A new acaricide, N-(2-methyl-4-chlorophenyl)-N',N'-dimethylformamidine, shows a strong ovicidal effect against insects and spider mites. The eggs of the Egyptian cotton leafworm, Prodenia litura F., were especially sensitive. Those of a lymantriid, Orgyia gonostigma F., were somewhat less sensitive and eggs of the Mexican bean beetle, Epilachna varivestis Mulsant, were still less sensitive. The compound kills Prodenia eggs whether they are in early or advanced stages of development. Vapors of the formamidine are also effective. Exposure of P. litura eggs for 1 hour in a satiated atmosphere (4 mg/3) resulted in 96% mortality and exposure for 15 minutes in 56% mortality. Tests of Prodenia eggs deposited on cotton plants showed that a direct contact with the spray is not essential for killing the eggs. The active vapor phase and penetration through the leaf tissue can be regarded as the cause of this action. The mode of action of the formamidine (code no. C-8514 and Schering 36268) with regard to integrated pest control is discussed.