INFLUENCE OF HUNGER LEVEL AND PREY DENSITIES ON MOVEMENT PATTERNS IN 3 SPECIES OF PTEROSTICHUS BEETLES (COLEOPTERA, CARABIDAE)

The foraging behavior of hungry and satiated individuals of three spec ies of polyphagous and predatory carabids was studied by tracking beet les in cereal fields, using a portable harmonic radar system. Fine-sca le movement patterns were investigated in both low and high density of the bird cherry-oat aphid, Rhopalosiphum padi (L.). In low aphid dens ity, hungry individuals of the day-active Pterostichus cupreus L. swit ched from directed to random movements (i.e., a correlated random walk ), whereas both satiated P. cupreus and hungry individuals of the nigh t-active P. melanarius Illiger displayed directed movements only. Conv ersely, the movement patterns of satiated P. melanarius and both satia ted and hungry individuals of the night-active P. niger Schaller could be described as a correlated random walk. In high aphid density, hung ry and satiated P. cepreus displayed directed movements. However, hung ry P. cupreus exhibited more efficient systematic search activities; f oraging on aphids near the base of cereal plants. The movement pattern s of both hungry and satiated P. melanarius could be described as a co rrelated random walk related to burrowing into the soil. Satiated P. n iger displayed directed movements but never foraged, whereas hungry P. niger exhibited a correlated random walk related to near-search activ ities, foraging on coccinelids near the base of cereal plants. No sex- related difference in maximum sprint speed was detected when the beetl es were released on a smooth, regular surface. Conversely, only female carabids were found to alter their speed of movement according to dif ferences in both hunger level and prey (aphid) density in cereal field s. The influence of motivation (hunger level) on movement patterns and foraging behavior exhibited by P. cupreus, P. melanarius, and P. nige r and the associated species-specific responses to differences in aphi d density are discussed in relation to energy costs and predation effi ciency.