Abstract
The foraging behavior of hungry and satiated individuals of three species of polyphagous and predatory carabids was studied by tracking beetles in cereal fields, using a portable harmonic radar system. Fine-scale movement patterns were investigated in both low and high density of the bird cherry-oat aphid, Rhopalosiphum padi (L.). In low aphid density, hungry individuals of the day-active Pterostichus cupreus L. switched from directed to random movements (i.e., a correlated random walk), whereas both satiated P. cupreus and hungry individuals of the night-active P. melanarius Illiger displayed directed movements only. Conversely, the movement patterns of satiated P. melanarius and both satiated and hungry individuals of the night-active P. niger Schaller could be described as a correlated random walk. In high aphid density, hungry and satiated P. cupreus displayed directed movements. However, hungry P. cupreus exhibited more efficient systematic search activities; foraging on aphids near the base of cereal plants. The movement patterns of both hungry and satiated P. melanarius could be described as a correlated random walk related to burrowing into the soil. Satiated P. niger displayed directed movements but never foraged, whereas hungry P. niger exhibited a correlated random walk related to near-search activities, foraging on coccinelids near the base of cereal plants. No sex-related difference in maximum sprint speed was detected when the beetles were released on a smooth, regular surface. Conversely, only female carabids were found to alter their speed of movement according to differences in both hunger level and prey (aphid) density in cereal fields. The influence of motivation (hunger level) on movement patterns and foraging behavior exhibited by P. cupreus , P. melanarius , and P. niger and the associated species-specific responses to differences in aphid density are discussed in relation to energy costs and predation efficiency.
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