Density-dependent predation of the ant Lasius niger (Hymenoptera: Formicidae) on two attended aphids Lachnus tropicalis and Myzocallis kuricola (Homoptera: Aphididae)

The ant Lasius niger was observed collecting honeydew and preying on I:he two aphid species Lachnus tropicalis and Myzocallis kuricola on the chestnut trees Castanea crenata. Observation determined how the ant L. niger controlled their predation on the aphids in response to the density and honeydew-productivity of the aphids. Lachnus tropicalis was a better honeydew source than M. kuricola for L. niger in terms of the amount of honeydew collected per unit time by the ants. The number of foraging workers on a tree increased with the number of L. tropicalis on the tree, but not with the number of M. kuricola. The density of L. tropicalis per L. niger worker on a tree had a positive effect on the predation activity of L. niger on both aphids, whereas the density of M. kuricola per ant did not have any significant effect. The predation pressure by the ant which increased with L. tropicalis density, however, directed to M. kuricola rather than to L. tropicalis. These facts suggest (1) that L. niger control their predation activities on aphids with regards to the densities of the attended aphids per worker, and (2) that the ants prey on the aphid species producing less honeydew. The effects of the ant predation on aphids and the importance of these predation effect in antaphids interactions were discussed.