Phenology of feeding preference in post‐diapause Baltimore checkerspot (Euphydryas phaeton) caterpillars

Abstract

1. Host plant use has important life history impacts for caterpillars, and this can change throughout development. Although food quality is important for all caterpillar instars, previous work has found a decreased diet preference in late instars, possibly owing to greater intake requirements.2. Baltimore checkerspot butterflies are highly specialised in their diet as pre‐diapause caterpillars but are less specialised post‐diapause. This study investigated phenological changes in Baltimore checkerspot caterpillar preference and performance on different post‐diapause host plants in the field and lab.3. Caterpillar preference and performance in the lab on four post‐diapause host plants followed the same rank order. The highest ranked plant was their main host plant, followed by an alternative host used for oviposition in some populations, then a commonly observed post‐diapause‐only host, and finally a previously unrecorded post‐diapause host plant.4. In contrast to lab results, field observations showed a decrease throughout the season in the use of the main host plant, turtlehead.5. This study's findings suggest that necessity and food availability drive the post‐diapause Baltimore checkerspot caterpillar diet in the field more than preference. These results also highlight that, even in relatively well‐studied species, field and laboratory observations can yield conflicting results. In this case, the contrast is most likely due to the different constraints in lab versus field conditions, such as the costs of finding preferred plants in the field.