Pathogenicity Of Metarhizium anisopliae (Metschinikoff) Sorokin To Spodoptera litura (Fabricius)
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Date
2012
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Mahatma Phule Krishi Vidyapeeth, Rahuri.
Abstract
The present investigation was undertaken during winter season of 2010 to study the pathogenicity of M.anisopliae to S. litura, at Biocontrol Research Laboratory, Department of Agricultural Entomology, Post Graduates Institute, Mahatma Phule Krishi Vidyapeeth, Rahuri, Dist. Ahmednagar, Maharashtra , India. It was determined by bioassay on I to V instar larvae of S. litura on the basis of LC50 values. Bioefficacy of M.anisopliae against S. litura was also studied. The bioefficacy study comprised of 6 treatments of each of 1.15% WP and 3% Aqua Suspension(AS) of the entomopathogenic fungus M.anisopliae. The cfu count of both the formulations was determined. At 0.1% it was 1.69×108 cfu ml-1 for 3% AS and 1.01×108 cfu ml-1 for 1.15% WP.
The results of pathogenicity revealed that LC50 values of 3% AS for I, II, III, IV and V instar larvae of the pest were 4.48×103 , 5.96×103, 2.50×104, 4.74×104 and 1.45×105 cfu ml-1, while that for 1.15% WP were 3.70×103, 4.86×103,1.47×104,2.08×104 and 1.2×105 cfu ml-1, respectively. The calculated LT50 values of M.anisopliae 3% AS for II,III,IV,V instar larvae at 1×103,1×104 ,1×104 and 1×105 cfu ml-1 were 9.29, 9.57, 11.43 and 14.85 as against the corresponding values of M.anisopliae 1.15% WP for II,III,IV,V instar larvae at 1×103,1×104 ,1×104 and 1×105 cfu ml-1 were 8.91, 10.17, 12.17 and 13.24, respectively. Larvae treated with 0.6 per cent M.anisopliae ceased feeding in 48 hours , their movement became slower and tend to gather at the closed portion of polythene bags, became dull and sluggish. The growth of green, fluffy mycelium of fungus on dead larvae was observed between 9th to 14th days of treatment. Some larvae succeeded in pupating showed mycosis on the pupal case. Early instar larvae when infected with the fungus showed profuse fungal growth than advanced instar larvae. Some bigger larvae although burst but did not show mycosis. However, their body fluid was rich with fungal growth. Bioefficacy study revealed that the mortality of III
instar larvae ranged between 24.44 and 67.78 per cent at 1.01×105 and 6.06×105 cfu ml-1 for 1.15% WP and 27.78 and 76.67 per cent at 1.69×105 and 1.014×106 cfu ml-1 for 3% AS at 14 days of treatment, respectively. Moderate mortality (46.6758.89 %) was observed at 0.6 % concentration on 9th day of treatment for both these formulations. But all the treatments were significantly superior to untreated control in reducing the population of the larvae.
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