Meeting Abstract

P3.62  Monday, Jan. 6 15:30  The effect of post-diapause development on respiratory function in the alfalfa leaf-cutting bee, Megachile rotundata OWINGS, AA*; YOCUM, G; RINEHART, J; KEMP, W; GREENLEE, K; North Dakota State University; USDA; USDA; USDA; North Dakota State University aowings27@hotmail.com

Megachile rotundata, the alfalfa leaf-cutting bee, is a solitary, cavity-nesting bee. M. rotundata develop inside brood cells constructed from leaf pieces and sealed with the female’s saliva. During development, M. rotundata may experience hypoxic conditions from the cavity in which they reside; oxygen levels may vary based on the bees’ positions within the cavity. They may also be exposed to hypoxia inside the enclosed brood cell itself. To date, no measurements have been made of the oxygen levels inside a brood cell. To test the hypothesis that pupal bees are tolerant of hypoxia, we measured critical PO₂ (Pc) in pupal M. rotundata of varying ages. Pc is defined as the minimum atmospheric oxygen that can sustain a rate process and provides information about respiratory capacity. We measured CO₂ emission rates using flow through respirometry. Bees were exposed to 21%, 10%, 6%, 5%, 4%, 3%, 2%, 1% and 0% oxygen. Pc was determined by comparing mean CO₂ emission in each gas mixture. In support of our hypothesis, the mean Pc was 4% oxygen and ranged from 0% to 10%, similar to that of other insects. Pc was positively correlated with age. As pupae aged, they were less tolerant of hypoxia. To determine if there were developmental changes in tracheal structures that account for the variation in Pc, we used synchrotron x-ray imaging. No visible respiratory movements were detected in hypoxia from bees at various stages of pupal development. Analyses of tracheal diameter showed that abdominal tracheae increased in size as animals aged, while those in the head did not. Understanding the structural basis for the change in Pc will require 3D modeling of whole animal tracheal systems.