Abstract
BackgroundThe cotton bollworm, Helicoverpa armigera is one of the most important crop pests worldwide. It has developed high levels of resistance to synthetic insecticides, and hence, Bacillus thuringiensis (Bt) formulations are used as a safer pesticide and the Bt genes have been deployed in transgenic crops for controlling this pest. There is an apprehension that H. armigera might develop resistance to transgenic crops in future. Therefore, we studied the role of gut microbes by eliminating them with antibiotics in H. armigera larvae on the toxicity of Bt toxins against this pest.ResultsCommercial formulation of Bt (Biolep®) and the pure Cry1Ab and Cry1Ac toxin proteins were evaluated at ED50, LC50, and LC90 dosages against the H. armigera larvae with and without antibiotics (which removed the gut microbes). Lowest H. armigera larval mortality due to Bt formulation and the Bt toxins Cry1Ab and Cry1Ac was recorded in insects reared on diets with 250 and 500 μg ml−1 diet of each of the four antibiotics (gentamicin, penicillin, rifampicin, and streptomycin), while the highest larval mortality was recorded in insects reared on diets without the antibiotics. Mortality of H. armigera larvae fed on diets with Bt formulation and the δ-endotoxins Cry1Ab and Cry1Ac was inversely proportional to the concentration of antibiotics in the artificial diet. Nearly 30% reduction in larval mortality was observed in H. armigera larvae from F1 to F3 generation when the larvae were reared on diets without antibiotics (with gut microbes) and fed on 0.15% Bt or 12 μg Cry1Ab or Cry1Ac ml−1 diet, indicating development of resistance to Bt in the presence of gut microflora. However, there were no differences in larval mortality due to Bt, Cry1Ab or Cry1Ac across generations in insects when they were reared on diets with 250 μg of each antibiotic ml−1 diet (without gut microflora).ConclusionsThe results suggested that antibiotics which eliminated gut microflora influenced the toxicity of Bt towards H. armigera, and any variation in diversity and abundance of gut microflora will have a major bearing on development of resistance to Bt toxins applied as foliar sprays or deployed in transgenic crops for pest management.
Highlights
The cotton bollworm, Helicoverpa armigera is one of the most important crop pests worldwide
Effect of different concentrations of antibiotics on the mortality of H. armigera larvae due to Bacillus thuringiensis (Bt) toxins Bt formulation The mortality of H. armigera larvae due to Bt at LC50 (0.15%) (Y = 72.67 – 7.58x, R2 = 90.65%; where Y = larval mortality, x = Bt concentration, and R2 = coefficient of determination, i.e. percentage variation in larval mortality explained by antibiotic concentrations) and LC90 (0.95%) (Y = 87.77 - 8.93x, R2 = 90.74%) concentrations decreased with an increase in the dosage of antibiotics from 1.95 to 500 μg ml−1 (Figure 1A)
Bt formulation at LC90 level resulted in 10.00% larval mortality in insects reared on diets with 250 and 500 μg of each antibiotic ml−1 diet as compared to 83.33% mortality in larvae reared on diets without antibiotics, suggesting that elimination of the gut microflora by antibiotics decreased the toxicity of Bt towards the larvae of H. armigera
Summary
The cotton bollworm, Helicoverpa armigera is one of the most important crop pests worldwide. It has developed high levels of resistance to synthetic insecticides, and Bacillus thuringiensis (Bt) formulations are used as a safer pesticide and the Bt genes have been deployed in transgenic crops for controlling this pest. We studied the role of gut microbes by eliminating them with antibiotics in H. armigera larvae on the toxicity of Bt toxins against this pest. Helicoverpa armigera control is currently heavily based on insecticide use, and it has developed. Increasing use of Bt as a conventional insecticide and large-scale cultivation of Bt-transgenic crops may lead to evolution of resistance in H. armigera populations to Bt toxins. There is a need to develop strategies to manage development of resistance to Bt toxins, taking into account the various resistance and/or detoxification mechanisms involved in the target and non-target insect pests in different eco-systems
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
