Host-plant quality alters herbivore responses to temperature: a case study using the generalist Hyphantria cunea

The nutritional quality of host plants is an important determinant of fitness in insect herbivores. However, it remains an open question whether the ingestion of a particular plant will have the same effects on an herbivore under differing thermal conditions. We measured the performance of the generalist-feeding caterpillars of Hyphantria cunea Drury (Lepidoptera: Arctiidae) raised on one of five natural host plants to determine their nutritional quality: Platanus occidentalis L. (Platanaceae), Sophora japonica (L.) Schott (Fabaceae), Prunusxyedoensis Matsum. (Rosaceae), Cornus kousa Hance (Cornaceae), or Betula platyphylla Sukaczev (Betulaceae). Caterpillars performed well on P.occidentalis, S.japonica, and P.x yedoensis, but poorly on C.kousa and B.platyphylla. The nutritional phenotype of caterpillars varied among host-plant groups, with the proportion of lipid-free body mass to lipid content being higher for caterpillars raised on P.occidentalis and S.japonica (3.8-4.2:1) than for caterpillars raised on P.x yedoensis (1.6-2.1:1). A multi-factorial experimental design was employed to investigate the interactive effects of host-plant quality and temperature on the performance of H.cunea caterpillars raised on either P.occidentalis or P.x yedoensis at three rearing temperatures (20, 25, or 30 degrees C). Caterpillars raised on P.occidentalis displayed a monotonic decrease in development time with increasing temperature, but the development time of those on P.x yedoensis decreased rapidly as temperature rose from 20 to 25 degrees C and then stayed unchanged despite further increase in temperature. The rate at which body size increased with decreasing temperature was much steeper for caterpillars raised on P.occidentalis than for those on P.x yedoensis. Collectively, these results indicate that host plant can alter the thermal reaction norms for the key life-history traits of herbivores. This study has implications for understanding the impacts of climate change on herbivore-plant interactions.