From a rare inhabitant into a potential pest – status of the nun moth in Finland based on pheromone trapping

Abstract

Forests are affected by climate change in various ways. This includes abiotic factors such as droughts, but also biotic damage by pest insects. There are numerous examples from cases where pest insects have benefitted from longer growing seasons or from warmer summers. Similarly, new pest insects have been able to expand their range due to climatic conditions that have changed from hostile to tolerable. Such seems to be the case with the nun moth (), an important defoliator of coniferous trees in Europe. For centuries, the species has had massive outbreaks across Central-Europe, while it has been a rare inhabitant in Northern Europe. Recently, the nun moth population in Finland has not only expanded in range, but also grown more abundant. This research note describes the results from the first years (2018–2019) of a monitoring program that is being conducted with pheromone traps across central and southern Finland. So far, the northernmost individuals were trapped near the 64 N degrees. However, there were more southern locations where no moths were trapped. The species was present in every trapping site below the latitude of 62 N degrees. More importantly, at some sites the abundance of the nun moth suggested that local forest damage may already occur. Given the current climatic scenarios for Fennoscandia, it is likely that the nun moth populations will continue to grow, which is why systematic surveys on their abundance and range expansions will be topical.Lymantria monacha

Bat aggregational response to pest caterpillar emergence

“…As expected, foliage loss was higher at infested sites, with levels of 6.8% at ZL and 12.5% at HL compared with 4.9% at the CL site. While such damage levels may seem insignificant in relation to the defoliation caused by other pests (e.g., the European gypsy moth Lymantria dispar 44 ; the nun moth Lymantria monachal 45 ), the reduction is visible in the first stages of foliage deficit and significantly slows down tree growth, with 1% foliage loss equivalent to a ~ 1% decrease in growth rate 43 , 46 . Furthermore, geometrid caterpillars tend to consume undamaged leaves and avoid previously damaged leaves 47 .…”

Pheromone-based monitoring of invasive alien insects along the border of Finland and Russia – methods and unintentionally caught species

“…50-70 individuals suggests that they were lured in by the pheromone. For future surveys, testing of different types of funnel traps for catching Dendrolimus moths would seem ideal as catches exceeding 900 L. monacha individuals per funnel in one season have been reported in Finland (Melin et al 2020). Therefore, a well-functioning funnel-type trap could result in higher catches of Dendrolimus individuals as well.…”

Climate-Smart Forestry: A Review of Approaches, Management Strategies, and Risk Mitigation

“…While bark beetle is a significant biotic damage risk in Europe, the increasing temperature is causing the abundance of other biotic damaging agents. Nun moth is a defoliator historically absent in Finland (Melin et al, 2020) due to the freezing winter, as the egg gets frozen at a temperature below -30 0 C (Fält-Nardmann et al, 2018). The increasing warmer winter has favoured the tremendously increase since the 1990s (Melin et al, 2020).…”

“…Nun moth is a defoliator historically absent in Finland (Melin et al, 2020) due to the freezing winter, as the egg gets frozen at a temperature below -30 0 C (Fält-Nardmann et al, 2018). The increasing warmer winter has favoured the tremendously increase since the 1990s (Melin et al, 2020). Also, snow duration and depth reduction have increased the severity of moose (Alces alces) damage on Birch and young Scots pine seedlings in Northern Europe (Herfindal et al 2015;Venäläinen et al, 2022).…”