The impact of an outbreak event of the Siberian larch casebearer moth Protocryptis sibiricella on the radial growth of Siberian larch

Abstract The Siberian larch casebearer Protocryptis sibiricella (Falkovitsh, 1972) (Lepidoptera, Coleophoridae) is among the most widelydistributed needle-mining insect species in Eurasia, causing defoliation over vast regions. In the absence of long-term documented data on population outbreaks, it is imperative to employ indirect evidence to reconstruct such events. Dendrochronological analysis is one of the most precise and informative methods for quantitatively reconstructing environmental and biotic pressures. In 2000, a transient outbreak of the larch casebearer was studied in even-aged larch stands in the Republic of Udmurtia (European part of Russia). The studied outbreak lasted two years, peaked in 2000, and occurred during warm and dry growing season conditions. Defoliation of 60–80% of the needles by casebearer larvae significantly suppressed tree growth. The reduction in growth was, on average, 1.3 times greater than that in the control group. Most trees that underwent complete defoliation did not survive. However, following the outbreak, the radial growth of the affected trees exhibited rapid recovery, typically within 1–3 years. In certain cases, resilience (Rs) exceeded 1, indicating significant resistance in the studied stand. Reconstruction of the larch casebearer outbreak frequency over the past 45 years based on growth dynamics revealed a periodicity of approximately 10–11 years.