The whitefly Bemisia tabaci Middle East‐Asia Minor 1 (MEAM1), previously known as B biotype, is a major agricultural pest with a reputation for developing resistance to insecticides. DNA‐based identification revealed that B. tabaci MEAM1 is the dominant species within Australian cotton cropping. Discriminating doses of 10 mg/L for pyriproxyfen and 300 mg/L for both diafenthiuron and bifenthrin were determined from bioassay data collected in 2010–2015. Resistance to these insecticides was tested in whitefly populations collected in 2017 from cotton crops in Queensland and New South Wales. This study reports on the presence of pyriproxyfen resistance in B. tabaci MEAM1 at seven locations in Queensland and New South Wales. One population from Goondiwindi was resistant to bifenthrin, whereas no populations tested had resistance to diafenthiuron. To determine the presence of resistance alleles to organophosphates and pyrethroids, reference populations of susceptible and resistant whiteflies (pyriproxyfen, bifenthrin and neonicotinoid) were tested. The resistance mutation L925I was found in a pyrethroid‐resistant population and in some individuals from the pyriproxyfen‐resistant population. The mutation F331W that confers organophosphate and carbamate resistance was found in all individuals tested including the susceptible reference population, indicative of a widespread distribution in Australian B. tabaci MEAM1. The cotton industry has revised the insecticide resistance management strategy for B. tabaci, to restrict the usage of pyriproxyfen to a single application within a 30‐day window. Our results argue against the use of organophosphate and carbamate insecticides in Australian cotton, because B. tabaci MEAM1 populations show significant resistance levels. Furthermore, both pesticide groups are highly disruptive to a diverse range of natural enemy populations, and as such, widespread use likely contributes to pest outbreaks.
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.
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