Micronized dust formulation of carbaryl, DDT, malathion, and Drione® (no. 797 product of the Niagara Chemical Division containing 1% pyrethrins, 1.88% ammonium fluosilicate, 10% piperonyl but oxide, 38.13% amorphous silica gel and 49% petroleum hydrocarbons by weight and used as a 51% active ingredient material) were tested in plywood chambers against adult Japanese beetles, Popillia japonica Newman, or European chafers, Amphimallon majalis (Razoumowsky), to find suitable materials for the disinsectization of transport vehicles. Carbaryl and DDT were the most suitable. One hour of exposure to applications of 1 g active material per 28 m3caused intoxication and some kill of Japanese beetles within 2 hours and complete kill within 24 hours. European chafers were less susceptible; after exposure to 4 g active material per 28 m3, carbaryl and DDT caused intoxication and some kill within 2 hours but did not cause complete kill within 48 hours. Intoxicated females of both species were able to emit eggs, but the severity of intoxication would probably interfere with normal deposition of eggs, and survival would be doubtful.