Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 9/7/2012
Publication Date: 1/3/2013
Citation: Owings, A., Yocum, G.D., Rinehart, J.P., Kemp, W.P., Greenlee, K. 2013. Critical PO2 of developing Megachile rotundata, the alfalfa leaf-cutting bee [abstract]. The Society for Integrative Comparative Biology Annual Meeting. January 3-7, 2013. San Francisco, CA. Abstract Book page 278. Interpretive Summary: With the significant decrease in recent years of the number of honey bee colonies due to disease and other factors, producers of crops requiring bee pollination are facing amounting crisis. Therefore, there is acute need for other pollinators that can be used to supplement the honey bee in pollination services. The alfalfa leafcutting bee, Megachile rotundata is a solitary bee species that can be used to pollinate a number of specialty crops such as melons, blueberry and in the production of seeds for alfalfa and onions. Currently, there are a number of key issues in M. rotundata husbandry that need to be addressed to insure the quantity and quality of bees to meet the demand for pollination services. One of these needs is the development of quality control biomarkers. In a series of experiments, we investigated the response of the M. rotundata respiratory system to various management manipulations. Results show that how the bees are managed during development affects adult respiratory physiology. Therefore, respiratory physiology can serve as a sensitive quality control biomarker for the development of optimized management practices for this key alternative pollinator.
Technical Abstract: The alfalfa leaf-cutting bee, Megachile rotundata, is a solitary, cavity-nesting bee. Juvenile bees develop inside brood cells constructed out of leaf pieces. During development inside the brood cell, pre-pupae may experience hypoxic conditions from both the cavity nesting behavior and brood cell itself. To test the hypothesis that pre-pupae are tolerant of hypoxia, we measured critical PO2 in developing M. rotundata of varying ages. Critical PO2 is defined as the minimum atmospheric PO2 that can sustain a rate process, and provides information about respiratory capacity. Using flow through respirometry, we measured CO2 emission rates in normoxia, 10%, 6%, 5%, 4%, 3%, 2%, and 1% oxygen, and anoxia. Critical PO2 was determined by comparing mean CO2 emission of an insect in each gas mixture. In support of our hypothesis, the average critical PO2 of all bees was 4% oxygen, similar to that of other insects and to adult M. rotundata. Critical PO2 values ranged from 0 to 10% oxygen. Critical PO2 was inversely correlated with body mass, which declined as pre-pupae developed. The finding that respiratory capacity decreases with developmental age suggests that tracheal remodeling during metamorphosis may negatively affect hypoxia tolerance. Alternatively, the decrease in hypoxia tolerance with age may be a signal for pupae to undergo adult emergence.