Dominant resistance to Bt cotton and minor cross‐resistance to Bt toxin Cry2Ab in cotton bollworm from China

Abstract

Evolution of resistance by insect pests threatens the long-term benefits of transgenic crops that produce insecticidal proteins from Bacillus thuringiensis (Bt). Previous work has detected increases in the frequency of resistance to Bt toxin Cry1Ac in populations of cotton bollworm, Helicoverpa armigera, from northern China where Bt cotton producing Cry1Ac has been grown extensively for more than a decade. Confirming that trend, we report evidence from 2011 showing that the percentage of individuals resistant to a diagnostic concentration of Cry1Ac was significantly higher in two populations from different provinces of northern China (1.4% and 2.3%) compared with previously tested susceptible field populations (0%). We isolated two resistant strains: one from each of the two field-selected populations. Relative to a susceptible strain, the two strains had 460- and 1200-fold resistance to Cry1Ac, respectively. Both strains had dominant resistance to a diagnostic concentration of Cry1Ac in diet and to Bt cotton leaves containing Cry1Ac. Both strains had low, but significant cross-resistance to Cry2Ab (4.2- and 5.9-fold), which is used widely as the second toxin in two-toxin Bt cotton. Compared with resistance in other strains of H. armigera, the resistance in the two strains characterized here may be especially difficult to suppress.

Mis-splicing of the ABCC2 gene linked with Bt toxin resistance in Helicoverpa armigera

“…As far as we know, the results reported here are the first showing that mis-splicing of an ABCC2 gene is associated with resistance to a Bt toxin. Based on the results here and previous reports, the mechanisms of resistance to Cry1Ac in laboratory- and field-selected strains of H. armigera are diverse, including the recessive mutation disrupting ABCC2 found here, recessive and dominant mutations disrupting the extracellular and intracellular domains of cadherin, reduced transcription of a protease that converts protoxin to toxin, reduced transcription of membrane-bound alkaline phosphatase, reduced activity of aminopeptidase N, elevated immune response, and non-recessive mutations in unidentified genes17232430313233343536. This diversity will continue to provide challenges for understanding, monitoring, and managing resistance of H. armigera to Bt cotton.…”

Genetic hitchhiking and resistance evolution to transgenic Bt toxins: insights from the African stalk borer Busseola fusca (Noctuidae)

“…Indeed, increased survival on Bt maize obtained in a F2 sib-cross clearly suggested the existence of at least one recessive resistance trait in A 2 . Similarly to what has already been reported in another pest (e.g., Zhang et al, 2012;Jin et al, 2013), diverse resistance mutations characterised by different levels of recessiveness might therefore be responsible for the observed pattern of widespread field resistance to Bt maize in South Africa.…”

Defining Terms for Proactive Management of Resistance to Bt Crops and Pesticides

“…For the populations from northern China surveyed in 2010, the mean survival at the diagnostic concentration was 1.3% (range: 0 Ð2.6%) compared with 0% for the populations from northwestern China and a susceptible laboratory strain (Zhang et al 2011). Results of screening in 2009 and 2011 also support the conclusion that exposure to Bt cotton increased the frequency of H. armigera resistance to Cry1Ac in northern China, with up to 5.4% resistant individuals in a population (Zhang et al 2012, Jin et al 2013.…”