Effects of temperature on metabolic rate during metamorphosis in the alfalfa leafcutting bee

Spring temperatures in temperate regions can fluctuate across ranges from optimal to sublethal while insects are actively developing. Fluctuations into sublethal ranges can result in physiological injuries, including disruptions to metabolic homeostasis. To determine how exposure to various temperatures during pupal development affects metabolism, we generated a thermal performance curve using oxygen consumption for insects in this stage. Typically, measuring oxygen consumption is difficult in small insects with low metabolic rates, such as in low temperatures. We measured oxygen consumption (VO₂) in Megachile rotundata pupae using two different closed respirometry systems. Overwintering prepupal bees were placed in 29°C to initiate metamorphosis. After 2 weeks, pupae (n = 40 for each temperature) were placed in 6, 10, 14, 18, 20, 22, 26, 29, 33, 35, or 40°C for 2 hours to measure metabolic rate using the Loligo microplate system. After measurement, bees were replaced in 29°C to continue development to adults, and sex was determined. Both the second and first hour were fit with polynomial curves indicating a nonlinear relationship. There was a significant interaction between temperature and the hour that VO₂ was measured in the microplate system (p < 0.0001). Sublethal temperatures during development can also have long-term effects extending into adulthood and offspring.