Short-term influence of partial cutting on hemlock looper (Lepidoptera: Geometridae) parasitism

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 (Guenee) (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 3years after partial cutting treatments. Two and threeyears 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%.