Browsing by Author "Smitha Ravi"

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    Bioefficacy of entomopathogenic fungi against cassava mealybug, phenacoccus manihotti matile-ferrero (Hemiptera: Pseudococcidae)
    (Department of Agricultural Entomology, College of Agriculture,Vellanikkara, 2024-02-21) Fasna, Sherin, K.; Smitha Ravi; Gowri Priya
    Cassava mealybug (CMB), Phenacoccus manihoti Matile-Ferrero (Hemiptera: Pseudococcidae) is a major insect pest of cassava. It causes severe damage by stunting the growth points of cassava plants, sometimes totally defoliating the plants. Level of infestation and yield loss by cassava mealybug varied from 30 to100 and 30 to 90 per cent respectively. In India, the occurrence of this pest was first noticed on cassava in Thrissur, Kerala during April 2020. Control of mealybugs commonly relies on the use of insecticides. But, it is difficult to control mealybugs using insecticides, due to their cryptic life cycle, presence of waxy coating, and formation of dense colonies. Management of insect pests using entomopathogens has received considerable importance in recent times. As part of AICRP programme of 2020-22, AICRP on BCCP, Thrissur centre conducted survey in cassava growing fields of Thrissur and Palakkad district to assess the species composition of mealybugs, damage intensity and associated natural enemies. During the survey, mycosed cadavers were collected and seven isolates of entomopathogenic fungi were obtained. Out of seven, five entomopathogenic fungal isolates were selected, characterized and evaluated under the present study entitled “Bioefficacy of entomopathogenic fungi against cassava mealybug, Phenacoccus manihoti Matile-Ferrero (Hemiptera: Pseudococcidae)”. The identity of five isolates was confirmed through morphological, cultural and molecular characterization. The fungal isolates were identified as two isolates of Simplicillium aogashimaense (EPF 2 and EPF 4), two isolates of Purpureocillium lilacinum (EPF 3 and EPF 7) and one isolate of Lecanicillium psallioate (EPF 5). Pathogenicity of these fungal isolates was tested against second instar nymphs of cassava mealybug, P. manihoti in the laboratory. A preliminary screening bioassay was carried out initially, and the superior isolates were subjected to dose-response and exposure-time response bioassay. In the preliminary screening bioassay, P. lilacinum isolates (EPF 7 and EPF 3) recorded more than 90.0 per cent mortality. S. aogashimaense (EPF 4) and L. psalliotae (EPF 5) registered mean mortality of 82.5 and 75.0 per cent respectively. S. aogashimaense (EPF 2) recorded the lowest mortality of 70.0 per cent, which was significantly lower than all other isolates. The best four isolates in the pre-screening were subjected to dose-response and exposure time- response bioassay. Spore suspensions of five different concentrations ranging from109 to 105 spores ml-1 were tested against mealybug. Ten days after treatment, two isolates of P. lilacinum (EPF 7 and EPF 3) recorded more than 80.0 per cent reduction in population of mealybug at the concentration of 109 spores ml-1 . The same isolates showed low LC50 and LT50 values. Efficacy of these two superior isolates of P. lilacinum (EPF 7 and EPF 3) at concentration of 1×108 spores ml-1 was evaluated in a pot culture experiment. The isolates were compared with a standard biocontrol check, NBAIR isolate of Lecanicillium lecanii @ 1×108 spores ml-1 , a botanical insecticide (neem oil emulsion @ 2%) and a chemical insecticide, dimethoate 30 EC @ 1.5 ml L-1 . Maximum reduction in the mealybug population was observed in dimethoate treated plants (99.86%). Even though, the neem oil emulsion (2%) showed significant effect on mealybugs, certain signs of phytotoxicity were observed in treated plants. Among three fungal isolates, significantly higher reduction in population was observed in P. lilacinum, EPF 7 (78.55%) followed by P. lilacinum, EPF 3 (74.92%), and both being on par with each other. In conclusion, the present study revealed that biological control of cassava mealybug, P. manihoti using two promising isolates of P. lilacinum could be a viable component in the integrated pest management. Two rounds of foliar application of any of the two isolates of P. lilacinum (EPF 3 and EPF 7), at 15 days interval at the dosage of 1×108 spores ml-1 was found effective against cassava mealybug, P. manihoti.
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    Endophytic fungi for the management of spotted pod borer, Maruca vitrata Fab.(Lepidoptera:Crambidae) in cowpea.
    (Department of Agricultural Entomology, College of Agriculture.Vellanikkara, 2022) Smitha Ravi; Madhu Subramanian
    The spotted pod borer, Maruca vitrata Fab. (Lepidoptera: Crambidae) is a major constraint in the production of legumes because of its wide host range, distribution and destructiveness. In cowpea, the loss due to pod borer infestation varies from 20 to 60 per cent, often reaching upto 80 per cent in severe cases. Application of pesticides can hardly be recommended in cowpea as the pods are harvested at alternate days. Biological control of M. vitrata using entomopathogenic microorganisms has received considerable attention in recent times. Previous studies have demonstrated the potential of entomopathogenic organisms to colonise an array of plants and confer protection from insect pests. In this context, a study entitled “Endophytic fungi for the management of spotted pod borer, Maruca vitrata Fab. (Lepidoptera: Crambidae) in cowpea” was undertaken with an objective of isolation and characterization of endophytic entomopathogenic fungi in cowpea, standardization of method of inoculation of entomopathogenic fungi in cowpea, and evaluation of selected endophytic fungi for management of the spotted pod borer, M. vitrata. Purposive sampling surveys were conducted in the major cowpea growing areas of Kozhikode, Thrissur, Kottayam and Thiruvananthapuram districts of Kerala. A total of 235 endophytic fungal isolates were obtained from the cowpea plant samples collected from 40 locations. This comprised of 103 isolates from roots, 63 from stems, 31 from leaves, 33 from pods and five from flowers. Nine accessions of cowpea with different levels of resistance were also screened for the isolation of fungal endophytes. All the accessions were found to harbor endophytic fungi and yielded 32 isolates. Among these accessions, Palakkadan thandan payar yielded the maximum number of seven endophytic fungi. Lola and Mysore local had the lowest number of isolates. In contrast to the results of survey, the leaves of cowpea plant harbored more endophytic fungi than other plant parts. A total of 267 isolates were obtained from survey samples and cowpea accessions. Three isolates were found to be pathogenic to M. vitrata. They were identified as Fusarium oxysporum (EEF 1) and two isolates of Purpureocillium lilacinum (EEF 4 and EEF 64) through morphological and molecular characterization. These isolates were evaluated along with Beauveria bassiana (NBAIR strain) for their bioefficacy against M. vitrata. The best two organisms in the bioefficacy studies, viz., B. bassiana (NBAIR strain) and P. lilacinum (EEF 4) were used for standardizing the inoculation technique for endophytic colonization in cowpea plant. Three different methods of inoculation viz., seed, soil and foliar inoculation were evaluated for identifying the best method for colonization of entomopathogenic fungi in cowpea plants. The effect of fungal colonization on infestation of spotted pod borer in cowpea was further assessed under field condition. Foliar inoculation with B. bassiana registered the lowest mean pod damage of 12.53 per cent. B. bassiana applied as foliar application resulted in the highest marketable pod yield of 152.83g plant-1 , followed by P. lilacinum as foliar application (149.33g plant-1 ). Based on the polyhouse and field studies, it was inferred that foliar application of B. bassiana was found to be the best treatment against the target pest, M. vitrata. In addition, the results of the current study suggested that that endophytic colonization in cowpea had little adverse impact on plant growth and yield. Foliar application of B. bassiana, which was identified as the most effective treatment against pod borer in the previous studies, was selected for comparative evaluation with the diamide insecticide, flubendiamide against M. vitrata. Cowpea plants treated with both flubendiamide and B. bassiana had significantly less number of infested pods than control, with 8.41 and 15.05 per cent infestation respectively. Control plants recorded the highest infestation of 21.28 per cent. Mean marketable pod yield showed significant difference between flubendiamide (166.14g plant-1 ) and foliar inoculation of B. bassiana (155.14g plant-1 ). Both these treatments also had significantly higher marketable pod yield compared to control plants (139.29g plant-1 ). In conclusion, the present study revealed that use of B. bassiana as an endophyte could be a useful tool in integrated pest management of pod borer in cowpea. However, further studies are needed to understand the mechanisms through which the endophytes protect plants from herbivores and promote plant growth and yield.