Thermal sensitivity of metabolic rate in a hemimetabolous insect: variation across life stages

The metabolic rate (MR) impacts pivotal dimensions of fitness such as development, survival and reproduction. Ultimately, MR affects resource demand, population growth, and ecological interactions. In ectothermic insects, it strongly depends on environmental temperature. Therefore, understanding the thermal sensitivity of insects' MR is essential for predicting the impacts of environmental thermal variations on their ecology. Previous studies have shown that thermal sensitivity of insects vary across species, populations, and individuals. However, most research has focused on adults, and ontogenetic variation has received less attention, especially for hemimetabolous insects. This study aimed to estimate MR's thermal sensitivity across the ontogeny of Rhodnius prolixus, a hemimetabolous insect and an important Chagas disease vector. For that, we measured real-time CO2 production by open flow-respirometry as a proxy for MR at six temperatures (10, 15, 20, 25, 30, and 35 ºC). Then, we approximated, for each stage, the thermal sensitivity of resting MR through instantaneous Q10 estimation. We found that thermal sensitivity of MR varies across ontogeny. Compared to adults, the nymphs showed higher thermal sensitivity at evaluated temperatures lower than 28°C (breeding temperature), but lower sensitivity at higher temperatures. Adults presented a constant thermal sensitivity of MR across the assayed thermal range. Our results provide novel insights into thermobiology of hemimetabolous insects and possible consequences in a warming world.