Influence of balsam fir stand condition on the abundance and diversity of eastern hemlock looper, Lambdina fiscellaria fiscellaria (Guen.) (Lepidoptera: Geometridae) natural enemies

Pardy, Shelley Ann (2000) Influence of balsam fir stand condition on the abundance and diversity of eastern hemlock looper, Lambdina fiscellaria fiscellaria (Guen.) (Lepidoptera: Geometridae) natural enemies. Masters thesis, Memorial University of Newfoundland.

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Abstract

To assess the impact of natural enemies on the distribution of eastern hemlock looper various balsam fir stands were examined at Black Pond, in central Newfoundland. In 1995, 1996 and 1997 insects were collected using Malaise traps suspended into the balsam fir canopy. First, natural enemy abundance was assessed based on balsam fir stand vigour. A non-continuous vigour gradient was established using three silvicultural methods (root pruning, thinning, and fertilizing) and control treatments. Natural enemy abundance, in general and known eastern hemlock looper natural enemy abundance and diversity was higher in balsam fir stands that were more vigourous. These more vigorous stands provided natural enemies with more alternate hosts or prey. Second, natural enemy abundance was estimated based on the time since thinning and vegetation diversity of balsam fir stands. Natural enemy presence in stands that were unthinned, thinned one year prior to the study and thinned 16 years prior to the study were examined. Natural enemy abundance, in general and known eastern hemlock looper natural enemy abundance and diversity was higher in balsam fir stands that had had vigour increased by thinning 16 years prior to the study. The diversity of vegetation in these stands was higher due to the length of time since thinning. This increased vegetation diversity resulted in more resources available to natural enemies: more alternative feeding sites for adults, more shelter and overwintering sites. Balsam fir stands that have low vigour and have little or no understory vegetation seem to provide looper with enemy free space.

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