Location: Southern Insect Management Research Unit
Title: Offspring from Sequential Matings between Bacillus thuringiensis-Resistant and Bacillus thuringiensis-Susceptible Heliothis virescens Moths (Lepidoptera: Noctuidae) Authors
Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 8, 2010
Publication Date: June 1, 2010
Citation: Blanco, C.A., Gould, F., Groot, A., Abel, C.A., Perera, O.P. 2010. Offspring from Sequential Matings between Bacillus thuringiensis-Resistant and Bacillus thuringiensis-Susceptible Heliothis virescens Moths (Lepidoptera: Noctuidae). Journal of Economic Entomology. 103:861-868 Interpretive Summary: The effectiveness of the genetically modified cotton expressing Bacillus thuringiensis protein(s) (Bt cotton) has relied on the potential ‘dilution’ of Bt-resistant genes by the random mating of Bt-resistant and Bt-susceptible moths in the agricultural landscape. The offspring of the cross between a Bt-susceptible moth and a Bt-resistant moth is Bt-susceptible, therefore preserving the susceptibility to Bt cotton on the next generation. Tobacco budworm moths, an important pest of cotton, can mate multiple times, creating the opportunity for a female moth to carry sperm of a Bt-susceptible AND a Bt-resistant moth. If this occurs the question may be, what type of offspring this moth will produce? Are they going to be Bt-susceptible or Bt-resistant? We conducted experiments to find out what happens during these types of matings, and we found that a female that carries sperm of the two males with different susceptibilities to Bacillus thuringiensis will produce progeny susceptible to Bt (the most of them, making them susceptible to Bt cotton) AND Bt-resistant progeny that will preserve resistance to Bacillus thuringiensis in the gene pool. Since a large proportion of tobacco budworm female moths copulate more than once (>65%), this is an important consideration to factor into the Bt-resistance mitigating strategies.
Technical Abstract: The moth, Heliothis virescens is an economically-important pest of the American Continent. The females of this species copulate multiples times during their lifetimes. The presence of sperm from multiple males inside a female could allow for a diversity of paternal genotypes in the offspring unless there was complete precedence of sperm from the first mating. If a female copulates with a male that is insecticide-susceptible and another that is insecticide-resistant, her progeny could vary in their resistance phenotypes. In some cases, this could impact the evolution of insecticide resistance in a population. We designed a series of experiments to determine if Bacillus thuringiensis-susceptibility is maintained when an H. virescens female that is homozygous for a genetically recessive form of B. thuringiensis resistance copulates with a Cry1Ac-susceptible and a Cry1Ac-resistant males. During the lifetime of double-copulated females, a proportion of F1 progeny were Cry1Ac-resistant. This indicates that when a B. thuringiensis-resistant H. virescens female copulates with two males, some of the progeny will carry resistance to this insecticide.