Immunological analysis of phloem sap of Bacillus thurigiensis corn and of the nontarget herbivore Rhopalosiphum padi (Homoptera : Aphididae) for the presence of Cry1Ab

Phloem sap of transgenic Bacillus thuringiensis (Bt) corn expressing a trun cated form of the B. thuringiensis delta -endotoxin Cry1Ab, sap sucking aph ids feeding on Bt corn and their honeydew were analysed for presence of Cry 1Ab using ELISA. Phloem sap of Bt and non-Bt corn was collected using a new ly developed technique with a microcapillary being directly inserted into t he phloem tubes. Using this technique, no Cry1Ab was detected in the phloem sap. In contrast, measurable concentrations of Cry1Ab in the range of 1 pp b were detected when phloem sap of pooled leaf samples was extracted using EDTA buffer. This was probably because of Cry1Ab toxin released from damage d cells. When analysing apterous adults of Rhopalosiphum padi L. and their honeydew, no Cry1Ab could be detected. In contrast, Cry1Ab was clearly dete cted in both larvae of the leaf chewing herbivore Spodoptera littoralis (Bo isduval) and their faeces, showing that Cry1Ab is detectable after ingestio n and excretion by herbivores. These results suggest that R. padi ingests o r contains no or only very low concentrations of Cry1Ab in the range of the detection limit. In consequence it is hypothesized that R. padi as an impo rtant prey for beneficial insects in corn is unlikely to cause any harm to its antagonists due to mediating Bt toxin.