This study was conducted to develop a mycoinsecticide against moth Lepidoptera, the world's largest and most serious pest to crops. It included the selection of entomopathogenic fungal strain and cultivation characteristics, the conidia production and formulation, the safety and field application of...
This study was conducted to develop a mycoinsecticide against moth Lepidoptera, the world's largest and most serious pest to crops. It included the selection of entomopathogenic fungal strain and cultivation characteristics, the conidia production and formulation, the safety and field application of trial-product.
By the comparison of insecticidal ratio, insecticidal rate (LT50), and insecticidal spore concentration (LC50) of the larvae of beet armyworm Spodoptera exigua, Beauveria bassiana No. 218 and Metarhizium anisopliae No. 500 strains were selected among 29 strains of entomopathogenic fungi tested. The optimal growth temperature of the mold hyphae was 25 and 30℃ for B. bassiana No. 218 and M. anisopliae No. 500, respectively. B. bassiana No. 218 and M. anisopliae No. 500 produced 2.2 × 108/㎖ and 1.9 × 108/㎖ blastospores, respectively, in SDB broth. As a result of production test of enzymes capable of degrading the insect cuticle layer, the maximum activity of chitinase were 1.49 ± 0.06 U/㎖ for B. bassiana No. 218 and 2.14 ± 0.08 U/㎖ for M. anisopliae No. 500 at 8 days of cultivation. In both strains, chitinase activity increased by 4~5 folds by adding chitin to the culture medium. The maximum activity of lipase of B. bassiana No. 218 and M. anisopliae No. 500 strains were 33.48 ± 3.75 U/㎖ and 21.83 ± 2.84 U/㎖, respectively, at the 8th day. The maximum activities of protease of B. bassiana No. 218 strain was 134.43 ± 11.54 U/㎖ at the 6th day and that of M. anisopliae No. 500 strains was 248.52 ± 17.9 U/㎖ at the 8th day. As a result of electron microscopic observation, it was confirmed that spores germinated and the hyphae covered eggs and larvae of S. exigua irrespective of the age.
From the results of the conidia production by solid culture of M. anisopliae No. 500, the white rice produced the highest number of conidia was selected as the raw material for production. Conidia of 5.8 x109 cfu/g wet substrate were produced from white rice with 25% moisture content under an optimized condition, which were 12-14 days of incubation time, 29℃, pH 5~6, 80% relative humidity and 3 days of liquid seed culture time. As the conidia recovery method, a conidia -harvesting device showed the superior conidial recovery ratio to the hand-sieve and sieve-vibrator. Auxiliary compounds to enhance the insecticidal efficacy of M. anisopliae No. 500 in the crop field were searched and 100~200 ppm of TDE-7 as a dispersant, 2.0% Na-PCA as a moisturizer, and 50 ppm of Lowilite 62: 4-hydroxy-2,2,4,6-tetramethyl-1-piperidine ethanol as a sunscreen were selected. And the silhouette with 3,000-fold dilution exhibited an efficient electro-deposition activity. As a result of investigating the storage stability of the oily suspension and the hydrating agent prepared with M. anisopliae No. 500 conidia, the conidial viability was found to be stable at 35℃ for 12 weeks, indicating that there would be no problems during distribution and storage of the product for more than one year.
As a result of one oral administration of the powdered trial-product containing 1.0 × 108 cfu conidia/animal of M. anisopliae No. 500 to the rat, there were no lethal animals and no general poisoning symptoms, and no pathological abnormalities were observed even at autopsy. In the rat acute transdermal toxicity test of the trial-product, there were no lethal animals and no general symptoms, and symptoms such as erythema and edema were not observed on administration site. Powdered trial-product containing 8.0 × 104 cfu of conidia/㎖ was treated to 30 carps and the carps were observed for 30 days. As a result, there were no fatal carp and neither of general poisoning symptoms or specific symptoms were observed.
At the 15th day of the field test using the liquid form and powdered form of trial-product of M. anisopliae No. 500 against S. exigua larvae, the insecticidal ratios were the same as 93 and 86% for 250 and 500 times diluted both trial-products, respectively. Control values of on-site application to diamondback moth (Plutella xylostella) and beet army worm were 84.2 and 85.4%, respectively, after 7 days of treatment with the trial-product, and the control values of commercially available powdered Bacillus thuringiensis and synthetic chemical flufenoxuron DC were 88.6 and 94.3%, respectively. The most effective on-site treatment against moths was at the beginning of treatment with a treatment cycle of 3 times every 7 days. At the same time, control value of 5% flufenoxuron dispersant was 95.3%. No signs of weakness of crops were observed for all the trial-product field treatments.
In conclusion, the mycoinsecticide of M. anisopliae No. 500 developed in this study was suitable for commercialization.
This study was conducted to develop a mycoinsecticide against moth Lepidoptera, the world's largest and most serious pest to crops. It included the selection of entomopathogenic fungal strain and cultivation characteristics, the conidia production and formulation, the safety and field application of trial-product.
By the comparison of insecticidal ratio, insecticidal rate (LT50), and insecticidal spore concentration (LC50) of the larvae of beet armyworm Spodoptera exigua, Beauveria bassiana No. 218 and Metarhizium anisopliae No. 500 strains were selected among 29 strains of entomopathogenic fungi tested. The optimal growth temperature of the mold hyphae was 25 and 30℃ for B. bassiana No. 218 and M. anisopliae No. 500, respectively. B. bassiana No. 218 and M. anisopliae No. 500 produced 2.2 × 108/㎖ and 1.9 × 108/㎖ blastospores, respectively, in SDB broth. As a result of production test of enzymes capable of degrading the insect cuticle layer, the maximum activity of chitinase were 1.49 ± 0.06 U/㎖ for B. bassiana No. 218 and 2.14 ± 0.08 U/㎖ for M. anisopliae No. 500 at 8 days of cultivation. In both strains, chitinase activity increased by 4~5 folds by adding chitin to the culture medium. The maximum activity of lipase of B. bassiana No. 218 and M. anisopliae No. 500 strains were 33.48 ± 3.75 U/㎖ and 21.83 ± 2.84 U/㎖, respectively, at the 8th day. The maximum activities of protease of B. bassiana No. 218 strain was 134.43 ± 11.54 U/㎖ at the 6th day and that of M. anisopliae No. 500 strains was 248.52 ± 17.9 U/㎖ at the 8th day. As a result of electron microscopic observation, it was confirmed that spores germinated and the hyphae covered eggs and larvae of S. exigua irrespective of the age.
From the results of the conidia production by solid culture of M. anisopliae No. 500, the white rice produced the highest number of conidia was selected as the raw material for production. Conidia of 5.8 x109 cfu/g wet substrate were produced from white rice with 25% moisture content under an optimized condition, which were 12-14 days of incubation time, 29℃, pH 5~6, 80% relative humidity and 3 days of liquid seed culture time. As the conidia recovery method, a conidia -harvesting device showed the superior conidial recovery ratio to the hand-sieve and sieve-vibrator. Auxiliary compounds to enhance the insecticidal efficacy of M. anisopliae No. 500 in the crop field were searched and 100~200 ppm of TDE-7 as a dispersant, 2.0% Na-PCA as a moisturizer, and 50 ppm of Lowilite 62: 4-hydroxy-2,2,4,6-tetramethyl-1-piperidine ethanol as a sunscreen were selected. And the silhouette with 3,000-fold dilution exhibited an efficient electro-deposition activity. As a result of investigating the storage stability of the oily suspension and the hydrating agent prepared with M. anisopliae No. 500 conidia, the conidial viability was found to be stable at 35℃ for 12 weeks, indicating that there would be no problems during distribution and storage of the product for more than one year.
As a result of one oral administration of the powdered trial-product containing 1.0 × 108 cfu conidia/animal of M. anisopliae No. 500 to the rat, there were no lethal animals and no general poisoning symptoms, and no pathological abnormalities were observed even at autopsy. In the rat acute transdermal toxicity test of the trial-product, there were no lethal animals and no general symptoms, and symptoms such as erythema and edema were not observed on administration site. Powdered trial-product containing 8.0 × 104 cfu of conidia/㎖ was treated to 30 carps and the carps were observed for 30 days. As a result, there were no fatal carp and neither of general poisoning symptoms or specific symptoms were observed.
At the 15th day of the field test using the liquid form and powdered form of trial-product of M. anisopliae No. 500 against S. exigua larvae, the insecticidal ratios were the same as 93 and 86% for 250 and 500 times diluted both trial-products, respectively. Control values of on-site application to diamondback moth (Plutella xylostella) and beet army worm were 84.2 and 85.4%, respectively, after 7 days of treatment with the trial-product, and the control values of commercially available powdered Bacillus thuringiensis and synthetic chemical flufenoxuron DC were 88.6 and 94.3%, respectively. The most effective on-site treatment against moths was at the beginning of treatment with a treatment cycle of 3 times every 7 days. At the same time, control value of 5% flufenoxuron dispersant was 95.3%. No signs of weakness of crops were observed for all the trial-product field treatments.
In conclusion, the mycoinsecticide of M. anisopliae No. 500 developed in this study was suitable for commercialization.
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#Mycoinsecticide Metarhizium anisopliae No. 500 Beauveria bassiana No. 218 moth chitinase condial production and recovery formulation trial-product safety stability field application
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