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Published on: November 16, 2014
Colonization Dynamics of Subcortical Insects on Forest Sites With Relatively Stressed and Unstressed Loblolly Pine
Christiane E Helbig1, David R Coyle2, Kier D Klepzig3
1Professorship of Forest Protection, Technische Universität Dresden, Pienner Strasse 8, 01737 Tharandt, Germany (Chr.Helbig@web.de), Daniel B. Warnell School of Forestry and Natural Resources, University of Georgia, 180 E. Green St., Athens, GA 30602 (drcoyle@uga.edu; kjgandhi@uga.edu).
Southern pine decline (SPD) in loblolly pines is linked to root-feeding insects. Stressed trees attracted more native insects, particularly weevils, confirming their role as secondary colonizers.
Area of Science:
- Forestry
- Entomology
- Plant Pathology
Background:
- Loblolly pine (Pinus taeda L.) is crucial for southeastern US commercial forestry.
- Southern pine decline (SPD) has been associated with reduced growth and increased mortality since the 1950s.
- The role of root-feeding (rhizophagous) insects in SPD is under increasing investigation.
Purpose of the Study:
- To investigate the impact of subcortical insects, specifically rhizophagous weevils, on loblolly pine health in northeastern Georgia.
- To determine the relationship between tree stress levels and insect colonization.
- To differentiate between primary and secondary insect colonizers in the context of SPD.
Main Methods:
- Experimental plots were established with varying levels of tree stress: ungirdled, ungirdled-baited (with ethanol and turpentine), and girdled trees.
- Subcortical insects were trapped over two years using pitfall traps.
- The feeding activity of key rhizophagous weevils (Hylobius pales and Pachylobius picivorus) was quantified.
Main Results:
- A total of 10,795 insects from four families and over 82 species were captured; 46% of individuals and 11% of species were nonnative.
- Insect captures were significantly higher in plots with girdled trees (187% more than ungirdled) compared to ungirdled-baited and ungirdled plots.
- Native insect captures, but not nonnative, were influenced by tree treatment, with higher numbers on stressed trees.
- Rhizophagous weevil feeding activity increased proportionally with tree stress, from 1% in ungirdled to 82% in girdled plots.
Conclusions:
- Native subcortical insects, particularly rhizophagous weevils, are strongly associated with highly stressed loblolly pines.
- These findings confirm that native rhizophagous weevils act as secondary colonizers, exploiting already weakened trees rather than initiating decline.
- Understanding insect-tree interactions is vital for managing southern pine decline and maintaining forest health.
