Validation of a new method for measuring oxygen consumption in insects

Abstract

Oxygen consumption is difficult to measure in small insects and those with very low metabolic rates, such as insects undergoing diapause or during exposure to low temperatures. One method that works well is the use of closed system respirometry. In this study, we validated the Loligo Systems microplate system for measuring individual respiration in air using the alfalfa leafcutting bee, Megachile rotundata. The Loligo system is a closed system that uses optical fluorescence and was designed for use with aquatic systems, with few studies in insects. We placed overwintering, pre-pupal bees in 29°C to initiate metamorphosis. After 2 weeks, bees were placed in 6, 10, 14, 18, 22, 26, 29, 33, or 35°C, and metabolic rate was measured using the microplate system. Bees (n = 32 for each temperature) were placed into one well of the 24 well-plate and oxygen consumption was measured for 3 hours. We also compared pupal bees dissected from brood cells to those that were undisturbed. Not surprisingly, oxygen consumption increased with temperature. Interestingly, there appeared to be a breakpoint around 18°C, which is the developmental threshold for M. rotundata. Bees remaining in the brood cells had metabolic rates that were not different from those that had been excised. Not only does this system allow for measuring low respiration rates, it opens the possibility of reducing abiotic stressors incurred during oxygen consumption measurements, including the low humidity required for most measurement devices and, in the case of M. rotundata, the need to remove the developing insect from its protective cocoon.