Impact of dietary sterols on life‐history traits of a caterpillar

Although lepidopteran larvae have been shown to metabolise a number of different phytosterols, their life‐history traits in response to these different phytosterols may vary with the species. Using the specialist moth, Plutella xylostella (Linaeus) (Lepidoptera), growth, development and fecundity on artificial diets containing host and non‐host phytosterols were measured over two generations. Because of the nature of the experimental design, maternal effects linked to dietary sterol could be assessed. In both generations, survival was highest on diets containing sitosterol as the primary phytosterol. A significant decrease in survival on stigmasterol, a non‐host phytosterol, was observed between generations. As expected, survival on a control diet with only trace‐sterols decreased between generations. Larval duration and pupal duration in both generations was longest on the diets containing the non‐host phytosterols, stigmasterol and spinasterol, and on the trace‐sterol diet. Finally, fecundity was affected by dietary sterol. In the first generation, fewer viable eggs were produced on the stigmasterol and trace‐sterol diets than on wheatgerm control diet. In both generations, dietary sterol significantly influenced percentage egg viability. Overall, these results indicate that differences in phytosterol structure can have pronounced effects on life‐history traits, especially when they are projected to the population level. The implications of these results are discussed with respect to phytosterol use by phytophagous insects and their host plant affiliations.