Toxicity of cycloprate (ZARDEX(R), ZR-0856, hexadecyl cyclopropanecarboxylate) to the egg, larva, nymph and adult of Tetranychus urticae was investigated by bioassay method using kidney bean leaves. Toxicity of cycloprate to eggs was evaluated by the hatch inhibition and larval mortality soon after hatching. Both activities decreased with the treatments at the later stage of egg development. Lethal effect of cycloprate on larvae and nymphs was lower in mobile stage than during the time of

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... ence, or soon after moulting. The lethal effect on adults was low and the surviving female adults deposited as many eggs as the controls, although the number of offspring was markedly reduced. Sterilizing effect of cycloprate on female adults was only a transitory