The efficacy of spiromesifen was evaluated against insecticide-resistant 'Q' biotypes of Bemisia tabaci from Israel and Spain. The compound was extremely effective against early instars (LC50S of 0.1 - 6.2 ppm for 12-d-old nymphs). One Spanish 'Q' type was significantly less susceptible (15-fold). Further selection of that strain with spiromesifen however, did not select for increasing resistance. Spiromesifen was highly effective against pyriproxyfen- and imidacloprid-resistant whitefly. It also hadpronounced transovariole effects on oviposition and egg hatch. Given the current difficulties experienced in the control of 'Q' biotype B. tabaci around the Mediterranean, it is likely that spiromesifen will be a valuable addition to the available chemical options. We consider that the efficacy of this compound is unlikely to be compromised by existing resistance mechanisms.
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