bangladesh Agricultural University (BAU), Mymensingh, during the period from August to October 2018. This place receives an average rainfall of 1295mm/annum. Temperature in the laboratory ranged from 25-31°C and the relative humidity also varied from 68-75% during the experimenting period. The laboratory was kept well aerated throughout the study.
2.1 Collection and De-Infestation of Maize Seeds: An open-pollinated maize variety “Khai Bhutta” sourced from Agronomy farm, Bangladesh Agricultural University (BAU), Mymensingh) was used because it has stable yields in adverse conditions such as drought due to its heterogeneity and commonly grown by most resource-poor smallholder farmers (ref). Dirt from the maize was removed through winnowing as suggested by Masiiwa (2004) and the grain cleaned using a 1mm sieve mesh screen so as to remain with intact kernels. The moisture content of the maize seed was maintained 11-12% following procedures described at the Manual of Seed Quality control (2006). The maize grain was graded manually and cleaned of broken kernels and debris (Fekadu et al., 2012). Before the artificial infestation of maize seeds with maize weevil, the maize seeds were dried in the sun for few days. Islam et al. (2000) reported that solar heat treatment of grains destroys the initial insect infestation in the grains before storage. The maize seed was kept in a plastic jar in the cool dry room to avoid the accumulation of moisture.
2.2 Botanical Species Tested as Biopesticides: Three different rates of four biopesticides (3, 4 and 5 gm/100g seeds) were used for the experiment, namely, Neem (Azadirachta indica – Meliaceae), Datura (Datura stramonium – Solanaceae), Garlic (Allium sativum L.- Liliaceae), Nishinda (Vitex negundo L. – Verbenaceae). Sevin 85SP, a chemical pesticide was also used as a treatment. What was the source of the biopesticides.
2.3 Test Insect: The present study was conducted with major stored grain pest of maize named maize weevil, Sitophilus zeamais Motschulsky under Curculionidae family of Coleoptera order.
2.4 Collection and Rearing of Insect: Maize weevils, S. zeamais were collected from a storeroom of a poultry feed wholesaler at Muktagacha upazilla of Mymensingh district. The insects were brought to the laboratory of the Department of Entomology, Bangladesh Agricultural University (BAU), Mymensingh. The insects were maintained in the growth chamber at 27-30°C and 70-75% RH. The insects were reared on fresh maize seeds in rectangular jars of size 14×10×30 cm. Each jar was set up with 20 pairs of adult beetles. Maize seeds were kept in an oven overnight at 300C temperature to avoid pre infestation. The moisture content of maize grain was adjusted to 12-13%. Then maize seeds were used as food for maize weevil. The jars were covered with a piece of cloth fastened with rubber band to prevent contamination and insect escape. After allowing free oviposition for a period of 14 days, all the adults of maize weevils were removed from each jar. Then the jars were put back into the growth chamber for completing the generation of insects. The F1 generation was used for the experiment.
2.5 Collection and Preparation of Tested Botanical Products: Neem, datura and Nishida leaves were collected from Bangladesh Agricultural University (BAU) premises and dried under the shed for 14 days. Then they were grinded by hand grinder in the Integrated Pest Management (IPM) Laboratory, Department of Entomology, BAU. Before grinding, leaves were dried in the oven at 700 C for 24 hours to make the leaves crispy which allowed them to fine grinding. Then the grinded materials were sieved with 1mm sieve to fine powders of botanical materials.
2.5.1 Garlic Tablet: The garlic tablets were prepared at the Plant Pathology laboratory on the Department of Plant Pathology, BAU, Mymensingh. For the preparation of garlic tablets, at first, garlic was collected from the K.R. market BAU campus, Mymensingh. After that, the garlic cloves were separated from each garlic bulb and washed in clean water. Then these cloves were blended in the blender machine. From the blended materials, tablets were prepared and kept in the open air for drying for three days. After that, the tablets were preserved in an air tied bottle.
2.6 Test Chemical Material (Sevin 85SP): Sevin 85SP is a contact and slightly systemic organo carbamate insecticide in powder formulation. It was purchased from a local insecticide store situated at Notun Bazar of Mymensingh Sadar packed in a 50g pack manufactured by Bayer Crop Science, Bangladesh Limited.
2.7 Tested Rates of Botanical Products and Chemical: In the experiment prepared neem, datura, Nishida leaf powder and garlic tablet powder were used at three different rates (w/w) as 3, 4 and 5g per 100g maize seeds ), while in control treatment there was no any botanicals added and in the standard check Sevin 85SP dust was added in 0.25g/100g of maize seed.
2.8 Treatment Application: Twenty pairs of S. zeamais were introduced into the plastic jar containing 100g grain maize in 0.5 liter plastic jars at 3, 4 and 5g% (w/w). Four botanicals and Sevin 85SP with their recommended dosage were weighed and added to the maize grain in each jar containing 100g grain maize in 0.5 liter plastic jars at 3, 4 and 5g% (w/w) and kept for 28 days and mortality rate was counted daily every 1, 7, 14, 21 and 28 days after application of treatments.
2.9 Mortality Test of Maize Weevil
Mortality rate determination periods selected based on an earlier report by Dobie, (1974) & Girma et al. (2008) and calculated by the following formula:
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% Weevil mortality = Number of dead insects/Total number of insects released x 100
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2.10 Seed Weight Loss Assessment of Maize Seeds: Percent insect damage of maize seeds in storage was computed according to the methods described in Haines (1991) as follows: Percent of weight loss = [(UNd-DNu)/U(ND-Nu)]x100
Where U = weight of undamaged seeds, D = weight of insect- damaged seeds, Nu = number of undamaged seeds and Nd = number of insect- damaged seeds
2.11 Seed Germination: The percent germination was computed according to the following formula:
Germination (%) =[NG/TG]x100
Where,
NG = Number of seeds that germinated
TG = Total number of test seeds.
2.12 Statistical Analyses: The experimental data were analysed by STATISTIX 10 software. The mean values were separated by Duncans multiple range test (DMRT) (Duncan, 1951).