MRID 49090504 CDPR IMI Citrus (2011)

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1. STUDY INFORMATION

Sponsor:

Bayer CropScience

2T.W. Alexander Drive

Research Triangle Park, 

NC USA 27709

Study Completion Date: March 30, 2011

Study Location:

1) Hemet, California

2) Lindcove Research and Extension Center

3) Ventura County, California

4) Temecula, California

5) Tulare County, California

6) University of California, Riverside

Sponsor Study ID: EBNTL056-7 PC Code: 129099

GLP Status: Non-GLP; Final protocol was submitted to CDPR for review. 

[CDPR study ID 253951, Data Volume 51950-0756, Tracking ID# 240317]

Study Type: Non-Guideline field residue study on Southern California Citrus Groves that had been 

previously treated with Imidacloprid to evaluate bee exposure.

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. STUDY VALIDITY

Guideline Followed: Non-guideline study (final protocol submitted by CDPR)

Guideline Deviations: N/A

Other Deviations: N/A

Classification: Supplemental

Rationale: N/A

Reparability: N/A

4. TEST MATERIAL CHARACTERIZATION

Test Material: 1) Admire Pro

2) Unknown Formulations

Percent Active 

Ingredient:

1) 42.8% A.I.

2) Unknown 

Description: 1) Suspension concentrate (SC)

2) Unknown

Density: 1.41-1.54 g/mL

Material Source: Bayer Corporation Solubility: 0.51 to 0.61 g/L

CAS #: 138261-41-3 pH (24°C): 7.8

5. EXECUTIVE SUMMARY

Reference

Byrne, F.; Morse, J.; Visscher, P.; Grafton-Cardwell, E.; Leimkuehler, W. (2011) Determination of exposure 

levels of honey bees foraging on flowers of citrus trees previously treated with imidacloprid. Project 

Number: EBNTL056/7, M/408424/012. Unpublished study prepared by University of California, Riverside. 

70p. MRID 49090504, CDPR Study ID 259131, Data Volume 51950-0787, Tracking ID# 246252
MRID 49090504 CDPR IMI Citrus (2011)

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A series of field investigations were conducted between 2008 and 2011 to determine to what extent 

honey bees foraging on citrus blossoms may be exposed to imidacloprid when citrus trees are treated 

with systemic applications (soil treatments) of this insecticide. 

The approach that was taken was to compare the imidacloprid residues in floral nectar with nectar 

extracted from the crops, foraging honey bees and from stored nectar within their hives. Two 

experimental systems were established. First, honey bee colonies were confined within large tunnel 

cage enclosures where foraging access to treated trees was limited. Second, honey bee colonies were 

situated in an open-field system, in which hives were placed in a large acreage of commercial citrus that 

had been treated with imidacloprid. In this second system, the foraging activity of the honey bees was 

not limited to any specific trees or to citrus.

In addition to the honey bee studies, the study quantifies the levels of imidacloprid in nectar from trees 

that had been treated under a number of different scenarios. The intent was to determine residues in 

trees treated in successive years to test for potential imidacloprid accumulation and persistence. For 

this, groves that were growing in different soil types were included because of the impact that soil has 

on the availability of imidacloprid for uptake. The effect of differing application rates were also 

evaluated on imidacloprid residues in nectar.

The subject study report consists of five different trials that will make up the composition of this Data 

Evaluation Report. Detailed findings, study limitations, study validity and results from each trial are 

found below.

6. SAMPLE COLLECTION, HANDLING, PROCESSING

Nectar Collections by Hand

Nectar was sampled from individual flowers using a micro-capillary tube inserted into a bulb dispenser. 

After insertion of the tip of the tube into the nectar at the base of the flower, the nectar was drawn into 

the tube by capillary action. The nectar was then transferred to an autosampler vial. The target volume 

for each sample was 150 μl. During field trips to collect the nectar, the samples were kept in an ice chest 

containing dry ice until they were stored in a -20°C freezer.

Nectar collections by Honey Bees

Nectar was collected from the crops of honey bees returning to their hives from foraging trips to 

determine the concentrations of imidacloprid and metabolites. Bees were intercepted at the entrance 

to the hives using a small net and were immediately transferred to a cooler containing dry ice to 

anesthetize them. After 30 seconds in the cooler, individual bees were forced to regurgitate the 

contents of their crops by pressing gently on the lateral sides of their abdomen region (the gaster) with 

paddle forceps. The nectar formed a droplet at the top of their mandibles where it was collected using a 

micro-capillary tube. The nectar was transferred to an autosampler vial and then placed in a cooler with 

dry ice. For each sample it was necessary to composite nectar from several bees in order to meet the 

minimum target volume of 75 μl. At least 5 bees were used to prepare 1 sample and a maximum of 20 

samples from each hive were collected. 

Stored Nectar
MRID 49090504 CDPR IMI Citrus (2011)

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In addition to the stomach nectar, nectar was also collected from deposits made to new comb within 

each hive. A sample consisted of pooled nectar from comb cells near each other. Sufficient nectar was 

collected for residue analysis and to measure sugar concentration using a refractometer to provide 

information on possible changes in imidacloprid concentration during conversion from nectar to honey. 

The target sample number was 10 samples from each hive.

7. ANALYTICAL METHODS

Nectar 

Nectar collected from citrus trees (orange, mandarins and grapefruit) was analyzed by dilution with 

mobile phase containing the stable isotope internal standards. 50 μL of nectar was pipetted into an 

autosampler vial containing a 300 μL conical insert. 50 μL of mobile phase (9:1 water/methanol 

containing 10 mM NH4HCO3) containing 10 ng/mL of the stable isotope internal standards was added 

and the sample mixed a couple times by pulling up and down with the Gilson Microman pipette. The 

final concentration in the diluted nectar of the internal standard was 5 ng/mL. The samples were 

analyzed by LC/MS/MS. Response ratios (NA/IS) were directly compared to a calibration curve having 

concentrations of 5 ng/mL for the internal standards and native analyte concentrations ranging from 0.1 

to 100 ng/mL and adjusted for dilution, i.e., 50 μL of nectar diluted to 100 μL (2X dilution). Recoveries 

(QC) samples were prepared by diluting control nectar with the QC dilution solution as described. 

Pollen

A 0.05 to 0.5 g sample of pollen was weighed into a 13 mL polypropylene conical screw cap centrifuge 

tube. 1.5 mL of HPLC grade water (pesticide residue grade) was added and the pollen dissolved. 20 ng of 

the stable isotope internal standard mixture of imidacloprid, imidacloprid olefin and 5-hydroxy 

imidacloprid was added followed by 4 mL of ACN. The tube was then shaken vigorously for one minute. 

Then 1 g of MgSO4 (anhydrous) and 0.5 g NaCl was added and the tube again shaken and vortexed 

vigorously for 1 minute. The tubes were then centrifuged at 4000 RPM for 5 minutes using an Eppendorf

5810 R centrifuge. 

The supernatant, nominally 4 mL, was decanted into another 13 mL centrifuge tube containing, 0.040 g 

BONDESIL-PSA and 170 g Mg SO4 (anhydrous). The tube was shaken and vortexed vigorously for 1 

minute. The tubes were centrifuged as before. A 1.0 mL portion of the supernatant (ACN) was 

transferred to a LC autosampler vial and the ACN was avaporated to dryness using a N-Evap or Tubovap. 

The residue was re-dissolved in 1.0 mL of HPLC mobile phase (9:1 water/MeOH containing 10 mM 

NH4HCO3) in preparation for analysis by LC/MS/MS. 

Recoveries (QC) samples (5 ppb) were prepared by fortifying control pollen (500 mg) with mixed native 

stds (25 μL of the 0.1 μg/mL mixed standard).

Imidacloprid, imidacloprid olefin and 5-hydroxy imidacloprid were measured in nectar and pollen. 

Nectar was measured directly by dilution with HPLC mobile phase and the pollen was extracted using 

QuEChERS methodology. The final extracts were analyzed by LC/MS/MS employing stable isotope

internal standards. The Limit of Detection (LOD) and Limit of Quantitation (LOQ) were calculated based 

on 3X and 10X, respectively, of the standard deviation of 4 QC recovery samples from stomach nectar at
MRID 49090504 CDPR IMI Citrus (2011)

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1 ppb. From this evaluation, the LOD and LOQ were calculated to be 0.018, 0.36 and 0.30 ppb (LOD) and 

0.6, 1.2 and 1 ppb (LOQ) for imidacloprid, 5-hydroxy imidacloprid, and imidacloprid olefin, respectively. 

8. TRIALS

8A. TRIAL INFORMATION

Title: Tunnel Cage Trial

Application Date: September 3, 2009 Sampling Date: April 24, 2010

Section of Study: Section 2 Trial Location: Lindcove Research and 

Extension Center (LREC)

TRIAL SUMMARY

The objective of this component of the study was to examine citrus groves that were treated with a soil 

application of imidacloprid systemic insecticide, to understand the levels of imidacloprid that occurred 

in (a) nectar extracted by hand from citrus flowers, (b) nectar collected by forager honey bees and 

transported back to the hive, and (c) nectar or "uncapped honey" deposited by bees in cells of the

Brood comb. 

Honey bee colonies were confined within tunnel cage enclosures, each containing 3 flowering citrus 

trees that had been treated with soil applications of systemic imidacloprid (Admire Pro®). Nectar was 

collected by hand from each tree within each tunnel cage. In addition, nectar was extracted from the 

stomachs of honey bees foraging within the tunnels so that a comparison could be made between handcollected and honey bee-collected nectar. At the end of the confinement period within the tunnels, 

stored nectar was sampled from new comb that had been placed within each hive at the start of the 

exposure period. Four tunnels were constructed, providing three imidacloprid-treated and one 

untreated control data set.

METHOD

APPLICATION TIMING AND RATES

Admire Pro® was applied at the maximum label rate of 14 fl oz per acre (0.104 fl oz per tree) on Sept. 3, 

2009. Trees were pre-irrigated for 2 hours prior to applications. The insecticide was applied to each tree 

using a watering can, taking care to apply the solution evenly within the irrigated area defined by the 

sprinklers. Watering cans were used to administer the insecticide to the trees in order to ensure that the 

correct amount of active ingredient, as defined by the insecticide label, was delivered to each tree.

Trees were irrigated for another 4 hours following completion of the applications, and then subjected to 

the standard 8 hour, once-per-week irrigation regime during the first 4 weeks post-treatment.

Thereafter, trees were irrigated according to tensiometer measurements.

STUDY SITE LOCATION AND CHARACTERISTICS 

This trial was conducted at the Lindcove Research and Extension Center (LREC) in Exeter, California. The 

trees were Washington Parent Navels on C35 rootstock, which were planted in June 1992 (17 years old 

at the time of the study). The soil type at LREC is a loam soil consisting of 15-25% clay and 00.5-1% 

organic matter. There were 134 trees per acre with a tree spacing of 18’ x 18’ in the 3.9 acre block. Each 
MRID 49090504 CDPR IMI Citrus (2011)

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tree was irrigated by 2 sprinklers located on opposite sides of the trunk with 10.3 gph output on a 

weekly schedule. 

The enclosures were constructed from transparent netting with a maximum light exclusion of 13%. The 

netting was supported on a frame constructed from 1" PVC tubing to provide a semi cylindrical tunnel 

that fully enclosed 3 citrus trees. There was sufficient clearance to allow movement of personnel 

between the citrus trees and the netting so that all sections of the trees could be used for nectar 

sampling. Tunnel dimensions were 26' x 96' x 16'.

The Italian honey bee, Apis mellifera ligustica, was used in the subject trial. When the trees were in full 

bloom, one small colony of bees (a nuclear hive consisting of 5 frames of comb, a queen, developing 

brood, and workers to cover about 4 frames) was introduced into each tunnel. Hives were initially

placed in the tunnels at 8.00 a.m. on April 20, 2010. Due to heavy rainfall, bees were confined within the 

hives until the morning of April 22, 2010 when the bees were released to begin foraging.

SAMPLING METHOD

Nectar was sampled directly from the flower by hand using a micro-capillary tube. The target volume for 

each sample was 150 μl, with nine composite nectar samples collected, three from each tree. Samples 

were also collected using honey bees that were contained over the three trees by a tunnel constructed 

from transparent netting (Combined Clear Net 13%) with 1” PVC tube frames. The bees were 

intercepted at the hive entrance and chilled with dry ice for 30 seconds. A composite sample from at 

least 5 bees was collected. In addition, stored nectar was collected from new combs within each hive. A 

pooled sample was collected from cells near each other with a target of ten samples per hive. Nectar 

sugar analysis was measured by refractometry.

RESULTS:

The mean residues of total imidacloprid in hand or bee collected citrus nectar ranged from 13.97-21.19 

ppb, while mean residues in hive stored nectar ranged from 44.65-72.81 ppb. The highest residues were 

found in hive stored nectar, corresponding with the highest sugar concentration.

Table 1. Summary of imidacloprid residues in nectar collected from orange trees within four tunnel 

enclosures that had been treated the previous two years as a soil drench at the maximum labelled rate. 

Maximum application rate applied to individual trees on 9/3/2009.

Lindcove Research and Extension Center (LREC)

Spring 2010

Loam Soil [15-25% clay, 0.5 – 1% organic matter]

Mean Residue Concentration (ppb)

(minimum – maximum)

Tunnel

Hand Collected Nectar

N1 = 9

[3 samples from each tree, 

3 trees per tunnel]

Sampling occurred 

4/22/2010

Bee Collected Nectar

N1 = 20

[one hive per tunnel, mean of 20 

samples]

Sampling occurred 4/22/2010

Uncapped Stored Nectar

N1 = varies

[one hive per tunnel, mean of up 

to 

10 samples]

Sampling occurred 4/24/2010

IMI Total IMI2 IMI Total IMI2 IMI Total IMI2

Control <1.0 <1.0 <1.0 <1.0 <1.0 <1.0

1 8.3 13.96 10.61

(5.6 – 21.22)

17.55

(9.17 – 37.12)

25.49

(19.71 – 36.06)

44.65

(35.40 – 62.75)
MRID 49090504 CDPR IMI Citrus (2011)

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Lindcove Research and Extension Center (LREC)

Spring 2010

Loam Soil [15-25% clay, 0.5 – 1% organic matter]

Mean Residue Concentration (ppb)

(minimum – maximum)

Tunnel

Hand Collected Nectar

N1 = 9

[3 samples from each tree, 

3 trees per tunnel]

Sampling occurred 

4/22/2010

Bee Collected Nectar

N1 = 20

[one hive per tunnel, mean of 20 

samples]

Sampling occurred 4/22/2010

Uncapped Stored Nectar

N1 = varies

[one hive per tunnel, mean of up 

to 

10 samples]

Sampling occurred 4/24/2010

IMI Total IMI2 IMI Total IMI2 IMI Total IMI2

(2.86 –

13.64)

(5.30 –

22.73)

2

7.64

(4.38 –

12.38)

14.01

(8.06 –

22.84)

8.97

(3.02 – 16.17)

15.08

(4.92 – 29.75)

27.33

(24.81 – 30.83)

49.65

(42.52 – 57.58)

3

12.81

(8.72 –

21.91)

21.19

(9.18 –

34.64)

8.00

(1.66 – 18.99)

13.38

(2.81 – 34.15)

40.12

(27.14 – 54.14)

72.81

(48.75 – 95.18)

Mean for 

Tunnels 1-

3

9.58

(7.64 –

12.81)

16.39

(13.96 –

21.19)

9.23

(8.00 – 10.61)

15.40

(13.38 – 17.55)

30.98

(25.49 – 40.12)

55.70

(44.65 – 72.81)

1 “N” is the total number of samples collected

2 “Total IMI” combines magnitude of residues of imidacloprid plus degradants IMI-olefin and IMI-5-OH

CONCLUSION TO TUNNEL CAGE

In this first trial, oranges (Washington Parent Navels on C35 rootstock) in a 3.9 acre block were treated 

in the fall of 2009 with 14 fl oz per acre (the maximum current U.S. label rate). The trial was located at 

the Lindcove Research and Extension Center (LREC) in Exeter, CA. The soil type at LREC is a loam soil 

consisting of 15-25% clay and 0.5-1% organic matter. Honey bee colonies were confined within tunnel 

cage enclosures, each containing 3 flowering citrus trees.

Nectar was collected by hand from each tree within each tunnel cage. In addition, nectar was extracted 

from the stomachs of honey bees foraging within the tunnels so that a comparison could be made 

between hand-collected and honey bee-collected nectar. At the end of the confinement period within 

the tunnels, stored nectar was sampled from new comb that had been placed within each hive at the 

start of the exposure period.

The mean residues of total imidacloprid in hand or bee collected citrus nectar ranged from 13.97-21.19 

ppb, while mean residues in hive stored nectar ranged from 44.65-72.81 ppb. The highest residues were 

found in hive stored nectar, corresponding with the highest sugar concentration.
MRID 49090504 CDPR IMI Citrus (2011)

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8B. TRIAL INFORMATION

Title: Open Field Trial

Application Date: Fall 2009 Sampling Date: April 25, 2010

Section of Study: Section 3 Trial Location: Lindcove Research and 

Extension Center (LREC)

TRIAL SUMMARY

Honey bee colonies were situated within a large area of treated commercial citrus. Within the area, 

there were multiple citrus varieties, some weeds, but no other commercial crops. The bees were 

allowed to forage freely. Nectar was collected by hand from trees within several different blocks within 

the perceived foraging area. In addition, nectar was extracted from the stomachs of honey bees foraging 

within the citrus region so that a comparison could be made between hand-collected and honey beecollected nectar. Whereas in the tunnel study, hand-collected and honey bee-collected sources were 

controlled, the foraging range of the honey bees was not controlled. At the end of the 3-day foraging 

period, nectar was sampled from new comb that had been placed within each hive at the start of the 

trial. Pollen traps were also included in the hives and these were operated for a 24-hour period prior to 

the completion of the experiment.

The Italian honey bee Apis mellifera ligustica was also used in this study. Five large colonies consisting of 

10 frames were situated in the citrus area on the evening of April 22. The bees were confined within the 

hives until the morning of April 23 when the bees were released to begin foraging. The larger hives used 

for the open field study were equipped with pollen traps that were set into operation for 24 hours 

beginning on April 24, 2010 and concluding on April 25, 2010.

Hand-collect nectar, bee-collected nectar, and stored nectar were collected in the same way as in the 

tunnel trial. Pollen samples were also collected from pollen traps within a 24-hour collection period 

prior to the completion of the experiment. Pollen samples from only two hives were available for 

residue analysis. It was found that the pollen load in each trap was very low given the 24-hour collection 

period. 

Pollen sources were not distinguished for residue analysis. Upon visual examination, there were clearly 

several pollen sources within the traps indicating that the bees were not foraging exclusively on citrus 

flowers. 

METHOD

APPLICATION TIMING AND RATES

All citrus groves in a radius of 1-2 miles on and around the LREC were treated for aphids with 

imidacloprid in the fall of 2009. A very large contiguous area of citrus had been treated in 2009 with 

various imidacloprid commercial formulations at half the maximum field rate (0.25 lb. a.i. per acre 

regardless of the commercial formulations used). A large block of citrus was selected in the center of 

such treatments for this honey bee study with the knowledge that bees can forage very long distances 
MRID 49090504 CDPR IMI Citrus (2011)

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from their hives. Although there were other blooming plants in the vicinity of this block that honey bees 

could have foraged from, there were no nearby agricultural crops other than citrus. All nearby citrus 

within 1 mile had been treated with the half rate of imidacloprid the previous fall.

STUDY SITE LOCATION AND CHARACTERISTICS 

The Lindcove Research and Extension Center (LREC) contains much of the collection of important 

rootstock and scions for the Citrus Clonal Protection Program (CCPP) and research projects for the State 

of California. In 2009, a higher than normal number of trees in the region became infected with Citrus 

tristeza virus (CTV). CTV is a pathogen vectored by several species of aphids. The LREC has soils 

characterized as loam soils (15-25% clay, 0.5-1% organic matter).

RESULTS:

In this trial, the mean residues of total imidacloprid in hand collected citrus nectar ranged from 1.81-

9.42 ppb while the mean residues in nectar extracted from foraging honey bees ranged from 1.11-7.59 

ppb. Also, the mean residues of total imidacloprid in hive stored nectar ranged from 6.95-11.63 ppb. 

Moreover, the maximum mean residues for hive pollen were found to be 10.2 ppb while the average 

residue measurement was 9.39 ppb. 

There appears to be large variations in the level of residues among citrus varieties. Due to the limited 

samples and information provided, it is unknown if this variation was due to citrus varieties or other 

factors, including age of the trees or level or irrigation.

Table 2. Summary of imidacloprid residues in hand collected nectar randomly selected within six blocks 

of citrus surrounding the location of five honey bee hives. Commercial citrus trees were treated in the 

Fall of 2009 at half (1⁄2X) the labelled rate.

Lindcove Research and Extension Center (LREC)

Spring 2010

Loam Soil [15-25% clay, 0.5 – 1% organic matter]

Mean Residue Concentration (ppb)

(minimum – maximum)

Citrus Variety Hand Collected Nectar

N1 IMI 5-OH Olefin Total IMI2

Valencia Oranges – South East 10 <1.0

(<1.0 – 1.18)

<1.0 <1.0 1.81

(1.15 – 2.48)

Valencia Oranges – South West 5 2.73

(1.53 – 3.55)

<1.0 <1.0

(<1.0 – 2.22)

5.18

(3.17 – 6.21)

Navel Oranges – North East 4 1.79

(<1.0 – 2.48)

<1.0 <1.0

(1.02 – 1.95)

3.51

(2.11 – 4.42)

Navel Oranges – South East 4 3.51

(2.03 – 6.15)

<1.0 <1.0

(<1.0 – 1.73)

4.87

(2.64 – 8.42)

Tangerines 10 6.82

(2.84 – 13.26)

<1.0 1.99

(<1.0 – 3.67)

9.42

(4.03 – 18.28)

Young Oranges 5 2.76

(1.34 – 4.21)

<1.0 <1.0

(<1.0 – 1.11)

3.73

(1.76 – 5.88)

Means 3.29

(<1.0 – 6.82) <1.0 1.19 4.75(1.81 – 9.42) 1 “N” is the total number of samples collected

2 “Total IMI” combines magnitude of residues of imidacloprid plus degradates IMI-olefin and IMI-5-OH
MRID 49090504 CDPR IMI Citrus (2011)

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Table 3. Summary of imidacloprid residues in nectar collected from free-ranging honey bees in 

commercial citrus trees treated in the fall of 2009 at half the labelled rate.

Lindcove Research and Extension Center (LREC)

Spring 2010

Loam Soil [15-25% clay, 0.5 – 1% organic matter]

Mean Residue Concentration (ppb)

(minimum – maximum)

Hive

Bee Collected Nectar

N1 = varies

[mean of up to 

20 samples]

Sampling occurred 4/23/2010

Uncapped Stored Nectar

N1 = varies

[mean of up to 

10 samples]

Sampling occurred 4/25/2010

Hive Pollen

[Each value represents a 

single measurement for the 

analysis of the entire pollen 

retrieved from traps within 

individual hives]

Sampling occurred 

4/25/2010

IMI Total IMI2 IMI Total IMI2 IMI Total IMI2

1 1.05

(<1.0 – 2.43)

2.11

(<1.0 – 5.07)

6.25

(4.73 – 8.67)

11.63

(9.31 – 15.53)

N/A

2 3.77

(<1.0 – 9.31)

7.59

(1.16 – 16.02)

N/A N/A

3 1.94

(<1.0 – 7.56)

3.59

(<1.0 – 12.16)

N/A N/A

4 <1.0

(<1.0 – 2.69)

1.11

(<1.0 – 3.71)

3.23

(2.47 – 4.98)

6.96

(4.47 – 9.25)

6.58 8.57

5 1.94

(<1.0 – 4.2)

3.23

(<1.0 – 7.29)

5.98

(3.81 – 8.18)

10.60

(8.13 – 13.98)

5.84 10.2

Mean for 

Hive 1-5

1.88

(<1.0 – 3.77)

3.53

(1.11 – 7.59)

5.15

(3.23 – 6.25)

9.72

(6.96 – 11.63)

6.21 9.39

1 “N” is the total number of samples collected

2 “Total IMI” combines magnitude of residues of imidacloprid plus degradates IMI-olefin and IMI-5-OH

CONCLUSION TO OPEN FIELD TRIAL

The second trial, also at the LREC, consisted of an open field area with multiple citrus varieties. A very 

large contiguous area of citrus had been treated in 2009 with various imidacloprid commercial 

formulations at 0.25 lbs. a.i./acre (half the maximum label rate).

Five large 10-frame colonies were situated in the citrus orchard area. Pollen was successfully collected 

from only two of five hives via pollen traps that were operated for 24 hours. Nectar was either hand 

collected from randomly selected citrus trees, extracted from honey stomachs of honey bees allowed to 

forage in the treated orchard and intercepted at the hive, and from the hive as uncapped honey. Nectar 

sugar analysis was measured by refractometry.

In this trial, the mean residues of total imidacloprid in hand collected citrus nectar ranged from 1.81-

9.42 ppb while the mean residues in nectar extracted from foraging honey bees ranged from 1.11-7.59 

ppb. Also, the mean residues of total imidacloprid in hive stored nectar ranged from 6.95-11.63 ppb. 
MRID 49090504 CDPR IMI Citrus (2011)

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Moreover, the maximum mean residues for hive pollen were found to be 10.2 ppb while the average 

residue measurement was 9.39 ppb. 

8C. TRIAL INFORMATION

Title: One Year Nectar Collections

Application Date: September 3 and 9, 2009 Sampling Date: Spring 2010

Section of Study: Section 4 Trial Location:

Lindcove Research and 

Extension Center (LREC)

and Bakersfield, CA

TRIAL SUMMARY

As research into the potential uses of imidacloprid for the management of Asian Citrus Psylliid 

(Diaphorina citri), different imidacloprid rates at several locations within the citrus producing areas of 

southern and central California were evaluated. Nectar from trees treated with either the maximum

label rate (1X) or double the maximum label rate (2X) of imidacloprid (Admire Pro) were evaluated to 

determine whether there was a relationship between application rates and residue levels. For this 

component of the trial, all data were derived from analysis of hand-collected nectar. 

METHOD

APPLICATION TIMING AND RATES

The treatments were applied by water can on September 3, 2009 and September 8, 2009 at the LREC 

and Bakersfield sites, respectively. Citrus trees were treated with Admire Pro at the maximum label rate 

(1X=14 fl oz/ acre) and double the maximum label rate (2X= 28 fl oz/acre) in the Fall of 2009. Residues of 

imidacloprid, 5-hydroxy imidacloprid, and imidacloprid olefin were then analyzed from hand-collected 

nectar samples.

STUDY SITE LOCATION AND CHARACTERISTICS 

For this trial, Lindcove Research and Extension Center (LREC) and a commercial citrus farm in Bakersfield 

were used to collect data from. The LREC trees were in the same block of navel oranges that were used 

for the honey bee trial. At the commercial citrus farm in Bakersfield, a 3.9 acre block of Valencia oranges 

that were planted in 1985 were provided. There were 100 trees per acre compared to the 134 trees 

were acre at the LREC site. The LREC has soils classified as loam soil (15-25% clay, 0.5-1% organic 

matter). Soil characteristics were not provided in the study for Bakersfield.

RESULTS:

The 1X label rate treatments resulted in an average residue measurement of 19.30 ppb in nectar at the 

Bakersfield grove and 16.30 ppb at the LREC. While the 2X label rate treatments resulted in an average 

residue measurement of 47.36 ppb at the Bakersfield grove and 35.83 ppb at the LREC.
MRID 49090504 CDPR IMI Citrus (2011)

11

Residues of imidacloprid, 5-hydroxy Imidacloprid and imidacloprid olefin were higher in nectar sampled 

from the trees treated with the 2X label rate compared with the 1X label rate, with the ca. twofold 

difference in residue levels reflecting the twofold difference in application rates. The imidacloprid and 

total residues were lower at the LREC site. The most likely reason for this difference is the higher tree 

density at the LREC site. Since the insecticide was applied on a per acre basis (1X=14 fl oz./acrea and 2X=28 

fl oz./acre), the amount of active ingredient per tree would have been higher at the Bakersfield site and 

this could, therefore, account for the higher residues in the nectar. 

Table 4. Summary of imidacloprid residues in hand collected nectar resulting from a soil treatment at 

maximum label rate (1X) and twice maximum label rate (2X). Application made by watering can to 

individual trees in Bakersfield on 9/8/2009 and LREC on 9/3/09.

Spring 2010

Mean Residue Concentration (ppb)

(minimum – maximum)

Location

Citrus Variety

Rate Hand Collected Nectar (N1 = 10)

IMI 5-OH Olefin Total IMI2

Bakersfield

Valencia Oranges

(soil type unknown)

1X 12.13

(3.62 – 18.82)

2.53

(1.10 – 3.61)

4.64

(1.58 – 6.93)

19.30

(6.30 – 29.10)

2X 31.10

(9.70 – 92.05)

5.67

(1.88 – 15.95)

10.60

(3.12 – 31.15)

47.36

(14.70 – 139.15)

LREC

Navel Oranges

[Loam Soil]

1X 9.51

(3.31 – 15.49)

3.09

(1.18 – 5.39)

3.70

(1.56 – 6.04)

16.30

(6.81 – 26.45)

2X 22.23

(5.98 – 43.94)

6.70

(2.25 – 11.74)

6.89

(1.70 – 13.06)

35.82

(9.93 – 68.30) 1 “N” is the total number of samples collected

2 “Total IMI” combines magnitude of residues of imidacloprid plus degradates IMI-olefin and IMI-5-OH.

CONCLUSION TO ONE YEAR NECTAR COLLECTIONS

The third trial was conducted at the LREC and a commercial citrus farm in Bakersfield, CA. Navel oranges 

(LREC) and Valencia oranges (Bakersfield) were treated with either 1X (the maximum label rate) or 2X the 

label rate in Fall 2009. Hand collected nectar was quantified in Spring 2010.

Residues of imidacloprid, 5-hydroxy Imidacloprid and imidacloprid olefin were higher in nectar sampled 

from the trees treated with the 2X label rate compared with the 1X label rate, with the ca. twofold 

difference in residue levels reflecting the twofold difference in application rates
MRID 49090504 CDPR IMI Citrus (2011)

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8D. TRIAL INFORMATION

Title: Citrus Nectar Collected from Field Sites Treated in Successive Years

Application Years: 2008 & 2009 Sampling

Date: Spring 2010

Section of Study: Section 5 Trial Location:

1) Hemet, California

2) Temecula, California 

3) Lindcove Research and 

Extension Center (LREC)

TRIAL SUMMARY

The objective of this trial was to determine if imidacloprid residues in nectar could persist and/or 

accumulate in situations where the insecticide was used on the same trees in successive years. Residues 

in nectar sampled from citrus trees that had been treated in 2 successive years were quantified. Sites 

were chosen with different soil types for the sampling program. Imidacloprid uptake into trees can be 

affected by soil type and this could potentially affect the residues in nectar. All analyses were conducted 

on nectar that was extracted by hand. 

METHOD

APPLICATION TIMING AND RATES

Hemet. The first treatments with Admire Pro were applied in Fall 2008 and the second treatments were 

applied in Fall 2009. The intent was to evaluate both the 1X label rate and the 2X label rate in all 

possible application sequences. In order to do this, the block was subdivided into four 2.5 acre plots so 

that the following sequences of treatments could be established: 1X (Fall 2008) followed by 1X (Fall 

2009), 1X (Fall 20.08) followed by 2X (Fall 2009), 2X (Fall 2008) followed by 1X (Fall 2009), and 2X (Fall 

2008) followed by 2X (Fall 2009). Nectar Samples were taken from trees chosen at random from within 

each plot.

Temecula. Six commercial orchards in Temecula, California that had been treated both years of 2008 

and 2009 in an area-wide control program were used in this study. The sites consisted of five Grapefruit 

and one Valencia orange orchard, which were first treated between June 7 and June 16, 2008 and then 

treated a second time between April 7 and May 27, 2009. The maximum label rate (1X) for Admire Pro 

was used in both treatment years.

Lindcove Research and Extension Center. Five citrus blocks at the LREC had been treated with 

imidacloprid for two successive years (2008 and 2009). The sites consisted of four navel oranges and one 

Valencia orange orchard, which were first treated on September 17 and September 18, 2008 and then 

treated a second time between September 10 and September 16, 2009. The maximum label rate (1X) for 

Admire Pro was used in both treatment years.

STUDY SITE LOCATION AND CHARACTERISTICS 
MRID 49090504 CDPR IMI Citrus (2011)

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Hemet. The trial was conducted in a 10 acre block of 50 year old Ruby Red Grapefruit trees on Troyer 

Rootstock. Soil type was sandy loam and irrigation was scheduled weekly according to tensiometer 

measurements. Nectar samples were collected from treated trees at random within the commercial 

grapefruit orchard.

Temecula. A total of 68.25 acres of Star Ruby Grapefruit and 1.65 acres of Valencia oranges were treated 

with imidacloprid for two successive years. The soil type at all six site locations is considered to be Sandy 

Loam. At each site, two trees were randomly selected for hand-collected nectar sampling.

Lindcove Research and Extension Center. Five citrus blocks with 2 successive years of imidacloprid 

applications were chosen from the LREC. These blocks were independent from the block used for the 

tunnel study. The soil type at all five site locations is considered to be Loam Soil. A total of 15.44 acres of 

navel oranges and 2.5 acres of Valencia oranges were treated with imidacloprid. Within each block, 2 

trees were randomly selected for hand-collected nectar sampling.

RESULTS:

Imidacloprid nectar residues in Hemet were lowest in the 1X – 1X label rate treatment with an average 

residue measurement of 23.84 ppb and highest in the 2X – 2X label rate treatment with an average 

residue measurement of 58.66 ppb. Following the 1X – 1X label rate treatments in two successive years 

at Temecula and LREC, an average residue measurement of the nectar residues were 5.15 ppb and 11.16 

ppb, respectively. The maximum mean residues of 21.65 ppb were measured at LREC.

The imidacloprid and total residues measured in the nectar sampled from trees treated with the 1X-2X 

label rate sequence were approximately 2-fold higher than those measured for the 1X- 1X label rate 

treatments, suggesting that the residue levels reflected the rate of imidacloprid used in the most recent 

application. Thus, residues for the 1X- 1X and 2X-1X rate sequences were not significantly different, and 

data for the 1X-2X and 2X-2X rate sequences were not significantly different. While the means for the 2X 

treatments exceeded the 1X measurements by more than twofold, the statistical analysis shows that 

imidacloprid and its metabolites did not accumulate significantly from one year to the next.

Data from six commercial groves in Temecula that were treated in two successive years (2008 and 2009) 

with the maximum label rate of imidacloprid (1X-1X) were completed by June each year. The highest 

total residues (9.56 ppb and 15.53 ppb for the two trees sampled) were measured at Site 6, where the 

youngest trees (seven years of age) used in the sampling program was located. The overall means for 

the Temecula samples were lower than those measured for the Hemet site where the 1X rate was 

applied for two successive years.

Data from five blocks at the LREC that were treated in two successive years (2008 and 2009) with the 

label rate of imidacloprid (1X-1X) had higher residues than those measured at the Temecula site, 

possibly reflecting the later timing of treatments. Despite the higher values at the LREC site, the residues 

were still lower than those measured for trees at Hemet. The major difference between the LREC and 

Hemet sites is the soil type and it seems that the lighter and sandier soil at Hemet allowed better uptake 

of imidacloprid into the trees resulting in higher residues in nectar the following spring.
MRID 49090504 CDPR IMI Citrus (2011)

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Table 5. Summary of imidacloprid residues in hand collected nectar of Ruby Red grapefruit trees resulting 

from two successive year soil treatments at maximum label rate (1X) and twice maximum label rate (2X) 

in Fall 2008/Fall 2009.

Hemet Site

Spring 2010

[Sandy Loam]

Mean Residue Concentration (ppb)

(minimum – maximum)

Rate Hand Collected Nectar

N IMI 5-OH Olefin Total IMI2

1X – 1X 10 16.07

(9.88 – 25.67)

5.05

(3.62 – 6.43)

2.72

(1.57 – 4.00)

23.84

(15.57 – 35.47)

1X – 2X 9 35.13

(13.28 – 63.60)

9.70

(6.70 – 12.33)

6.04

(3.77 – 9.31)

50.87

(27.54 – 85.03)

2X – 1X 7 14.50

(11.77 – 22.66)

4.78

(3.63 – 7.49)

2.44

(1.73 – 3.66)

21.73

(17.62 – 33.81)

2X – 2X 7 41.41

(28.62 – 62.67)

10.78

(7.14 – 13.56)

6.47

(4.38 – 10.48)

58.67

(40.14 – 86.71) 1 “N” is the total number of samples collected

2 “Total IMI” combines magnitude of residues of imidacloprid plus degradates IMI-olefin and IMI-5-OH.

Table 6. Summary of imidacloprid residues in hand collected nectar sampled in Spring 2010 from citrus 

trees receiving a soil treatment at maximum label rate (1X) in successive years 2008 and 2009.

Spring 2010

Mean Residue Concentration (ppb)

(minimum – maximum)

Sampling occurred 4/2010

Location Rate N1 Hand Collected Nectar

IMI 5-OH Olefin Total IMI2

Temecula 1X – 1X 11 3.17

(<1.0 – 10.60)

<1.0

(<1.0 – 1.18)

1.48

(<1.0 – 3.76)

5.15

(<1.0 – 15.54)

LREC 1X – 1X 9 6.51

(<1.0 – 13.65)

1.80

(<1.0 – 5.40)

2.86

(<1.0 – 8.42)

11.17

(1.53 – 21.64) 1 “N” is the total number of samples collected

2 “Total IMI” combines magnitude of residues of imidacloprid plus degradates IMI-5-OH and IMI-olefin

CONCLUSION FOR FIELD SITES TREATED IN SUCCESSIVE YEARS

The fourth trial was conducted to determine if imidacloprid residues in nectar could accumulate from year 

to year following successive year applications at three different locations (Hemet, Temecula, and LREC). 

Hand collected nectar samples were obtained with either 1X or 2X soil applications were made in two 

successive years (2008, 2009) prior to sampling during bloom 2010.

Imidacloprid residues at the Hemet site appear to be a function of the rate applied at the most recent 

application only, with no evidence of carryover from previous years. The overall means for the Temecula 

samples were lower than those measured for the Hemet site where the 1X rate was applied for two 

successive years. Data from five blocks at the LREC that were treated in two successive years (2008 and 

2009) with the label rate of imidacloprid (1X-1X) had higher residues than those measured at the 
MRID 49090504 CDPR IMI Citrus (2011)

15

Temecula site, possibly reflecting the later timing of treatments. Despite the higher values at the LREC 

site, the residues were still lower than those measured for trees at Hemet. The major difference 

between the LREC and Hemet sites is the soil type and it seems that the lighter and sandier soil at 

Hemet allowed better uptake of imidacloprid into the trees resulting in higher residues in nectar the 

following spring.

8E. TRIAL INFORMATION

Title: Citrus Nectar Collection from Field Sites Treated in Successive Years

Application Years: 2008, 2009 and 2010 Sampling

Date: Spring 2011

Section of Study: Appendix B 

(Supplemental)

Trial 

Location:

1) Tulare County, California 

2) Temecula, California

3) Lindcove Research and 

Extension Center (LREC) 

4) Ventura County, California

5) University of California, 

Riverside

6) Hemet, California

TRIAL SUMMARY

The objective of this trial was to determine if residues of imidacloprid and its important metabolites 

could persist and/or accumulate in nectar in situations where the insecticide was used on the same 

trees in successive years. Also, because imidacloprid uptake into trees can be affected by soil type, sites 

were chosen to reflect the variety of soil types where citrus is gown in California. In section 3 of this 

Data Evaluation Report, data and information was provided for several sites where citrus was grown in 

soils that ranged from sandy loam to loam. To expand on the previous trial, this study will include data 

and information on heavier clay soils and lighter soils. Nectar was extracted from flowers by hand at all 

sites during bloom and imidacloprid, imidacloprid olefin and 5-hydroxy imidacloprid were quantified by 

LC/MS/MS. 

METHOD

APPLICATION TIMING AND RATES

Tulare County. Five of the citrus sites had been treated with the full label rate of imidacloprid for at least 

3 previous years. The sixth citrus site was treated with the full label rate of imidacloprid for 2 successive 

years. Two composite nectar samples were collected from each grove and all nectar samples were handcollected.

Temecula Valley. Nectar samples were hand-collected from six groves where the trees have been 

treated for three successive years with the full label rate of imidacloprid. 

Lindcove Research and Extension Center. Nectar samples were hand-collected from five citrus blocks at 

the LREC that had been treated with the full label rate of imidacloprid for three successive years 

(September 2008, 2009, and 2010). 
MRID 49090504 CDPR IMI Citrus (2011)

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Ventura County. Nectar samples were hand-collected from a lemon grove where the trees had been 

treated with the full label rate of imidacloprid at different timings during the season. The treatment 

timings were in May, July and September of 2010. The subject grove had not been treated in 2009. Two 

composite nectar samples were collected from trees treated at application timing 1 and 3, while one 

composite nectar sample was collected from trees treated at application 2.

University of California, Riverside. In October of 2010, nectar samples were collected from a citrus block 

where the trees had been treated with the full label rate of imidacloprid. Sixteen composite samples 

were collected from the trees. 

Hemet. In the previous trial titled “Citrus Nectar Collected from Field Sites Treated in Successive Years” 

(Section 5 of study report), data was provided for a grapefruit grove that had been treated in successive 

years (Fall 2008 nad Fall 2009) with different combinations of application rates. The initial trial began 

with either a 1X label rate of imidacloprid (Admire Pro at 14 fl oz/ acre) or a 2X label rate (Admire Pro at 

28 fl oz/ acrea). In 2009, the same trees were treateed to give different treatment rate scenarios. To 

expand on the subject trial, an additional year of treatment was provided to the trees in 2010. 

STUDY SITE LOCATION AND CHARACTERISTICS 

Table 7. Site location with information regarding soil type and treated commodity. 

SITE AND COMMODITY INFORMATION

TEMELCULA SOIL TYPE COMMODITY

1 FALLBROCK ROCKY SANDY LOAM STAR RUBY GRAPEFRUIT 

2 FALLBROCK ROCKY SANDY LOAM STAR RUBY GRAPEFRUIT

3 FALLBROCK ROCKY SANDY LOAM VALENCIA ORANGE

4 FALLBROCK ROCKY SANDY LOAM STAR RUBY GRAPEFRUIT

5 FALLBROCK ROCKY SANDY LOAM STAR RUBY GRAPEFRUIT

6 GREENFIELD SANDY LOAM STAR RUBY GRAPEFRUIT

TULARE COUNTY

1 PORTERVILLE CLAY TANGELOS

2 CENTERVILLE CLAY NAVEL ORANGES

3 PORTERVILLE CLAY NAVEL ORANGES

4 PORTERVILLE CLAY NAVEL ORANGES

5 PORTERVILLE CLAY NAVEL ORANGES

6 PORTERVILLE CLAY VALENCIA ORANGES

OTHER SITES

LINDCOVE RESEARCH AND EXTENSION 

CENTER

SAN JOAQUIN LOAM NAVEL AND VALENCIA ORANGES

UNIVERSITY OF CALIFORNIA,

RIVERSIDE

ARLINGTON LOAM VALENCIA ORANGES 

VENTURA COUNTY MOCHO LOAM LEMON

RESULTS:

Total mean residues in nectar of imidacloprid from trees treated three years in a row at the Temecula 

site ranged from 1.02 to 5.91 ppb with an average residue measurement of 2.57 ppb. Mean nectar

residues from Tulare County ranged from 0.29 to 4.21 ppb with an average residue measurement of 
MRID 49090504 CDPR IMI Citrus (2011)

17

1.54 ppb. Total mean nectar residues from trees at the LREC with a loam soil ranged from 0.52 to 23.95 

ppb with an average residue measurement of 4.55 ppb. Total mean nectar residues from the UCR site 

with a loam soil ranged from 0.83 to 13.88 ppb with an average residue measurement of 3.68 ppb.

Imidacloprid nectar residues from Ventura County sites treated at various times during 2010 were all

less than 1 ppb regardless of the application timing. Following three years of treatments at the Hemet 

site at various application rates, the average residue measurement in nectar for the 1X-1X-1X treatment 

regimen was 24.40 ppb. The average residue measurement following the third year of treatment for

sites treated once per year with 2X the label rate (2X-2X-2X) was 44.81 ppb. For the 1X-2X-0X and 2X-1X0X treatments the average residue measurement was 31.67 and 32.97 ppb. The residues following three 

years of applications at 2X the maximum label rate were slightly lower than residues after just two 

years.

Table 8. Summary of imidacloprid residues in hand collected nectar sampled in Spring 2011 from citrus 

trees receiving a soil treatment at maximum label rate (1X) in successive years 2008, 2009, and 2010.

Spring 2011

Mean Residue Concentration (ppb)

(minimum – maximum)

Location Rate N1 Hand Collected Nectar

IMI 5-OH Olefin Total IMI2

Temecula 1X – 1X – 1X 12 1.68

(<1.0 – 3.48) <1.0 <1.0(<1.0 – 1.62)

2.58

(1.01 – 5.91)

LREC 1X – 1X – 1X 10 3.50

(<1.0 – 16.87)

<1.0

(<1.0 – 3.88)

<1.0

(<1.0 – 3.20)

4.95

(<1.0 – 23.95) 1 “N” is the total number of samples collected

2 “Total IMI” combines magnitude of residues of imidacloprid plus degradates IMI-olefin and IMI-5-OH

Table 9. Supplement to Table E-10. Summary of imidacloprid residues in hand collected nectar resulting 

from successive year soil treatments at maximum label rate (1X), twice maximum label rate (2X), and no 

application (0X) in Fall 2008/Fall 2009/Fall 2010.

Hemet Site

Spring 2011

[Sandy Loam]

Mean Residue Concentration (ppb)

(minimum – maximum)

Rate Hand Collected Nectar (N1 = 10)

IMI 5-OH Olefin Total IMI2

1X – 1X – 1X 19.68

(12.26 – 33.82)

3.13

(2.02 – 4.31)

1.59

(<1.0 – 4.96)

24.40

(17.56 – 39.86)

1X – 2X – 0X 26.01

(23.05 – 30.00)

3.93

(3.35 – 4.37)

1.73

(1.44 – 1.92)

31.67

(28.97 – 36.27)

2X – 1X – 0X 27.02

(20.01 – 33.45)

3.87

(2.28 – 5.43)

2.08

(1.51 – 3.11)

32.97

(25.12 – 41.99)

2X – 2X – 2X 36.86

(26.67 – 41.92)

5.18

(3.86 – 5.76)

2.77

(2.27 – 3.16)

44.81

(32.80 – 50.35) 1 “N” is the total number of samples collected

2 “Total IMI” combines magnitude of residues of imidacloprid plus degradates IMI-olefin and IMI-5-OH
MRID 49090504 CDPR IMI Citrus (2011)

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Table 10. Information on trees used for hand collected nectar collected from six commercial orchards in 

Tulare County during bloom in Spring 2011 after three successive years of imidacloprid application for 

control of glassy-winged sharpshooter 2008, 2009, 2010.

Tulare County

[Porterville Clay – 40% clay]

Spring 2011

Site Citrus Variety

2008

Treatment

Date

2009

Treatment

Date

2010

Treatment

Date

1 Tangelos Not treated 6/16/2009 5/21/2010

2 Navel Oranges 5/22/2008 6/29/2009 6/18/2010

3 Navel Oranges 7/8/2008 6/18/2009 6/9/2010

4 Navel Oranges 5/17/2008 6/18/2009 6/6/2010

5 Navel Oranges 5/21/2008 6/29/2009 6/15/2010

6 Valencia Oranges 7/3/2008 6/26/2009 6/16/2010

Table 11. Information on trees used for hand collected nectar collections during bloom in Spring 2011 

after three successive years of imidacloprid application at the label rate 2008, 2009, 2010.

Temecula

[Sandy Loam]

Spring 2011

Site Citrus Variety

2008

Treatment

Date

2009

Treatment

Date

2010

Treatment

Date

1 Star Ruby Grapefruit 6/7/2008 5/27/2009 5/22/10

2 Star Ruby Grapefruit 6/9/2008 4/13/2009 6/11/10

3 Valencia Orange 6/6/2008 4/7/2009 6/12/10

4 Star Ruby Grapefruit 6/9/2008 4/21/2009 5/17/10

5 Star Ruby Grapefruit 6/7/2008 4/10/2009 6/2/10

6 Star Ruby Grapefruit 6/16/2008 4/17/2009 5/14/10

LREC

[Loam Soil]

Spring 2011

Site Citrus Variety

2008

Treatment

Date

2009

Treatment

Date

2010

Treatment

Date

1 Atwood Navel 9/18/2008 9/10/2009 9/13/2010

2 Atwood Navel 9/17/2008 9/10/2009 9/10/2010

3 Caracara Navel 9/18/2008 9/16/2009 9/09/2010

4 Parent Navel 9/18/2008 9/16/2009 9/09/2010

5 Red Valencia 9/17/2008 9/14/2009 9/13/2010
MRID 49090504 CDPR IMI Citrus (2011)

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Table 12. Summary of imidacloprid residues in hand collected nectar sampled in Spring 2011 from citrus 

trees receiving a soil treatment at maximum labelled rate as part of the area side control program for 

glassy-winged sharpshooter in successive years 2008, 2009 and 2010.

Spring 2011

Mean Residue Concentration (ppb)

(minimum – maximum)

Location Rate N1

Hand Collected Nectar

IMI 4/5-OH Olefin Total IMI2

Tulare County 1X3 – 1X – 1X 12

1.29

(<1.0 – 3.31)

<1.0 <1.0 1.70

(<1.0 – 4.21) 1 “N” is the total number of samples collected

2 “Total IMI” combines magnitude of residues of imidacloprid plus IMI-olefin and IMI-5-OH 3 One site did not receive an application in 2008.

CONCLUSION 

In 2011, the researchers followed up with a third year of treatments at the Temecula, LREC, and Hemet 

sampling sites. Nectar was again collected from six groves previously treated in Temecula where the soil 

type is sandy loam and five citrus blocks at the LREC with a loam soil (20% clay).

In addition, sites were added at University of California, Riverside (UCR), Ventura County and Tulare 

County to address different soil types not previously represented. Nectar was collected from six citrus 

groves in Tulare County grown in Porterville clay (clay content 40%). Of these six sites, five had been 

treated with 1X imidacloprid for the past three years and the remaining site was treated similarly the 

past two years. A new site in Ventura County with a soil consisting of 23% clay/35% sand was sampled 

following applications at the full label rate of imidacloprid at different times during the season. The 

treatment timings for this site were May, July and September 2010 and untreated in 2009. Also, a citrus 

block from the farm at UCR, where the soil type is loam, was treated in October 2010 and sampled in 

2011.

In Temecula and Tulare County, the 2010 treatments at the 1X label rate were made in mid-May to midJune. The LREC and UCR 2010 treatments at 1X label rate were made in September and October. 

Treatments at the four Hemet sites were 1X-1X-1X, 1X-2X-0X, 2X-1X-0X, or 2X-2X-2X representing years 

2008, 2009 and 2010, where 1X-1X-1X represents a single application at the maximum label rate per 

year for three consecutive years.

9. STUDY VALIDITY/CLASSIFICATION AND STUDY LIMITATIONS 

Classification/Utility for Bee Risk Assessment. This study is classified as supplemental for use in risk 

assessment due to no pollen data available and a potential underestimation of a worst case scenario 

due to current labels not restricting pre bloom and during bloom applications whereas this study done 

post bloom. The study results characterize expected imidacloprid residues in citrus nectar from 

applications in various soils ranging from fine to coarse and following different application rates and 
MRID 49090504 CDPR IMI Citrus (2011)

20

application timing in California. These results may not extrapolate directly to expected results in other 

regions of the U.S.

Concentrations in nectar extracted from the stomachs of free-ranging bees (open field study) were 

somewhat lower than samples collected directly from flowers of nearby trees. This may reflect a 

"dilution effect" from bees foraging on other (untreated) flower types. The few pollen samples obtained 

during the open field study had imidacloprid concentrations roughly equal to the nectar sampled from 

the same hives. Concentrations in flower nectar samples appear to be linearly related to the application 

rate, based on ca. twofold increases in residue levels with doubling the application rate in the Hemet 

trials.

Temporal Variability in Residues. Nectar samples were obtained from two locations (citrus blocks in the 

Temecula region and at LREC) where the 1X soil application rate of imidacloprid had been made in two 

successive years (2008, 2009) prior to sampling in April 2010. Residue levels at these 11 sites averaged 

8 ppb and ranged from 1 to 18 ppb. The application timing (May, July, September, October) appears to 

be an important factor in determining residue levels in flower nectar the following year particularly for 

sites planted to coarse soils which consistently yielded the higher imidacloprid residues. Fall (Sept) 

applications resulted in about twofold higher residue concentrations than spring (April-June) 

applications.

Spatial Variability in Residues. The six locations for the citrus trials were in relatively close proximity. 

Soil types reflect sandy loam, loam or clay compositions (20-40% clay) and low organic carbon content 

(0.35-1.9%). Weather conditions (temperature and precipitation) were similar across the three trials. As 

a result of the close proximity of trial sites, this study provides very limited information on how 

differences in environmental conditions across different areas of the U.S. may affect accumulation of 

total imidacloprid in pollen and nectar.

Pesticide Carryover. The authors speculated that imidacloprid residues at the Hemet site appear to be a 

function of the rate applied at the most recent application only, with no evidence of carryover from 

previous years. However, following the third year of application at the Hemet site, residues were higher

at the two sites receiving no treatment in 2010 than at the site treated all three years with 1X. This 

indicates some degree of carryover from previous application years, at least for sites treated with the 2X 

rate during one of the two years prior to the no treatment year. This was the only site where samples 

were collected following a year without treatment.