Meeting Abstract

P1.107  Friday, Jan. 4  Water loss, respiration, and critical PO₂ in Cetoniinae CAMPBELL, JB*; DUELL, ME; KLOK, CJ; HARRISON, JF; Arizona State University jacob.campbell.1@asu.edu

Observations indicate that as insect size increases, ventilation and metabolic rates scale allometrically, while some studies indicate that critical PO₂ is mass-independent. This has not been confirmed in entirety. Scarab fruit chafer beetles in subfamily Cetoniinae were chosen for this investigation because species vary in mass by several orders of magnitude, therefore representing an excellent model taxon for mass-scaling comparisons. By slowly decreasing oxygen from 21% to 0% we found critical PO₂ simultaneously with water loss, CO₂ emission, and activity in six species of Cetoniinae beetles (Euphoria fulgida holochloris, Dicronorrhina derbyana, Coelorrhina hornimani, Mecynorrhina torquata, Trypoxylus dichotomus, Goliathus goliathus) ranging in size from 0.1-14g. While manipulating oxygen concentrations we observed patterns that allowed us to quantify cuticular, trans-spiracular, and ventilatory respiration and water loss. Cuticular water loss and respiration were measured during periods of discontinuous gas exchange to ensure full spiracular closure; ventilatory water loss was measured in normoxia; trans-spiracular water loss was quantified during anoxia, assuming that as individuals became unresponsive, spiracles remained open throughout the duration of anoxia. Preliminary data suggest that critical PO₂ does not vary by species and is mass-independent. However, species do show differences in water loss rates during different levels of hypoxia indicating various strategies of water conservation. Our quantifications of cuticular, ventilatory, and trans-spiracular water loss will allow us to better explain physiological events in respiration and make further predictions about ventilatory responses to oxygen variation.