Causes of cyclicity of Epirrita autumnata (Lepidoptera, Geometridae): grandiose theory and tedious practice

Abstract

Creating multiyear cycles in population density demands, in traditional models, causal factors that operate on local populations in a density-dependent way with time lags. However, cycles of the geometrid Epirrita autumnata in northern Europe may be regional, not local; i.e., successive outbreaks occur in different localities. We review possible causes of cycles of E. autumnata under both local and regional scenarios, including large-scale synchrony. Assuming cyclicity is a local phenomenon, individual populations of E. autumnata display peaks but populations all over the outbreak range fluctuate in synchrony. This concept assumes that the peaks at most localities are so low that they do not lead to visible defoliation and easily remain unnoticed. In this scenario, populations are able to start recovery a few years after the crash, i.e., at the time of the mitigation of detrimental delayed density-dependent factors, such as delayed inducible resistance of the host plant or parasitism. In that case, the same factors that lead to crashes also explain the periodicity of cyclic fluctuations. According to the regional cyclicity scenario, different factors can be important in different phases of the cycle. The key is to identify the factors that tend to produce outbreaks with a periodicity of about 10 years. Initiation of the increase phase seems to coincide with maxima in sunspot activity, but causal connections remain unclear. Climatic factor(s) associated with the solar cycle could contribute to the large-scale geographic synchrony.

Spatially mismatched trophic dynamics: cyclically outbreaking geometrids and their larval parasitoids

“…(b) Methodological approach Obtaining data on the demographic impact of larval parasitism relevant for analysis of large-scale and long-term spatio-temporal patterns is difficult (Ruohomäki et al 2000), but possible if targeted adequately in time and space. An appropriate timing is the onset of the population cycle's crash phase, when parasitism should most strongly affect population growth rate, i.e.…”

Foliar Phenolics are Differently Associated with Epirrita autumnata Growth and Immunocompetence

“…czerepanovii (mountain birch) is the dominant tree in Northern Finland, and forms the tree line in NW Europe (Kallio and Mäkinen 1978). The most harmful herbivore of is Epirrita autumnata, which has cyclic large-scale outbreaks (Tenow 1972;Ruohomäki et al 2000). E. autumnata has several species of parasitoids (Ruohomäki 1994;Ruohomäki et al 2000) and pathogens (Bylund 1995).…”

Defensive Effect of Surface Flavonoid Aglycones of Betula pubescens Leaves Against First Instar Epirrita autumnata Larvae

“…It is a destructive pest, especially in northern and high-altitude populations of mountain birch [Betula pubescens ssp. czerepanovii (Orlova) Hämet-Ahti] (Tenow, 1972;Haukioja et al, 1988;Ruohomäki et al, 2000). The larvae hatch in the spring, simultaneously with bud break, and feed on the young foliage.…”