Effect of Bt toxin Cry1Ab on two freshwater caddisfly shredders \u2013 an attempt to establish dose-effect relationships through food-spiking

Antonia Pott,Mirco Bundschuh,Ralf Schulz,Rebecca Bundschuh,Mathias Otto

doi:10.1038/s41598-020-62055-2

Abstract

Genetically modified organisms (GMOs), which produce Bacillus thuringiensis (Bt) toxins, are widely used in agriculture in some parts of the world. Despite this, ecotoxicological methods, tailored to GMOs, are lacking to assess effects on aquatic environments. With the objective to investigate a food-related exposure pathway for aquatic shredders, we used a new food-spiking method while caddisfly larvae (Chaetopteryx spec., Sericostoma spec.) served as test species. Pure Cry1Ab toxins were spiked on black alder leaf discs and subsequently used in a feeding experiment. The toxin did not influence larval mortality compared to the control. The results, however, showed significant effects on larval lipid content (Chaetopteryx spec.) and development (Sericostoma spec.) at concentrations of 17.2 and 132.4 ng Cry1Ab/mg leaf, respectively. These changes are indicative for impacts on the fitness of the specimen and thus relevant in a risk assessment context. Ultimately, the food-spiking method allowed applying different Bt toxin concentrations leading to the establishment of dose-response relationships for various response variables. The use of long test durations and sublethal endpoints (consumption, lipid content, growth, larval instars) is, moreover, advisable when testing GMO effects.

Highlights

Modified organisms (GMOs), which produce Bacillus thuringiensis (Bt) toxins, are widely used in agriculture in some parts of the world
Despite their close taxonomic relationship to Lepidoptera, which are targeted by a variety of Bt toxins expressed in transgenic crops, only few studies examined the hazard of Bt toxins on caddisflies[6]
Our results add to that knowledge and suggest that at least some groups of caddisfly larvae may be sensitive to the Cry1Ab toxin when exposed through their food over an extended period of time

Summary

Introduction

Modified organisms (GMOs), which produce Bacillus thuringiensis (Bt) toxins, are widely used in agriculture in some parts of the world. Studies that address the impact of GM-crop residues on detritus feeding caddisfly larvae (Trichoptera), which are taxonomically closely related to Lepidoptera targeted by some Cry toxins such as Cry1Ab, showed high variability in their responses[5,10,11] This inconclusive picture with regards to the sensitivity of caddisfly larvae, suggests a complex interaction between toxins and the quality of plant material influencing the exposure of detritus feeding organisms and their responses. In this context, it seems sensible to define potential exposure pathways based on which a testing strategy can be developed[12]. The lipid content in caddisfly larvae was measured, as it is an important energy resource for insects during starvation and metamorphosis[22]

Methods

Results

Conclusion