Relationships between elm spanworm, Ennomos subsignaria, juvenile density and defoliation on mature sycamore maple in an urban environment |
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Authors: | Heidi RC Fry Dan T Quiring Krista L Ryall Peggy L Dixon |
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Institution: | 1. Population Ecology Group, Department of Biology, University of New Brunswick, Fredericton, New Brunswick, Canada E3B 5P7;2. Population Ecology Group, Faculty of Forestry and Environmental Management, University of New Brunswick, Fredericton, New Brunswick, Canada E3B 5P7;3. Natural Resources Canada, Canadian Forest Service - Atlantic Forestry Centre, P.O. Box 960, Corner Brook, Newfoundland and Labrador, Canada A2H 6J3;4. Agriculture and Agri-Food Canada, Atlantic Cool Climate Crop Research Centre, P.O. Box 39088, St. John''s, Newfoundland and Labrador, Canada A1E 5Y7 |
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Abstract: | Using field surveys, we established sampling procedures for estimating defoliation resulting from elm spanworm, Ennomos subsignaria (Hübner) (Lepidoptera: Geometridae), feeding on mature sycamore maple, Acer pseudoplatanus L. (Aceraceae), in St. John's, Newfoundland and Labrador. We also determined whether densities of E. subsignaria eggs, egg masses, early- or late-instar larvae could predict the amount of defoliation at the end of the larval feeding period. Defoliation estimates acquired by sampling branches from only the lower, mid or upper crown explained ≥80% of the variation in tree-level defoliation, suggesting that density–defoliation relationships established using defoliation data from any crown level would also be useful for predicting tree-level defoliation. In linear regressions, egg and egg mass densities explained ≤20% of variation in defoliation and thus only provide a crude relative estimate of the amount of defoliation that will occur. Early- and late-instar larval density in the lower crown explained 53 and 29%, respectively, of the variation in defoliation in the lower crown, where defoliation levels were highest. Thus monitoring early-instar density in the lower crown should provide pest managers with reliable information for decisions regarding whether to apply suppression tactics while allowing enough time to implement these tactics, if necessary. |
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Keywords: | Ennomos subsignaria Elm spanworm Sycamore maple Density&ndash defoliation relationship Integrated pest management Within-tree distribution |
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