Within‐plant variation in chemical defence of Erysimum cheiranthoides does not explain Plutella xylostella feeding preference

Plants invest a substantial fraction of their resources into defence against herbivores, with the highest levels of defence often allocated only to the most valuable tissues. Plants in the genus Erysimum (Brassicaceae) have evolved the ability to produce novel cardenolides, in addition to ancestrally conserved glucosinolates. While these plants co‐express both defences, differences in tissue‐specific expression might represent an effective cost‐saving strategy. Larvae of the glucosinolate‐resistant diamondback moth Plutella xylostella occasionally feed on Erysimum cheiranthoides but tend to avoid younger leaves. Here, we predict that caterpillar feeding preference is shaped by variations in cardenolide levels. Thus, we quantified within‐plant variations in defence and nutritional traits of vegetative or early reproductive plants and performed feeding assays to evaluate the relative importance of cardenolides. In accordance with optimal defence theory (ODT), the youngest leaves contained..., , , # Within-plant variation in chemical defence of *Erysimum cheiranthoides* does not explain *Plutella xylostella* feeding preference [https://doi.org/10.5061/dryad.73n5tb35b](https://doi.org/10.5061/dryad.73n5tb35b) ## Description of the data and file structure Raw data provided as .csv files and complete R code used in the analysis of the data and visualization of results. *01_Whole_plant_choice.csv*: Data from two whole-plant choice assays. In the first assay (**Assay** = 1), caterpillars of *Plutella xylostella* were left to feed on 4-week or 6-week old plants (**Plant_age** = W4/W6) for 24 hours, after which leaves of assay plants (**Plant** = 1-18) were numbered from bottom to top of each plant (**Leaf_number_b-t**), removed and glued to sheets of paper for scanning. Total leaf area with damage was quantified (**Leaf_area_damaged**), intact leaf area was estimated by masking damage (**Leaf_area_whole**), and consumed leaf area was calculated as the difference (**Area_consumed**)...,