PH 70-23 is a new benzoylphenylurea interfering with chitin deposition. In larvae of Spodoptera littoralis, incorporation of N-acetyl-glucosamine into chitin was equally inhibited by PH 70-23 and diflubenzuron, the first commercially available benzoylphenylurea. In contrast to diflubenzuron, which is active only against insects and eriophyid mites, PH 70-23 has the advantage of also being highly active on spider mites. The latter activity might be partly due to leaf penetration of PH 70-23. Laboratory experiments indicate PH 70-23 to have a better ovo-larvicidal activity than the commercial acaricides tested (cyhexatin, dicofol, fenbutatin oxide and tetradifon) against Tetranychus cinnabarinus, T. turkestani, T. urticae and Panonychus ulmi. A method in which eggs were deposited on residues of cyhexatin or fenbutatin oxide resulted in much lower activities than application of the spray liquid after egg deposition. Activities of PH 70-23, dicofol and tetradifon were hardly influenced by this difference in the test method. The direct contact activity of PH 70-23 on eggs of mites is influenced by the relative humidity and the age of the eggs. The total ovolarvicidal activity of PH 70-23 is only slightly positively influenced by the relative humidity, however. Ovicidal activity of PH 70-23 is also achieved by transovarial transmission. The compound does not influence the fertility of the mites. Comparison of a strain of T. urticae, resistant to dicofol, parathion and tetradifon, with a susceptible strain indicated absence of cross-resistance to PH 70-23. Compared to diflubenzuron, PH 70-23 shows an interesting shift in the spectrum of insecticidal activity. [ABSTRACT FROM AUTHOR]