Browsing by Author "Weidhaas, John A. Jr."
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- The effect of the white-pine weevil (Pissodes strobi Peck) on white pine (Pinus strobus L) in southwestern VirginiaEgan, Peter Joseph John (Virginia Tech, 1973-06-15)Thirteen white pine plots, ranging from 15-26 years of age and one tenth acre in size, were sampled in six counties of southwestern Virginia. The number of trees attacked by the white-pine weevil ranged from 3.5 percent to 98.6 percent with an average of 40.0 percent. The incidence of forking was found to be 4.1 percent of the trees weevi1ed. Enough trees in the dominant and co-dominant crOvffi categories were either free of weevil attacks or only attacked once that 250 to 300 trees are available for final harvest. Most of the weevil attacks occurred between 5 to 12 years of age. Analysis of Covariance for non-weevi1ed terminals and lateral lengths developed the following relationship for three age classes of terminals and laterals.
- Population dynamics of overwintering life stages of the alfalfa weevil, Hypera postica (Gyllenhal)Hilburn, Daniel J. (Virginia Tech, 1985-12-01)Virginia is a natural laboratory for studying overwintering habits of the alfalfa weevi1. At higher elevations, winters are relatively harsh and weevil pressure on the alfalfa crop is usually light. Much heavier pressure is the rule at lower elevations where winters are milder. The goal of this study was to examine the effects of fall and winter temperatures, parasites, and fall regrowth management on population dynamics of overwintering stages of this insect. Sixteen commercial alfalfa fields in Montgomery Co. (elevation 610 m) and Bedford Co. (elevation 300 m) were used in the study. Approximately half the fields each year were either harvested or grazed to remove fall regrowth. In the other fields, fall regrowth was left standing through the winter. Six different pitfall trap designs were compared for collection efficiency, installation and servicing effort, and cost. Barrier traps outperformed the other trap designs and were inexpensive and easy to install and service. Sweepnet samples were used to monitor weevil adults during their fall migration. A newly designed sampling device which removes all plant material, litter, and approximately 2 cm of soil from a 1/20 m² area, was used to measure absolute densities during fall and winter. Based on these absolute density samples fewer adults overwintered within fields in which fall regrowth was removed. Dissections revealed the presence of three parasites: Hyalomyodes trianqulifer (Loew), Microctonus aetheopoides Loan, and M. colesi Drea. Total parasitization rates were low. The highest measured rate was 16.1% in Bedford Co. in 1984-85. Female reproductive development also was determined through dissection. Females reach sexual maturity shortly after returning to alfalfa fields in the fall. Most contain full-size eggs in their oviducts from late fall through the winter. Egg densities as measured by laboratory incubation of field collected plant material indicated no differences related to elevation in early February, but significantly more viable eggs were present by late March at the low elevation site. In 1984, Bedford Co. samples indicated significantly more eggs in fields receiving no fall regrowth management. A simulation model called OAWSIM (Overwintering Alfalfa Weevil Simulation) was developed to examine the influence of factors which affect overwintering life stages. Model predictions indicate fall and winter temperatures, and fall regrowth management are major influences on the population dynamics of this insect.
- The Southern pine beetle, Dendroctonus frontalis Zimm., and associated Coleoptera attracted to dead loblolly pine, Pinus taeda L.Egan, Peter Joseph John (Virginia Tech, 1978-06-05)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.