No 2 (2023)

Data on the species composition and dynamics of outbreaks of needle- and leaf-eating pests that pose a danger to forest stands in the Arkhangelsk, Leningrad and Murmansk regions,as well as in the Republics of Karelia and Komi were summarized and analyzed. A significant decrease in the frequency of reproduction outbreaks of certain types of needle- and leaf-eating pests was shown, which corresponds to the trends for some other regions. For the pine looper (Bupalus piniaria (L.)), the pine beauty (Pannolis flammea), the buff-tip (Phalera bucephala (L.)), the rusty tussock moth (Orgyia antiqua (L.)) and the white satin moth (Leucoma salicis (L.)), who have had a few mass reproduction outbreaks in the aforementioned regions, no significant increase in population density was observed for 25 years or more. An increase in outbreak activity and expansion of the damage area to the north is likely for the winter moth (Operophtera brumata (L.)) and the autumnal moth (Epirrita autumnata). The larch tortrix (Zeiraphera griseana) and the spruce sawfly (Gilpinia hercynia) are in the list of potential dangers as well. These species have only one, but an extremely extensive reproduction outbreak. The red pine sawfly (Neodiprion sertifer Geoffr.) and possibly the common pine sawfly (Diprion pini (L.)) will continue to play a significant role as pests of young stands. The dynamics of their outbreaks, apparently, is determined by climatic changes and, to no lesser extent, by the presence of large areas of conifers’ regeneration. An increase in the fluctuations’ amplitude of the pests populations’ density in urban plantations is likely to occur, especially the miner moths (Phyllonorycter isskii, Ph. populifoliella and Ph. apparella), for which the current climate warming is a fundamentally important factor.

Long-term studies are necessary for effective forecasting and management of the harmful forest insects populations. This article is aimed at the quantitative description of the population dynamics mechanisms of the gypsy moth (Lymantria dispar L.) and the green oak moth (Tortrix viridana L.) during their joint and simultaneous mass reproduction. To do this, a comparative analysis of data from stationary observations of insect populations in 1975–2021 was carried out. It has been established that outbreaks of mass reproduction of gypsy moth and green oak moth with the formation of complex foci in weakened forest-steppe oak forests have a periodic nature. The duration of a mass reproduction of the gypsy moth is 10–11 years, and of the green oak moth – about 20 years. A characteristic feature is the constant readiness of populations for mass reproduction, the number of gypsy moth does not stabilise at a low level and practically does not fluctuate around the equilibrium point, but immediately begins to increase. The mechanisms of the interspecific competition are shown, and its impact on population dynamics is assessed quantitatively. With the dominance of the green oak moth in the foci, the mass reproduction of the gypsy moth does not stop, but becomes less intense. The proportion of the gypsy moth population in pure oak plantations is declining. Due to the deterioration of living conditions and an increase in the caterpillars’ mortality, a slow increase in numbers and a significantly lower maximum level are observed. The efficiency of entomophages increases, the gypsy moth population does not get out of their control, therefore, a less intensive mass reproduction scheme is realised. For the green oak moth, on the contrary, the biocenotic regulation of the population is less effective and is characterized by a strong inertia. The green oak moth is characterised by the formation of chronic foci due to an increase in the maximum outbreak of mass reproduction stage and its duration as a whole. Mass reproduction is very intensive, the population stabilises at a high level of abundance. Gypsy moth with simultaneous reproduction does not have a significant negative impact on the green oak moth.

Population outbreaks of such species as Dendrolimus sibiricus Tschetv., in Siberian taiga forests begin with areas of several hectares and develop up to hundreds of thousands of hectares, resulting in significant damage to forests. Boundaries of foci change with time depending on external factors, population dynamics, and the state of forage trees. In this regard, it is important to determine the beginning of an outbreak and the affected area in advance as predictors of increasing pest numbers. To assess necessary conditions for an outbreak, a method for assessing state of forest stands is proposed based on remote sensing data. In this regard, it is important to assess risks of outbreaks and to determine in advance their onset times and starting zones. In order to evaluate necessary conditions for an outbreak, a “cascade” of factors is considered: geophysical (solar activity), weather, and the state of forest stands. Each of these factors is characterized by its own area, within the bounds of which any changes in this particular factor affect the insect population.

The work is dedicated to the discussion of the possibilities of describing the dynamics of the forest insect outbreaks development on different spatial scales. The properties of outbreaks were considered on a microspatial scale, where the distribution patterns of individuals across different food sources within the boundaries of a local territory or a stand were analysed, and on a macrospatial scale, where the focus of the analysis were the indicators of the photosynthetic apparatus (leaves or needles) removal over the entire territory of the locus, including primary, secondary and migratory loci. When analysing the microspatial distribution of caterpillars on trees within loci on different stages of gradation, the model of the individuals’ distribution on fodder trees was used as a second order stage transition. The macrospatial processes that occur during the outbreak development include, firstly, the growth of an existing outbreak and the emergence of new connected damaged areas of the forest, and secondly, the emergence of new unconnected secondary foci. To characterise the outbreaks, their fractal dimension D and the characteristics of the “viscous fingers” on the border of the outbreaks were used. Remote sensing data were used to calculate these characteristics. The proposed approaches can be used to predict the development of forest insects outbreak. When constructing and verifying the models, we used data from the Siberian silkworm census and the trees colonisation rate in the outbreak zone, as well as the remote sensing data on the areas and shapes of the foci in the regions of the Krasnoyarsk Territory during an outbreak of the Siberian silk moth Dendrolimus sibiricus Tschetv. in 2015–2019.

This paper presents a review of publications on the relationship between the phyllophagous insects and the forest communities in the current ecological situation, when ongoing climate changes, manifested primarily in an increase in the air temperature and a change in the precipitation amount and distribution, affect all processes in natural communities. Changes in the ranges of many plants and animals species are observed – moving up northwards and up in altitude. The spring phenophases come earlier, the autumn ones come later, the vegetation period lengthens and the terrestrial plants biomass increases. Such phenomena, together with changes in climatic parameters, affect herbivorous animals, which include insects with various food specialisations and different life cycles. As before, despite the growing number of observations in different parts of the Earth, there remains a lot of uncertainty about how individual plant and insect species and their functional groups function under the changing external conditions. It is emphasized that it is necessary to continue long-term studies in specific natural conditions in order to more accurately determine the reaction of the interactions’ participants to local climate changes and understand what the forestry strategy should be in the current and the predicted future situation.