Larval consumption of Cry1F maize pollen causes adverse effects in four non-target Lepidoptera species

The cultivation of genetically modified maize expressing Bt proteins against Lepidopteran pests poses a risk for non-target (NT) Lepidoptera, particularly for species inhabiting agroecosystems and whose larvae are susceptible to Bt toxins expressed in maize pollen. Here, laboratory studies were conducted to determine the adverse effects of larval exposure to Cry1F pollen (event TC1507) on host plants on two butterfly (Pieris napi, Aglais io) and two moth species (Plutella xylostella, Ematurga atomaria). All NT Lepidoptera tested were affected by the Cry1F toxin in the pollen, albeit in different degrees depending on the species and the recorded parameter. Adverse sublethal effects of increasing Bt pollen concentrations included reduced larval feeding, lower larval body weight and prolonged development times, but no significant effects on adult size or fecundity were observed. Dose-response mortality, measured when all survivors reached adult stage, showed that three species were susceptible to field-realistic pollen concentrations (LC₅₀ = 76, 126 and 171 Cry1F pollen grains/cm² on host plants for P. xylostella, E. atomaria, and A. io, respectively), whereas P. napi was only affected by higher concentrations (5070 Cry1F pollen grains/cm²). Assessing mortality at day seven substantially underestimated effects compared to the end of the larval period highlighting the importance of experiment duration until adulthood to detect delayed effects, and stressing the need for more ecologically realistic testing conditions for risk assessment. Given the fact that only few data exist on the susceptibility of non-pest Lepidoptera to Cry1F, our results indicate that NT Lepidoptera populations may be more vulnerable to the cultivation of Cry1F maize TC1507 than previously assumed.