Baseline susceptibility of Bemisia tabaci MEAM1 (Hemiptera: Aleyrodidae) in Australia to spirotetramat, cyantraniliprole and dinotefuran, with reference to pyriproxyfen cross-resistance

Silverleaf whitefly, Bemisia tabaci (Gennadius) Middle East-Asia Minor 1 (MEAM1), previously known as B biotype, is an agricultural pest of global significance and has developed resistance to many commonly used insecticides. Toxicity of spirotetramat, cyantraniliprole and dinotefuran to B. tabaci MEAM1 populations from eastern Australia was determined by laboratory bioassay, using either a foliar leaf dip or systemic uptake methodology. All field-collected populations tested were susceptible to spirotetramat (12 tested from 2011 to 2015), cyantraniliprole (23 tested from 2014 to 2017) and dinotefuran (16 tested from 2015 to 2017). Based on LC50 values, there was a 2.1-fold difference in the response of field populations to spirotetramat, a threefold difference in response to cyantraniliprole, while the response to dinotefuran varied depending on assay used, 1.8 vs. 2.6 with a foliar assay and systemic uptake assay, respectively. Testing of spirotetramat and cyantraniliprole against a pyriproxyfen-resistant strain, AY09-1R demonstrated no evidence of cross-resistance to pyriproxyfen. When tested against dinotefuran, AY09-1R had a resistance factor of two indicating possible weak cross-resistance to pyriproxyfen, although it is also possible that the strain carries other forms of resistance given its origin. Discriminating doses of 100 mg/L for spirotetramat, 1 mg/L for cyantraniliprole and 60 mg/L (systemic) and 600 mg/L (foliar) for dinotefuran were calculated from the bioassay data. All three insecticides demonstrated good efficacy against silverleaf whitefly, and for the Australian cotton industry, they add three modes of action to the insecticide resistance management strategy, providing greater flexibility in control options. This study has established baseline toxicity data and discriminating doses for spirotetramat, cyantraniliprole and dinotefuran, which will serve as a useful reference for future monitoring and management of B. tabaci MEAM1 insecticide resistance in Australian cotton.