Melissa Churchel1, Jim Hanula2, Wayne Berisford1 and Jim Vose2

1 Department of EntomologyUniversity of Georgia

2 USDA Forest ServiceSouthern Research Station

Environmental Fate of Imidacloprid

University ofGeorgia

Chemical Control Options

Horticultural Oil

Soil Injection withImidacloprid

Stem Injection withImidacloprid

What’s the Forest Service Doing?

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

Saving a Remnant Population

Trying to save 60 trees in selected areas using soil injectionof imidacloprid

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

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?

Imidacloprid Toxicity

• Toxic to aquatic organisms

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

Our Objectives

1) Determine if imidacloprid entered the streams using the guidelines

2) Determine if the treatments outlined by the national forests were affecting stream insects

3) Determine if the treatments were effectively controlling HWA

Methods – Study Sites

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

Holcomb Tributary

Addie Branch

Billingsley Creek

• 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

Methods

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

Surber Sampler

Samplingfor Larger Insects and Their Relatives

• Started 1 week after insecticide application

• Sampled bi-weekly for first 4 months

• Sampled monthly for rest of study (2 years)

Post-treatment Sampling

Water 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

Post-treatment Sampling

Drain the MeCl2 layer; repeat Step 2-3 twice more; combine all drained layers.

Analyze on HPLC

500 ml sample into 1-L Separatory Funnel

Add 75 mL methylene chloride

Stopper funnel; shake; allow layers to separate.

Concentrate the extract under nitrogen

Add sodium sulfate to flask & swirl (removes excess water)

Filter the extract (removes sodium sulfate)

Extraction and Analysis of Imidacloprid from Water

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

Data Analysis

NCBI = ∑ TVi Ni

Total NWhere:

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

North Carolina Biotic Index (NCBI)

• 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

Data Analysis

Results

• Collected 217,587 insects and relatives

• 83 taxa from 18 orders and 66 families

• Trichoptera and Diptera most diverse

Spring Summer Fall Winter Spring SummerAddie Branch 28.75a 21.88b 23.17ab 24.08ab 26.42ab 24.00ab

Groups within the same row that share the same letter are not significantly different

2006 2007

Average Number of Taxa

Mayflies, Stoneflies and Caddis Flies

Spring Summer Fall Winter Spring SummerAddie Branch 16.63a 11.13b 14.33ab 15.25ab 16.33a 14.08ab

Groups within the same row that share the same letter are not significantly different

2006 2007

Average Abundance

Spring Summer Fall Winter Spring Summer FallAddie Branch 5300.00a 1537.50b 1468.52b 2187.04b 4145.37a 2806.48abDryman Fork 6172.22a 2382.87b 2195.14b 3528.70ab 5056.25a 4560.92ab 4983.33a

Groups within the same row that share the same letter are not significantly different

2006 2007

NCBI Scores

Mountain Ecoregion: Water Quality Class

< 4.18 Excellent

4.17 - 5.09 Good

5.10 - 5.91 Good-Fair

5.92 - 7.05 Fair

> 7.05 Poor

Water Samples

• A water sample was collected each time we sampled insects

• Holcomb Tributary - Oct. 22, 2007– < 1.0 ppb– No evidence of an impact on aquatic

macroinvertebrates

HWA Control

• ????

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

• 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

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

Insect Sampling Summary

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

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