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

Abstract

Since transgenic crops expressing Bacillus thuringiensis (Bt) toxins were first released, resistance evolution leading to failure in control of pests populations has been observed in a number of species. Field resistance of the moth Busseola fusca was acknowledged 8 years after Bt maize was introduced in South Africa. Since then, field resistance of this corn borer has been observed at several locations, raising questions about the nature, distribution and dynamics of the resistance trait. Using genetic markers, our study identified four outlier loci clearly associated with resistance. In addition, genetic structure at neutral loci reflected extensive gene flow among populations. A realistically parameterised model suggests that resistance could travel in space at speed of several kilometres a year. Markers at outlier loci delineated a geographic region associated with resistance spread. This was an area of approximately 100 km radius, including the location where resistance was first reported. Controlled crosses corroborated these findings and showed significant differences of progeny survival on Bt plants depending on the origin of the resistant parent. Last, our study suggests diverse resistance mutations, which would explain the widespread occurrence of resistant larvae in Bt fields across the main area of maize production in South Africa.

Role of dispersal in resistance evolution and spread

“…But, as explained by Peterson et al [40], this is a pest with high dispersal capacity, and resistance could have spread quickly from a single location, especially given it is not a recessive trait. Population genetics analyses suggest that both phenomena are at work [41 ]. Even in extreme cases, such as independent evolution of pyrethroid resistance in the Chagas' disease vector, Triatoma infestans, at a micro-scale -for example, between neighboring dwellings -local spread from a focal point also seems to occur [42].…”

Taxonomy of Non-sporulating Bacteria Tested in Biological Control Against Spodoptera frugiperda (J.E. Smith, 1797) (Lepidoptera: Noctuidae)

“…The development of resistance also was observed in Sesamia nonagroides (Lepidoptera: Noctuidae), Ostrinia nubilalis (Lepidoptera: Pyralidae) and in genetically modified maize fields in Spain (Kranthi et al, 2006). In South Africa, a specific case of resistance by Busseola fusca (Lepidoptera: Noctuidae) over GM Cry2Ab maize crops was well studied and the resistance was effect of the evolution and inheritance of a recessive autosomal gene by the pest, conferring the tolerance trait (Berg & Campagne, 2015;Campagne et al, 2017).…”

Plant Abandonment by Busseola fusca (Lepidoptera: Noctuidae) Larvae: Do Bt Toxins Have an Effect?

“…Furthermore, B. fusca populations in maize in different regions of South Africa are in contact with each other and continued gene-flow occurs between them [65]. Molecular markers reflected extensive gene flow among populations indicating a largely homogenous population [66] in which haplotypes are not restricted to particular geographic regions, but instead have a wide geographic distribution [67].…”