Effects of ant exclusion during outbreaks of a defoliator and a sap-sucker on birch
Article first published online: 4 JAN 2002
Blackwell Science Ltd, Oxford
Volume 23, Issue 2, pages 185–194, May 1998
How to Cite
KARHU, K. J. (1998), Effects of ant exclusion during outbreaks of a defoliator and a sap-sucker on birch. Ecological Entomology, 23: 185–194. doi: 10.1046/j.1365-2311.1998.00116.x
- Issue published online: 4 JAN 2002
- Article first published online: 4 JAN 2002
- Cited By
1. The influence of a wood ant, Formica aquilonia, on the defoliation of the white birch, Betula pubescens, and on its invertebrate community was studied in ant-exclusion experiments during two outbreaks, the decline phase of the autumnal moth, Epirrita autumnata, and the peak year of the birch aphid, Euceraphis punctipennis, not tended by ants.
2. The numbers of the wood ant and Symydobius oblongus, a tended aphid, in birch foliage showed a strong positive correlation, and the former decreased rapidly when the distance from the ant mound increased, confirming that there was a distance-related gradient in arboreal ant predation. There may have been a parallel reduction in soil amelioration by ants through nest construction and food gathering.
3. The application of a glue ring around the trunk excluded ants totally from the canopy, inhibiting predation but not fertilization.
4. Ant-exclusion resulted in a 90–95% reduction in the growth of tended aphid colonies by mid-season.
5. Outbreak populations of the autumnal moth and the birch aphid were reduced by 45–67% and 77%, respectively, in control trees and correlated negatively with ant numbers.
6. The total percentage of leaf area damaged by moth larvae was 34% lower in ant-foraged than in unforaged trees.
7. Neither the distance from the ant mound nor its interaction with the glue treatment had any effect on the herbivores or folivory, indicating that the possible soil-ameliorating effect was weaker than predation, which reduced herbivore numbers at every distance studied (4–20 m).
8. Predation by ants also affected the abundance of syrphid larvae, predatory on both aphids, the percentage parasitism by a wasp, Aleiodes testaceus, on the autumnal moth, and thereby (or directly) its age (size) distribution. The presence of ants had no influence on spider abundance.
9. It is concluded that predation rather than soil amelioration is likely to be the reason why the degree of folivory and, during serious outbreaks, the mortality of trees are lower in the vicinity of wood-ant mounds.