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20111
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Subject: Agricultural Entomology × Author: Amritha Kumari, S × Start date: 1986 × Thesis Type: M.Sc ×
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    ThesisItemOpen Access
    Potency of bioinsecticides against the cowpea bruchid, Callosobruchus maculatus (F.) (Coleoptera:Cysomelidae) in storage
    (Department of Agricultural Entomology, College of Horticulture, Vellanikkara, 2011) Amritha Kumari, S; KAU; Sosamma, Jacob
    The present study entitled ‘Potency of bioinsecticides against cowpea bruchid, Callosobruchus maculatus (F.) (Coleoptera: Chrysomelidae) in storage’ was undertaken to understand the feasibility of utilizing few biologically based grain protectants in post harvest storage of cowpea by investigating their biological efficacy and persistent/ residual toxicity. The bioinsecticides under study were two entomopathogenic fungi Beauveria bassiana and Metarhizium anisopliae; spinosad, an actinomycete based broad spectrum insecticide with low mammalian toxicity and lemongrass oil- an essential oil from the aromatic plant, Cymbopogon flexuosus. Laboratory bioassays were carried out to investigate the dosage-mortality response of the bioinsecticides against C. maculatus. Toxicity of entomopathogens was studied by two bioassay techniques-direct dipping and residue film. B. bassiana and M. anisopliae were tested at five different concentrations 1 x 104, 1 x 105, 1 x 106, 1 x 107 and 1 x 108 spores/ml. Observations on mortality were taken at 24 hours interval upto five days. Results on the mortality of C. maculatus indicated an increase in mortality with increase in dosage and period of exposure. Cumulative mortality data of C. maculatus by B. bassiana and M. anisopliae at five days after treatment with five concentrations revealed no significant difference in mortality between the two entomopathogens and the two bioassay methods. Probit analysis of dosage-mortality response of B. bassiana and M. anisopliae indicated lower LC50 value for M. anisopliae than B. bassiana (5.12 x 106 and 6.7 x 106 spores/ml) than B. bassiana (5.38 x 106 and 7.49 x 106 spores/ml). However the difference was not remarkable. Time-mortality effect of B. bassiana and M. anisopliae indicated an increase in LT50 values as the spore concentration decreased. Toxicity of spinosad to C. maculatus was also investigated by direct dipping and residue film bioassay methods. LC50 of spinosad was 4.02 ppm by direct dipping where as a higher LC50 value (36.39 ppm) was observed by residue film bioassay. Spinosad brought about 50 per cent mortality in 20.51 to 33.09 hours and 90 per cent mortality in 2.6 to 3.3 days. Lemongrass oil, at eight concentrations (1 to 8 μl/l of air), was tested to study the fumigant toxicity action against C. maculatus and the mortality ranged from 16.67 to 96.67 per cent. Lemongrass oil caused 50 per cent mortality at 3.93 ppm in one day and 90 per cent mortality at 7.51 ppm in 2.6 days. Bio-efficacy of the four bioinsecticides along with coconut oil as a recommended check was assessed for a period of 30 days in the storage by studying their effects on adult mortality, fecundity, egg hatchability, progeny emergence, developmental period, extent of infestation, grain weight loss and seed viability. Regarding adult toxicity, lemongrass oil caused highest adult mortality (87.1 to 100%) followed by spinosad (75.87 to 100%) at three days after treatment. Spinosad was most effective as an inhibitor of oviposition and egg hatchability. On comparing the progeny emergence in different treatments, no progenies were produced in the cowpea grains treated with coconut oil. Spinosad and lemongrass oil also showed higher inhibition of progeny emergence. Data on the effect of bioagents on the extent of infestation by C. maculatus revealed that coconut oil was the most effective treatment as it caused zero infestation. Spinosad and lemongrass oil were the next effective ones as they resulted in 49 and 52 per cent reduction of seed damage. Entomopathogens were found to be ineffective in reducing bruchus damage to seeds. Effects on weight loss also recorded the same trend. Results on the impact of bioagents on seed viability indicated that spinosad treated grains showed the highest germination followed by lemongrass oil and coconut oil. Results of the persistent toxicity action of the tested bioinsecticides revealed that spinosad had highest persistence with a PT value of 5699.7. All other bioagents showed less persistence. Lemongrass oil showed the least persistent toxicity against in storage. It can be concluded from the present investigation that among the four bioagents, spinosad is the most effective one in terms of bioefficacy as well as persistent action in cowpea seeds. It can be recommended as an alternative option for bruchid management in storage. The existing recommendation of coconut oil is also proved to be effective against C. maculatus in storage of cowpea seeds. Lemongrass oil is also a very effective bioagent as a fumigant for protecting cowpea grains from C. maculatus with a limitation of short persistence that warrants frequent applications in storage. B. bassiana and M. anisopliae are not effective against C. maculatus in cowpea storage.