MRID 49090501 CDPR IMI Melon

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Reference

Beedle, E. (2012) Determination of Residues of Imidacloprid and its Metabolites 5-hydroxy 

Imidacloprid and Imidacloprid Olefin in Bee Relevant Matrices Collected from Melons Grown at 

Locations Treated with Imidacloprid at Least Once per Year During Two successive Years: Amended. 

Project Number: EBNTL056/02, EBNTL056/02/1/AMENDED. Unpublished study prepared by Bayer 

Cropscience LP and Bee Alert Technology, Inc. 237p. MRID 49090501, CDPR Study ID 268741, Data 

Volume 51950-0811, Tracking ID# 256591

1. STUDY INFORMATION

Chemical: Imidacloprid PC Code 129099

Test Material:

Multiple formulations were 

used during this study and 

some materials are 

unknown.

Percent Active 

Ingredient:

Various and unkown

Study Type:

Non-Guideline field residue study on melons to establish imidacloprid and 

metabolite levels in bee collected nectar, bee collected pollen and leaves in site 

locations that have been previously treated with imidacloprid at least once for 

two successive years.

Sponsor:

Bayer CropScience

2T.W. Alexander Drive

Research Triangle Park, NC 

USA 27709

Experiment Start and

End Date:

April 4, 2011 –

December 12, 2012

Sponsor Study 

ID: EBNTL056-02

Study Locations:

Ten trial sites located in 

Imperial County of 

California. Study 

Completion 

Date:

December 27, 2012

GLP Status: Non-GLP; protocol reviewed by CDPR. 

[CDPR study ID 259804, Data Volume 51950-0789, Tracking ID# 246838]

2. REVIEWER INFORMATION

Study Reviewed by: 

California Department 

of Pesticide Regulation 

Richard Bireley, Sr. Environmental Scientist (Specialist) 

John Troiano, Ph.D., Research Scientist III

Alexander Kolosovich, Environmental Scientist 

Brigitte Tafarella, Environmental Scientist

Denise Alder, Sr. Environmental Scientist (Specialist) 

Russell Darling, Environmental Scientist 

3. EXECUTIVE SUMMARY

Ten trials were conducted in California in soils classified as either “heavy” (fine-textured), or "medium” 

(medium-textured) to determine the residues of imidacloprid and its metabolites (5-hydroxy

imidacloprid and imidacloprid olefin) in bee collected nectar (hive deposited), bee collected pollen 

(pollen traps), and leaves (hand collected) from melon plants (cucurbits) grown at locations treated 

previously with imidacloprid. 
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Imidacloprid application rates and application methods for the trial locations during the years of 2008 

through 2011 were collected from grower communications. Individual application rates ranged from 

0.23 to 0.38 lb. imidacloprid/acre/application. Applications in 2011 were made at or near the melon 

transplants.

Within each field site, two plots were established, each with a bee-tight, ventilated mesh tent (24 ft. x 

100 ft. x 10 ft. tall) for sample collection. One normally developed, apparently healthy and queen-right 

honey bee colony was placed in each tented area shortly after the beginning of flowering when enough 

blossoms were open to allow orientation and foraging of the bees.

Leaves (hand collected), bee collected nectar (hive deposited) and pollen (pollen traps) were collected

from each plot. Composite nectar samples were collected by syringe at several sampling intervals over 

several days. Sampling was from several cells of a brood frames, as no nectar was stored in an empty 

frame placed next to the brood frame. Composite pollen samples were collected from plastic pollen 

traps that were mounted at the entrance of each hive for over a period of two to three weeks. 

Composite leaf samples were collected from each plot near the middle of the nectar and pollen 

sampling period.

The residues of imidacloprid, 5-hydroxy imidacloprid, and imidacloprid olefin were quantitated by high 

performance liquid chromatography/triple stage quadrupole mass spectrometry (LC/MS/MS) using 

stable isotopically labeled internal standards. The individual analyte residues were summed to give a 

total imidacloprid residue. The limits of quantitation (LOQs) and limits of detection (LODs) are shown 

below in section 5F.

4. STUDY VALIDITY

Guideline Followed: Non-guideline study (protocol was reviewed by U.S. EPA/PMRA/CDPR)

Guideline Deviations: N/A

Other Deviations: N/A

Classification: Supplemental

Rationale: N/A

Reparability: N/A

5. MATERIALS AND METHODS

Test Material Characterization

Test item: Admire Pro, Alias and 

Unknown Formulations

pH (24°C) 17.4% A.I. 

Description: Unknown Density (20°C): 1.54 g/mL

CAS #: 138261-41-3 Solubility: 0.51 to 0.61 g/L

5A. STUDY DESIGN

The non-GLP sampling phase of this study was conducted in April and May, 2011. The GLP experimental 

start date (first analysis) was on November 30, 2012, and the experimental end date (last analysis) was 

December 12, 2012.

Ten treated field sites in California representing two soil categories classified as either “heavy” (finetextured), or “medium” (medium-textured) were selected based on previous applications of 

imidacloprid according to grower communications. Classification of the soils was obtained from the Soil 
MRID 49090501 CDPR IMI Melon

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Survey Geographic (SSURGO) Database provided by the Natural Resources Conservation Service. Each 

site contained a treated area of at least one acre (from placement of a pair of tents and sample 

collection) that was located in a larger field ranging from approximately 30 acres to more than 100 

acres. Individual application rates ranged from 0.23 to 0.38 lb. imidacloprid/acre/application. 

Applications to the sites in 2011 were made at or near the melon (cucurbits) transplants.

Shortly after the beginning of flowering within each melon site, two bee-tight, ventilated mesh tents

(each approximately 24 ft. x 100 ft. x 10 ft. tall) were placed in each of the ten selected field sites 

covering three rows of established melon plants. Tents were placed between April 4, 2011 and April 20, 

2011.

One queen-right honey bee colony, Apis mellifera L. (Hymenoptera, Apidae) was placed in each tent 

when enough blossoms were present to allow orientation and foraging of the bees. Colonies were 

chosen from nearby colonies on pallets surrounding each field provided by commercial beekeepers to 

pollinate the imidacloprid treated fields. Each colony was elevated on plastic stands to reduce dust 

infiltration and placed about 6 feet from the end of the tent. Each colony consisted of at least six frames 

of bees housed in a two-story hive, consisting of a standard Langstroth Hive body on the bottom, and 

either a shallow or standard hive body as a second story. 

The collection of the pollen (pollen traps), nectar (hive deposited), and leaves (hand collected) was 

performed at the test site. Sample analysis and report preparation was performed at Bayer CropScience 

located in Research Triangle Park, North Carolina. 

All raw data associated with this study are retained along with the protocol, protocol amendments and 

the final report under Notebook Number EBNTL056-02 at locations specified by Bayer CropScience. 

5B. APPLICATION TIMING AND RATES

Table 1. Application History a Field Number Field Identification Location 

(City, State, NAFTA Region)Soil Type b

Application Method b

YearDateRate (lb. a.i./A) 

c

1 NT209 Imperial 

County, 

CA, NAFTA 

Region 10

Holtville Silty 

Clay (Heavy)

Injected 2011 Jan 10 0.36

None 2010 NA d NA

Injected 2009 Oct 30 0.36

Injected 2008 Oct 5 0.31

2 NT210 Imperial 

County, 

CA, NAFTA 

Region 10

Holtville Silty 

Clay (Heavy)

Injected 2011 Jan 10 0.36

None 2010 NA NA

Injected 2009 Oct 30 0.36

Injected 2008 Oct 5 0.31

3 NT201 Imperial 

County, 

CA, NAFTA 

Region 10

Holtville Silty 

Clay (Heavy)

Injected 2011 Jan 7 0.29

Injected 2010 Jan 25 0.29

None 2009 NA NA

None 2008 NA NA
MRID 49090501 CDPR IMI Melon

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Field NumberField IdentificationLocation (City, State, NAFTA Region)Soil Type b

Application Method b

YearDateRate (lb. a.i./A) 

c

4 NT202 Imperial 

County, 

CA, NAFTA 

Region 10

Meloland 

Very Fine 

Sandy Loam 

(Medium)

Injected 2011 Jan 10 0.29

None 2010 NA NA

Injected 2009 Jan 24 0.29

None 2008 NA NA

5 NT203 Imperial 

County, 

CA, NAFTA 

Region 10

Holtville Silty 

Clay (Heavy)e

Injected 2011 Jan 10 0.29

None 2010 NA NA

Injected 2009 Jan 24 0.29

None 2008 NA NA

6 NT208 Imperial 

County, 

CA, NAFTA 

Region 10

ImperialGlenbar Silty 

Clay Loam 

(Medium)

Seed Line 2011 Jan 3 0.36

None 2010 NA NA

Seed Line 2009 Oct 4 0.30

None 2008 NA NA

7 NT206 Imperial 

County, 

CA, NAFTA 

Region 10

ImperialGlenbar Silty 

Clay Loam 

(Medium)

None 2011 NA NA

Seed Line 2010 Oct 21 0.28

Seed Line

Seed Line

2009

2009

Nov 21

March 2

0.23

0.28

None 2008 NA NA

8 NT205 Imperial 

County, 

CA, NAFTA 

Region 10

Meloland 

Very Fine 

Sandy Loam 

(Medium)

Seed Line 2011 Jan 9 0.38

None 2010 NA NA

None 2009 NA NA

None 2008 NA NA

9 NT204 Imperial 

County, 

CA, NAFTA 

Region 10

Holtville Silty 

Clay (Heavy)

Seed Line 2011 Jan 3 0.36

None 2010 NA NA

None 2009 NA NA

None 2008 NA NA

10 NT207 Imperial 

County, 

CA, NAFTA 

Region 10

Meloland 

Very Fine 

Sandy Loam 

(Medium)

Injected 2011 Jan 20 0.36

None 2010 NA NA

Injected 2009 Jan 20 0.36

None 2008 NA NA a All rates, methods and dateswere collected from verbal communications with the growers and could not be 

confirmed.

b Classification of the soils was obtained from the Soil Survey Geographic (SSURGO) Database provided by the 

Natural Resources Conservation Service. “Heavy” class represents soil with slow drainage capacity.

c Applications were made either by injection to a drip issigation system or with a drench application over the seedline. 

d NA- Per grower information, an imidacloprid application was not made during the year. e One tent was in Holtville Silty Clay. The other tent in this site was divided between Holtville Silty Clay and 

Imperial-Glenbar Silty Clay Loam. The trial was designated “heavy” since the majority of the sampling was from 

Holtville Silty Clay. 
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5C. STUDY SITE LOCATION AND CHARACTERISTICS 

Table 2. Trial Site Conditions for Melon Grown at Sites Previously Treated with Imidacloprid 

Trial (Field) 

Identification

Trial Location (County, 

State)

Soil Types a Rainfall 

(in) b

Temperature 

Range (°F) b

1 (NT209) Imperial County, CA Holtville Silty Clay 

(Heavy)

0.00 54-101

2 (NT210 Imperial County, CA Holtville Silty Clay 

(Heavy)

0.00 54-101

3 (NT201) Imperial County, CA Holtville Silty Clay 

(Heavy)

0.00 54-101

4 (NT202) Imperial County, CA Meloland Very Fine 

Sandy Loam 

(Medium)

0.00 54-101

5 (NT203) Imperial County, CA Holtville Silty Clay 

(Heavy) c

0.00 54-101

6 (NT208) Imperial County, CA Glenbar Silty Clay 

Loam (Medium)

0.00 54-101

7 (NT206) Imperial County, CA Glenbar Silty Clay 

Loam (Medium)

0.00 54-101

8 (NT205) Imperial County, CA Meloland Very Fine 

Sandy Loam 

(Medium)

0.00 54-101

9 (NT204) Imperial County, CA Holtville Silty Clay 

(Heavy)

0.00 54-101

10 (NT207) Imperial County, CA Meloland Very Fine 

Sandy Loam 

(Medium)

0.00 54-101

a Classification of the soils was obtained from the Soil Survey Geographic (SSURGO) Database provided by the 

Natural Resources Conservation Service. “Heavy” class represents soil with slow drainage capacity. b Meteorological data is from a NOAA station in El Centro, CA, a location in the same vicinity of all trials and covers 

the sampling period from April 23, 2011 through May 8, 2011.

c From this site, the location of one tent was in Holtville Silty Clay soil, and the other tent was divided between 

Holtville Silty Clay and Imperial-Glenbar Silty Clay Loam. The trial was designated “heavy” since the majority of the 

sampling was from Holtville Silty Clay. 

5D. SAMPLE COLLECTION, HANDLING, PROCESSING

When each colony was placed in a tent, a frame closest to the edge of the brood frame was replaced 

with either an empty, fully drawn, new plastic frame or an empty, drawn wax comb; however, no nectar 

was stored in these frames. Therefore, hive-deposited nectar samples were collected from several cells 

of a brood frame nearest the brood, taking care not to sample nectar from cells near parts of a comb 

containing capped stored honey. Nectar collection began one to two days after the hives were placed in 

the tents. Sampling occurred between April 23 and May 8, 2011, although the majority of the nectar 

samples were collected between May 2 and May 4, 2011. 

Pollen collected by the bees was collected in plastic pollen traps that were mounted at the entrance of 

the hive. Pollen traps were affixed to the hive and left in the open position at least one day prior to 
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sampling. To collect pollen, the screens were closed. A few, small pollen pellets were available after two 

to three days; therefore, a composite sample was collected for each hive which consisted of repeated 

visits over a period of two to three weeks. 

Composite leaf samples were collected from a minimum of 12 plants distributed throughout the four 

quadrants inside the tent. From each plant, a basal, a terminal, and a middle leaf were collected, 

yielding a sample size of 36 leaves. Leaf samples were generally collected near the middle of the nectar 

and pollen sampling period. Leaves were collected on April 26 and 27, 2011 except for two fields which 

were collected on May 2 and May 8, 2011. 

A chronological listing of significant study dates are given in Appendix 1 of the study report. Appendix 2 

of the study report contains a field report summary for each trial location, the history of imidacloprid 

applications and a field report describing all field activities including placement of tents, placement of 

hives, sampling, etc. 

Composite samples of nectar and pollen were collected in labeled amber glass vials. The vials were 

transported to each tent for each sampling event in a cooler with dry ice. New, disposable gloves were 

used for each sampling event in each tent to prevent sampling contamination. A new plastic pipette tip 

was used for each nectar sample. Pollen samples were transferred from the pollen trap to vials using 

forceps. Leaves were placed in plastic-lined cloth bags. Care was taken to protect all samples from 

sunlight before placement in the ice chest. 

All samples were placed in an iced chest containing dry ice and the transit (spiked) stability samples. At 

the end of each day, all samples, along with the transit stability samples, were transferred to local frozen 

storage. All samples, including the transit stability samples, were shipped frozen via freezer truck to 

Bayer Research Park (BRP) in Stilwell, Kansas, where they were placed together in frozen storage. During 

storage at BRP, all samples remained frozen.

Sample Storage.

The nectar and pollen samples, along with the transit stability samples, were shipped frozen to Bayer 

CropScience, Research Triangle Park (RTP), North Carolina, via freezer truck. Homogenization of the leaf 

samples was conducted at BRP and shipped frozen via FedEx overnight delivery to RTP.

Freezer storage stability studies have indicated the imidacloprid residues are stable (<30% 

decomposition) for 24 months (728 to 769 days) or freezer storage in the following representative crops: 

an oilseed (cottonseed), a non-oily grain (wheat), a leafy vegetable (lettuce), a root crop (potato), a tree 

fruit (apple), and a fruiting vegetable (tomato). 14-19 The nectar, pollen, and leaf samples analysed in this 

study were held in frozen storage for a maximum of 598 days (20 months) prior to extraction. 

Samples remained frozen at all times at RTP, except during preparation for analysis and the following 

exception. During storage at RTP, the pollen and nectar samples and the transit stability samples 

reached room temperature for approximately three days due to freezer failure. 

5E. ANALYTICAL METHODS
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The analytical method11 used in this study measured the residues of imidacloprid, 5-hydroxy 

imidacloprid, and imidacloprid olefin in nectar, pollen, and leaves collected from melon plants. These 

data are reported in Appendix 3 of the study report.

All neat analytical reference standards were stored frozen prior to dilution. All reference standard

solutions were prepared in parent equivalents and corrected for purity during initial preparation. The 

reference standard solutions were stored refrigerated (average temperature <5 °C ) and have been 

shown to be stable for the length of storage time required for this study. 12 All reference standard 

solutions were prepared in parent imidacloprid equivalents and corrected for purity during initial 

preparation.

Leaf samples were extracted by blending them with 2:1 acetonitrile/water (ACN/H20). The mixture was 

amended with magnesium sulfate (MgS04), sodium chloride (NaCI), and isotopically labeled internal 

standards, mixed well, and centrifuged. An aliquot of the supernatant was transferred to a centrifuge 

tube containing MgS04 and Bondesil-PSA. The contents of the tube were mixed well and centrifuged. 

About aliquot of the supernatant was percolated through a C18 solid phase extraction (SPE) cartridge 

(Bond Elut) into a culture tube. The eluate was evaporated to dryness and the residue was reconstituted 

with 1:9 methanol/water (MeOH/H20) for analysis by high performance liquid chromatography/tandem 

mass spectrometry (LC/MS/MS). 

For nectar, a sample was weighed into a culture tube and dissolved in water. The mixture was amended 

with isotopically labeled internals standards, mixed well and applied to a C18 Bond Elute cartridge. The 

analytes were extracted from the cartridge with methanol/water (2:1 v/v). The eluate was evaporated 

to dryness and the residue was reconstituted with 1:9 methanol/water (MeOH/H2O) for analysis by 

LC/MS/MS. 

For pollen, a sample was extracted by shaking with water for 10 minutes, adding CAN and shaking for an 

additional 55 minutes. The mixture was amended with isotopically labeled internal standards, mixed 

well and centrifuged. The supernatant was drawn off, evaporated to an aqueous remainder, amended 

with water and applied to a Chem Elute cartridge. The analytes were extracted from the cartridge with 

hexane/ethyl acetate (1:1 v/v). The eluate was evaporated to dryness and the residue was reconstituted 

with 1:9 methanol/water (MeOH/H2O) for analysis by LC/MS/MS.

Quantitation of each analyte was based on the daughter ion transitions of the analytes and the 

respective internal standard analogs. The response of the LC/MS/MS system to each analyte and its 

internal standard were measured in samples and in standards and a relative response was calculated as 

the ration of the analyte and the stable isotopically labeled internal standard responses. The relative 

response of the analyte in each sample was compared to the relative response of the analyte in the 

standards (Appendix 3 of the report study).

The relative responses of imidacloprid, 5-hydroxy imidacloprid, and imidacloprid olefin in solvent were 

measured over the range of 1 ppb to 2000 ppb for each analyte. The coefficients of determination (r2

) 

were calculated using linear regression analysis (XCalibur 2.0 data handling software). 

The total imidacloprid residue is the sum of the individual measured residue values of imidacloprid, 5-

hydroxy imidacloprid, and imidacloprid olefin in parent equivalents. For the purpose of calculating total 

imidacloprid residues where individual analyte residue values were less than the limit of detection 
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(LOD), the residues were assigned a finite value of 1⁄2 the value of the respective LOD. This value is only 

an estimate of potential residue in a sample, not a measured value. 

To conduct method validation, LOD determination and concurrent recoveries, commercial honey was 

diluted to approximately 25% sugar content to produce control nectar surrogate, and commercially 

obtained bee pollen was used as a surrogate for control pollen.

The analytical method for determining imidacloprid, 5-hydroxy imidacloprid, and imidacloprid olefin 

residue was validated by measuring the recoveries of these analytes from the nectar surrogate, the 

control bee pollen, and leaves (control strawberry used as a surrogate). Nectar and pollen were fortified 

at 1 ppb with each analyte and leaves were fortified at 10 ppb. Recoveries from the fortified control 

samples were corrected for any apparent residue in the associated controls before the method 

efficiency was conducted. Additional recoveries at higher fortification levels validated the method for 

the highest residues observed in individual matrices. Concurrent recoveries of imidacloprid, 5-hydroxy 

imidacloprid, and imidacloprid olefin were measured with each set of samples to verify method 

performance. 

5F. QUALITY ASSURANCE RESULTS

The responses of the LC/MS/MS system to imidacloprid, 5-hydroxy imidacloprid, and imidacloprid olefin 

were linear in solvent over the range of .5 ppb to 30 ppb for imidacloprid, 5-hydroxy imidacloprid, and 

imidacloprid olefin. The coefficients of determination (R2

) were >0.99. 

Average control interferences in the nectar, pollen, and leaves were less than their respective 

determined Limits of Quantitation (LOQs) for each analyte. All recoveries were corrected for any 

interferences in corresponding controls. The overall mean of the recoveries of each analyte from each 

matrix was within the acceptable range of 70% to 110%. All percent standard deviation (%SD) values

were below 20%.

The limit of quantitation LOQ is defined as the lowest fortification level of an analyte at which 

acceptable recovery has been achieved. The LOQ for a total residue is the highest of the LOQ values 

assigned to the individual analytes for a particular matrix. 

The limit of detection (LOD) is defined as the lowest concentration of an analyte that can be determined 

to be statistically different from a blank. The LODs were determined from method validation data 

obtained from control samples fortified at the respective analyte LOQs. The LODs were calculated by 

multiplying the standard deviation of recovery measurements at the LOQ by t0.99 [where t0.99 is the onetailed t-statistic at the 99% confidence level for the number of replicates (n)].13 The LOD for the total 

imidacloprid residue in each matrix is the highest LOD value of any one individual analyte for that 

particular matrix.

Summary of LOQs and LODs

Matrix Analyte LOQ (ppb, parent equivalents) LOD (ppb, parent equivalents)

Melon Nectar Imidacloprid 1.0 0.03

5-hydroxy Imidacloprid 1.0 0.79

Imidacloprid olefin 1.0 0.57

Total Imidacloprid 1.0 0.79

Melon Pollen Imidacloprid 10 1.7
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5-hydroxy Imidacloprid 10 2.2

Imidacloprid olefin 10 5.0

Total Imidacloprid 10 4.6

Melon Leaves Imidacloprid 10 2.2

5-hydroxy Imidacloprid 10 3.0

Imidacloprid olefin 10 4.6

Total Imidacloprid 10 4.6

Any analyte (or total) residue measured to be less than the LOQ was reported as less than the LOQ 

value. Measured residue values between the LOQ and LOD are provided in Appendix 3 of the study 

report; any residue value that was below the LOD was reported as less than the LOD. The total 

imidacloprid residue is a sum of the analyte residue values that are greater than the respective analyte 

LODs. If the analyte value was less than the LOD, a default value equal to 1⁄2 the LOD was added into the 

sum.

6. RESULTS:

In all matrices (nectar, pollen, and leaves) concentrations of total imidacloprid were higher in melons 

grown in medium soil than in fine soil. Melons grown in coarse soil were not included in this study. The 

maximum total residues in melon pollen were measured to be 12 ppb (mean ± SD, <10 ± 2.8) and 32 ppb 

(mean ± SD, 13 ± 8.6) grown in fine and medium-textured soils, respectively. The maximum total 

residues in melon nectar were measured to be 5.3 ppb (mean ± SD, 3.0 ± 1.5) and 8.0 ppb (mean ± SD, 

3.9 ± 2.5) grown in fine and medium-textured soils, respectively. The maximum total residues in melon 

leaves were measured to be 28 ppb (mean ± SD, 16 ± 6.7) and 71 ppb (mean ± SD, 27 ± 25) grown in fine 

and medium-textured soils, respectively. Summary statistics for concentration of total imidacloprid in 

melon nectar, pollen and leaves are contained in Table 3.

The imidacloprid, 5-hydroxy imidacloprid, and imidacloprid olefin residue data for bee collected nectar 

(hive deposited), bee collected pollen (pollen traps), and leaf samples are provided in Table 4 through 

Table 6. The total imidacloprid residue data are summarized below.

Table 3. Magnitude of total imidacloprid residues in melon pollen, nectar and leaves.

Commodity

Soil Texture 

Categorya

Total Imidacloprid Residue Levels (ppb)b

N Min Max

Highest 

Avg. Site 

Residue Median Mean

Standard 

Deviation

Bee collected 

(hive deposited)

melon nectar

Fine 10 1.2 5.3 3.9 2.4 3.0 1.5

Bee collected 

(hive deposited)

melon nectar

Medium 10 1.6 8.0 4.9 3.0 3.9 2.5

Bee collected 

(pollen traps)

melon pollen

Fine 10 <10 12 11 <10 <10 2.8
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Bee collected 

(pollen traps)

melon pollen

Medium 10 <10 32 19 <10 13 8.6

Melon leaves Fine 10 <10 28 27 13 16 6.7

Melon leaves Medium 10 <10 71 55 10 27 25 a Classification of the soils was obtained from the Soil Survey Geographic (SSURGO) Database provided by the 

Natural Resources Conservation Service and converted to soil texture categories.

b Abbreviations used are as follows: Min is the lowest treated residue value; Max is the highest treated residue 

value; Median is the geometric median of the treated residue values; Mean is the mathematical average of the 

treated residue values; Standard Deviation is the standard deviation for a small population of “N” samples.

Table 4. Total Imidacloprid Residue in/on Nectar (Hive Deposited) from Melon Plants Grown in Soil 

Previously treated with Imidacloprid. a * Trial Identification Location (County) Crop Bee Relevant Matric

Soil TypeImidacloprid Olefin Residue (ppb)5-Hydroxy Imidacloprid Residue (ppb)Imidacloprid Residue (ppb)Total Imidacloprid Residue (ppb)

NT209 Imperial, 

CA

Melon Nectar Heavy <1.0

<1.0

<1.0

2.8

1.5

2.2

2.5

5.3

Average

3.9

NT210 Imperial, 

CA

Melon Nectar Heavy <1.0

<1.0

<1.0

1.0

1.2

1.0

1.9

2.3

Average

2.1

NT201 Imperial, 

CA

Melon Nectar Heavy <1.0

<1.0

1.3

<1.0

<1.0

<1.0

2.2

1.2

Average

1.7

NT202 Imperial, 

CA

Melon Nectar Medium 1.6

1.2

2.7

1.4

1.9

<1.0

6.3

3.5

Average

4.9

NT203 Imperial, 

CA

Melon Nectar Heavy <1.0

1.2

2.1

<1.0

2.7

<1.0

5.1

2.5

Average

3.8

NT208 Imperial, 

CA

Melon Nectar Medium <1.0

<1.0

<1.0

<1.0

6.4

<1.0

8.0

1.6

Average

4.8

NT206 Imperial, 

CA

Melon Nectar Medium <1.0

<1.0

2.0

1.1

<1.0

<1.0

2.6

1.9

Average
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Trial IdentificationLocation (County)CropBee Relevant MatricSoil TypeImidacloprid Olefin Residue (ppb)5-Hydroxy Imidacloprid Residue (ppb)Imidacloprid Residue (ppb)Total Imidacloprid Residue (ppb)

2.3

NT205 Imperial, 

CA

Melon Nectar Medium <1.0

<1.0

<1.0

1.6

1.1

1.5

1.8

3.4

Average

2.6

NT204 Imperial, 

CA

Melon Nectar Heavy <1.0

1.1

<1.0

1.4

1.2

1.7

1.9

4.2

Average

3.0

NT207 Imperial, 

CA

Melon Nectar Medium <1.0

<1.0

<1.0

<1.0

1.3

5.7

2.0

7.5

Average

4.7 a See Appendix 3 of the study report for the analytical data summaries used to prepare this summary. Total 

imidacloprid residue is the sum of imidacloprid, 5-hydroxy imidacloprid, and imidacloprid olefin residues, in parent 

equivalents. Any analyte residue measured to be less than the LOQ was reported in this table as less than the LOQ 

value (1.0 ppb). Measured residue values between the LOQ and LOD are provided in Appendix 3 of the study 

report. The total Imidacloprid residue is a sum of the analyte residue values that are greater than the respective 

analyte LODs. If the analyte value was less than the LOD, a default value equal to 1⁄2 the LOD was added into the 

sum.

*Table 6 in study report. 

Table 5. Total Imidacloprid Residue in/on Pollen (Pollen Traps) from Melon Plants Grown in Soil 

Previously treated with Imidacloprid. a * Trial Identification Location (County) Crop Bee Relevant 

MatricSoil TypeImidacloprid Olefin Residue (ppb)5-Hydroxy Imidacloprid Residue (ppb)Imidacloprid Residue (ppb)Total Imidacloprid Residue (ppb)

NT209 Imperial, 

CA

Melon Pollen Heavy <1.0

<1.0

<1.0

<1.0

<1.0

<1.0

<1.0

<1.0

Average

<1

NT210 Imperial, 

CA

Melon Pollen Heavy <1.0

<1.0

<1.0

<1.0

<1.0

<1.0

1.0

1.2

Average

1.1
MRID 49090501 CDPR IMI Melon

12

Trial IdentificationLocation (County)CropBee Relevant MatricSoil TypeImidacloprid Olefin Residue (ppb)5-Hydroxy Imidacloprid Residue (ppb)Imidacloprid Residue (ppb)Total Imidacloprid Residue (ppb)

NT201 Imperial, 

CA

Melon Pollen Heavy <1.0

<1.0

<1.0

<1.0

<1.0

<1.0

<1.0

<1.0

Average

<1.0

NT202 Imperial, 

CA

Melon Pollen Medium <1.0

<1.0

<1.0

<1.0

<1.0

<1.0

<1.0

<1.0

Average

<1.0

NT203 Imperial, 

CA

Melon Pollen Heavy <1.0

<1.0

<1.0

<1.0

<1.0

<1.0

<1.0

1.1

Average

<1.0

NT208 Imperial, 

CA

Melon Pollen Medium <1.0

<1.0

<1.0

<1.0

<1.0

2.9

<1.0

3.2

Average

1.8

NT206 Imperial, 

CA

Melon Pollen Medium <1.0

<1.0

<1.0

<1.0

<1.0

<1.0

1.3

1.2

Average

1.3

NT205 Imperial, 

CA

Melon Pollen Medium <1.0

<1.0

<1.0

<1.0

<1.0

<1.0

<1.0

<1.0

Average

<1

NT204 Imperial, 

CA

Melon Pollen Heavy <1.0

<1.0

<1.0

<1.0

<1.0

<1.0

<1

1.0

Average

<1

NT207 Imperial, 

CA

Melon Pollen Medium <1.0

<1.0

<1.0

<1.0

1.5

1.5

1.9

1.8

Average

1.9 a See Appendix 3 of the study report for the analytical data summaries used to prepare this summary. Total 

imidacloprid residue is the sum of imidacloprid, 5-hydroxy imidacloprid, and imidacloprid olefin residues, in parent 

equivalents. Any analyte residue measured to be less than the LOQ was reported in this table as less than the LOQ 

value (1.0 ppb). Measured residue values between the LOQ and LOD are provided in Appendix 3 of the study 

report. The total Imidacloprid residue is a sum of the analyte residue values that are greater than the respective 

analyte LODs. If the analyte value was less than the LOD, a default value equal to 1⁄2 the LOD was added into the 

sum. 

*Table 7 in study report
MRID 49090501 CDPR IMI Melon

13

Table 6. Total Imidacloprid Residue in/on leaves from Melon Plants Grown in Soil Previously treated 

with Imidacloprid. a * Trial Identification Location (County)

CropBee Relevant MatricSoil TypeImidacloprid Olefin Residue (ppb)5-Hydroxy Imidacloprid Residue (ppb)Imidacloprid Residue (ppb)Total Imidacloprid Residue (ppb)

NT209 Imperial, 

CA

Melon Leaves Heavy <1.0

<1.0

<1.0

<1.0

<1.0

<1.0

1.1

1.2

Average

1.1

NT210 Imperial, 

CA

Melon Leaves Heavy <1.0

<1.0

<1.0

<1.0

2.3

2.2

2.8

2.6

Average

2.7

NT201 Imperial, 

CA

Melon Leaves Heavy <1.0

<1.0

<1.0

<1.0

<1.0

<1.0

1.2

<1.0

Average

1.1

NT202 Imperial, 

CA

Melon Leaves Medium <1.0

<1.0

<1.0

<1.0

<1.0

<1.0

1.0

1.1

Average

1.0

NT203 Imperial, 

CA

Melon Leaves Heavy <1.0

<1.0

<1.0

<1.0

<1.0

1.5

1.2

1.9

Average

1.5

NT208 Imperial, 

CA

Melon Leaves Medium <1.0

<1.0

<1.0

<1.0

4.4

5.3

5.2

5.8

Average

5.5

NT206 Imperial, 

CA

Melon Leaves Medium <1.0

<1.0

<1.0

<1.0

<1.0

<1.0

1.0

<1.0

Average

<1.0

NT205 Imperial, 

CA

Melon Leaves Medium <1.0

<1.0

<1.0

<1.0

<1.0

<1.0

<1.0

<1.0

Average

<1.0

NT204 Imperial, 

CA

Melon Leaves Heavy <1.0

<1.0

<1.0

<1.0

<1.0

1.7

1.4

2.0
MRID 49090501 CDPR IMI Melon

14

Trial IdentificationLocation (County)CropBee Relevant MatricSoil TypeImidacloprid Olefin Residue (ppb)5-Hydroxy Imidacloprid Residue (ppb)Imidacloprid Residue (ppb)Total Imidacloprid Residue (ppb)

Average

1.7

NT207 Imperial, 

CA

Melon Leaves Medium <1.0

<1.0

<1.0

<1.0

6.0

3.0

7.1

3.6

Average

5.3 a See Appendix 3 of the study report for the analytical data summaries used to prepare this summary. Total 

imidacloprid residue is the sum of imidacloprid, 5-hydroxy imidacloprid, and imidacloprid olefin residues, in parent 

equivalents. Any analyte residue measured to be less than the LOQ was reported in this table as less than the LOQ 

value (1.0 ppb). Measured residue values between the LOQ and LOD are provided in Appendix 3 of the study 

report. The total Imidacloprid residue is a sum of the analyte residue values that are greater than the respective 

analyte LODs. If the analyte value was less than the LOD, a default value equal to 1⁄2 the LOD was added into the 

sum. 

*Table 8 in study report. 

7. STUDY VALIDITY/CLASSIFICATION AND STUDY LIMITATIONS 

Classification/Utility for Bee Risk Assessment. This study is classified as SUPPLEMENTAL primarily due 

to the many uncertainties which may have confounded the results and could have caused the reported 

residues to be not representative of actual field conditions. The study design outlined by the 

Department of Pesticide Regulation (DPR) requested that sites be selected with a preference to sites 

receiving soil applications of imidacloprid during two successive years. However, half of the field sites 

used in this study did not have sequential applications. In two sites there was only one application in 

2011, with no data indicating any previous applications had been made. Additionally, in one site no 

pesticide applications were made during the study year. If the data is to be used as part of a risk 

assessment, then the data should be re-analyzed taking these variations into consideration: (1) It is 

unclear how much of the composite nectar samples was collected before the hives were moved to the 

treated field; (2) It is not known how much of the nectar was collected before the bees were exposed to 

imidacloprid; and (3) Additional uncertainties exist for crops grown in coarse soil.

Temporal Variability in Residues. Applications were made from January 3 to January 20, 2011 (except 

the one site that did not receive any application in 2011), and sampling was conducted from April 23 to 

May 8, 2011. This study was not designed for temporal analysis of declining concentrations, but rather, 

to provide a snapshot of residue concentrations during flowering.

Spatial Variability in Residues. All ten sites in this study were in Imperial County in Southern California. 

All of the sites had similar climatic conditions. Five of the sites had soil with fine texture and five sites 

had soil that was described as medium texture. Coarse soil was not included in this study. 

Concentrations of total imidacloprid were higher in melons grown in medium soil than in fine soil.
MRID 49090501 CDPR IMI Melon

15

Pesticide Carryover. The extent to which prior year applications of imidacloprid contributed to year-toyear carryover was not analyzed by the study authors. There was substantial variability in the 

application history but the study authors did not consider application history in their data analysis. 

Therefore, the effects of pesticide carryover in melons are unknown.

Additional Limitations. Using bee hives to collect pollen and nectar samples appeared to be 

inappropriate in this study. Both pollen and nectar samples may not reflect the real concentrations of 

imidacloprid and its transformation products in plant nectar and pollen. Nectar was collected from 

brood cells where the source of nectar cannot be confirmed (although care was taken to not sample 

nectar from cells near any parts of a comb containing capped, stored honey). Pollen was collected in 

pollen traps for a long period of time when degradation of imidacloprid may occur. 

Melon flowers are considered to be attractive to bees. However, there appeared to have insufficient 

amount nutritional sources to support the hive development in this study. All 20 colonies in this study 

were under severe stress and continually shrank while colonies were in the tents. No nectar storage was 

observed in new frame inserted in the hives that was designed to collect nectar from. The small

amounts of nectar observed in bee stomachs confirm very low level of foraging on the test crops and 

low nectar collection activity. In addition only a few pollen loads were found in pollen traps even during 

couple of days. Degradation of imidacloprid could not be excluded in pollen samples that were 

combined from collection during multiple days, over a period of two to three weeks. 

8. CONCLUSION

Ten trials were conducted in California in soils classified as either “heavy (fine-textured)”, or “medium 

(medium-textured)” to determine the residues of imidacloprid and its metabolites (5-hydroxy 

imidacloprid and imidacloprid olefin) in bee collected nectar (hive deposited), bee collected pollen 

(pollen traps), and leaves (hand collected) from melon plants (cucurbits) grown at locations treated 

previously with imidacloprid.

In all matrices (nectar, pollen, and leaves) concentrations of total imidacloprid were higher in melons 

grown in medium soil than in fine soil. The maximum total residues in melon pollen were measured to 

be 12 ppb (mean ± SD, <10 ± 2.8) and 32 ppb (mean ± SD, 13 ± 8.6) grown in fine and medium-textured 

soils, respectively. The maximum total residues in melon nectar were measured to be 5.3 ppb (mean ± 

SD, 3.0 ± 1.5) and 8.0 ppb (mean ± SD, 3.9 ± 2.5) grown in fine and medium-textured soils, respectively.

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