Abstract
The goal with our research is to produce knowledge that can be used to develop environmentally friendly and sustainable methods for controlling insect pests. To achieve this we must understand the processes involved in the natural regulation. The most efficient way to gain such an understanding is via field experiments. In many systems it is difficult to conduct large-scale field experiments. We work with a system - willow leaf beetles and their natural enemies - with exceptionally good opportunities for such experiments. Here we describe two types of experiments that aim at estimating the relative role of plant quality (bottom-up) and natural enemies (top-down), and occurrence of a potentially scarce resource (overwintering sites). The first type of experiments are possible because harvesting takes place every 3rd to 5th year, a relevant disturbance frequency when trying to quantify the role of different ecological processes. The second experiment aims to establish small, isolated stands of susceptible and resistant willows. In half of the susceptible and resistant stands we will add low numbers of natural enemies, in the other half high numbers. Equal numbers of leaf beetles will be added to all stands. Beetle population growth rate will be used as dependent variable. We also intend to continue to follow and analyse the population dynamics of leaf beetles and their natural enemies in a number of willow stands, using data collected since 1998.
Sweden