Melissa Churchel1, Jim Hanula2, Wayne Berisford1 and Jim Vose2

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Environmental Fate of Imidacloprid

• Melissa Churchel1, Jim Hanula2, Wayne
  Berisford1 and Jim Vose2
• 1 Department of Entomology
• University of Georgia
• 2 USDA Forest Service
• Southern Research Station

University of Georgia
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Chemical Control Options
Stem Injection with Imidacloprid
Horticultural Oil
Soil Injection with Imidacloprid
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Whats the Forest Service Doing?

• National Forests in the south are trying to save
  a remnant population of hemlocks throughout their
  forest

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Saving a Remnant Population
Trying to save 60 trees in selected areas using
soil injection of imidacloprid
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Guidelines for Soil Injection on National
Forests in GA and NC

• Sample soil to determine presence of highly
  permeable soils (sands or gravel)
• Scout area for presence of surface water
  (springs, creeks, ponds, bogs, etc.)
• Eliminate any trees with a direct vegetative
  connection to surface water from soil injection.
• Treat 60 trees per selected area

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Imidacloprid

• PROBLEM
• Highly mobile but soil absorption increases with
  increasing organic matter content
• Does imidacloprid make its way through the soil
  after injected and enter nearby streams?

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Imidacloprid Toxicity

• Toxic to aquatic organisms
• LC50 values range from 10.5 to 10440 ppb for
  aquatic insects

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Our Objectives

• Determine if imidacloprid entered the streams
  using the guidelines
• Determine if the treatments outlined by the
  national forests were affecting stream insects
• Determine if the treatments were effectively
  controlling HWA

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Methods Study Sites
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Methods

• Selected 4 small streams with moderate flow rates
  and sufficient hemlocks
• 2 treatment methods used
• Holcomb Tributary, Addie Branch, and Billingsley
  Creek
• Treated 60 trees around each stream using Kioritz
  soil injector to inject imidacloprid (Merit 75
  WSP)
• 1 g ai per inch diam in 10 ml H2O
• Injected 2 inches deep, 1 injection/inch diameter
  in a ring 12 inches from tree bole.
• 670g ai. applied per site
• Treated November 1, 2005

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Holcomb Tributary
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Addie Branch
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Billingsley Creek
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Methods

• Dryman Fork
• 2000 ft treatment area
• Treated all trees within 50 ft on either side of
  stream with at least 10 inch diameter at base
• 88 trees next to stream treated with Mauget II
  Generation Tree Injector
• 109 trees treated with soil injections
• Treated May 17, 18, and 19 2006
• Adjacent watershed used as reference condition

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Insect Sampling

• 4 riffles sampled in each stream using a Surber
  sampler with fixed area of 1 m2
• Collected all contents with sampler down to 5 cm
• Large cobble was scrubbed to remove insects
• Samples preserved in 95 alcohol
• Large samples were subsampled as needed
• All larger insects were identified to genus or
  lowest taxonomic level possible

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Surber Sampler
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Samplingfor Larger Insects and Their Relatives
Post-treatment Sampling

• Started 1 week after insecticide application
• Sampled bi-weekly for first 4 months
• Sampled monthly for rest of study (2 years)

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Water Sampling
Post-treatment Sampling

• Grab samples taken downstream of treatment area
  using 1000 ml glass bottle
• Samples stored in cold room until analysis
• Analysis conducted by the University of Georgia,
  Pesticide and Hazardous Waste Laboratory

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Extraction and Analysis of Imidacloprid from Water
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Data Analysis

• Number of taxa
• Number of mayflies, stoneflies and caddis flies
  collectively (EPT)
• Abundance
• North Carolina Biotic Index (NCBI) for each
  stream and sample date
• Index specific to SE U.S.
• Indicator of general health of stream biotic
  community

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Data Analysis
North Carolina Biotic Index (NCBI)

• NCBI ? TVi Ni
• Total N
• Where
• TVi tolerance value of the ith taxa
• Ni abundance of the ith taxa
• Total N number of individuals in the sample
• Tolerance values range from 0 to 10
• Abundance values are transformed into Rare (1-2
  per sample), Common (3-9 per sample), or Abundant
  (10 per sample

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Data Analysis

• Data for each stream pooled by season
• Compared each stream to reference
• If results were significantly lower than in the
  reference, we analyzed seasonal variability
  within that stream
• Determine if a significant reduction in the
  macroinvertebrate community occurred

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Results

• Collected 217,587 insects and relatives
• 83 taxa from 18 orders and 66 families
• Trichoptera and Diptera most diverse

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Average Number of Taxa
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Mayflies, Stoneflies and Caddis Flies
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Average Abundance
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NCBI Scores
Mountain Ecoregion Water Quality Class lt
4.18 Excellent 4.17 - 5.09 Good 5.10 -
5.91 Good-Fair 5.92 - 7.05 Fair gt 7.05 Poor
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Water Samples

• A water sample was collected each time we sampled
  insects
• Holcomb Tributary - Oct. 22, 2007
• lt 1.0 ppb
• No evidence of an impact on aquatic
  macroinvertebrates

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HWA Control

• ????

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Insect Sampling Summary

• Avg. Number of Taxa
• Addie Branch Winter 2006/07 significantly lower
  than reference stream
• But not lower than Fall 06
• Due to seasonal variation smaller community of
  invertebrates overall than in reference

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Insect Sampling Summary

• EPT Taxa
• Addie Branch Summer 2006 significantly lower
  than reference stream
• Also significantly lower than Spring 2006
• Follows same pattern of seasonal variation due to
  emergence of adults as other streams
• More pronounced due to smaller community

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Insect Sampling Summary

• Abundance
• Addie Branch Fall 06 Winter 06/07
• Dryman Fork Fall 07
• Significantly lower than reference stream
• Not significantly different from previous season
• NCBI
• None with significantly lower scores than
  reference stream

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Conclusion

• Good news treatments had no effect on
  macroinvertebrate communities in mountain streams
• A small amount of imidacloprid was detected in
  Holcomb Tributary, but had no effect on
  invertebrates

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Implications

• Soil injections can safely be used in the
  southern Appalachians
• Only a trace amount of imidacloprid entered the
  streams over a 2 year period
• Not enough to significantly impact the aquatic
  organisms