Host plant use has important life history impacts for herbivorous insects such as caterpillars, and this can change through development. The quality of the food consumed is more important for late instars than for earlier instars, but late instar caterpillars must consume large amounts of food and have shown decreased diet preference. Baltimore checkerspot (Euphydryas phaeton) caterpillars are highly specialized in their prediapause diet, but are less specialized as postdiapause caterpillars in the spring. We investigated Baltimore checkerspot caterpillar preference and performance on four different postdiapause host plants, and whether it changed through time.
Results/Conclusions
The four postdiapause host plants followed the same rank order in both caterpillar preference and performance tests. The highest ranked species was their main host plant (white turtlehead, Chelone glabra), followed by an introduced species that some populations use as a main host (English plantain, Plantago lanceolata), then a commonly observed postdiapause host (arrowwood viburnum, Viburnum dentatum), and lastly a previously unrecorded postdiapause host plant (blue vervain, Verbena hastata). Field observations showed a decrease throughout the season in the use of the main host plant, turtlehead, compared to other species, while lab results showed a strong preference for turtlehead in late instar caterpillars. Our findings suggest that postdiapause Baltimore checkerspot caterpillar diet in the field is more determined by necessity and food availability than by caterpillar preference. This is also a reminder that our perceptions based on observations in the field may be obscured by subtleties that are only distinguishable though laboratory experiments.