PURPOSE: An insecticide and acaricide, containing B-41 compound and piperonly butoxide as active constituents, and having a remarkably improved insecticidal effect by the synergistic action of the piperonyl butoxide.

CONSTITUTION: An insecticide and acaricide containing B-41 compound of formula I and piperonyl butoxide of formula II. The amount of the B-41 compound is 2pts.wt. or more, preferably 5pts.wt. or more, based on one pt.wt. B-41 compound. The compounds are incorporated with a carrier, surfactant, etc., formulated into a dust, wettable powder, emulsion, granule, etc., diluted to an adequate concentration and suitably applied or directly applied without dilution.