Browsing by Author "Asna Sharin."

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    Pellet formulations of entomopathogenic fungi and their bioefficiacy in managing soil inhabiting pests
    (Department of Entomology, College of Agriculture,Vellayani, 2024-02) Asna Sharin.; Reji Rani, O P
    The study entitled “Pellet formulations of entomopathogenic fungi and their bioefficacy in managing soil inhabiting pests” was carried out at Department of Entomology, College of Agriculture, Vellayani during the year 2020-2023 with an objective to develop biopellet formulations of entomopathogenic fungi for the management of soil inhabiting insect pests. Pathogenicity test carried out in soil inhabiting pests such as pepper root mealy bug, Formicoccus polysperes Williams and later stages of cucurbit fruit fly, Bactrocera cucurbitae (Coquillett) using spore suspensions of entomopathogenic fungi such as Metarhizium anisopliae (Metsch.) Sorokin NBAIR isolate Ma4, Beauveria bassiana (Bals.) Vuillemin NBAIR isolate Bb5, B. bassiana KAU isolate ITCC 6063 and Lecanicillium saksenae (Kushwaha) Kurihara and Sukarno KAU isolate ITCC 7714 each at 108 spores mL-1 revealed that all the tested fungi were infective to pepper root mealybug, at varying levels. Apart from the normal symptoms of mycosis, L. saksenae infection resulted in sudden dissolution of the mealy coating, unlike in B. bassiana isolates, indicating its fast action. For the last instar larvae and pupae of cucurbit fruit fly, M.anisopliae was found to be the effective pathogen compared to B.bassiana isolates. Infectivity of L. saksenae was very low in fruit fly. Dose-mortality response of L. saksenae to root mealybug, F. polysperes unveiled that 107 and 108 spores mL-1 were equally effective resulting in 92 and 100 per cent mortality within four days of treatment, hence 107 spores mL-1 was determined as the effective dose. In the case of B. cucurbitae, the effective dose was 108 spores mL-1 for both larvae and pupae causing 77.5 per cent and 55 per cent mortality, respectively. The LC50 and LC90 values of L. saksenae computed on the fourth day after treatment on root mealy bug was 2.2x105 and 2.6x107 spores mL-1, respectively. The lethal time recorded for 50 per cent mortality was 23.13 h and for 90 per cent mortality it was 83.76 h, indicating its high virulence. In fruit fly larvae, for M. anisopliae, the LC50 and LC90 values were 2.5x106 and 6.6x108 spores mL-1, respectively on the 10th day after treatment, indicating a moderate virulence. Experiment to assess the effect of carrier materials on conidial viability and virulence of L. saksenae based on its germination percentage and mortality to test 125 insects revealed the superiority of the talc + chitin in the ratio 95:5 with 78.54 per cent germination and 87.5 per cent mortality of mealybugs even five weeks after storage (WAS). Other carrier materials such as talc + chitosan (90:10), talc alone and chitosan alone, exhibited only 50.62 to 74.58 per cent germination and 55.0 to 67.5 per cent mortality. The spores in chitin exhibited only 33.96 per cent viability and 50 per cent mortality. Based on conidial viability the best carrier material for formulating M. anisopliae pellets was found to be talc + chitosan in the ratio 90:10 as it recorded highest conidial viability (69.75 per cent) 5 WAS and mortality of 32.5 per cent, to the 3rd instar larvae of B. cucurbitae. When talc and talc + chitin (95:5) were used as the carrier materials the corresponding viability and mortality recorded were 61.46 to 65 and 7.5 to 20 per cent. Suitability of binding agents for formulating L. saksenae pellets was tested using various binders such as Carboxy Methyl Cellulose (CMC) 6%, Microcrystalline Cellulose (MCC) 6% and Acacia Gum arabic (AG) 5%. It was found that the combination of talc + chitin (95:5) + the binding agent CMC (6%) was superior for L. saksenae spores compared to its combination with MCC (6%) and AG (5%). CMC maintained 80.63 per cent germination and 92 per cent mortality on five WAS. The corresponding viability and mortality recorded in MCC was 51.5 and 68 per cent and in AG, it was 30.67 and 50 per cent, respectively. CMC was proved to be superior for formulating M. anisopliae pellets also, as it recorded 79.33 per cent germination and 42 per cent mortality on fifth WAS. Pellets formulated at 109 spores mL-1, using a mixture of talc + chitin (95:5) + CMC 6% were tested at varying moisture levels of 8, 10, 12 and 15%. Pellets with 15% moisture content were superior with 67.44 per cent conidial viability and 80 per cent virulence, when observed after two months. Thereafter, though there was a decrease in germination rate below 55 per cent, the virulence could be retained up to 60 per cent till three months after storage. L. saksenae pellets stored for a period of three months under ambient conditions revealed that the shelf life declined gradually after two months. After three months, conidial viability of pellets reduced from 87.25 to 38.74 per cent at 15 % 126 moisture level and from 84.99 to 32.32 per cent at 12% moisture. The mortality decreased from 90 to 60 per cent and 85 to 45 per cent in 15% and 12 % moisture levels, respectively. However, the extent of contamination noted was 2.75x105 cfu mL-1 which was beyond the permissible level as per CIBRC standards. Therefore, the pellets prepared with moisture content between 12 to 15 % where the contaminant count was within the permissible limit, 1.2x104 cfu mL-1 was fixed as ideal for pelleting. Laboratory assay carried out to standardize the dosage of L. saksenae biopellets for managing root mealybugs revealed that, 1.0 (2 pellets), 1.5 (3 pellets), 2.0 (4 pellets) and 2.5 g (5 pellets) biopellets per 100 g of soil were found to be equally effective causing 75 to 82.5 per cent mortality, two WAT. On further evaluation under pot culture, after 4 weeks of treatment the dosage 1.5 g/100g was found to be superior (74.99 per cent mortality). The corresponding mortality in chlorpyriphos 20 EC @ 0.075% was 83.33 per cent. A comparison of population density in different treatments revealed that, L. saksenae was the superior treatment as it was on par with chlorpyriphos 20 EC (0.075%). There was no population buildup upto two weeks after treatment. Hence, the dosage for pot application was fixed as 1.5 g bio pellets for 100 g of soil. The study concluded that L. saksenae biopellets, formulated at 109 spores mL-1 using talc + chitin (95:5) + 6% CMC at 12% to 15% moisture level is effective for the management pepper root mealybugs at 1.5 g of bio pellets (3 pellets) for 100 g of soil. These biopellets can be stored for a period of three months, under ambient conditions.