Abstract
Collembolans are common soil arthropods that may be exposed to insecticidal proteins produced in genetically engineered (GE) plants by ingestion of crop residues or root exudates. In the present study, a dietary exposure assay was validated and used to assess the lethal and sublethal effects of two Bacillus thuringiensis (Bt) insecticidal proteins, Cry1C and Cry2A, on Folsomia candida. Using the insecticidal compounds potassium arsenate (PA), protease inhibitor (E-64), and Galanthus nivalis agglutinin (GNA) mixed into Baker’s yeast, we show that the assay used can detect adverse effects on F. candida. Survival and development were significantly reduced when F. candida was fed a diet containing PA, E-64, and GNA at 9, 75, and 100 μg/g diet, respectively, but not when fed a diet containing 300 μg/g Cry1C or 600 μg/g Cry2A. The activities of test antioxidant-, detoxification-, and digestion-related enzymes in F. candida were unaltered by a diet containing 300 μg/g Cry1C or 600 μg/g Cry2A, but were significantly increased by a diet containing 75 μg/g E-64. The results confirm that Cry1C and Cry2A are not toxic to F. candida at concentrations that are much higher than those encountered under field conditions.
Highlights
Collembolans, such as Folsomia candida (Isotomidae), are commonly found in plant rhizospheres, including those of insect-resistant genetically engineered (IRGE) rice plants, where they can be exposed to transgene-derived proteins exuded from roots
When compared to the control, the body length of F. candida was significantly reduced by day 7 at the highest concentration of Potassium arsenate (PA) (36 μ g/g fresh weight (FW) diet), while at day 14, 21, and 28, significant reductions were caused by PA at 9.0 μ g/g FW diet (P < 0 .05)
Evaluation of the potential negative effects of an IRGE crop on non-target arthropods is an important part of the environmental risk assessment that is performed before a GE crop can be commercialized[6]
Summary
Collembolans, such as Folsomia candida (Isotomidae), are commonly found in plant rhizospheres, including those of IRGE rice plants, where they can be exposed to transgene-derived proteins exuded from roots. While most previous studies have used GE plant tissue or artificial soil treated with plant tissue in order to expose the test insects to the insecticidal proteins, in the current study we used baker’s yeast to expose F. candida to known concentrations of purified Cry proteins Such dietary exposure assays (often referred to as Tier-1 assays) are regarded as more conservative (i.e., more likely to detect toxic effects) than assays in which test species are exposed to insecticidal compounds by feeding on GE plant tissue or are exposed in other ways[19,20,21]. The activity of antioxidant-, detoxification-, and digestion-related enzymes in F. candida was measured after the collembolan was fed Cry1C or Cry2A protein because changes in enzyme activities would indicate potential sublethal effects of the Bt proteins
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