Siberian Federal University Scientists Measure Risks of Outbreaks of Insect Pests in the Siberian Taiga
Scientists from the Siberian Federal University and specialists from the SB RAS’s Krasnoyarsk Research Centre have studied the population dynamics of five species of forest insects that feed on tree needles in the Siberian taiga. To do this, they created and analyzed a series of data on the dynamics of the number of insects for the period from 1979 to 2017. This information helps to assess how various factors — food, natural phenomena, human intervention — affect the dynamics of the development of the insect pest population and make it possible to identify the zone in which an outbreak may begin.
As is known, outbreaks of mass reproduction are another most important factor in the death of taiga forests, the second only to fires. To predict and take measures to prevent outbreaks, it is necessary to understand the mechanisms of their occurrence. For example, how the growth in the number of different species of forest insects in one habitat or one species in different habitats relate to each other. At the same time, these data need to be accumulated over decades, and such field studies are carried out quite rarely.
“In total, three of the longest series of data on the dynamics of insect abundance are known in world forest entomology — a 120-year series of the larch tortrix in the Swiss Alps and a 60-year series of the pine looper in Thuringia (Germany) and the Southern Urals. Our series for five species of needle-eating insects in the Krasnoturansk pine forest in the south of Krasnoyarsk Territory, the number of which we annually estimated from 1979 to 2017, apparently, is the fourth in the world in terms of length. There are much more short time series, but it is practically impossible to obtain reliable statistical estimates of the relationships between pest densities in different years,” said Olga Tarasova, one of the authors of the work, professor of the Department of Ecology and Environmental Management at the School of Ecology and Geography, Siberian Federal University.
According to Ms. Tarasova, the work proposes a method for calculating the regulatory characteristics of the population dynamics of phytophagous insects. It allows determining the characteristics of the dynamics of these populations and assessing the risk of outbreaks of mass reproduction of each species of insects.
Interactions between generations of insect populations are characterized by positive feedbacks (when the insect population density increases from generation to generation) and negative feedbacks (when the current population density decreases relative to the density in previous years). It is safe to say that the combination of positive and negative feedbacks locks the population in a stable state, prevents outbreaks of mass reproduction, and stabilizes the ecosystem. However, these relationships do not always hold the population in a stable state, and in order to assess the risk of loss of stability, it is necessary to evaluate the regulatory properties of the populations.
“To assess the nature of the regulation of population dynamics, we used such an indicator as the stability margin. This indicator helps to quantify the possibility of a population “ejection” beyond the boundaries of the system’s stability. Calculations of the stability margins for different species of insects in various habitats showed that the minimum stability margin is typical for populations of the pine looper in habitats where an outbreak of mass reproduction of this species was previously observed. The results we obtained make it possible to assess the risks of outbreaks of mass reproduction and approach the solution of the problem of predicting such outbreaks more accurately,” summed up Vladislav Soukhovolsky, co-author of the study, professor of the Department of Hunting Resource Studies and Nature Reserve Management of the School of Ecology and Geography, Siberian Federal University..