Title: The effect of post-diapause development on respiratory function in the alfalfa leaf-cutting bee, Megachile rotundata Authors
Submitted to: Annual Meeting of Society of Integrative and Comparative Biology
Publication Type: Abstract Only
Publication Acceptance Date: September 6, 2013
Publication Date: January 3, 2014
Citation: Owings, A.A., Yocum, G.D., Rinehart, J.P., Kemp, W.P., Greenlee, K.J. 2014. The effect of post-diapause development on respiratory function in the alfalfa leaf-cutting bee, Megachile rotundata [abstract]. Annual Meeting of Society of Integrative and Comparative Biology. January 307, 2014. Austin, TX. Abstract Book page 255. Interpretive Summary: Seventy percent of crops grown for human food production are dependent on pollinators. The value of this pollination service worldwide is estimated to be over 100 billion dollars annually. This value does not include agriculture products that are not directly consumed by humans such as alfalfa that is used as an input for meat and milk production. The alfalfa leafcutting bee Megachile rotundata is the primary pollinator used in the production of alfalfa seed in North America. There is also growing interest in M. rotundata for pollination of various specialty crops. The alfalfa leafcutting bees are reared in vast quantities, raising the question of how much ventilation is required during incubation and storage to ensure high quality pollinators. This presentation reports on the first of a series of planned experiments exploring this species’ tolerance of low oxygen levels. This information is needed to optimize the husbandry of this vital pollinator.
Technical Abstract: 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.