The Southern pine beetle, Dendroctonus frontalis Zimm., and associated Coleoptera attracted to dead loblolly pine, Pinus taeda L.
Egan, Peter Joseph John
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This study tests the hypothesis: Bark beetles initially locate their host trees in a non-random manner. The association of the southern pine beetle (Dendroctonus frontalis Zimm.) and associated Coleoptera with stressed trees suggested the direction for this study. Loblolly pine trees, Pinus taeda L., were stressed by severing and girdling. The bark beetle population trapped at stressed trees was then compared to the bark beetles trapped at unstressed control trees. The experiments were conducted in an apparently normal, old-field mixed pine-hardwood forest located in Nottoway County, Virginia, during 1975 through 1977. The girdling technique consisted of three circumferential chain saw cuts 5 cm deep at approximately 1 m above the ground. The severing technique was accomplished by guying the trees with 3.2 mm wire rope to maintain the trees' normal vertical position. The bole was then severed with a chain saw. The control trees were not treated in any manner. The insects associated with the treated and control trees were trapped with a four-way glass baffle placed over an aluminum funnel attached to a 1 liter jar containing 2.5 cm of water. The traps were placed at mid-bole and collected weekly during the growing season. The bark beetle complex studied in this experiment consisted of the following species: Dendroctonus frontalis Zimm, D. terebrans Oliv., Ips avulsus Eichh., I. grandicollis Eichh., I. calligraphus Germ., Hylastes spp., Cossonus spp., and Pityophthorus spp. The bark beetles were not trapped at the treated trees until the trees' foliage had begun to fade. The time period varied from two weeks to two years and also with the month of treatment. The number of bark beetles trapped at trees with faded needles was 40.06/trap-week for the first week the bark beetles were trapped at the tree. Control trees trapped the same number of bark beetles per trap-week as treated trees with green needles, .06 bark beetles per trap-week. The southern pine beetle and associated Coleoptera during endemic population levels exhibit a non-random directed attraction to the treated trees after they died, as evidenced by the fading of the trees' foliage. The conclusion is reached that these insects have the ecological role of scavengers in pine forests.
- Doctoral Dissertations