Study on microbial control of scarab larvae by entomopathogenic microbes, Metarhizium anisopliae and Paenibacillus lentimorbus
2005
Yokoyama, T.(Chiba-ken. Agriculture Research Center (Japan))
Larvae of scarab beetles feed on the roots of various plants, arresting plant growth and degrading the commercial value of crops. Although large quantities of insecticides have been applied to crop fields to control scarab larvae, it has been difficult to develop adequate control measures. To date, various entomopathogenic microbes have been studied to assess their ability to control scarab larvae. This study was conducted to determine the potential for microbial control of scarab larvae by Metarhizium anisopliae and Paenibacillus lentimorbus. The results are summarized below. 1. Production of a more virulent mutant of M. anisopliae. Enhancement of the infectivity of a wild strain of M. anisopliae, F1011, against Anomala cuprea was attempted by ultraviolet irradiation of protoplasts isolated from mycelia. The protoplasts were regenerated in L-broth containing 2% agar in 0.7 M KCl. Among the 38 regenerants obtained, regenerant No. 31 (RNO31), which originated from protoplasts irradiated by UV for 30 seconds, was 16 times more virulent than the original F1011 strain against first-stadium larvae of A. cuprea, based on LC50 values. Less time was required to achieve a 50% death rate by RNO31 than by F1011. RNO31 also exhibited stronger insecticidal activity against Popillia japonica and Anomala daimiana than did F1011. The number of surviving larvae of A. cuprea was lower in the RNO31-treated pots than in the F1011-treated pots. The effects of temperature and agricultural chemicals on the growth of RNO31 were similar to those of F1011, whereas the effect of pH was not. The germination rate of conidia from RNO31 was ca. 2.5 times higher than from F1011 at 16 h after the inoculation.
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