Microbial control of scarab beetle larvae by a formulation of Metarhizium anisopliae (Deuteromycotina: Hyphomycetes) in a sweet potato field

Abstract

Control efficacy of Metarhizium anisopliae RNO31 formulation against larvae of the scarab beetle and a population of this fungus were investigated in a sweet potato field. The formulation was made by addition of vegetable oil to bran pellet cultures of the fungus, drying at room temperature to a moisture content of approximately 15% and granulation to about 2 mm in diameter. Insecticidal activity of the formulation was high against the 1st stadium larvae of Anomala cuprea at 105 and 106 colony forming units/g air dried soil. The formulation was applied in ridges or over the entire area of experimental plots at 100 g/m2 prior to planting cuttings of sweet potato stems. The percentage of undamaged roots was significantly higher in the plots with application over the entire area than in the control plots on the day of harvest. The percentages of undamaged roots in the fungus application plots were the same as in the fenthion plots. Larvae of Maladera japonica, Holotrichia parallela, Blitopertha orientalis, Anomala rufocuprea and A. cuprea were found in the experimental field. Numbers were very low in the plots with application over the entire area. Populations of M. anisopliae in these plots and in the ridge application plots showed little change from the day of application to the day of harvest.