| Summary: | Plants may be genetically modified to express an entomopathogenic protein from the bacterium <italic>Bacillus thuringiensis</italic> (Berliner) (Bt plants). Bt plants are known to affect some above-ground invertebrates, with significant effects on species closely related to target invertebrates and on their natural enemies. Bt proteins may enter the soil through root exudates and decomposition of plant material. This study aimed to analyse the effects of Bt broccoli (<italic>Brassica oleracea</italic> L. var. italica Plenk) on six soil-dwelling invertebrates. No significant differences were detected in nematode (<italic>Panagrellus redivivus</italic> L.) populations living in compost in which Bt and non-5/ broccoli had grown. The other species were introduced to combinations of Bt and non-5/ leaves, and compost in which Bt and non-5/ plants had grown. No differences were detected in Collembola (<italic>Folsomia candida</italic> Willem) populations, but significantly more young woodlice (<italic>Porcellio scaber</italic> Latrielle) survived, and weighed more, in the Bt than the non-5/ treatments. Slugs (<italic>Deroceras reticulatum</italic> Muller) weighed more in the presence of Bt proteins. A higher percentage of earthworm (<italic>Lumbricus terrestris</italic> L.) cocoons hatched in Bt than non-5/ treatments. In contrast, at a third trophic level, fewer predatory beetles (<italic>Nebria brevicollis</italic> Fabricius) survived when feeding on slugs that had fed on Bt leaves than on those fed on non-5/ leaves. Leaves from Bt plants affected more parameters than compost in which Bt plants had grown. Attempts were made to use molecular techniques to analyse the effects of Bt broccoli on soil micro-organisms. Individual Bt broccoli plants expressed different concentrations of Bt protein. The Bt plant's control of three Lepidoptera species was tested and only one species was susceptible. These results show that non-target invertebrates, including pest species, can be affected by Bt broccoli, sometimes beneficially, and underlines the need for prior testing of GM crops on a range of non-target species.
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