An entomopathogenic fungus, Metarhizium anisopliae, has been recognized as a safe control agent against scarab larvae and many other insects. However, in many cases, M. anisopliae is not sufficiently effective when used alone. To enhance its effectiveness, we attempted to use M. anisopliae together with a small amount of synthetic insecticides against 1st stadium larvae of Anomala cuprea. Our results indicated adequate effectiveness for practical use under the laboratory conditions. However, under field conditions, control effects were unstable against grubs. We speculated that the joint action between M. anisopliae and synthetic insecticides resulted from easy penetration of this fungus under conditions of disturbance or decline of the grub defense system caused by the existence of a small quantity of synthetic insecticides.