Relative Fitness of Cry1A-Resistant and -Susceptible <I>Helicoverpa armigera</I> (Lepidoptera: Noctuidae) on Conventional and Transgenic Cotton

Abstract

Glasshouse and laboratory experiments were conducted to evaluate the relative fitness of Cry1A-susceptible and laboratory-selected resistant strains of Helicoverpa armigera (Hübner). Life history parameters of H. armigera larvae feeding on young cotton plants showed a significant developmental delay of up to 7 d for the resistant strain compared with the susceptible strain on non-Bacillus thuringiensis (Bt) cotton. This fitness cost was not evident on artificial diet. There was no developmental delay in the F1 hybrid progeny from the reciprocal backcross of the resistant and susceptible strains, indicating that the fitness cost is recessive. In two cohorts tested, survival to pupation of resistant larvae on Bt cotton expressing Cry1Ac was 54 and 51% lower than on non-Bt cotton, whereas all susceptible and F1 larvae tested on Cry1Ac cotton were killed. Mortality of susceptible larvae occurred in the first or second instar, whereas the F1 larvae were able to develop to later instars before dying, demonstrating that resistance is incompletely recessive. The intrinsic rate of increase was reduced by >50% in the resistant strain on Cry1Ac cotton compared with the susceptible strain on non-Bt cotton. There was a significant reduction in the survival of postdiapausal adults from the resistant strain and the F1 strains, indicating that there is a nonrecessive overwintering cost associated with Cry1A resistance in H. armigera.

Effects of Pink Bollworm Resistance to <I>Bacillus thuringiensis</I> on Phenoloxidase Activity and Susceptibility to Entomopathogenic Nematodes

“…2b). Typically, Þtness costs affecting rs individuals are accompanied by lower Þtness for homozygous resistant (rr) individuals (Carriè re et al 2001(Carriè re et al , 2004Bird and Akhurst 2004; Huang et al 2005;Bird and Akhurst 2007), although some studies have reported Þtness costs only affecting rs individuals Wright 2001, Janmaat andMyers 2005). We do not know why a cost affecting only rs individuals was found for SAF97-H4.…”

Resistance of Trichoplusia ni Populations Selected by Bacillus thuringiensis Sprays to Cotton Plants Expressing Pyramided Bacillus thuringiensis Toxins Cry1Ac and Cry2Ab

“…The slower larval development of resistant T. ni on BollGard II plants indicates that, in the field, there may be asynchrony of mating between the T. ni populations from non-Bt cotton and BollGard II cotton plants. Slower larval development on Bt plants than on non-Bt plants has been reported for several insect species, based on both laboratory and field observations (44)(45)(46)(47)(48). Asynchrony of mating between insects from non-Bt plants and Bt plants in the field has been reported to be a factor that may affect the refuge strategy for resistance management (44,49).…”

Frequency and fitness cost of resistance to Bacillus thuringiensis in Chrysomela tremulae (Coleoptera: Chrysomelidae)

“…Indeed, if resistance entails a fitness cost, the spread of a recessive allele could be prevented by an appropriate resistance management strategy (Lenormand and Raymond, 1998;Carrière and Tabashnik, 2001;Carrière et al, 2004;Bates et al, 2005). Although fitness costs associated with Bt resistance were not always detected (eg Gould and Anderson, 1991;Tang et al 1997), they have been reported in many pests (Groeters et al, 1994;Trisyono and Whalon, 1997;Alyokhin and Ferro, 1999;Oppert et al, 2000;Carrière et al, 2001a, b;Akhurst et al, 2003;Janmaat and Myers, 2003;Higginson et al, 2005. Bird and Akhurst (2004 showed that, in H. armigera, most fitness costs associated with Bt resistance (eg a lower percentage of survival or a longer mean time to pupation) are recessive.…”