Abstract
Bacillus thuringiensis (Bt) crops have been widely planted and the effects of Bt-crops on populations of the target and non-target insect pests have been well studied. However, the effects of Bt-crops exposure on microorganisms that interact with crop pests have not previously been quantified. Here, we use laboratory and field data to show that infection of Helicoverpa armigera with a densovirus (HaDV2) is associated with its enhanced growth and tolerance to Bt-cotton. Moreover, field monitoring showed a much higher incidence of cotton bollworm infection with HaDV2 in regions cultivated with Bt-cotton than in regions without it, with the rate of densovirus infection increasing with increasing use of Bt-cotton. RNA-seq suggested tolerance to both baculovirus and Cry1Ac were enhanced via the immune-related pathways. These findings suggest that exposure to Bt-crops has selected for beneficial interactions between the target pest and a mutualistic microorganism that enhances its performance on Bt-crops under field conditions.
Highlights
Transgenic crops expressing insecticidal Cry proteins from Bacillus thuringiensis bacteria, known as Bt-crops, have become important tools for the management of insect crop pests (Carriere et al, 2003; Cattaneo et al, 2006; Hutchison et al, 2010; Shelton et al, 2002; Tabashnik et al, 2010)
To explore the generality of this finding, we first analyzed the effect of HaDV2 infection in different H. armigera populations that differ in their susceptibility to Cry1Ac due to different mechanisms of resistance
We show that there appears to have been a strong positive selection for HaDV2-infected H. armigera in populations exposed to Cry1Ac-cotton in the field, especially when this exposure has been for prolonged periods of time
Summary
Transgenic crops expressing insecticidal Cry proteins from Bacillus thuringiensis bacteria, known as Bt-crops, have become important tools for the management of insect crop pests (Carriere et al, 2003; Cattaneo et al, 2006; Hutchison et al, 2010; Shelton et al, 2002; Tabashnik et al, 2010). Planting of Bt-crops effectively suppresses the targeted insects, decreasing insecticide use and promoting biocontrol services (Bravo et al, 2011; Carriere et al, 2003; Cattaneo et al, 2006; Hutchison et al, 2010; Lu et al, 2010; Lu et al, 2012; Shelton et al, 2002; Tabashnik et al, 2002; Wu, 2010; Wu et al, 2008). We have previously shown that the commercialization of transgenic Bt-cotton in China brought significant changes in the ecology of insects utilizing the crop (Lu et al, 2010; Swiatkiewicz et al, 2014; Wu et al, 2008). The effect of Bt-crops on other organisms, such as microbes, which could be playing important roles in the life cycle of insect populations, remains largely unknown
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