RNAi-mediated plant sterol modification: a novel strategy for controlling pest caterpillars

All eukaryotes use sterols as structural components in cell membranes and as precursors for key hormones. However, arthropods are unique among eukaryotes because they are unable to synthesize sterols de novo and must acquire sterols through their diet. Cholesterol is the dominant sterol in most insects, but because plants contain little cholesterol, most insect herbivores convert phytosterols to cholesterol. However, metabolic constraints limit which phytosterols insect herbivores can convert to cholesterol. In this study we used RNA interference to modify the sterol profile of Arabidopsis thaliana to generate phytosterols that would be problematic for insect herbivores. We did this by silencing the Δ 8 -Δ 7 -sterol isomerase gene ( HYD1 ) that is responsible for the conversion of Δ 8 -sterols into Δ 7 -sterols. Sterol production decreased in Arabidopsis lines with > 95% transcript reduction and half of the total sterol profile in these plants showed a Δ 8 configuration. These sterol-modified lines exhibited normal growth, but caterpillars ( Plutella xylostella ) reared on these plants showed reduced growth and survival, while adults showed decreased reproductive output. Sterol analysis of the pupae reared on sterol-modified plants suggests these negative effects are a function of reduced cholesterol levels and the accumulation of Δ 8 -sterols. Finally, we used our collective performance and reproduction data to model the effects of sterol-modified plants at the population level. We show that population numbers are significantly reduced, and generation time extended, after only two generations. Our results suggest that modifying plant sterols has real potential for management of pest caterpillars, especially multivoltine species.