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2019 - 201912020 - 20231
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Subject: Nematology × Author: BHARATH, AMURI × Start date: 2010 ×
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    ThesisItemOpen Access
    BIO EFFICACY OF NATIVE ENTOMOPATHOGENIC NEMATODES AGAINST MAJOR INSECT PESTS OF CRUCIFEROUS CROPS IN ASSAM
    (2023) BHARATH, AMURI; Bhagawati, Bhabesh
    A survey was conducted during the year 2020-2022 for isolation of entomopathogenic nematodes (EPNs) in cruciferous and vegetable growing areas of Jorhat district of Assam from 7 locations viz., Experimental Farm, Dept. of Horticulture, ICR Farm, AAU, Jorhat, Tea Plantations, AAU, Jorhat, Nemati Ghat, Moran Gaon, Titabor and 7 different isolates of EPN were recovered with 3.50 percent frequency of occurrence. Based on morphological and morphometric studies the isolates were identified to be Oscheius chongmingensis (EPN 1and 2), Heterorhabditis indica (EPN 3, 4and 5) and H. bacteriophora (EPN 6 and 7). Further, molecular characterization was done by amplification of ITS region of 5.8s mtDNA. The sequences of genus Heterorhabditis and Oscheius isolates were subjected to BLAST at NCBI and on the basis of aligned sequences, the isolates were identified to be Heterorhabditis indica, H. bacteriophora and Oscheius chongmingensis by using construction of phylogentic tree in MEGA 11.00. Efficacy of Oscheius chongmingensis, Heterorhabditis indica and H. bacteriophora were tested against Diamond backmoth (Plutella xylostella) and Cabbage butterfly (Pieris brassicae) under in-vitro conditions with six different concentrations of infective juveniles (IJs). With the increase in the concentration of IJs and with time of exposure, there was a corresponding increase in the mortality of the insect larvae. Heterorhabditis indica and H. bacteriophora showed 100 per cent mortality of P. xylostella and P. brassicae at 96 h of exposure with highest concentration of IJs/larva (i.e. 300 IJs/larva) as compared to O. chongmingensis (50.00 % mortality). The LD50 values of both the EPNs decreased when exposure period was increased. A pot experiment was also conducted to study the efficacy of two best EPNs viz. H. indica and H. bacteriophora against P. xylostella taking different doses viz. 200, 400 and 600 IJs/ pot with another treatment with water as control. H. indica exhibited maximum mortality at 600IJs after 72hrs of exposure and was found to be at par with the treatment with H. bacteriophora. The effective EPN species has to be further tested under filed conditions to identify the proper doses and method of delivery.
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    ThesisItemOpen Access
    EFFICACY OF ENTOMOPATHOGENIC NEMATODES (EPNs) AGAINST MAJOR INSECT PESTS OF TEA
    (AAU, Jorhat, 2019-07) BHARATH, AMURI; Devi, Gitanjali
    A total 200 soil samples were collected from tea plantation areas of district, Jorhat, Assam and were assessed for entomopathogenic nematodes using the Galleria baiting technique. Out of 200 soil samples, EPNs were found in 2 soil samples with 1% frequency of occurrence. One isolate of Oscheius sp. (0.5%), was isolated from Experimental farm for plantation crops, Section-4, 10, 19 AAU, Jorhat and another Heterorhabditis sp. (0.5%) was isolated from Chetiagoan, Jorhat. Morphological and morphometrical characters were used in the identification of nematode isolates. The identified species were Heterorhabditis bacteriophora, and Oscheius chongmingensis. In infectivity study, indigenous isolates of EPNs, Heterorhabditis bacteriophora and Oscheius chongmingensis tested in the laboratory bioassay, caused mortality of tea mosquito bug, Helopeltis theivora and bunch caterpillar,Andraca bipunctata. Fifty, 60 and 70 per cent mortality of Helopeltis theivora by H. bacteriophora at 150 IJs/insect was observed at 48 h, 72 h and 96h respectively. With the increase in the exposure period to 96 h, H. bacteriophora could induce up to 90% mortality of the tested insect at the dose of 250 IJs. Similarly, mortality of Helopeltis theivora increased with increase in the dosage of O. chongmingensis and recorded 50, 60 and 70 per cent mortality at 200 IJs/insect at 48 h, 72 h and 96h. Bioassay of H. bacteriophora and O. chongmingensis against the 3rd instar larvae of Andraca bipunctata indicated that at 250 IJs/larva recorded 70 and 60% mortality in 48 hours of exposure, while 100 and 90% mortality of Andraca bipunctata was recorded at 96h. H. bacteriophora was more pathogenic than Oscheius chongmingensis against Helopeltis theivora and Andraca bipunctata based on LD50 values at 48 h, 72 h and 96 h.