Behavioral responses of three plant-inhabiting predators to different prey densities

While measuring the predatorsʹ functional response for the assessment of their aptitude as biological control agents, the time that predators allocate to activities other than handling or searching for the prey, the preference to allocate some of these activities to different locations, and the patch departure tendencies dependent on prey density, are ignored. We test whether these factors have an effect on the predation rates of three plant-inhabiting predators that are used as biological control agents, Dicyphus tamaninii Wagner, Macrolophus caliginosus Wagner, and Orius majusculus (Reuter), at high and low densities of pupae of Trialeurodes vaporariorum Westwood. Continuous behavioral observations of the three species were done on a non-enclosed plant, thus allowing predators to visit different plant locations and to leave the plant at their will. We compared the current results with the ones obtained in a previous functional response experiment. We found that predatorsʹ plant-departure tendency at low prey density was the main reason for differences found in attack rates between experiments. The predatorsʹ preference for laying eggs in the stem, thus spending time in prey-free areas, explained the differences found in attack rates at high prey density. Our results provide more realistic information on predatorsʹ performance to better assess their suitability as biological control agents. Predator behavioral differences depending on prey densities allow for a complementary use of these predators for biological control.