Bodybuilding Bumblebees: How exercise affects bumblebee (Bombus impatiens) flight muscle

Insect flight muscle is the most metabolically active tissue known, allowing for production of the large forces necessary for flight. Flight ability varies among insects and with insect age, which is partially due to differences in muscle. However, very little work has examined whether and how insect muscle may respond to exercise. One key response may be a change in the amount of flight muscle relative to body mass ("flight muscle ratio", FMR), analogous to bulkier muscle in bodybuilders. We examined differences in FMR among bumblebee (Bombus impatiens) sisters differing in body size and in "training". We trained the bees by periodically having them lift beaded strings during flight. This approach allows direct observation of how many weights are being lifted (their performance), and ultimately, provides a starting point for determining how exercise may affect insect flight muscle. Aside from changes in FMR, bees that regularly exercise may have elevated mitochondrial density and increased enzymatic activity.