Foraging behaviour influences the outcome of predator-predator interactions

1. Interactions among predators may influence the total efficiency of a predator complex. The effect of intra- and interspecific interactions of the generalist predators Orthotylus marginalis (Heteroptera: Miridae) and Anthocoris nemorum (Heteroptera: Anthocoridae) was investigated in a laboratory experiment. Outcomes of the interactions were determined by comparing predation rates on eggs and larvae of the blue willow beetle Phratora vulgatissima of single individuals with those of two individuals of the same or different species. 2. A non-additive, antagonistic effect on predation rates due to intraspecific interactions was found between individuals of A. nemorum. No such effect was found in O. marginalis. These results are as expected as a consequence of differences in behaviour of the two predator species: A. nemorum is a much more active and mobile predator than O. marginalis. 3. Contrary to expectation, interspecific interactions between A. nemorum and O. marginalis did not affect the total predation rate. 4. An observation from the field corroborated the results obtained in the laboratory study; there was no negative relationship between the densities of the two predator species, indicating that the two species do not interact negatively in the field at their natural densities. 5. It is concluded that the additive effect of multiple predator species is of potential value in biological control.