Using synchrotron X‐ray imaging to visualize tracheal changes during development in American locusts

Abstract

During their eight‐week development, Schistocerca americana grasshoppers hatch as 15 mg 1st instars and grow into nearly 3 g adults. It has been suggested that larger insects may have more problems with O2 delivery. In support of this idea, S. americana CO2 emission rates only scale with body mass0.76 during development, and larger, older grasshoppers fatigue more rapidly during repeated jumping. Furthermore, the jumping muscle of larger, older grasshoppers relies more on anaerobic metabolism. To test the hypothesis, that larger, older grasshoppers have decreased O2 delivery, we used synchrotron X‐ray imaging to visualize tracheal air sac compressions in the abdomen, proximal femur, and distal femur of developing S. americana in 21% and 5% O2. For all ages, hypoxia significantly increased air sac ventilation rates throughout the body. There was no effect of body size across development on ventilation rates of abdominal or distal femoral air sacs in either 21% or 5% O2. However, larger, older grasshoppers had ventilation rates in the proximal femoral air sacs that were 70% lower in both 21% and 5% O2 than those of smaller, younger animals. The reduced ventilation rate of femoral air sacs in larger grasshoppers provides a respiratory mechanism that explains their greater reliance on anaerobic metabolism and also supports the hypothesis that they have more problems with O2 delivery. (Support provided by NSF, NIH, US DOE).