Meeting Abstract

P1.113  Friday, Jan. 4  Critical PO₂ of developing Megachile rotundata, the alfalfa leaf-cutting bee OWINGS, A/A*; YOCUM, G; RINEHART, J; KEMP, W; GREENLEE, K; North Dakota State University, Fargo; USDA-ARS Red River Valley Agricultural Research Center, Fargo; USDA-ARS Red River Valley Agricultural Research Center, Fargo; USDA-ARS Red River Valley Agricultural Research Center, Fargo; North Dakota State University, Fargo aowings27@hotmail.com

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.