Effects of tobacco genetically modified to express the protease inhibitor
bovine spleen trypsin inhibitor (BSTI) were examined in laboratory assays
against three earthworm and one collembolan species. BSTI is a serine
protease inhibitor that can bind to the digestive trypsins of insects feeding
on modified plants, resulting in reduced growth and survival. Protease
inhibitors are active against a broad range of insects, so may have a large
impact on non-target organisms. Survival and fecundity of the collembolan
Folsomia candida were unaffected by consumption of artificial diet containing
BSTI-expressing tobacco leaf or powdered freeze-dried BSTI-expressing
tobacco leaf that was added to soil. Similarly, mortality and growth of
earthworms Aporrectodea caliginosa and Lumbricus rubellus did not differ significantly between soil augmented with
BSTI-expressing tobacco leaves or unmodified control leaves. The redworm
Eisenia fetida gained less weight when provided with BSTI-expressing leaves in one assay,
but when the experiment was repeated, there was no significant difference
between treatments. BSTI-expressing tobacco and unmodified control leaves
decomposed at the same rate, indicating that the inhibitor had no effect on
the overall function of the decomposer community of micro-flora and fauna in
soil.