Gene flow from transgenic crops allows novel traits to spread to sexually compatible weeds. Traits such as resistance to insects may enhance the fitness of weeds, but few studies have tested for these effects under natural field conditions. We created F2 and F3 crop-weed hybrid lineages of genetically engineered rice (Oryza sativa) using lines with two transgene constructs, cowpea trypsin inhibitor (CpTI) and a Bt transgene linked to CpTI (Bt/CpTI). Experiments conducted in Fuzhou, China, demonstrated that CpTI alone did not significantly affect fecundity, although it reduced herbivory. In contrast, under certain conditions Bt/CpTI conferred up to 79% less insect damage and 47% greater fecundity relative to non-transgenic controls, and a 44% increase in fecundity relative to the weedy parent. A small fitness cost was detected in F3 progeny with Bt/CpTI when grown under low insect pressure and direct competition with transgene-negative controls. We conclude that Bt/CpTI transgenes may introgress into co-occurring weedy rice populations and contribute to greater seed production when target insects are abundant. However, the net fitness benefits that are associated with Bt/CpTI could be ephemeral if insect pressure is lacking, for example, due to widespread planting of Bt cultivars that suppress target insect populations.

Detailed morphological data and insect indexThe three sheets in this file describe the morphological data and insect index from all the experimental plots (N=4) in F2 and F3 generations: Sheet-1 describes the relevant data from wa strain in F2 generation; Sheet-2 describes the relevant data from wb strain in F2 generation; and Sheet-3 describes the relevant data in F3 generation. The morphological traits include plant height (cm), number of tillers per plant, number of panicles per plant, number of seeds per plant, seed set (%), and 1000-seed weight under low vs. natural insect pressure, as well as pure vs. mixed cultivation.