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Microbial based insecticides have great potential for management of various agricultural insect pests. This study was conducted to evaluate the efficacy of indigenous nuclear polyhedrosis virus (NPV) for the management of Spodoptera litura (Fabricius) on cotton. A field survey was conducted for collection of NPV infected larvae of S. litura with specific symptoms of polyhedrosis and soil samples were collected to observe the presence of NPV in the soil from four districts Faisalabad, Multan, Vehari and Bahawalpur. From 80 soil samples six samples were positive to S. litura NPV as those soil samples showed infection in S. litura larvae when mixed with artificial diet. Out of 38 collected NPV infected isolates (larvae) the best isolate (VHR4) showed maximum mortality in S. litura larvae in two screening experiments. The selected isolate was given the name V-SpltNPV and was multiplied for further experimentation. The V-SpltNPV identified by Giemsa stain under an inverted microscope. Concentrations of V-SpltNPV were prepared by dilution with distilled water and counted by hemocytometer under an inverted microscope. Efficacy of native isolate V-SpltNPV was compared with Indian commercial viral biopesticide SomstarTM- SL against 2nd, 3rd and 4th instar larvae of S. litura in laboratory. The cotton plant population were maintained in green house and used in bioassay studies. Cotton leaf discs were contaminated with various concentrations (1×108, 1×107, 1×106, 1×105 and 1×104 OBs/ml) of V-SpltNPV and SomstarTM- SL and offered to S. litura larvae. At highest concentration (1×108 OBs/ml) V-SpltNPV caused 88.08% mean mortality while SomstarTM- SL caused 61.12% of 2nd instar larvae of S. litura. LC50 and LC90 values of tested concentrations were increased with increase in larval age. The 2nd instar larvae were most susceptible than 3rd and 4th instar against all tested concentrations. In greenhouse experiment, the larval mortality was reduced to 52.63% and 37.89% for local isolate V-SpltNPV and SomstarTM- SL at highest concentration (1×108 OBs/ml) respectively on potted cotton plants. Similarly, the combination of viral formulations with spinosad showed higher mortality of S. litura larvae than alone application of tested concentrations. A combined application of spinosad with V-SpltNPV (1×108 OBs/ml) caused 100% mean mortality while combination of spinosad with SomstarTM- SL (1×108 OBs/ml) caused 78.94% mean mortality of 2nd instar larvae. All combinations used in experiment showed additive interaction. The heat stress reduced more than 50% efficacy of NPV isolates. Increase in heat stress decreased the activity of viruses in terms of larval mortality. However, combined application of V-SpltNPV with spinosad (after heat stress at 45°C) showed 75.87 % mean mortality of 2nd instar larvae of S. litura. Conclusively, local isolate V-SpltNPV proved best for the management of S. litura population alone and in combination with spinosad even after heat stress. The V-SpltNPV can be used in integrated manner with other integrated pest management tactics to significantly reduce the use the toxic chemical pesticides
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