Journal of Economic Entomology (2010) 103, 2147-2154

S. Downes, T.L. Parker and R.J. Mahon (2010)
Characteristics of resistance to Bacillus thuringiensis toxin Cry2Ab in a strain of Helicoverpa punctigera (Lepidoptera: Noctuidae) isolated from a field population
Journal of Economic Entomology 103 (6), 2147-2154
Abstract: In 1996, the Australian cotton industry adopted Ingard that expresses the Bacillus thuringiensis (Bt) toxin gene cry1Ac and was planted at a cap of 30%. In 2004-2005, Bollgard II, which expresses cry1Ac and cry2Ab, replaced Ingard in Australia, and subsequently has made up >80% of the area planted to cotton, Gossypium hirsutum L. The Australian target species Helicoverpa armigera (Hübner) and Helicoverpa punctigera (Wallengren) are innately moderately tolerant to Bt toxins, but the absence of a history of insecticide resistance indicates that the latter species is less likely to develop resistance to Bt cotton. From 2002-2003 to 2006-2007, F₂ screens were deployed to detect resistance to Cry1Ac or Cry2Ab in natural populations of H. punctigera. Alleles that conferred an advantage against Cry1Ac were not detected, but those that conferred resistance to Cry2Ab were present at a frequency of 0.0018 (n = 2,192 alleles). Importantly, the first isolation of Cry2Ab resistance in H. punctigera occurred before significant opportunities to develop resistance in response to Bollgard II. We established a colony (designated Hp4-13) consisting of homozygous resistant individuals and examined their characteristics through comparison with individuals from a Bt-susceptible laboratory colony. Through specific crosses and bioassays, we established that the resistance present in Hp4-13 is due to a single autosomal gene. The resistance is fully recessive. Homozygotes are able to survive a dose of Cry2Ab toxin that is 15 times the reported concentration in field grown Bollgard II in Australia (500 µg/ml) and are fully susceptible to Cry1Ac and to the Bt product DiPel. These characteristics are the same as those described for the first Cry2Ab resistant strain of H. armigera isolated from a field population in Australia.
(The abstract is excluded from the Creative Commons licence and has been copied with permission by the publisher.)
Link to article at publishers website
Database assignments for author(s): Sharon Downes, Rod J. Mahon

Research topic(s) for pests/diseases/weeds:
biocontrol - natural enemies
Research topic(s) for beneficials or antagonists:
resistance/tolerance/defence of host

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Pest and/or beneficial records:

Beneficial	Pest/Disease/Weed	Crop/Product	Country	Quarant.
	Helicoverpa punctigera
Bacillus thuringiensis Cry1A-toxin (entomopathogen)	Helicoverpa punctigera	Cotton (Gossypium)
Bacillus thuringiensis Cry2A-toxin (entomopathogen)	Helicoverpa punctigera	Cotton (Gossypium)