Abstract
BackgroundWinter moth (Operophtera brumata) and mottled umber moth (Erannis defoliaria) are forest Lepidoptera species characterized by periodic high abundance in a 7–11 year cycle. During outbreak years they cause severe defoliation in many forest stands in Europe. In order to better understand the spatio-temporal dynamics and elucidate possible influences of weather, stand and site conditions, a generalized additive mixed model was developed. The investigated data base was derived from glue band catch monitoring stands of both species in Central and North Germany. From the glue bands only female moth individuals are counted and a hazard code is calculated. The model can be employed to predict the exceedance of a warning threshold of this hazard code which indicates a potential severe defoliation of oak stands by winter moth and mottled umber in the coming spring.ResultsThe developed model accounts for specific temporal structured effects for three large ecoregions and random effects at stand level. During variable selection the negative model effect of pest control and the positive model effects of mean daily minimum temperature in adult stage and precipitation in early pupal stage were identified.ConclusionThe developed model can be used for short-term predictions of potential defoliation risk in Central and North Germany. These predictions are sensitive to weather conditions and the population dynamics. However, a future extension of the data base comprising further outbreak years would allow for deeper investigation of the temporal and regional patterns of the cyclic dynamics and their causal influences on abundance of winter moth and mottled umber.
Highlights
The vitality of oak on many European forest sites is repeatedly threatened by outbreaks of herbivorous insects
Study species and study area The life cycle of the univoltine geometrid species mottled umber (Erannis defoliaria) and winter moth (Operophtera brumata) in Europe is characterized by an overwintering egg-stage close to the buds of the host tree, hatching in spring in synchrony with the host plant’s budburst, a long pupation stage from summer to autumn in the soil and emergence of the adults from the ground in autumn, usually after the first frost nights, with highest activity from evening hours until midnight (Schwenke 1978)
The Mottled umber moth and winter moth (MUWM) populations were monitored with glue band catches
Summary
The vitality of oak on many European forest sites is repeatedly threatened by outbreaks of herbivorous insects. These insect infestations play a significant role in the decline of individual trees and sometimes even of complete stands of oak. Winter moth (Operophtera brumata) and mottled umber moth (Erannis defoliaria) are forest Lepidoptera species characterized by periodic high abundance in a 7–11 year cycle. During outbreak years they cause severe defoliation in many forest stands in Europe. The model can be employed to predict the exceedance of a warning threshold of this hazard code which indicates a potential severe defoliation of oak stands by winter moth and mottled umber in the coming spring
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