R. Dolch et T. Tscharntke, Defoliation of alders (Alnus glutinosa) affects herbivory by leaf beetles on undamaged neighbours, OECOLOGIA, 125(4), 2000, pp. 504-511
The effects of defoliation of alder (Alnus glutinosa) on subsequent herbivo
ry by alder leaf beetle (Agelastica alni) were studied in ten alder stands
in northern Germany. At each site, one tree was manually defoliated (c. 20%
of total foliage) to simulate herbivory. Subsequent damage by A. alni was
assessed on ten alders at each site on six different dates from May to Sept
ember 1994. After defoliation, herbivory by A. alni increased with distance
from the defoliated tree. Laboratory experiments supported the field resul
ts. Not only leaf damage in the field, but also the extent of leaf consumpt
ion in laboratory feeding-preference tests and the number of eggs oviposite
d per leaf in another laboratory test were positively correlated with dista
nce from the defoliated tree. Resistance was therefore induced not only in
defoliated alders, but also in their undamaged neighbours. Consequently, de
foliation of alders may trigger interplant resistance transfer, and therefo
re reduce herbivory in whole alder stands.