The monitoring and prognosis of insect pests

Our most important forest insects are continually monitored with different methods. With information, attained through surveillance monitoring, one can draw conclusions about the size of the populations and their development potential, and out of that recognise the resulting dangers, as well as apply the necessary countermeasures if need be.

Different factors play a role in the development of pest populations. Important abiotical parameters are, for example, climate and weather conditions. Biotical and other parameters are the trees themselves – as a brood chamber or food source – as well as the natural opponents of insect pests. What is also important is defining the vitality of the forest trees and how well they can resist outbreaks (for instance, intensive resinosis by healthy spruce trees is used as a defence against boring bark beetles). Weather conditions, climate, the soil condition and air quality work as stress factors for the trees, and when the conditions are right this can lead to degradation and simultaneously an insect outbreak. Also, interactions within a species or the intervention of human beings, for example different forms of forest management as well as the selection of certain tree species affect tree populations.

All living things tend to mass propagate under optimal conditions (e.g. gradation), including insect species that are important for the forest. The gradation always follows a consistent pattern of expiry. In the latency phase the population is sparse, that is to say, there are comparatively fewer individuals of a population and therefore less damage done to the trees. There reigns a balance of power between insect pests and their opponents. In the phase of progradation the population density enters the optimal conditions for development and approaches a culmination point, which means a highpoint of gradation, and then it reaches the retrogradation stage and after that again sinks back to the latent level. (See figure. 1)

In forest science there are different monitoring procedures applied and adapted for insect species (this is also called forest protection reporting). Forest practitioners and scientists continuously develop these procedures. The monitoring is an important pillar of integrated forest protection. Depending on the species of insect, their different development stages will be observed at different points in time over the year. The species specific thresholds and critical numbers will also determine the intensity of monitoring and they will be continuously coordinated in a multi-stage process according to the gradation trend.

The forest practitioners will, with considerable effort, release early statements about the development of a monitored population and in the following phase develop appropriate defense strategies which will be continuously adapted.

The monitoring results and recommendations are then promptly published in the traditional forest protection information and also often on the internet.