The Gypsy Moths and the Green Oak Moths Population Dynamics during a Joint Mass Reproduction Outbreak

Abstract

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.