Efficacy and Resistance Management Potential of a Modified Vip3C Protein for Control of Spodoptera frugiperda in Maize

Theodore W Kahn,Tom Walsh,Bill James,Juan Ferré,Jessica Monserrate,Maissa Chakroun,Jayme Williams

doi:10.1038/s41598-018-34214-z

Abstract

A modified Vip3C protein has been developed that has a spectrum of activity that has the potential to be commercially useful for pest control, and shows good efficacy against Spodoptera frugiperda in insect bioassays and field trials. For the first time Vip3A and Vip3C proteins have been compared to Cry1 and Cry2 proteins in a complete set of experiments from insect bioassays to competition binding assays to field trials, and the results of these complementary experiments are in agreement with each other. Binding assays with radiolabelled toxins and brush border membrane vesicles from S. frugiperda and Helicoverpa armigera show that the modified Vip3C protein shares binding sites with Vip3A, and does not share sites with Cry1F or Cry2A. In agreement with the resulting binding site model, Vip3A-resistant insects were also cross-resistant to the modified Vip3C protein. Furthermore, maize plants expressing the modified Vip3C protein, but not those expressing Cry1F protein, were protected against Cry1F-resistant S. frugiperda in field trials.

Highlights

In the present study we tested and compared the four proteins listed above in a variety of experiments
Previous studies on Vip3Aa provided LC50 values of 620 ng/cm[2] for S. frugiperda[22] and 1660 ng/cm[2] for H. armigera[23], while Vip3Ca was much less toxic to both insect species: a concentration as high as 4000 ng/cm[2] of Vip3Ca3 killed 27% of neonate S. frugiperda larvae and 65% of neonate H. armigera larvae after 10 days[24]
Despite the low toxicity reported for Vip3Ca3 against S. frugiperda, in the current study ARP150v02, which differs from Vip3Ca3 in eight amino acid positions near the N-terminus, showed substantial activity against this insect pest, with an LC50 value of 450 ng/cm[2] (Table 2), not significantly different from the value obtained for Vip3Aa

Summary

Introduction

In the present study we tested and compared the four proteins listed above in a variety of experiments. We evaluated a modified version of Vip3Ca, called ARP150v02, with improved activity against Spodoptera frugiperda, www.nature.com/scientificreports/. In field efficacy trials, insect bioassays, and brush border membrane binding studies, to explore the extent of cross resistance with commercial Bt proteins. We performed competition binding assays with S. frugiperda and Helicoverpa armigera BBMV, and use these data to propose a binding site model for these insecticidal toxins. Laboratory insect bioassay results and field trial results were consistent with the in vitro binding data, suggesting that binding experiments can be used to help predict the resistance management usefulness of an insecticidal protein used as a trait in crops. The fact that the different types of experiments were in agreement with each other will allow for greater confidence in the use of laboratory-based studies during the development of new commercially relevant toxins such as ARP150v02

Methods

Results

Conclusion