Data from diet C:N ratio and temperature influence the performance and coloration of tobacco hornworms

Insect coloration mediated by melanization can assist in dealing with
environmental temperatures. However, melanin synthesis can be costly and
depends on the ability of insects to acquire enough energy and nutrients
from their diets. Due to the increased plant C:N ratio associated with
elevated CO2 concentrations, insect herbivores’ melanization could be
limited by the amount of nitrogen they acquire from their host plants. To
investigate how diet C:N impacts the potential color response to
temperature, we used Manduca sexta caterpillars reared at different
combinations of temperatures and diet C:N ratio, and measured pupal mass
and development time (performance metrics) and color morphology. The
high-temperature treatment (27°C) had a positive impact on larvae
performance, whereas a nitrogen-poor diet was related to lower
performance. Using a fitness metric that considers both pupal mass and
development time, we found a positive effect of both high-temperature and
nitrogen-rich diet treatments on larvae fitness. We found that diet and
temperature affected the coloration of larvae, in which larvae reared at
the low-temperature treatment (18°C) and fed a nitrogen-rich diet were
darker than their counterparts. Our results provide experimental evidence
of the impact of diet on melanization and suggest that CO2-related changes
in plant quality could be associated with changes in insect herbivore
performance and coloration.