THE TOXICITY OF CERTAIN SYNTHETIC ORGANIC COMPOUNDS TO THE FRUIT‐TREE RED‐SPIDER MITE

Abstract

The acaricidal activity of ninety synthetic organic compounds has been investigated in the laboratory. Considerable differences were found between the winter eggs, the summer eggs and the adult female stages of the fruit‐tree red‐spider mite (Meta‐tetranychus ulmi (Koch)) in their susceptibility to many of the compounds but two substances, namely azoxybenzene and n‐dodecyl thiocyanate, were appreciably toxic to all three stages. Of the compounds showing promise against summer eggs and mites, bis‐(p‐chlorophenyl) methyl carbinol and 4‐chloroazobenzene were the best, being highly toxic to both summer stages. Of the remainder, diphenylsulphone, 4‐chlorodiphenylsulphone, azobenzene and hydrazobenzene were highly ovicidal, while C12‐C13 alkyl thiocyanates and sec.‐dodecyl thiocyanate gave high kills of the adult female mite.Relationships between molecular structure and acaricidal activity have been sought. In a series of compounds characterized by the presence of two benzene nuclei connected by certain bridging groups, it has been found that activity to the summer stages of the mite can be influenced by alterations to the bridging group and by substitution in the benzene nuclei. Maximum activity appears to be associated with chlorine substitution in the para position in one nucleus and also with compounds of this type having unsubstituted nuclei.