PhD Thesis
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Item Acaricide resistance in spider mites (Acari: Tetranychidae) Infesting major crops of Central Kerala(Agricultural Entomology, College of Agriculture, Vellanikkara,, 2025-08-18) Penuballi Swathi; Haseena BhaskarSpider mites (Acari) inhabit a wide array of environments and pose significant threat to a variety of commercially grown vegetable crops and ornamental plants. Chemical management measures using synthetic acaricides remains the primary means of mite management, globally. However, the repeated use of chemical pesticides has led to the development of resistance in mite populations, including resistance to acaricides with novel modes of action, resulting in control failures. TetranychustruncatusEhara and Tetranychusgloveri Banks are the predominant spider mite pests on vegetable crops and ornamental plants in Kerala. Mite management in vegetable fields and horticultural nurseries of Kerala primarily relies on synthetic acaricides like spiromesifen, fenazaquin and diafenthiuron. Increased instances of control failures, despite the application of recommended doses of these acaricides, have recently been reported by the farmers and nursery owners. Sole dependence on acaricides for a prolonged period might have resulted in the reduced susceptibility of mite populations to commonly used acaricides. Hence, a study was carried out to investigate the susceptibility of the field populations of T. truncatus and T. gloveri to commonly used acaricides, the possible development of cross /multiple resistance and to elucidate the underlying mechanisms of resistance. Purposive sampling surveys were conducted across commercial horticultural nurseries, vegetable fields and tissue culture (TC) hardening units in central Kerala (Thrissur, Ernakulam, Palakkad and Malappuram) to collect spider mite populations. Isoline cultures of eight T. truncatus populations collected on marigold (Mg1Tr) and vegetable crops (Cp1Pt, Cu1Pt, Ok1Pt, Am2Pt, Am3Vt, Cp2Tv and Am4Tv), and nine T. gloveri populations collected on adenium (Ad1Rg and Ad2Sd), gerbera (Gr1Pt), dahlia (Da1Vt), anthurium (An1Bv) and tissue culture banana (Bn3Tr, Bn2Kn, Bn1Gn and Bn4Ak) were maintained in the laboratory with unique accession numbers. The laboratory maintained populations of T. truncatus (SST) for more than 10 years (>300 generations) and T. gloveri (SSO) for more than six years (>180 generations), without exposure to acaricides were designated as susceptible reference populations. The laboratory bioassay of T. truncatus with fenazaquin showed moderate levels of resistance in the populations on amaranthus (Am2Tr- 39.70 folds) and marigold (Mg1Tr- 25.60 folds) populations from Thrissur, cucumber from Pattambi (Cu1Pt- 12.90 folds) and amaranthus from Vyttila (Am3Vt- 10.50 folds). The other populations collected on amaranthus from Tavanur (Am4Tv) and on okra (Ok1Pt), and cowpea (Cp1Pt) from Pattambi, recorded low levels of resistance (RR 3.70- 7.90 folds). Among the T. gloveri populations, adenium population from National Rose Garden, Thrissur (Ad1Rg- 57.20 folds) and TC banana population from Kannara (Bn2Kn- 41.04 folds) recorded high levels of resistance to fenazaquin, while the mite populations collected on TC banana plants from Vyttila (Bn1Gn- 15.72 folds) and Thrissur (Bn3Tr- 15.80 folds), and on dahlia from Vyttila (Da1Vt- 13.31 folds) recorded moderate level of resistance. Other T. gloveri populations collected on gerbera, anthurium and adenium showed only low levels of resistance. Tetranychustruncatus collected on marigold (81.90 folds) and amaranthus (79.75 folds) from Thrissur recorded very high levels of spiromesifen resistance. The amaranthus population from Vyttila (Am3Vt- 33.41 folds); cowpea (Cp1Pt-25.16 folds) and okra (Ok1Pt- 25.83 folds) populations from Pattambi, showed moderate levels of resistance, while populations on cowpea (RR 07.08) and amaranthus (RR 05.90) collected from Tavanur recorded low levels of resistance. Susceptibility studies of T. gloveri with spiromesifen showed that the population on adenium from National Rose Garden (76.33 folds) and on TC banana from Kannara (71.33 folds) exhibited high levels of resistance. Populations collected on TC banana from Vyttila (30.33 folds), Thrissur (28.17 folds) and Anakkayam (13.79 folds) recorded moderate levels of resistance. The populations collected on the ornamental plants viz., dahlia (24.33 folds), anthurium (19.08 folds) and adenium (17.25 folds) also recorded moderate levels of resistance to spiromesifen. Low to moderate levels of resistance to diafenthiuron were recorded in T. truncatus (1.94- 17.56 folds) and T. gloveri (1.95- 15.57 folds), where marigold population from Thrissur (17.56 folds) and adenium population from National Rose Garden (15.57 folds) recorded significantly higher levels of resistance, respectively. Tetranychustruncatus and T. gloveri populations with resistance to fenpyroximate showed moderate levels of cross-resistance to fenazaquin and the propargite resistant populations showed cross resistance to diafenthiuron. However, the field populations recorded only low levels of multiple resistance to chlorfenapyr and hexythiazox (acaricides with different modes of action) in T. truncatus (1.20- 5.40 folds; 1.00- 1.50 folds) and T. gloveri (1.10- 2.35 folds; 2.08- 12.00 folds). Assay of detoxification enzymes in T. truncatus and T. gloveri showed significantly elevated activities of carboxylesterase (CarE) (1.27-2.27fold; 1.59-2.10 folds), cytochrome P450 monooxygenase (CytP450) (1.36- 4.98 folds; 1.08-3.10 folds), and glutathione S-transferase (GST) (1.00- 2.12 folds; 1.09- 1.98 folds) in resistant populations. The highest activity of detoxifying enzyme was recorded in T. truncatus population on marigold for CytP450. The study on differential gene expression and sequence variation of the CYP392E10 gene (encodes CytP450 enzyme) in the spiromesifen and fenazaquin resistant marigold population of T. truncatus showed a lower CT value with 7.61 folds higher gene expression than the susceptible population. Sequence analysis of CYP392E10 gene in the resistant population showed four single nucleotide polymorphisms (SNPs), where T is substituted by A (256th, 676th and 1356th) and A is replaced with G (708th position). The alignment of amino acid sequences of the susceptible and resistant T. truncatus populations showed substitution of Lleucine with methionine at 86th position and phenylalanine with isoleucine and lysine at 226th and 452nd positions, respectively. This study reports alarming levels of acaricide resistance in the spider mites, T. truncatus and T. gloveri in central Kerala, to commonly used acaricides. The mite species were also found to have developed significant levels of cross resistance to many unexposed acaricides. However, significantly low level of multiple resistance to the acaricides, chlorfenapyr and hexythiazox suggests their suitability as alternatives to commonly used acaricides in mite management. The study highlights the role of detoxifying enzymes and the overexpression of the related gene, particularly CytP450 in the development of resistance against commonly used acaricides (fenazaquin, spiromesifen and diafenthiuron). The study also provides new insights into the resistance mechanisms in the mite species in response to sustained acaricide pressure, exhibiting metabolic and target-site insensitivity, which further needs functional validation.Item Endophyte mediated bio-intensive management of pests of cowpea Vigna unguiculata (L.) Walp(Department of Agricultural Entomology, College of Agriculture, Vellayani, 2025-06-28) Rajeshwaran, B; Faizal, M HThe present study entitled “Endophyte mediated bio-intensive management of pests of cowpea Vigna unguiculata (L.) Walp.” was conducted in the Department of Agricultural Entomology, College of Agriculture, Vellayani, during the period 2020 2024. The primary objective of this research was the characterization and utilization of native endospore-forming endophytic bacteria (EEB) for the bio-intensive management of pests in cowpea. This approach aimed to provide an eco-friendly alternative to conventional pest control methods, contributing to sustainable agricultural practices. A total of 54 bacterial endophytes were isolated from vegetable and bush-type cowpea plants, of which 49 were confirmed as endospore-formers using the Schaeffer Fulton method. These endospore-forming bacteria underwent a series of bioassays to assess their pathogenicity and feeding deterrence against the chewing insect Spodopteralitura. The evaluation included direct exposure methods and exposure through primed cowpea seedlings in both choice and no-choice experimental conditions. Among the isolates tested, ten isolates viz., CPB 1a, CPB 2a, CPB 5a, CPB 8b, CPV 06, CPV 08, CPV 14, CPV 18, CPV 21, and CPV 32 were found effective in the in planta choice assessment. These isolates significantly reduced damage with lower damage intensity scores of 1.73 to 2.07 compared to unprimed controls (4.87) and other isolate-primed plants (2.47 - 4.93). The selected ten isolates were further subjected to in planta no-choice conditions, where the fitness of feeding insects was tested using relative growth rates and antifeedant activity of second and fourth instar S. litura. Three isolates, namely CPB 1a, CPV 18, and CPV 14, primed cowpea plants substantially reduced larval relative growth rates for both 2nd instar (0.35 mg/day, 0.46 mg/day, and 0.58 mg/day, respectively) and 4th instar (0.42 mg/day, 0.49 mg/day, and 0.59 mg/day, respectively). Similarly, the antifeedant activity, in terms of percentage weight gain reduction compared to larvae on control plants, was 80.53%, 73.58%, and 65.94% for the 2nd instar and 71%, 65.77%, and 54.44% for the 4th instar in these three isolates. The priming effects of endophytes were prominently observed in cowpea plants treated with CPB 1a and CPV 18 when exposed to S. litura. These plants showedenhanced and sustained production of antioxidants (SOD, CAT, POD, APX, GR) and defense enzymes (PAL, PPO, TP) compared to infested control plants. GC-MS analysis of plant volatiles revealed the release of 1-octen-3-ol and 9-octadecanoic acid, precursors of the plant defense signalling molecule jasmonic acid, in CPB 1a and CPV 18-primed plants, confirming their role in strengthening plant defense against S. litura. The efficacy of these bacterial isolates was evaluated against the sap-sucking insect Aphis craccivora through in-planta choice assays using the Aphid Quantity Ratio (AQR). Isolates CPB 1a, CPV 8, CPV 14, and CPV 18-primed plants demonstrated moderate resistance, with AQR values of 0.5, 0.42, 0.52, and 0.49, respectively, compared to unprimed control plants, which recorded an AQR value of 1.58, classifying them as highly susceptible. Furthermore, in-planta no-choice assays analyzing life table parameters revealed significant impacts of CPV 08- and CPV 18-primed plants on A. craccivora's biological and demographic traits. Relatively shorter oviposition periods of 6.27 and 7.25 days were observed in CPV 8 and CPV 18 treatments, respectively, whereas prolonged oviposition of 11.37 days was noticed in control plants. Consequently, the fecundity of aphids was reduced to 15.42 progeny per aphid for CPV 08 and 19.77 progeny per aphid for CPV 18, compared to 39.8 progeny per aphid in the control. Additionally, the intrinsic rate of population increase was lower for CPV 08 (1.24) and CPV 18 (1.26) than for the control (1.38). The higher production of antioxidants and defense enzymes, along with the release of volatile compounds such as methyl salicylate, betulinaldehyde, and trans-farnesol, confirmed the induction of plant defense responses by these isolates in cowpea plants challenged with A. craccivora. Promising bacterial isolates were identified through 16S rRNA gene sequencing. CPB 1a was identified as Bacillus velezensis, CPV 08 as Bacillus zanthoxyli, and CPV 18 as Bacillus subtilis, with sequence similarity percentages of 100%, 99.13%, and 99.57%, respectively. Comparative studies of potential endophytes such as B. velezensis CPB 1a and B. subtilis CPV 18 for S. litura along with other entomopathogens revealed that, upon seed priming, B. thuringiensis BTG4 and B. velezensis CPB 1a significantly reduced leaf damage to 17.29% and 20.56%, respectively. This was followed by B. subtilis CPV 18-treated plants, which recorded 30.18% leaf damage compared to77.24% in control plants exposed to feeding by S. litura. Additionally, plants primed with these bacteria exhibited enhanced resilience, maintaining better plant biometric characteristics such as increased fresh and dry weight under S. litura feeding conditions. Similarly, the comparative effectiveness of identified potential isolates against A. craccivora, such as B. zanthoxyli CPV 8 and B. subtilis CPV 18, alongside other entomopathogens, demonstrated that the priming effects of these microbes were most pronounced in B. zanthoxyli CPV 8 and B. subtilis CPV 18. These isolates effectively reduced the population build-up of A. craccivora to 29.66 and 32.66 aphids per plant, respectively, compared to 81.66 aphids per plant in the control. Furthermore, plants treated with these isolates showed significant improvements in plant biometric traits, such as improved fresh and dry weight under A. craccivora-infested conditions. All the effective isolates B. velezensis CPB 1a, B. zanthoxyli CPV 8, and B. subtilis CPV 18, including B. thuringiensis BTG4, were successfully reisolated from the primed plants during the observation period of two to four weeks after sowing ensure their effective colonisation as endophytes in cowpea. An in-vitro compatibility study was conducted to assess the potential of integrating these effective endophytic bacteria with entomopathogens. The results indicated that Beauveriabassiana NBAIR 05, Lecanicilliumlecanii NBAIR VL8, and B. subtilis CPV 18 were compatible with one another, enabling the creation of a microbial consortium. Pest incidence in cowpea plants treated with a microbial consortium, along with other promising endophytes and entomopathogens applied singly or in various combinations using different application techniques, was analyzed to assess their pest management potential under natural conditions in a pot culture experiment. Soil drenching with the microbial consortium provided early protection against A. craccivora, reducing populations by 29.45% to 31.28% up to five weeks after sowing (WAS). Foliar applications combining B. bassiana or L. lecanii with the consortium (treatments T18 and T19) yielded results comparable to chemical insecticides by 6 WAS after the first foliar application, with effects sustained until the final observation. Similarly, treatment T18 significantly reduced the incidence of S. litura after the first foliar application by 95%, matching the efficacy of chemical insecticides. T18(Consortium + B. bassiana) also demonstrated enhanced plant biometric characteristics, including increased plant height, number of leaves, number of pods, pod length, and pod yield, while effectively reducing the incidence of Maruca sp. and Riptortus sp. The microbial consortium consisting of Beauveriabassiana NBAIR-05, Lecanicilliumlecanii NBAIR VL-8, and B. subtilis CPV 18 developed in the current study along with foliar application of B. bassiana was proved to be effective in managing major insect pest of cowpea across different feeding guilds and have the potential to be integrated as one of the tactics in integrated pest management in cowpea.Item Andrographolide based biopesticide for the management of pest complex of vegetable cowpea Vigna unguiculata (L.) Walp(Department of Entomology, College of Agriculture ,Vellayani, 2024-08-16) Neethu, G Raj; Santhoshkumar, TThe present study entitled ‘Andrographolide based biopesticide for the management of pest complex of vegetable cowpea Vigna unguiculata (L.) Walp’. was carried out at Department of Entomology, College of Agriculture, Vellayani, during 2019-2023 with an objective to develop and standardize an “andrographolide” based biopesticide formulation against pests of vegetable cowpea V. unguiculata and its insecticidal and antifeedant effect on developmental stages of pests and natural enemy. Extraction and isolation of the bioactive compound from Andrographis paniculata, were isolated using the modified procedure of Pundarikakshudu et al., 2016 and resulting compound was further confirmed to be andrographolide through Fourier-transform infrared spectroscopy (FTIR) and Liquid chromatography-mass spectrometry (LC-MS) analysis. The effectiveness of isolated andrographolide based compound were studied on cowpea aphids (Aphis craccivora) and spotted pod borer (Maruca vitrata). The LC50 and LC90 were calculated at 24 hours after treatment and recorded concentration of 2064.51ppm and 3206.52ppm, respectively. A significant mortality was observed in the second and third instar larvae of M. vitrata. Studies were conducted to develop formulations showing stable emulsions (bloom test) and five combinations were found to be forming stable emulsions. Stable five combination were Andrographolide (70%) + Neem oil (20%) + Triton X 100 (10%), Andrographolide (70%) + Pungam oil (20%) + Triton X 100 (10%), Andrographolide (60%) + castor oil (30%) + Tween 80 (10%), Andrographolide (60%) + Palm oil (30%) + Tween 80 (10%) and Andrographolide (60%) + sunflower oil (30%) + Tween 20 (10%) and effectiveness of these five combinations were tested against A. craccivora at various concentration (3, 5 and 7%). The treatments Andrographolide (70%) + Neem oil (20%) + Triton X 100 (10%) (Formulation A) and Andrographolide (70%) + Pungam oil (20%) + Triton X 100 (10%) (Formulation B) were found to be superior among the other treatments. The invitro evaluation of formulations A and B against A. craccivora revealed that the LC50 values of formulations A and B were 1.51 and 1.42% respectively and the LC90 values of formulations A and B were recorded as 4.52 and 4.40%. Another study conducted to evaluate the safety of predatory 198 coccinellids, Cheilomenes sexmaculata and the result revealed that the formulations A and B exhibited a relatively safer profile with minimal adverse effects on the predatory coccinellid even at higher concentrations, as mortality rates remained below 50%. Observations on the orientation behaviour of M. vitrata and L. boeticus larvae revealed a significant decrease in mean larval orientation towards treated floral buds and pods with various concentrations of formulations A and B and this highlights the deterrent impact of the formulations on larval orientation. Antifeedant activity of formulations A and B towards 3rd instar larvae of M. vitrata and L. boeticus at 7% of the formulations showed extremely antifeedant activity followed by 5 and 3% of formulations. Larvae fed with treated flowers exhibited a reduction in size compared to the control. Both M. vitrata and L. boeticus larvae exhibited a shortened larval duration and extended pupal period when provided with different concentration of formulations A and B. Considering the adult emergence rate of M. vitrata minimum emergence recorded in 7% of formulation B (31.25%), which on par with 7% of formulation A (37.5%). Conversely, no significant difference in adult emergence was observed between treatments in L. boeticus. The antifeedant effect on pod bug, R. pedestris using different concentrations of formulations A and B recorded significant feeding deterrence effect. All the treatments showed significant antifeedant activity at 12 HAT, and at 7% of both formulations A and B recorded more than 95% of antifeedant activity, and were found to be on par with 5% of formulation B. The assessment of the repellent activity of formulations A and B against A. craccivora revealed a significant repellent activity on aphids and maximum repellency was recorded at 7% of both formulation A and B (98 and 96 per cent, respectively) at 24 HAT. The efficacy of formulations A and B at various concentrations on egg hatching and larval development in L. boeticus and R. pedestris were studied and the result revealed concentration-dependent effects of formulations A and B on the egg hatchability and developmental stages of both L. boeticus and R. pedestris, with lower hatching rates and prolonged incubation periods observed at higher concentrations compared to the untreated control.Item Tolerance of entomopathogenic fungi Lecanicillium saksenae(Kushwaha) Kurihara and Sukarno and Lecanicillium lecanii (Zimm.) Zare and Gams to abiotic stress(Department of Agricultural Entomology, College of Agriculture, Vellayani, 2022-11-09) Tejaswi G Gowda.; Reji Rani, O PThe study entitled “Tolerance of entomopathogenic fungi Lecanicillium saksenae (Kushwaha) Kurihara and Sukarno and Lecanicillium lecanii (Zimm.) Zare and Gams to abiotic stress” was conducted at Department of Agricultural Entomology, College of Agriculture, Vellayani, Thiruvananthapuram, during the period 2017-22. The objective of study was to assess the tolerance level of L. saksenae and L. lecanii to insecticides, fungicides, temperature and UV radiation and explore the possibilities of developing tolerant strains. Results of the experiment to study the tolerance of L. saksenae and L. lecanii to insecticides revealed that the new generation insecticides viz., flubendiamide 39.35% SC, chlorantraniliprole 18.5% SC, imidacloprid 17.8% SL and thiamethoxam 25% WG were compatible with both the fungi in half dose, recommended dose and double the recommended doses. Among the old generation insecticides, only dimethoate 30% EC was found to be compatible at half and recommended doses. Malathion 50% EC, quinalphos 25% EC and chlorpyrifos 20% EC were found to be toxic to both the fungi at all the test doses. Among all the insecticides quinalphos 25% EC was found to be highly toxic with a Biological Index (BI) of 14 to 22. Among the fungicides tested, azoxystrobin 23% SC was found to be compatible with L. saksenae and it was moderately toxic to L. lecanii. Copper oxychloride 50% WP was found to be moderately toxic to L. lecanii and toxic to L. saksenae. Carbendazim 50 % WP, mancozeb 75% WP, hexaconazole 5% EC and tebuconazole 25 % EC were found to be toxic to both the fungi based on BI values. Artificial selection to induce tolerance to incompatible insecticides and fungicides was attempted by subculturing fungi in respective poisoned media for ten successive generations. No improved strain could be developed for quinalphos tolerance in both the fungi. Induction of fungicide tolerance resulted in two tolerant 183 strains in L. saksenae but no improved strain could be developed in L. lecanii. Hexaconazole tolerant strain of L. saksenae was able to tolerate the recommended field dose (0.15 %). Carbendazim tolerant strain exhibited increase in growth, sporulation and germination at the recommended dose (0.2%) compared to those in the non-selected culture. REP-PCR data revealed the genotypic variation of the strains. The variation quantified based on Jaccard’s coefficient analysis revealed that carbendazim tolerant strain and hexaconazole tolerant strain were 42 per cent and 38 per cent dissimilar from mother culture. Temperature tolerance study carried out at varying regimes of 30, 32, 34, 36, 38 and 40 oC (8h exposure) revealed that increase in temperature significantly affected the growth parameters of both the fungi. Growth of L. lecanii and L. saksenae was completely inhibited at 36 and 40 oC, respectively. In terms of sporulation, no exponential reduction (>10 7 spores mL-1 ) was observed till 34 o C in L. saksenae, while in L. lecanii it was reduced to 105 spores mL-1 and it was terminated at 36 oC. Comparative tolerance between the species revealed that L. saksenae performed better than L. lecanii. No significant reduction (<15 per cent) in terms of germination was observed in L. saksenae till 36 oC, while in L. lecanii more than 70 per cent reduction was observed at 34 oC. L. saksenae spores were able to germinate till 40 oC while in L. lecanii germination was completely inhibited at this temperature. Attempts to induce temperature tolerance by subculturing the fungi at highest tolerant temperature for ten generations did not yield any tolerant strain. UV tolerance study conducted with two irradiances wave length viz., UVA - 365 nm and UVB - 290 to 315 nm for 10, 20, 30 min, 1h, 2h, 3h and 4h exposure durations, revealed that the growth of both the fungi was not significantly affected when exposed for shorter durations (10, 20 and 30 min), whereas when exposed for longer durations (1, 2, 3 and 4h), there was significant reduction in growth. In both the wave lengths and across the exposure durations, L. saksenae exhibited higher colony growth than L. lecanii. In UVA irradiance, the growth reduction ranged 184 between 13 to 75 per cent in L. saksenae and it was 23 to 81 per cent in L. lecanii. In UVB irradiance, colony reduction was between 12 to 85 per cent in L. saksenae and 31to 89 per cent in L. lecanii. In terms of sporulation, no exponential reduction was observed in both the fungi. There was germination inhibition in both the fungi exposed to UVA and UVB irradiance. In shorter exposures, L. lecanii exhibited higher germination (30 to 51 per cent) while in longer exposures L. saksenae exhibited higher germination (13 to 16 per cent). UV mutagenesis resulted in two UV mutants one each in L. saksenae and L. lecanii. L. lecanii mutant was named as LlUVM1 and L. saksenae mutant was named as LsUVM. Both the mutants were superior in terms of growth parameters when tested under UVA and UVB irradiance when compared to their mother culture. The REP-PCR analysis revealed that UV mutants LsUVM and LlUVM1 varied genotypically from the mother culture. Based on Jaccard’s coefficient there was 32 per cent dissimilarity with their respective mother cultures. Bioassay carried out to study the effect of artificial selection on the pathogenicity of fungicide tolerant strains of L. saksenae on rice bug Leptocorisa oratorius Fab. revealed that spore suspensions of carbendazim and hexaconazole tolerant strains of L. saksenae (107 spores mL -1 ) in the presence of respective fungicide, exhibited higher virulence than the mother culture. Mortality caused by the tank mix formulation of carbendazim tolerant strain + 0.2 % carbendazim 50 % WP caused 86.67 per cent mortality, while its mother culture resulted in 36.67 per cent mortality. Hexaconazole tolerant strain caused 60 per cent mortality while the mother culture did not cause mortality with tank mix of hexaconazole 5 % EC 0.15 %. Pathogenicity assay of L. saksenae UV mutant revealed that there was no significant difference in mortality of L. oratorius between the mother culture and the mutant. In L. lecanii the UV mutant (LlUVM1) exhibited higher virulence on the 185 brinjal mealybug, Coccidohystrix insolita Green. LlUVM1 caused 100 per cent mortality on the eighth day, while the mother culture of L. lecanii caused 83.75 per cent mortality. Therefore, the study concludes that the indigenous isolate L. saksenae is comparatively more tolerant to insecticides, temperature and UV exposure than L. lecanii. Strains of L. saksenae developed for carbendazim and hexaconazole tolerance performed better in terms of phenotypic characters. Genotypically, they expressed variation of 42 and 38 per cent respectively from mother culture. The UV tolerant strain developed in both the species were superior to the mother culture under UV irradiance. The findings pave way to the utilization of the indigenous isolate of L. saksenae and its fungicide tolerant mutants and the UV mutant of L. lecanii in pest management as they can combat abiotic stress in prevailing climatic conditions.Item Tolerance of entomopathogenic fungi Lecanicillium saksenae(Kushwaha) Kurihara and Sukarno and Lecanicillium lecanii (Zimm.) Zare and Gams to abiotic stress(Department of Agricultural Entomology, College of Agriculture, 2022-11-09) Tejaswi G Gowda.; Reji Rani, O PThe study entitled “Tolerance of entomopathogenic fungi Lecanicillium saksenae (Kushwaha) Kurihara and Sukarno and Lecanicillium lecanii (Zimm.) Zare and Gams to abiotic stress” was conducted at Department of Agricultural Entomology, College of Agriculture, Vellayani, Thiruvananthapuram, during the period 2017-22. The objective of study was to assess the tolerance level of L. saksenae and L. lecanii to insecticides, fungicides, temperature and UV radiation and explore the possibilities of developing tolerant strains. Results of the experiment to study the tolerance of L. saksenae and L. lecanii to insecticides revealed that the new generation insecticides viz., flubendiamide 39.35% SC, chlorantraniliprole 18.5% SC, imidacloprid 17.8% SL and thiamethoxam 25% WG were compatible with both the fungi in half dose, recommended dose and double the recommended doses. Among the old generation insecticides, only dimethoate 30% EC was found to be compatible at half and recommended doses. Malathion 50% EC, quinalphos 25% EC and chlorpyrifos 20% EC were found to be toxic to both the fungi at all the test doses. Among all the insecticides quinalphos 25% EC was found to be highly toxic with a Biological Index (BI) of 14 to 22. Among the fungicides tested, azoxystrobin 23% SC was found to be compatible with L. saksenae and it was moderately toxic to L. lecanii. Copper oxychloride 50% WP was found to be moderately toxic to L. lecanii and toxic to L. saksenae. Carbendazim 50 % WP, mancozeb 75% WP, hexaconazole 5% EC and tebuconazole 25 % EC were found to be toxic to both the fungi based on BI values. Artificial selection to induce tolerance to incompatible insecticides and fungicides was attempted by subculturing fungi in respective poisoned media for ten successive generations. No improved strain could be developed for quinalphos tolerance in both the fungi. Induction of fungicide tolerance resulted in two tolerant 183 strains in L. saksenae but no improved strain could be developed in L. lecanii. Hexaconazole tolerant strain of L. saksenae was able to tolerate the recommended field dose (0.15 %). Carbendazim tolerant strain exhibited increase in growth, sporulation and germination at the recommended dose (0.2%) compared to those in the non-selected culture. REP-PCR data revealed the genotypic variation of the strains. The variation quantified based on Jaccard’s coefficient analysis revealed that carbendazim tolerant strain and hexaconazole tolerant strain were 42 per cent and 38 per cent dissimilar from mother culture. Temperature tolerance study carried out at varying regimes of 30, 32, 34, 36, 38 and 40 oC (8h exposure) revealed that increase in temperature significantly affected the growth parameters of both the fungi. Growth of L. lecanii and L. saksenae was completely inhibited at 36 and 40 oC, respectively. In terms of sporulation, no exponential reduction (>10 7 spores mL-1 ) was observed till 34 o C in L. saksenae, while in L. lecanii it was reduced to 105 spores mL-1 and it was terminated at 36 oC. Comparative tolerance between the species revealed that L. saksenae performed better than L. lecanii. No significant reduction (<15 per cent) in terms of germination was observed in L. saksenae till 36 oC, while in L. lecanii more than 70 per cent reduction was observed at 34 oC. L. saksenae spores were able to germinate till 40 oC while in L. lecanii germination was completely inhibited at this temperature. Attempts to induce temperature tolerance by subculturing the fungi at highest tolerant temperature for ten generations did not yield any tolerant strain. UV tolerance study conducted with two irradiances wave length viz., UVA - 365 nm and UVB - 290 to 315 nm for 10, 20, 30 min, 1h, 2h, 3h and 4h exposure durations, revealed that the growth of both the fungi was not significantly affected when exposed for shorter durations (10, 20 and 30 min), whereas when exposed for longer durations (1, 2, 3 and 4h), there was significant reduction in growth. In both the wave lengths and across the exposure durations, L. saksenae exhibited higher colony growth than L. lecanii. In UVA irradiance, the growth reduction ranged 184 between 13 to 75 per cent in L. saksenae and it was 23 to 81 per cent in L. lecanii. In UVB irradiance, colony reduction was between 12 to 85 per cent in L. saksenae and 31to 89 per cent in L. lecanii. In terms of sporulation, no exponential reduction was observed in both the fungi. There was germination inhibition in both the fungi exposed to UVA and UVB irradiance. In shorter exposures, L. lecanii exhibited higher germination (30 to 51 per cent) while in longer exposures L. saksenae exhibited higher germination (13 to 16 per cent). UV mutagenesis resulted in two UV mutants one each in L. saksenae and L. lecanii. L. lecanii mutant was named as LlUVM1 and L. saksenae mutant was named as LsUVM. Both the mutants were superior in terms of growth parameters when tested under UVA and UVB irradiance when compared to their mother culture. The REP-PCR analysis revealed that UV mutants LsUVM and LlUVM1 varied genotypically from the mother culture. Based on Jaccard’s coefficient there was 32 per cent dissimilarity with their respective mother cultures. Bioassay carried out to study the effect of artificial selection on the pathogenicity of fungicide tolerant strains of L. saksenae on rice bug Leptocorisa oratorius Fab. revealed that spore suspensions of carbendazim and hexaconazole tolerant strains of L. saksenae (107 spores mL -1 ) in the presence of respective fungicide, exhibited higher virulence than the mother culture. Mortality caused by the tank mix formulation of carbendazim tolerant strain + 0.2 % carbendazim 50 % WP caused 86.67 per cent mortality, while its mother culture resulted in 36.67 per cent mortality. Hexaconazole tolerant strain caused 60 per cent mortality while the mother culture did not cause mortality with tank mix of hexaconazole 5 % EC 0.15 %. Pathogenicity assay of L. saksenae UV mutant revealed that there was no significant difference in mortality of L. oratorius between the mother culture and the mutant. In L. lecanii the UV mutant (LlUVM1) exhibited higher virulence on the 185 brinjal mealybug, Coccidohystrix insolita Green. LlUVM1 caused 100 per cent mortality on the eighth day, while the mother culture of L. lecanii caused 83.75 per cent mortality. Therefore, the study concludes that the indigenous isolate L. saksenae is comparatively more tolerant to insecticides, temperature and UV exposure than L. lecanii. Strains of L. saksenae developed for carbendazim and hexaconazole tolerance performed better in terms of phenotypic characters. Genotypically, they expressed variation of 42 and 38 per cent respectively from mother culture. The UV tolerant strain developed in both the species were superior to the mother culture under UV irradiance. The findings pave way to the utilization of the indigenous isolate of L. saksenae and its fungicide tolerant mutants and the UV mutant of L. lecanii in pest management as they can combat abiotic stress in prevailing climatic conditions.Item Exploration of the feasibility of developing races of trichograma Australicum girault ( trichogramatidar, hymenoptera) suitable for different environments(Division of entomology ,Agricultural college and research institute ,Vellayani., 1970) Abraham, C C; Pradhan, SItem Studies on the rice swarming caterpillar , Spodoptera mauritia boisduval in Kerala(Division of entomology ,Agricultural college and research institute ,Vellayani., 1967) Thomas, B; M R G K NairItem Studies on the chemical control and insect-plant relationships of the rice leafroller, cnaphalocrocis medinalis guenee (Pyraustidae:Lepidoptera)(Department of Entomology, College of Agriculture, Vellayani, 1975) Mohandas, N; Gopalakrishnan Nair, M RThe series of laboratory and field experiments were conducted to study the relative toxicity of 24 insecticides to noths and larvae of the rice leaf roller, cnaphalocreoois medinalis the relative effiency of these insecticides in controlling the pest in the field and the insect plant relationships between c.medinalis and different rice varieties. Suitable methods for the collection of moths of c.mdinalis from the field for the collection of their eggs and first instar larvae in sufficiently large numbers and for rearing the insect in the laboratory were eveloved.