EVALUATION OF ENTOMOPATHOGENIC FUNGI AGAINST Spodoptera litura (Fabricius)
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Date
2009
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Punjab Agricultural University, Ludhiana
Abstract
Natural mortality of Spodoptera litura due to entomopathogens was recorded on different available crops during May to October, 2008. Among the microorganisms, the incidence was highest due to virus (6.45 %) followed by bacteria (5.00%) and fungi (3.00%). The mortality of S. litura due to virus, bacteria and fungi was maximum during 2nd fortnight of July, 2nd fortnight of May and 2nd fortnight of August, respectively. The maximum mean per cent mortality due to bacteria (5.00%) was on cabbage and due to fungi and virus (3.00% and 6.45%, respectively) was on arvi (Colocasia esculenta) crop. Five entomopathogenic fungi and four locally isolated fungal isolates were characterized on the basis of morphological characteristics. Beauveria bassiana isolates showed regular colony borders with white cottony and powdery mycelium, conidia were oval in shape, smooth and hyaline and spore size ranged from 2.1 x 2.0 to 2.2 x 2.0 μm. Colonies of Nomuraea rileyi were white initially and later turned pale green and hyphae were septate and hyaline and size of conidium ranged from 2.4 x 2.2 to 2.6 x 2.1 μm. In case of Metarhizium anisopliae, conidia were cylindrical, tapering and aspetate and their size ranged from 5.5 x 3.1 to 5.5 x 3.3 μm. All locally isolated fungi were initially white in colour and later turned to pale green (PAUF1 and PAUF2) or olive green (PAUF3 and PAUF4). Among the four different media studied for radial growth, N.rileyi-MTCC, N.rileyi-DOR, PAUF1 and PAUF2 showed good growth on SMAY, while B.bassiana showed good growth on PCA and in case of M.anisopliae, PAUF3 and PAUF4 best growth was observed on SDAY medium. Efficacy of different entomopathogenic fungal isolates at three different concentrations were evaluated against second instar larvae of Spodoptera litura at 25°C and was observed that the mortality at higher concentration (108 conidia /ml) was significantly better than middle concentration (107 conidia /ml) which in turn were significantly better than lower concentration (106 conidia /ml). At higher concentration, i.e. 108 conidia /ml, N. rileyi -MTCC showed cent per cent mortality followed by B.bassiana-PDBC and B.bassiana-MTCC which gave 76.67 and 66.67 per cent mortality, respectively at the same concentrations. N. rileyi-MTCC gave LT50 value of five days followed by B. bassiana-MTCC and B. bassiana-PDBC which gave LT50 of eight and seven days, respectively. Bioassay studies at different temperatures viz. 20ºC, 25ºC and 30ºC against second instar larvae of S.litura under laboratory conditions revealed that fungal isolates were more virulent at 25ºC and 30ºC than at 20ºC.
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