Effect of insecticide—synergist combinations on the survival of Spodoptera exigua

Abstract

AbstractThe chitin synthesis inhibitors diflubenzuron and teflubenzuron have recently become ineffective for the control of Spodoptera exigua in floricultural crops. An extended laboratory test with second‐instar larvae of S. exigua on Vicia faba plants was carried out to determine the influence of synergists on the biological activity of three benzoylphenyl ureas (BPUs). The co‐application of piperonyl butoxide, an oxidase inhibitor, did not increase the activity of diflubenzuron, teflubenzuron or hexaflumuron. The best results were obtained with diethyl maleate, for suppressing glutathione S‐transferase activity, and with dimethoate, as a hydrolase inhibitor. A joint application of diflubenzuron (at a concentration which resulted in 43% survival) with diethyl maleate or dimethoate gave only 6.2 and 8.9% surviving larvae, respectively. In addition, development to fourth‐instar larvae was inhibited. The more stable teflubenzuron was synergized by both compounds to a much lesser extent than diflubenzuron. None of the synergists had a significant effect on the activity of hexaflumuron, which was the most potent insecticide of the three BPUs tested against S. exigua.