Abstract
Transgenic crops expressing Bacillus thuringiensis (Bt) toxins have been adopted worldwide, notably in developing countries. In spite of their success in controlling target pests while allowing a substantial reduction of insecticide use, the sustainable control of these pest populations is threatened by the evolution of resistance. The implementation of the “high dose/refuge” strategy for managing insect resistance in transgenic crops aims at delaying the evolution of resistance to Bt crops in pest populations by promoting survival of susceptible insects. However, a crucial condition for the “high dose/refuge” strategy to be efficient is that the inheritance of resistance should be functionally recessive. Busseola fusca developed high levels of resistance to the Bt toxin Cry 1Ab expressed in Bt corn in South Africa. To test whether the inheritance of B . fusca resistance to the Bt toxin could be considered recessive we performed controlled crosses with this pest and evaluated its survival on Bt and non-Bt corn. Results show that resistance of B . fusca to Bt corn is dominant, which refutes the hypothesis of recessive inheritance. Survival on Bt corn was not lower than on non-Bt corn for both resistant larvae and the F1 progeny from resistant × susceptible parents. Hence, resistance management strategies of B . fusca to Bt corn must address non-recessive resistance.
Highlights
The role agricultural biotechnologies could play in reducing yield gaps of important crops in the developing world [1] depends on the sustainability of genetically modified crops [2]
The Bacillus thuringiensis (Bt) crop strategy appeared successful in China and the USA where it had been deployed for control of lepidopteran pests of cotton and corn
The low mating success in R × S crosses resulted in susceptible female and resistant male pairs only. This experiment showed that the inheritance of resistance traits in B. fusca reared on Bt plant stems was not functionally recessive
Summary
The role agricultural biotechnologies could play in reducing yield gaps of important crops in the developing world [1] depends on the sustainability of genetically modified crops [2]. Engineered crops such as maize and cotton, expressing insecticidal toxins of Bacillus thuringiensis (Bt), have been adopted at high rates in both developed and developing countries [3]. In this regard, the questions of ‘how’ and ‘how rapidly’ target pests evolve resistance to crops expressing Bt toxins have received fair amount of scientific attention [4]. Populations of four target pests remain susceptible after more than a decade of intensive Bt crop use in the USA, including Heliothis virescens, Diatraea grandiosella and the two pests mentioned above [12]
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