The utilization of patchy thermal microhabitats by the ectothermic insect predator, Cicindela sexguttata
1998
Schultz, T.D.
Tiger beetles (Cicindela) of open habitats have served as model ectotherms in studies of the dependence of activity and habitat utilization on temperature. Potential departures from the cicindelid model were investigated in Cicindela sexguttata, a species inhabiting forests where thermal resources are patchy and ephemeral. Body temperatures (Tb) were determined by inserting thermocouples into beetles immediately after observing specific behaviours in the field. Cicindela sexguttata elevated Tb by basking, foraged at a preferred Tb of 32.8 degrees C, and stilted, sun-faced, or sought shade when Tb exceeded 35 degrees C. Although these behaviours were typical of Cicindela, their set points were lower than those of species in more open habitats. Illuminated substrates were utilized for basking and foraging. Beetles were dispersed throughout the forest floor in early spring, but became aggregated in light gaps when the canopy leafed out. Operative temperatures of thermal models indicated that beetles were unable to maintain the preferred Tb in shade and would not be able to maintain a preferred Tb in light gaps during the autumn, when adults are normally in diapause. Beetles were confined to foraging in light gaps once the canopy was closed. Foraging rate and searching speed were independent of Tb, in contrast to other cicindelids. Adults rarely searched for prey, but ambushed small arthropods that alighted in the light gap. Dependence on patches of illumination as thermal resources may increase prey capture, intraspecific encounters, and risk of predation, and preclude foraging in the autumn when Cicindela species of open habitats are also active.
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