Abstract
Busseola fusca (Fuller; Lepidoptera: Noctuidae) is an important pest of maize in Africa and can be effectively controlled by Bt maize. However, the sustainability of this technology is threatened by resistance evolution, which necessitates the implementation of the high-dose/refuge insect resistance management (IRM) strategy. Despite the success of this IRM strategy, it is based on several assumptions about insect-hostplant interactions that are not always valid for different pest species. In this study, the plant abandonment behavior of Cry1Ab-resistant and susceptible B. fusca larvae were evaluated on a non-Bt, single toxin (Cry1Ab), and a pyramid event (Cry1.105 + Cry2Ab2) of maize over a four-day period. The aim was to determine if larvae are more likely to abandon maize plants that contain Bt-toxins than conventional non-Bt plants, and if resistance to the Cry1Ab-toxin affects this behavior. This study found that both Bt-resistant and susceptible B. fusca neonate larvae show feeding avoidance behavior and increased plant abandonment rates when exposed to Bt maize leaf tissue. The implications of these findings for the design of IRM strategies and choice of refuge structures are discussed in the context of Bt maize in Africa.
Highlights
The repeated measures ANOVA of plant abandonment data indicated that the main factors were significant (p < 0.05) for both the Cry1Ab-resistant and susceptible populations (Table 1), whereas the interaction between these two factors were only significant for the resistant population
This study improves our understanding of B. fusca larval host preference and migration behavior on maize and will contribute valuable information to aid the design of resistance management strategies for this pest in Africa
The results of this study support the observation made by Visser et al [41] and found that both resistant and susceptible B. fusca neonate larvae show feeding avoidance behavior and increased plant abandonment when exposed to Bt maize leaf tissue
Summary
Since the commercial release of genetically engineered Bt maize in South Africa in 1998 [1,2], this technology has been used as an effective control method against Busseola fusca (Fuller; Lepidoptera: Noctuidae) [3], a major pest of maize and sorghum in Africa [4,5,6].The sustainability of Bt maize technology is threatened by the evolution of resistance by pest populations [7,8,9,10,11] due to the sustained selection pressure exerted throughout the growing season [11,12,13]. The high-dose/refuge (HDR) approach is one of the most widely applied IRM strategies [8,12,16]. This strategy calls for the combined use of Bt toxins with a level of expression that kills heterozygous-resistant individuals, and a source of non-Bt host plants (refuge area) near the Bt field [17,18]. This refuge acts as a source of homozygous susceptible individuals. The proportion of resistance genes that are present in the subsequent generation is limited, since the heterozygous offspring of these mating pairs are eliminated by the high-dose of Bt toxins [13,18,19,20,21]
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