A comprehensive assessment of the effects of Bt cotton on Coleomegilla maculata demonstrates no detrimental effects by Cry1Ac and Cry2Ab.

Yunhe Li,Yufa Peng,Jörg Romeis,Ping Wang,Anthony M Shelton,Hany A El-Shemy

doi:10.1371/journal.pone.0022185

Yunhe Li, Yufa Peng + Show 4 more

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https://doi.org/10.1371/journal.pone.0022185

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Abstract

The ladybird beetle, Coleomegilla maculata (DeGeer), is a common and abundant predator in many cropping systems. Its larvae and adults are predaceous, feeding on aphids, thrips, lepidopteran larvae and plant tissues, such as pollen. Therefore, this species is exposed to insecticidal proteins expressed in insect-resistant, genetically engineered cotton expressing Cry proteins derived from Bacillus thuringiensis (Bt). A tritrophic bioassay was conduced to evaluate the potential impact of Cry2Ab- and Cry1Ac-expressing cotton on fitness parameters of C. maculata using Bt-susceptible and -resistant larvae of Trichoplusia ni as prey. Coleomegilla maculata survival, development time, adult weight and fecundity were not different when they were fed with resistant T. ni larvae reared on either Bt or control cotton. To ensure that C. maculata were not sensitive to the tested Cry toxins independent from the plant background and to add certainty to the hazard assessment, C. maculata larvae were fed artificial diet incorporated with Cry2Ab, Cry1Ac or both at >10 times higher concentrations than in cotton tissue. Artificial diet containing E-64 was included as a positive control. No differences were detected in any life-table parameters between Cry protein-containing diet treatments and the control diet. In contrast, larvae of C. maculata fed the E-64 could not develop to the pupal stage and the 7-d larval weight was significantly negatively affected. In both feeding assays, the stability and bioactivity of Cry proteins in the food sources were confirmed by ELISA and sensitive-insect bioassays. Our results show that C. maculata is not affected by Bt cotton and is not sensitive to Cry2Ab and Cry1Ac at concentrations exceeding the levels in Bt cotton, thus demonstrating that Bt cotton will pose a negligible risk to C. maculata. More importantly, this study demonstrates a comprehensive system for assessing the risk of genetically modified plants on non-target organisms.

Highlights

Cotton is one of the most important economic crops worldwide
The Bacillus thuringiensis (Bt) cotton variety used in the present study was shown to express Cry2Ab at levels ranging from16.8 to 22.7 mg/g fresh weight of cotton leaves and Cry1Ac-resistant strain when fed Bt (Cry1Ac) from 1.3 to 1.5 mg/g fresh weight of cotton leaves, respectively (Fig. 1)
The survival of resistant T. ni larvae were 72.4% and 79.3% when fed leaves from Bt cotton or control plants, respectively

Summary

Introduction

Cotton is one of the most important economic crops worldwide. In 2006, it was grown in .75 countries with a total production of 27 billion kilograms, and supplied almost 40% of the global demand for fiber [1,2]. Many species of insect pests attack cotton plants, and the resulting damage can cause enormous yield losses. A substantial part of the cotton production budget is allocated to controlling insect pests. Before the use of insect-resistant genetically engineered (IRGE) cotton, the cotton crop accounted for an estimated 22.5% of the total insecticide used worldwide [1,2]. Because of the effectiveness of Bt cotton and the resulting significant reduction in the use of broader spectrum insecticides [7], the area grown to Bt cotton has increased rapidly around the world [8]

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