PG Thesis
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Item Characterization and bioefficacy of Beauveria bassiana RB PTB on rice bug Leptocorisa sp.(Department of Agricultural Entomology, College of Agriculture, Vellanikkara, 2025-01-31) Aany, M; Sreeja, PMicrobial control is a safer alternative to chemical pesticides and a potential tool in eco-friendly pest management. Identification and characterisation of indigenous isolates which are more virulent than exotic strains is important for developing potential entomopathogens for pest management. Beauveria bassiana RB PTB is a new indigenous isolate obtained from rice bugs from Pattambi, Kerala and was identified as a new isolate of B. bassiana (Bals.) Vuill. (Ascomycota: Hypocreales) based on molecular and morphological characters. The present study entitled “Characterization and bioefficacy of Beauveria bassiana RB PTB on rice bug Leptocorisa sp.” was conducted at the Department of Agricultural Entomology, College of Agriculture, Vellanikkara, during 2022-2024, with the objective to characterize and evaluate the pathogenicity of B. bassiana RB PTB to hemipteran pests and its compatibility with pesticides. Morphological characterization of the isolate revealed that the conidiogenous cells were densely clustered with swollen stalk, consisting of sub-globose to flask shaped venter, zig-zag shaped denticulate rachis. Conidia was hyaline, smooth walled, globose to sub- globose, with a rounded and slightly pointed base with size of 3.38 µm × 2.53 µm, hyphal width of 3.44 µm. To identify the suitable medium, for the optimum growth of B. bassiana RB PTB, cultural characteristics like colour, shape, texture, and growth rate of the mycelium were studied in five different media viz., Sabouraud Maltose Agar and Yeast (SMAY), White media (NIPHM), Czapek Dox Agar (CDA), Sabouraud Dextrose Agar (SDA), and Potato Dextrose Agar (PDA). SMAY medium favoured optimum growth of B. bassiana RB PTB with mean colony diameter of 5.20 cm at 14 DAI and colonies were pure white, woolly and densely floccose with pale yellow colour on the reverse side. The optimum temperature for the growth of B. bassiana RB PTB, was 27℃ which recorded a mean colony diameter of 5.25 cm at 14 DAI. The optimum pH for the growth of B. bassiana RB PTB was identified by culturing the fungus in SMY broth under various pH viz., 5.0, 5.5, 6.0, 6.5, 7.0, 7.5, 8.0, 8.5, 9.0, and 9.5 and a slightly acidic pH of 6 yielded the highest spore count of 7.65×108 spores mL-1. The infectivity of B. bassiana RB PTB to hemipteran pests was assessed by topical application of spore suspension at a concentration of 1×108 spores mL-1. Host range studies revealed that B. bassiana RB PTB was infective to pod bug, Riptortus pedestris F., brinjal mealybug, Coccidohysterix insolita Green, cowpea aphid, Aphis craccivora Koch, white fly, Bemisia tabaci Gennadius, and the brown planthopper, Nilaparvata lugens with a mortality from 40 to100 per cent at 120 HAT. Safety of B. bassiana RB PTB to non-target organisms viz., predators (Micraspis discolor and Tetragnatha mandibulata), parasitoids (Goniozus nephantidis, Trichogramma chilonis and T. japonicum) and productive insect (Apis cerana indica) were assessed. It was found safe to all predators and parasitoids except T. mandibulata with 33.33 per cent mortality. B. bassiana RB PTB was infective to Apis cerana indica, with 100 per cent mortality at 120 HAT. To evaluate the bioefficacy of B. bassiana RB PTB on rice bug, Leptocorisa acuta, a multiple dose bioassay was carried out with concentrations ranging from 103 to 108 spores mL-1. The effective concentration was identified as 1×108 spores mL-1 with the highest mortality of 100 per cent at 120 HAT and lowest LT50 value of 1.63 days. A comparative bioefficacy of indigenous entomopathogenic fungal isolates viz., B. bassiana RB PTB, B. bassiana VKA 01, and Lecanicillium saksenae were tested against third instar nymphs and adults of L. acuta. Spore suspension of B. bassiana @ 1×108 spores mL-1 recorded 100 per cent mortality at 96 HAT, while the corresponding mortality was observed in L. saksenae and B. bassiana (VKA 01) at 120 and 144 HAT respectively, whereas in adult rice bug B. bassiana RB PTB and L. saksenae recorded 100 per cent mortality at 144 HAT. The compatibility of B. bassiana RB PTB with selected fungicides and insecticides were assessed in vitro using poisoned food technique. Among tested fungicides, copper hydroxide 77 WP at 0.1 per cent was found to be highly compatible with mean colony diameter of 5.15 cm at 14 DAI and 0.96 per cent inhibition, while carbendazim 50 WP (0.1%), mancozeb 75 WP (0.2%), hexaconazole 5 EC (0.2%) and tebuconazole 50% + trifloxystrobin 25% 75 WG (0.04) were incompatible with 100 per cent growth inhibition. Among insecticides, flubendiamide 20% WG and thiamethoxam 25% WG were compatible with 10.58 and 12.02 per cent inhibition with colony diameter 4.65 and 4.57 cm respectively, while acephate and malathion recorded 66.35 and 59.61 per cent inhibition. In conclusion, B. bassiana RB PTB was found to be a promising isolate against hemipteran pests and safe to natural enemies in rice ecosystem. This novel isolate can be uplifted as a potential candidate for pest management.Item Factors responsible for the population buid up of rice bug, Leptocorisa acuta Thunb and the control of the pest(Department of Entomology, College of Agriculture, Vellayani, 1986) Krishna Kumar, R; Visalakshi, AThe rice bug Leptocoria acuta Thunb, was reared on the rice varieties Jaya, Jyothi, Triveni, Pavizham and Karthika in order to study the effect of varieties on the insect's biological features. Statistical analysis of the data obtained showed that varieties have no significant influence on the biological features of L. acuta. Studies made on the duration/survival of L. acuta on eleven common rice land weeds found in paddy fields showed that the bugscould complete their life cycle only on Echinoedria colonum and E. crusgalli. The bugs survived for short periods on a few of the otherweed hosts.Item Studies on insect pests and diseases of rice earhead and their control(Department of Entomology, College of Agriculture, Vellayani, 1987) Annie Thomas; Rajan Asari, P AA random sample survey on insect pests and diseases infesting rice during, flowering stage was conducted to collect information on the occurence of pests and diseases on rice earhead of different localities in Trivandrum district. Itcould be observed that L.acuta was the most important pest occurring throughout the area surveyed . The importance of rice bug was further proved by the mean number of insect present in different localities. The mean number of rice bug varied from 0.25 to 2.45 which showed the existence of considerable variation according to localities and varieties. The high yielding varieties invariably were seen more susceptible to the pest infestation than the local cultivars.