PG Thesis

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    Bioefficacy of native fungal isolates against different pests
    (Department of Agricultural Entomology, College of Agriculture , Vellanikkara, 2025-01-30) Anagha, P K.; Smitha Revi
    Entomopathogenic fungi are widely used for the biological control of different crop pests. They are commonly derived from a number of sources, including soil, plants, decaying wood and mycosed cadavers. Isolation, identification, and evaluation of native entomopathogenic fungi are essential to develop a diverse pool of biocontrol agents adapted for effective pest management. Fungi from other regions may not perform well due to varying environmental conditions. In this background, the native fungal isolates viz., two isolates of Simplicillium aogashimaense (EPF 2 and EPF 4), one isolate of Lecanicillium psalliotae (EPF 5) and two isolates of Purpureocillium lilacinum (EPF 3 and EPF 7) maintained at AICRP on BCCP, College of Agriculture, Vellanikkara were evaluated for their pathogenicity against different pests. The present study entitled “Bioefficacy of native fungal isolates against different pests” was carried at Department of Agricultural Entomology during 2022-2024 with the objectives of evaluating the pathogenicity of native fungal isolates against different pests and standardizing the suitable medium for promising fungal isolates. These five fungal isolates were assessed for their pathogenicity against second instar larvae of tobacco caterpillar Spodoptera litura Fab., adults of red flour beetle Tribolium castaneum Herbst, adults of cowpea aphid Aphis craccivora Koch and adult gravid females of red spider mite Tetranychus truncatus Ehara. The preliminary screening bioassay with the five fungal isolates at 108 spores ml-1 showed no mortality of S. litura. However, the larvae treated with P. lilacinum (EPF 7) resulted in malformed pupae (36.67%) and adults (23.33%). No mortality was recorded for adults of T. castaneum by any of these fungal isolates. The promising isolates found against A. craccivora were L. psalliotae (EPF 5) and two isolates of P. lilacinum (EPF 7 and EPF 3), which resulted in more than 75.0 per cent mortality. T. truncatus showed mortality of 76.67 and 73.33 per cent for isolates of P. lilacinum (EPF 7 and EPF 3), respectively. These treatments were followed by L. psalliotae (EPF 5), which recorded 56.67 per cent mortality. The isolates of S. aogashimaense (EPF 2 and EPF 4) recorded lower mean mortality against A. craccivora (60.0 and 63.33%) and T. truncatus (33.33 and 40.0%), respectively. The three most promising fungal isolates in the preliminary screening bioassay against A. craccivora and T. truncatus were subjected to dose-response and exposure time-response bioassay. Spore suspensions of five different concentrations ranging from 105 to 109 spores ml-1 were tested against these pests by contact toxicity method. Lecanicillium psalliotae (EPF 5) at a concentration of 109 spores ml-1 recorded the highest mortality of 100.0 per cent against A. craccivora, ten days after treatment. At the same concentration, P. lilacinum (EPF 7 and EPF 3) registered 86.29 and 79.63 per cent mortality, respectively. L. psalliotae (EPF 5) exhibited the lowest LC50 (1.3 ×105 spores ml-1) and LT50 (3.95 days) at 109 spores ml-1. Purpureocillium lilacinum (EPF 7) recorded the highest mortality of 83.33 and 76.67 per cent at 109 and 108 spores ml-1 followed by P. lilacinum (EPF 3) at 109 spores ml-1 (73.33%) against adult gravid females of T. truncatus, ten days post treatment. P. lilacinum (EPF 7) showed the lowest LC50 (1.04×106 spores ml-1) and LT50 (6.40 days) among the three isolates. The promising isolates against A. craccivora and T. truncatus were grown in six different media. For this, Potato Dextrose Agar (PDA), Czapek Dox Agar (CDA), Sabouraud Maltose Agar (SMA), Sabouraud Maltose Agar with Yeast Extract (SMAY), Sabouraud Dextrose Agar (SDA) and Sabouraud Dextrose Agar with Yeast Extract (SDAY) and their broths were used to assess the effect of media on radial growth, sporulation, viability of spores, production of biomass and virulence against target pests. The effect of media on the virulence of fungal isolates was assessed by treating the test pests with spore suspension from each medium at the concentration of 1×108 spores ml-1. Lecanicillium psalliotae (EPF 5) showed maximum radial growth (58.5 mm), sporulation (7.87×108 spores ml-1), viable spores (3.5×108 cfu ml-1) and mycelial biomass (1.93g) in SMAY. The spore suspension from SMY broth recorded the highest mortality (95.0%) against A. craccivora, which was on par with SDY and PD broths (92.5%). Purpureocillium lilacinum (EPF 7) recorded the maximum radial growth (70.75 mm), sporulation (4.25×109 spores ml-1), and viable spores (15×108 cfu ml-1), in SDY broth while the highest mycelial biomass was obtained in PD broth (5.15g). The spore suspension from SDY broth recorded the highest mortality (85.0%) against gravid females of T. truncatus, which was on par with PD broth (82.5%) and SMY broth (80.0%). In conclusion, the study highlights the potential of native entomopathogenic fungi as sustainable biocontrol agents. Among the isolates, L. psalliotae (EPF 5) demonstrated unparalleled efficacy against A. craccivora. Its optimal growth and virulence in SMAY make it a prime candidate for large-scale application. Similarly, P. lilacinum (EPF 7) proved to be the most pathogenic isolate against gravid females of T. truncatus, demonstrating significant mortality rate when cultured in SDAY. These findings not only reinforce the significance of selecting native fungal isolates but also emphasize the critical role of optimized growth media in enhancing biocontrol efficiency.
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    Impact of botanicals on pests and defenders in rice ecosystem
    (Department of Entomology, College of Agriculture, Vellayani, 2000) Ajaya Kumar, C; Nalina Kumari, T
    The magnitude and intensity of insect pest and their defenders at different growth stages of rice were assessed in a survey during the virippu season of 1998, adopting random sampling technique, in three taluks of Thiruvananthapuram district. The survey revealed that the occurrence and distribution of the population of pests and defenders were same in the various locations, where the tolerant variety Jyothi was cultivated. The total population of pests and defenders observed at different growth stages of the crop followed a definite pattern in the three locations. Different concentrations of the leaf extracts of A. indica, and C. infortunatum and nimbecidine were evaluated in the laboratory for their antifeedant and deterrent activity and contact toxicity against important pests of rice and their defenders. Based on the percentage of leaf protection, the plant products tested were superior to control against C. medinalis. The same effect was noticed with N. depunctalis, only with the highest dose of leaf extracts of A. indica and nimbecidine. Seventy five per cent deterrent effect was observed to N. lugens at the highest dose of the plant products. None of the plant products showed any deterrent action against L. acuta or exhibited contact toxicity to L. acuta, C. medinalis. N. depunctalis andN. lugens. Both the defenders tested CL. pseudoannulata and O. nigrofasciatay; were safe with the plant products. 2 Replicated experiment was conducted on rice to evaluate the efficacy of plant products in suppressing the pests as well as in augmenting the defenders under field conditions. The leaf extract of C. infortunatum was found to be efficient in suppressing the population of C. medinalis. The effect was same as that with insecticides. The population of N. depunctalis was reduced by the leaf extracts of A. indica and C. infortunatum as observed in treatment with carbaryl. The suppressing effect observed on N. lugens was same with both the leaf extracts and insecticides, whereas, none of the treatments showed reduction in the population of L. acuta. The total population of the pests in general, showed a varying effect of plant products at different growth stages of the crop. Leaf extracts of C. infortunatum resulted in an immediate suppression of the total population of the pest at 20 DAT, whereas, A. indica gave significant reduction at 40 DAT. The treatments didnot show any effect on the total pest population at 60 DAT. The effect of plant products on spider population revealed that they were found to be safe. The leaf extract of A. indica increased the spider population at 20 DAT and C. infortunatum at 60 DAT, whereas, insecticides showed harmful effect up to three days after application. Adverse effect with plant products on the population of 0. nigrofasciata was not observed in any of the treatments. An increase in the population of the predator was observed with leaf extracts of A. indica at 20 DAT and with C. infortunatum at 40 and 60 DAT. Significant reduction in the population of Agriocnemis spp. was recorded in treatment with leaf extract of C. infortunatum, whereas, significantly higher population was observed in treatment with leaf extract of A. indica. The population of M crocea was reduced due to the application of plant products and the effect was retained up to three days after application. 3 The influence of plant products on the total population of defenders has clearly indicated that the leaf extracts of A. indica and C. infortunatum were safe to the defenders. Based on the P:D ratio, these products were found to have the best effect in augmenting the population of defenders and suppressing the population of pests. Significant differences in the grain and straw yield was not recorded either in treatments with plant products or with insecticides when compared with control. Overall assessment of the results obtained revealed that A. indica and C. infortunatum can be effectively and safely used for the management of important pests of rice with out much adverse effect on non target organisms in the rice ecosystem. Just like A. indica, C. infortunatum could also be utilised for developing effective plant protection chemicals for replacing undesirable synthetic insecticides in integrated pest management.
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    Management of the sucking pest complex coconut eriophyid mite, coreid bug and button mealy bug infesting coconut bunches
    (Department of Agricultural Entomology, College of Agriculture, Vellayani, 2001) Priya Mohan; Faizal, M H