Canadian Forest Service Publications
Short-term influence of partial cutting on hemlock looper (Lepidoptera: Geometridae) parasitism. 2015. Seehausen, L.; Bauce, É.; Régnière, J.; Berthiaume, R. Agric. For. Ecol.
Issued by: Laurentian Forestry Centre
Catalog ID: 36074
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Silvicultural treatments are suggested as an option for controlling insect defoliators, although the effects of treatment on parasitism remain widely unknown. Therefore, in the present study, the influence of partial cutting on hemlock looper Lambdina fiscellaria (Guenée) (Lepidoptera: Geometridae) parasitism is studied by comparing two cutting intensities (25% and 40% reduction of stand basal area) against controls.
Laboratory reared hemlock looper pupae are periodically exposed in each plot to determine parasitism rates for a period of 3 years after partial cutting treatments. Two and three years after partial cutting, wild hemlock looper larvae are also collected in the same plots. Malaise traps and meteorological data loggers are installed to measure the influence of partial cutting on parasitoid abundance and microclimate.
Parasitism of hemlock looper pupae is significantly lower in plots with the higher partial cutting intensity compared with control plots. Also temperature and humidity, as well as the number of Apechthis Ontario (Cresson) (Hymenoptera: Ichneumonidae) females in plots, are significantly influenced by partial cutting. However, only mean and minimum temperature can significantly explain parasitism of hemlock looper pupae.
To sustain parasitism rates in forest stands vulnerable to hemlock looper defoliation at naturally high levels, it is recommended to refrain from partial cutting or to conduct this treatment at intensities lower than 40%.
Plain Language Summary
In this study, the researchers found that there was a lower rate of parasitism affecting hemlock looper larvae in stands that had undergone 40% partial cutting compared with stands that had undergone 25% partial cutting or unharvested stands.
Parasitism helps to reduce the damage caused by the hemlock looper. Therefore, in order to maintain high rates of parasitism in forest stands vulnerable to this pest, the researchers recommend that partial cutting be avoided or that the partial cutting intensity be lower than 40%.
The hemlock looper is a major pest of eastern Canadian forests. It can kill trees after a single year of defoliation. In eastern Canada, balsam fir is the main host of the hemlock looper, whereas in the provinces of western Canada, its main host is hemlock.