ArticlePDF Available

Uptake, translocation and metabolism of imidacloprid in plants

Authors:
  • Bayer AG

Abstract and Figures

The insecticide imidacloprid is mainly applied as a seed dressing formulation. After root uptake, imidacloprid is translocated ac-ropetally within the xylem and degraded quickly in the plants. Three principal metabolic pathways have been identified in various plant metabolism studies with different crops and types of application showing a nearly uniform quantitative and qualitative pat-tern in all test systems.
Content may be subject to copyright.
Bulletin of Insectology 56 (1): 35-40, 2003
ISSN 1721-8861
Uptake, translocation and metabolism of
imidacloprid in plants
Robin SUR, Andreas STORK
Bayer CropScience AG, Metabolism/Environmental Fate, Monheim, Germany
Abstract
The insecticide imidacloprid is mainly applied as a seed dressing formulation. After root uptake, imidacloprid is translocated ac-
ropetally within the xylem and degraded quickly in the plants. Three principal metabolic pathways have been identified in various
plant metabolism studies with different crops and types of application showing a nearly uniform quantitative and qualitative pat-
tern in all test systems.
Key words: imidacloprid, metabolism, nectar, pollen, residue analysis, sunflower, translocation, uptake.
Introduction
Imidacloprid is the first commercially available repre-
sentative of a new chemical class, the chloronicotinyl or
neonicotinoid insecticides. It was synthesized in 1985 and
the first registration was achieved in France (1991) in
sugar beet. It is a systemic broad-spectrum insecticide
and acts as a contact and stomach poison against sucking
and some biting insects (rice hoppers, aphids, thrips,
whitefly, termites etc.). It can be applied for seed, soil or
foliar treatment. The molecule exhibits a novel mode of
action as it is an agonist of the nicotinic acetylcholine re-
ceptor leading to paralysis and death of pest organisms
(Bai et al., 1991; Nauen et al., 1998; Schmuck et al.,
2003). The mammalian toxicity is about 700-fold lower
than that of nicotine having a similar chemical structure
and the same mode of action (Elbert et al., 1998).
Experiments have been carried out to determine up-
take, translocation and metabolic pathways of imidaclo-
prid after different types of application (foliar, soil and
seed treatment, stem injection, painting application) on
various plant species including apples (Vogeler et al.,
1992), corn (Vogeler and Dräger, 1989), cotton (Voge-
ler and Brauner, 1993), eggplant (Yoshida, 1992), hop
(Reckmann, 1998), potatoes (Dräger et al., 1992; Vo-
geler et al., 1991), rape (Clark, 1997), rice (Kurogochi
and Araki, 1989; Kurogochi et al., 1989; Sakamoto,
1991), sunflower (Stork, 1999; Schmuck et al., 2001),
tobacco (Clark and Brauner, 1994), tomatoes (Dräger et
al., 1989), wheat and sugar beet (Stein-Dönecke et al.,
1989). In addition, the behaviour in cell suspension
cultures (Köster et al., 1988; Köster, 1990) and rota-
tional crops (Vogeler et al., 1992) was investigated.
The objective of these investigations was to determine
the nature of the residue in different crops and crop
parts and to set up a uniform residue definition for all
crops as a basis for succeeding pre-registration residue
studies as well as for post-registration residue enforce-
ment and monitoring purposes.
Materials and methods
As this article reviews a lot of metabolism studies per-
formed with imidacloprid over a span of a decade, only
general information about the used instrumentation,
equipment and materials is given. During that time and
depending on crop, nature of the residues and author
different types of instrumentation and analytical proce-
dures may have been applied. A more detailed insight
can be taken from the individual studies cited above.
Radioactively labelled [methylene-14C]imidacloprid
was applied mainly as a spray, seed dressing or granular
formulation in all greenhouse trials. The use of a 14C-
labelled active substance (a.s.) allowed very sensitive
and selective analyses. Certified non-radiolabelled com-
pounds were used as reference substances for metabolite
identification by co-chromatography. Extraction of plant
samples was performed with different solvents or sol-
vent mixtures, containing methanol, acetone, acetoni-
trile, ethyl acetate or water. Radioactivity in extract so-
lutions and solid samples was determined by liquid
scintillation counting (LSC) and combustion/LSC, re-
spectively. For separation, detection and quantitation of
parent compound and metabolites within extracts, thin-
layer chromatography (TLC) in combination with a Bio-
Imaging Analyser or high-performance liquid chroma-
tography (HPLC) with a radioactivity flow-through de-
tector were used. Where identification with reference
compounds was not possible, isolation, purification and
subsequent structure elucidation was performed by
means of mass and/or nuclear magnetic resonance
spectroscopy.
Results and discussion
Following seed dressing or granular application of
imidacloprid on cotton, eggplant, potato and rice, uptake
of the applied activity ranged from 1.6 to 4.9% (Kuro-
gochi et al., 1989; Sakamoto, 1991; Vogeler and
Brauner, 1993; Vogeler et al., 1991; Yoshida, 1992; Ku-
rogochi and Araki, 1989). After seed treatment of corn
the uptake amounted to 20% (Vogeler and Dräger,
1989). The ratio of the activity in the reproductive or-
gans compared to the activity of the whole plant was
very low in corn, cotton, eggplant and rice ranging from
36
0.7 to 1.4%; in potato this ratio amounted to 12% (table
1).
Uptake and translocation have also been studied after
spray application of imidacloprid 25 WP on apple and
tomato (Vogeler et al, 1992; Dräger et al., 1989). Four-
teen days after the treatment of apple and tomato fruits
28 and 21% of the applied activity, respectively, was
recovered in or on the fruits; between 65 and 76% of
this recovered activity was located on the surface of the
fruits (table 2). In additional translocation experiments
the a.s. was applied only onto apple and tomato leaves,
while the fruits were covered with plastic foil during the
application to prevent contamination. At harvest, 14
days later, the amount of radioactivity in the fruit com-
pared to the activity applied was 0.1% at maximum
(Vogeler et al., 1992; Dräger et al., 1989).
Table 1. Uptake, distribution and main metabolites of imidacloprid after soil application/seed treatment (TRR: total
radioactive residue, 6-CNA: 6-chloronicotinic acid, 6-CPA: 6-chloropicolyl alcohol, *Nitrosimine<<1% of TRR in
reproductive organs).
Crop
Harvest
[days after treat-
ment/seeding]
Uptake of
applied
activity [%]
Activity in reprod. organ
relative to the activity in
whole plant [%]
Nature of the Residue
(Compounds >1% of TRR)
Corn 134 20 1.2
Imidacloprid, Guanidine, 5-Hydroxy,
Olefine, Nitrosimine*, Ring-open-
guanidine, 6-CNA, 6-CPA, Dihydroxy
Cotton 211 4.9 1.4
6-CPA-conj., Guanidine, 6-CPA-
Glucoside, Imidacloprid, 6-CNA, 6-
CPA, Olefine, Nitrosimine*
Eggplant 69 1.6 1.0 Guanidine, Imidacloprid, , 6-CPA-
Glucoside, 5-Hydroxy, Olefine, 6-CNA
Potato 129 2.5 12
Imidacloprid, 6-CNA, Guanidine, 5-
Hydroxy, Olefine, Nitrosimine*, 6-
CPA-Glucoside
Rice 79 4.5 1.1 Guanidine, Imidacloprid, 6-CNA, 5-
Hydroxy, Nitrosimine*
Rice 124 4.4 0.7 Guanidine, Imidacloprid, 5-Hydroxy, 6-
CNA, Olefine
Table 2. Uptake and main metabolites after spray application of imidacloprid.
Crop Harvest [days after
treatment]
Uptake of applied
activity [%]
% TRR
on surface
Nature of the Residue
(Compounds >1% of TRR)
Apple fruit 14 28 65 Imidacloprid, Olefine, 5-Hydroxy, Gua-
nidine, 6-CPA-Glucoside, Urea, Dihydroxy
Tomato fruit 14 21 76 Imidacloprid, Guanidine, Urea, 5-Hydroxy
TRR: total radioactive residue
Table 3. Residues of imidacloprid, hydroxy- (4- and 5-hydroxy) and olefine-metabolites in nectar and pollen sam-
ples of corn, sunflower and summer rape (field trial results).
Crop Formulation Sample
Material Residues in treated and control samples [mg/kg]
Imidacloprid Hydroxy-metab. Olefine-metab.
Corn
1 trial (France)
WS 70
1 mg a.s./seed Pollen <<0.005 <<0.005 <<0.01
Sunflower
2 trials (Germany)
WS 70
0.7 mg a.s./seed
Nectar
Pollen
<<0.005
<<0.005
<<0.005
<<0.005
<<0.01
<<0.01
Summer Rape
3 trials
(France, Sweden, UK)
FS 500
0.04 mg a.s./seed
Nectar
Pollen
<<0.005
<<0.005
<<0.005
<<0.005
<<0.01
<<0.01
a.s.: active substance (=imidacloprid)
37
Translocation experiments examine the mobility and
distribution of chemical compounds within the vascu-
lar system and the tissues of plants. The results of
these experiments for imidacloprid with different ap-
plication types show, that there is a good acropetal
translocation of the a.s. to shoots and leaves (excellent
xylem mobility) on the one hand and on the other hand
a poor basipetal translocation to sinks, i.e. storage or-
gans, roots and fruits (negligible phloem mobility).
Consequently, highest residues are expected to occur
in the older leaf parts of the plants. The systemic prop-
erties of a molecule are a function of its physico-
chemical properties, mainly water solubility, octa-
nol/water-partition coefficient (log POW) and dissocia-
tion constant (pKa) determining e.g. its ability to
penetrate through biomembranes. These properties are
responsible for the kinetics of root uptake and translo-
cation into the xylem, which is a prerequisite for en-
tering the phloem and in turn to be taken up by suck-
ing insects. According to the BRIGGS model (Briggs et
al., 1982) the loading of the xylem by organic com-
pounds due to root-systemic uptake can be described
by a bell-shaped curve with maximum xylem mobility
between log POW of 1.0 and 2.5. As a measure of xy-
lem mobility the transpiration stream concentration
factor (TSCF) has been introduced relating the con-
centration of the compound in the transpiration stream
(xylem) to the exposure concentration. This model
predicts for imidacloprid with log POW = 0.51 a con-
siderable high xylem mobility of about TSCF = 0.6,
which was qualitatively confirmed in the translocation
experiments mentioned above.
Xylem and phloem have different pH values of about
5 and 8, respectively. Therefore, especially weak acids
with pKa values of about 5.0-5.5 and log POW between
1.0 and 2.5 (molecules with this lipophilicity properties
can cross membranes very easily), e.g. 6-chloronicotinic
acid, tend to accumulate in the phloem sieve tubes (ion
trap mechanism). Imidacloprid with its high pKa of 14 is
nonionized and therefore these pH differences do not
affect the distribution between the compartments and
the a.s. moves freely between phloem and xylem ac-
cording to its biomembrane permeability. However,
since there is no active loading of imidacloprid to the
phloem and due to the far greater water flow (50- to
100-fold) imidacloprid is predominantly transported
within the xylem vessels (Bromilow and Chamberlain,
1989). Once imidacloprid has entered the leaves it will
be trapped by this counter current principle in the leaf
and not re-transported into the plant stem.
Despite the wide variety of crops and application
types having been investigated a rather uniform picture
of the metabolic behaviour of imidacloprid in plants was
found consisting of three principal biotransformation
pathways (figures 1-3). Especially after soil application
or seed treatment a quick degradation of the a.s. was ob-
served after root uptake of the a.s. In the case of spray
application only a part of the a.s. is translocated into the
plant and metabolized there, so the degree of metabo-
lism tends to be lower in this case.
N
Cl
NNH
NNO2
N
Cl
NNH
NNO2
(OH)
OH
N
Cl
NNH
NNO2
OH OH
N
Cl
NNH
NNO2
5(4)-Hydroxy
4,5-Dihydroxy
Olefine
Imidacloprid
N
Cl
NNH
NNO2
O
conj.
5-Hydroxy-conjugate
Figure 1. Metabolism of imidacloprid (I): ethylene-bridge hydroxylation of the imidazolidine ring and elimination of
water.
38
N
Cl
NNH
NNO2
N
Cl
NNH
NNO N
Cl
NNH
NH
N
Cl
NNH
NNH2
N
Cl
N
HNH2
NH
N
Cl
N N
NN
O
N
Cl
NNH
O
Guanidine
Nitrosimine
Imidacloprid Ring-open-guanidine
Urea
Triazinone
Aminoguanidine
(Nitroguanidine)
Bound residues
Figure 2. Metabolism of imidacloprid (II): nitro-group reduction to nitrosimine and further loss of NO to form gua-
nidine.
N
Cl
NNH
NNO2
Imidacloprid
N
Cl
OH
N
Cl
OH
O
O
N
Cl
O
OH
OH OH
OH
O
OH
OH OH
OH
O
O
N
Cl
O
OH OH
OH
Bound residues
N
Cl
Oconj.
Glucoside Gentiobioside
6-Chloronicotinic acid
6-Chloropicolyl alcohol
(6-CPA) (6-CNA)
Figure 3. Metabolism of imidacloprid (III): Oxidative cleavage of the methylene bridge to form 6-chloropicolyl al-
cohol and subsequent oxidation to 6-chloronicotinic acid.
In figure 1 the ethylene-bridge hydroxylation at the
imidazolidine (dihydroimidazole) ring of the a.s. leads
to the formation of the hydroxy-metabolite, which
mainly undergoes a subsequent dehydration to form the
olefine-compound. Secondly, as depicted in figure 2, a
nitro-group reduction takes place to form the nitro-
simine compound. In a further step, after loss of the
NO-group the cyclic guanidine and urea metabolites are
formed. Starting with nitrosimine a cyclisation with en-
dogeneous pyruvic acid (created in respiration during
glycolysis) to the triazinone metabolite via a supposed
but not found aminoguanidine intermediate occurs.
However, minute amounts of this compound were found
only in potato leaves. Thirdly, imidacloprid is oxidized
to 6-chloropicolyl alcohol and in turn to 6-
chloronicotinic acid. In addition, alcohol conjugates
with glucose and isomaltose to glucopyranoside and
gentiobioside, respectively, are also formed (figure 3).
39
In the reproductive organs of seed-treated crop plants,
only very low amounts of imidacloprid metabolites
were detected. Based on the quantitative aspect the 5-
hydroxy-, olefine-, dihydroxy-, urea- and 6-CNA-
metabolite were most commonly found in these parts of
seed-dressed crop plants.
It has to be mentioned that the findings of the metabo-
lism and translocation experiments reflect worst-case
scenarios and that under practical field conditions lower
amounts of metabolites and a more rapid degradation
are observed. This is on the one hand due to UV-
photolysis and weather conditions being only of negli-
gible importance in greenhouse trials and the low
amount of soil in the plant boxes compared to the root
mass causing exaggerated uptake of imidacloprid.
As far as bee-relevant matrices are concerned, a me-
tabolism study in sunflower after seed-dressing with
imidacloprid WS 70 was carried out (Stork, 1999;
Schmuck et al., 2001). The applied amount was 0.79 mg
a.s./seed. During flowering, the nectar was collected
after sampling the female florets from the inflorescence
by tweezers and extracting the nectar using glass capil-
laries. Pollen samples were collected in plastic boxes
fixed below the inflorescences before flowering. The
total radioactive residue (TRR) in nectar and pollen was
very low and amounted to 0.0019 and 0.0039 mg/kg,
expressed as parent compound equivalents, respectively.
In nectar 100% of the TRR consisted of imidacloprid. In
pollen, the whole extractable radioactivity (85.8%,
0.0033 mg/kg) represented imidacloprid. The remaining
radioactivity in pollen (= non-extractable residues) was
not further analysed due to the very low absolute
amount. As only imidacloprid was found in the metabo-
lism study, this was considered as the only relevant
residue in those sample materials and consequently, the
residue definition was expressed as “parent only”.
Field-residue trials with non-labelled imidacloprid on
sunflower, corn and rape were additionally carried out
to confirm the findings of the metabolism study under
practical conditions (Schmuck, 1999). The samples of
these studies were not only analyzed for imidacloprid
but also for hydroxy- and olefine-metabolites, as these
compounds also show biological activity against certain
insect species (Nauen et al., 1999; Nauen et al., 2001).
The results of all six field trials are compiled in table 3.
Neither in pollen nor in nectar samples of corn, sun-
flower and summer rape any residues of imidacloprid
and the two other metabolites have been determined
above the limit of quantitation (LOQ of imidacloprid
and hydroxy-imidacloprid = 0.005 mg/kg, LOQ of ole-
fine metabolite = 0.01 mg/kg).
Conclusions
More than 15 studies with imidacloprid have been car-
ried out concerning uptake, translocation and metabo-
lism in various plant species mainly after foliar, soil or
seed treatment. The uptake after soil or seed treatment is
about 5% of the applied dose and the a.s. shows good
acropetal mobility within the xylem and poor basipetal
translocation within the phloem. Three principal meta-
bolic pathways of imidacloprid in plants were identified
showing a quick degradation of the a.s., especially after
seed or soil application. The findings of the metabolism
studies show a clear and consistent picture. It can be
concluded that in nearly all crops the metabolic pathway
of imidacloprid runs via the same three routes and re-
sults in qualitative and quantitative similar composition
of the metabolic spectrum. All identified metabolites
still contain the 6-chloropicolyl moiety of imidacloprid.
Hence, the relevant residue to be analysed in field resi-
due trials can be defined as the sum of imidacloprid and
its metabolites containing the 6-chloropicolyl moiety,
expressed as imidacloprid.
The nature of the residue in bee-relevant matrices of
oilseeds (sunflower nectar and pollen) was determined
to consist of the parent compound imidacloprid only.
Field residue trials with imidacloprid after seed-dressing
of sunflower, corn and rape revealed that no residues
above the limit of quantitation of the residue analytical
method were present in pollen and nectar.
Acknowledgements
Thanks are expressed to all persons having been invol-
ved in the successful development of imidacloprid.
References
BAI D., LUMMIS S. C. R., LEICHT W., BREER H., SATTELLE D.
B., 1991.- Actions of imidacloprid and a related nitrometh-
ylene on cholinergic receptors of an identified insect motor
neurone.- Pestic. Sci., 33: 197-204.
BRIGGS G. G., BROMILOW R. H. AND EVANS A. A., 1982.- Re-
lationships between lipophilicity and root uptake and trans-
location of non-ionised chemicals by barley.- Pestic. Sci.,
13: 495-504.
BROMILOW R. H., CHAMBERLAIN K., 1989.- Designing mole-
cules for systemicity.- In: Mechanisms and regulation of
Transport Processes (ATKIN R.K., CLIFFORD D.R., Eds),
Monograph 18, British Plant Growth Regulator Group.
CLARK T., 1997.- Uptake of NTN 33893 in Phacelia and
Summer Rape.- Unpublished report no. 4293, Bayer Crop-
Science AG, Metabolism/Environmental Fate, Monheim,
Germany.
CLARK T., BRAUNER A., 1994.- Metabolism of NTN 33893 in
Tobacco.- Unpublished report no. 3997, Bayer CropScience
AG, Metabolism/Environmental Fate, Monheim, Germany.
DRÄGER G., BRAUNER A., BORNATSCH W., 1989.- NTN
33893: Metabolism in tomatoes.- Unpublished report no.
3257, Bayer CropScience AG, Metabolism/Environmental
Fate, Monheim, Germany.
DRÄGER G., BORNATSCH W., BRAUNER A., 1992.- Study on the
Metabolism of NTN 33893 after Spray Application to Pota-
toes.- Unpublished report no. 3678, Bayer CropScience AG,
Metabolism/Environmental Fate, Monheim, Germany.
ELBERT A., NAUEN R., LEICHT W., 1998.- Imidacloprid, a
novel chloronicotinyl insecticide: biological activity and ag-
ricultural importance.- In: Insecticides with novel modes of
action: Mechanism and application (ISHAAYA I., DEGHEELE
D., Eds), Springer Verlag, Berlin Heidelberg, Germany, 50-
74.
KÖSTER J., BORNATSCH W., BRAUNER A., 1988.- Metabolism
of [pyridinyl-14C-methyl]NTN 33893 in Potato, Wheat and
40
Corn Cell Suspension Cultures.- Unpublished report ID M
1710181-9, Bayer CropScience AG, Metabo-
lism/Environmental Fate, Monheim, Germany.
KÖSTER J., 1990.- Comparative Metabolism of [pyridinyl-
14C]NTN 33893 in plant cell suspension cultures.- Unpub-
lished report no. 3667, Bayer CropScience AG, Metabo-
lism/Environmental Fate, Monheim, Germany.
KUROGOCHI S. AND ARAKI Y., 1989.- Isolation and Identifica-
tion of Metabolites of NTN 33893 in Rice by Water Cul-
ture.- Unpublished report no. 1282, Nihon Bayer Agrochem
K.K., Yuki Research Center, Environmental Science Re-
search, Yuki, Ibaraki, Japan.
KUROGOCHI S., MARUYAMA M., ARAKI Y., 1989.- Absorption
and Translocation of 14C-NTN 33893 in Eggplants and Rice
Plants.- Unpublished report no. 1273, Nihon Bayer Agro-
chem K.K., Yuki Research Center, Environmental Science
Research, Yuki, Ibaraki, Japan.
NAUEN R., TOLLO B., TIETJEN K., ELBERT A., 1998.- An-
tifeedant effect, biological efficacy and high affinity binding
of imidacloprid to acetylcholine receptors in Myzus persicae
and Myzus nicotianae.- Pestic. Sci., 51: 52-56.
NAUEN R., RECKMANN U., ARMBROST S., STUPP H.-P., ELBERT
A, 1999.- Whitefly-active metabolites of imidacloprid: bio-
logical efficacy and translocation in cotton plants.- Pestic.
Sci., 55: 265-71.
NAUEN R., EBBINGHAUS-KINTSCHER U., SCHMUCK R., 2001.-
Toxicity and nicotinic acetylcholine receptor interaction of
imidacloprid and ist metabolites in Apis mellifera (Hy-
menoptera: Apidae).- Pest. Manag. Sci., 57: 577-586.
RECKMANN U., 1998.- Translocation of 14C-imidacloprid in
hop after stem application (translated title; report available
in German language).- Unpublished report no. RMU 501,
Bayer CropScience AG, Formulation Development, Mon-
heim, Germany.
SAKAMOTO H., 1991.- Metabolism of [pyridyl-14C-methyl]
NTN33893 in Rice Plants (Nursery Box Application).- Un-
published report no. 1284, Nihon Bayer Agrochem K.K.,
Yuki Research Center, Environmental Science Research,
Yuki, Ibaraki, Japan.
SCHMUCK R., 1999.- No causal relationship between Gaucho
seed dressing in sunflowers and the French bee malady.-
Pflanzenschutz-Nachrichten Bayer, 52(3): 267-309.
SCHMUCK R., SCHÖNING R., STORK A., SCHRAMEL O., 2001.-
Risk posed to honeybees (Apis mellifera L, Hymenoptera)
by an imidacloprid seed dressing of sunflowers.- Pest.
Manag. Sci., 57: 225-238.
SCHMUCK R., NAUEN R., EBBINGHAUS-KINTSCHER U., 2003.-
Effects of imidacloprid and common plant metabolites of
imidacloprid in the honeybee: toxicological and biochemi-
cal considerations.- In: Proceedings of the 8th International
Symposium “Hazards of pesticides to bees”, September 4-
6, 2002, Bologna, Italy (PORRINI C., BORTOLOTTI L., Eds).
Bulletin of Insectology, 56 (1): 27-34.
STEIN-DÖNECKE U., FÜHR F., WIENECKE J., 1989.- Container
tests with the insecticidal active ingredient NTN 33893 con-
cerning uptake, translocation and action in wheat and sugar
beet plants.- Internal report IRA 8/89, Institute for Radio-
agronomy, Research Centre Jülich.
STORK A., 1999.- Residues of 14C-NTN 33893 (Imidacloprid)
in Blossoms of Sunflower (Helianthus annuus) after Seed
Dressing.- Unpublished report no. MR-550/99, Bayer Crop-
Science AG, Metabolism/Environmental Fate, Monheim,
Germany.
VOGELER K., DRÄGER G., 1989.- Investigations on the me-
tabolism of NTN 33893 in corn.- Unpublished report no.
3256, Bayer CropScience AG, Metabolism/Environmental
Fate, Monheim, Germany.
VOGELER K. AND BRAUNER A., 1993.- Addendum to NTN
33893 Cotton Report PF No.: 3675, Metabolism of NTN
33893 in Cotton after Seed Treatment.- Unpublished report
no. 3675, Bayer CropScience AG, Metabo-
lism/Environmental Fate, Monheim, Germany.
VOGELER K., DRÄGER G., BRAUNER A., 1991.- Investigation of
the metabolism of NTN 33893 in potatoes following granu-
lar application.- Unpublished report no. 3628, Bayer Crop-
Science AG, Metabolism/Environmental Fate, Monheim,
Germany.
VOGELER K., CLARK, T., BRAUNER, A., 1992.- Metabolism of
[14C]NTN 33893 in Apples.- Unpublished report no. 3676,
Bayer CropScience AG, Metabolism/Environmental Fate,
Monheim, Germany.
VOGELER K., LINKE-RITZER P., BRAUNER A., 1992.- [Pyri-
dinyl-14C-methyl]NTN 33893 Residues in Rotational
Crops.- Unpublished report no. 3674, Bayer CropScience
AG, Metabolism/Environmental Fate, Monheim, Germany.
YOSHIDA H., 1992.- Metabolism of NTN 33893 in eggplant by
planting hole application.- Unpublished report no. 1290, Ni-
hon Bayer Agrochem K.K., Yuki Research Center, Envi-
ronmental Science Research, Yuki, Ibaraki, Japan.
Corresponding author: Robin SUR, Bayer CropScience
AG, Metabolism/Environmental Fate, Alfred-Nobel Strasse
50, 40789 Monheim, Germany.
E-mail: robin.sur@bayercropscience.com
... Imidacloprid [1-(6-chloro-3-pyridylmethyl)-N-nitroimidazolidin-2-ylideneamine] ( Figure 1) has been used extensively to manage sucking insects, soil insects, termites and chewing insects in agriculture worldwide (Sur and Stork 2003;Laycock et al., 2012) [13,8] . The chemical works by interfering with the transmission of stimuli in the insect nervous system. ...
... Imidacloprid [1-(6-chloro-3-pyridylmethyl)-N-nitroimidazolidin-2-ylideneamine] ( Figure 1) has been used extensively to manage sucking insects, soil insects, termites and chewing insects in agriculture worldwide (Sur and Stork 2003;Laycock et al., 2012) [13,8] . The chemical works by interfering with the transmission of stimuli in the insect nervous system. ...
Research
Full-text available
Imidacloprid is a systemic insecticide that acts as an insect neurotoxin and belongs to class of chemicals called the neonicotinoides which act on central nervous system of insects. Three concentration of imidacloprid (0.134 µl, 0.195 µl and 0.285 µl) have been used during the experiment for evaluation of enzymatic activity. The increase in superoxide dismutase (SOD) activity suggests that SOD has the capacity to scavenge reactive oxygen species (ROS) under the stress at lower concentration of imidacloprid and it also indicated that the activity of the superoxide dismutase had shown different responses to toxicity of various concentrations of imidacloprid for different exposure periods in earthworm Eisenia fetida. Imidacloprid at concentrations of 0.195 µl and 0.285µl had shown the SOD activities of 6.773 and 7.263 U/mg protein respectively at 48 hr of exposure, while a concentration of 0.285µl has showed an enzyme activity of 6.835 U/mg protein at 24 hr of exposure. The study revealed that the activity of antioxidant enzyme of earthworms is altered due to stress produced by neonicotinoid insecticide. The statistical data of pesticide is highly significant with respect to treatment and time of exposure.
... As many neonicotinoids are used as seed coatings they are likely to be found in the crops grown from treated seeds including the leaves, pollen, and nectar. It is estimated that 2" 20% of the neonicotinoid coating is absorbed by the crop (Sur and Stork, 2003;Alford and Krupke, 2017) and the amount of neonicotinoids in the leaves or pollen can vary. Neonicotinoids have also been detected in wildflowers adjacent to agricultural areas indicating their potential to move away from the point of application area and to be taken up by other nontarget plants. ...
... Studies of the uptake of neonicotinoid seed dressings into the target crop suggest that between 1.6 and 20% of the active ingredient is absorbed by the crop (Sur and Stork, 2003). Thus, although seed dressings are often stated to provide accurate targeting of the crop , they result in a considerably smaller proportion of the active ingredient ending up in or on the crop than do traditional spray applications to foliage, which commonly exceed 50% efficiency (Graham-Bryce, 1977). ...
Article
Full-text available
Neonicotinoids are the most widely used insecticides in the world. They are systemic in action, travelling through plant tissues and protecting all parts of the crop, and are widely applied as seed dressings. Neonicotinoids are registered globally in more than 120 countries and found to be effective against sucking pests. In terms of area treated almost 90% of the use is as seed treatments. Some of these active substances are approved for use as seed treatments (clothianidin), some as foliar applications (acetimiprid and thiacloprid) and some for both (imidacloprid and thiamethoxam). They are nicotinic acetylcholine receptor agonists; they bind strongly to nicotinic acetylcholine receptors (nAChRs) in the central nervous system of insects, causing nervous stimulation at low concentrations, but receptor blockage, paralysis and death at higher concentrations. Neonicotinoids bind more strongly to insect nAChRs than to those of vertebrates, so they are selectively more toxic to insects; and present no hazard to mammals; they provide effective pest control and have numerous uses in arable farming and horticulture. They provide an alternative mode of action to organophosphate, carbamates and pyrethroid insecticides. This allows them to play a key role in helping to prevent the buildup of resistance in the pests concerned. These show higher efficacy and used at a lower dosage as compared to other conventional insecticides. There is absence of cross-resistance in neonicotinoids with pyrethroids, carbamates, organophosphates and organochlorines. The information on hazards of neonicotinoids to bees including honey bees, bumble bees and solitary bees is reviewed. Neonicotinoids affect the nicotinic acetylcholine receptor (nAChR) which directly links with the health of pollinators.
... Neonicotinoids are particularly toxic to insects by acting as a powerful nicotinic acetylcholine receptor blocker (Matsuda et al. 2001;Pisa et al. 2015;Tomizawa et al. 2000). On average, just 5% of neonicotinoids applied as seed coatings are actually taken up by the target plant, leaving 95% of the compound in the surrounding soil and water (Sur and Stork 2003). This runoff introduces neonicotinoids into the environment surrounding agricultural areas, where they can remain persistent for long periods of time under certain conditions Hladik et al. 2018). ...
Article
Full-text available
There is increasing awareness of the negative ecological and environmental effects of widespread use of pesticides on the landscape. Spillover or drift of pesticides from agricultural areas has been shown to impact species health, reproduction, and trophic dynamics through both direct and indirect mechanisms. Neonicotinoid insecticides are associated with observed declines of insectivorous and grassland birds, and these environmental pollutants are a significant conservation concern for many species that have experienced past or current population declines. Due to the high efficacy of these modern insecticides in depressing local insect populations, insectivorous birds can be negatively impacted by a pesticide-mediated reduction in food supply. Neonicotinoids may act synergistically with other stressors, such as habitat loss, to exacerbate threats to species or population viability. The Tricolored Blackbird is an insectivorous grassland bird of conservation concern in California, USA. Due to the high association of this species with agricultural habitats, we sought to quantify the amount of neonicotinoid residues in Tricolored Blackbird carcasses as a first step in assessing how this species may be impacted by pesticides. Out of 85 salvaged carcasses sampled ( N = 24 adults, N = 3 fledglings, and N = 58 nestlings), only two contained detectable levels of target compounds. These were an adult and one nestling that contained clothianidin residue (40 ppb and 7 ppb, respectively); both of these birds were salvaged from breeding colonies associated with dairy farms in Kern County, California. We suggest that further work is needed to assess neonicotinoid exposure of Tricolored Blackbirds in dairy-associated breeding colonies.
... Neonicotinoids are commonly applied as seed dressing (Jeschke et al. 2011;Alford and Krupke 2017), due to a benefit of extended crops protection resulting in a reduction in the insecticide application frequency. However, on average, only 5 % of the active ingredient is taken up by and distributed throughout the developing plant (Sur and Stork 2003). The remainder enters the wider environment, including soils, where they can have a negative effect on inhabiting worm species. ...
Thesis
An ability of insecticides to selectively target pests without affecting non-target species is a key determinant of success of compounds used in agriculture. Neonicotinoids which encompass seven different types of chemical representing three distinct chemical classes, namely the cyanoamidines, nitroguanidines and nitromethylenes, are a major class of insecticides. They effectively control a wide range of insect pests and have low toxicity against mammals, however they can also negatively impact on non-target species of bees, threatening food safety. Neonicotinoids act by targeting insect nicotinic acetylcholine receptors (nAChRs), which are major excitatory receptors in the insect central nervous system. Difficulties in heterologous expression of these proteins hinders their pharmacological characterisation and identification of the molecular determinants of neonicotinoid-toxicity. This thesis describes efforts into developing Caenorhabditis elegans (C. elegans) as a platform in which the mode of action and selective toxicity of neonicotinoid-insecticides can be studied. We determined the effects of neonicotinoids on C. elegans behaviours governed by the cholinergic neurotransmission. The cyanoamidine represented by clothianidin, the nitroguanidine represented by thiacloprid and the nitromethylene represented by nitenpyram showed low efficacy on locomotion, pharyngeal pumping, egg-laying and egg-hatching of young adult wild-type C. elegans. Exposure of mutant worm with enhanced cuticular permeability showed increased susceptibility of worms to all three neonicotinoids tested, suggesting an adult cuticle limits drug access. The role of the cuticle in neonicotinoids susceptibility was investigated in C. elegans cut-head preparation, in which the cuticle is removed and the effects of compounds on pharyngeal pumping are scored. Out of the three neonicotinoids applied, clothianidin showed the greatest efficacy. It stimulated pharyngeal pumping at ≥ 75 µM (18.75 ppm). Generally, the concentrations effective against the function of the pharynx are an order or magnitude lower than the residual, average concentration of neonicotinoids in the soil, suggesting C. elegans is not impacted in the field, and at least several fold lower than lethal doses in insect-pests. The difference in neonicotinoid-susceptibility between adult C. elegans and insects precludes the use of C. elegans pharynx as a platform for the mode of action studies, but highlights its potential as a suitable background for the heterologous expression of insect nAChRs. Further experiments showed that C. elegans eat-2 nAChR mutant is a suitable genetic background, in which the expression of heterologous nAChRs can be Expression of the exogenous receptor, human α7 in the pharynx of eat-2 mutant led to a cell-surface expression, as shown by staining with labeled α-bungarotoxin (α-bgtx). However the feeding and pharmacological phenotypes of the mutant were not rescued. C. elegans strain in which human α7 is expressed in the wild-type genetic background was also generated to determine whether the pharmacology of the human receptor can be imposed on the C. elegans pharynx. No difference in the pharyngeal response to nAChR agonists cytisine, nicotine or acetylcholine were noted. The lack of apparent functionality of α7 receptor could be due to the incorrect cellular localisation of this protein. α-bgtx staining showed that α7 receptor is expressed in the specific cells of the pharyngeal muscle, however this localisation does not overlap with the localisation of native EAT-2 receptors. A transgenic strain in which exogenous proteins are expressed using EAT-2 native promoter should be made. scored. Expression of C. elegans nAChR EAT-2 in the pharyngeal muscle rescued the blunted feeding phenotype and 5-HT insensitivity of the eat-2 mutant.
... With the widespread use of IMD, there is growing evidence that IMD residues increase the potential risk to non-target organisms, including humans, through food chain transmission [5]. Out of the agriculturally applied IMD, only about 5% are absorbed by crops [6], while most are dispersed into the environment, causing pollution and continuous accumulation in soil [7]. Due to its hydrophilic property, after being applied to the crop, IMD distributes thoroughly across plant tissues [8], which cannot be effectively removed by washing peels or surfaces [9]. ...
Article
Full-text available
Background: Imidacloprid (IMD) is a widely used neonicotinoid-targeting insect nicotine acetylcholine receptors (nAChRs). However, off-target effects raise environmental concerns, including the IMD's impairment of the memory of honeybees and rodents. Although the down-regulation of inotropic glutamate receptor (iGluR) was proposed as the cause, whether IMD directly manipulates the activation or inhibition of iGluR is unknown. Using electrophysiological recording on fruit fly neuromuscular junction (NMJ), we found that IMD of 0.125 and 12.5 mg/L did not activate glutamate receptors nor inhibit the glutamate-triggered depolarization of the glutamatergic synapse. However, chronic IMD treatment attenuated short-term facilitation (STF) of NMJ by more than 20%. Moreover, by behavioral assays, we found that IMD desensitized the fruit flies' response to mechanosensitive, nociceptive, and photogenic stimuli. Finally, the treatment of the antioxidant osthole rescued the chronic IMD-induced phenotypes. We clarified that IMD is neither agonist nor antagonist of glutamate receptors, but chronic treatment with environmental-relevant concentrations impairs glutamatergic plasticity of the NMJ of fruit flies and interferes with the sensory response by mediating oxidative stress.
... The soluble nature of these insecticides also allows them to migrate beyond the intended plants. Less than 20%, and as little as 1-2%, of the neonicotinoids applied as seed coatings are typically taken up by target crops (Alford & Krupke, 2017;Goulson, 2013;Sur & Stork, 2003). Although some of the residual chemicals are rapidly degraded (Baskaran et al., 1999), the remainder can move into the surrounding environment . ...
Article
Full-text available
Soil organic matter retains and attenuates many contaminants; however, its interactions with neonicotinoid insecticides under field conditions remain poorly understood. The goal of this study was to determine if soil organic matter influences the persistence or leaching of two neonicotinoid insecticides: thiamethoxam and its transformation‐product clothianidin. Thiamethoxam‐coated soybeans were planted into a clay soil containing different soil organic carbon concentrations. Leachate and soil samples were collected for ten weeks after planting, and were analyzed for insecticide concentrations using liquid chromatography/tandem mass spectrometry. Single‐ and multiple‐linear regressions were performed between soil organic carbon, leaching volumes, and measured insecticide concentrations, focusing on rainfall events near the beginning, middle, and end of the study. Correlations were also tested between soil organic carbon and cumulative mass of leached insecticides. Neither soil organic carbon nor per‐event leachate volumes explained variability in thiamethoxam leaching or residual clothianidin concentrations in soils, yet the cumulative volume of water leached was positively correlated with residual thiamethoxam concentrations in soil at the study conclusion. Initially, the concentration and total mass of leached clothianidin were significantly and negatively correlated with soil organic carbon content; however, this effect faded with time. Leachate dynamics also affected clothianidin transport, with positive correlations between leachate volume and clothianidin concentration during the latter events. This analysis demonstrates that soil organic matter can reduce peak loading of neonicotinoids, but may not alter cumulative leaching over the entire growing season. This article is protected by copyright. All rights reserved
... Only about 5 % of the active ingredients of neonicotinoids are absorbed by crops after being applied in agricultural lands (Han et al., 2018;Stehle et al., 2018;Sur and Stork, 2003;Zhang et al., 2018). The residual neonicotinoids undergo multiple transportations from agricultural lands to rivers, lakes, groundwaters, coastal aquatic environments, and eventually marine environments due to the high water solubility (Struger et al., 2017;Wettstein et al., 2016;Wood and Goulson, 2017). ...
Article
Full-text available
Neonicotinoid insecticides are widely and exceedingly applied in farmlands worldwide and are ubiquitous in various environments, including surface water, soil, river sediments, etc. However, few studies reported neonicotinoid residues in the marine environment. Considering the large application of neonicotinoids in China, here, we collected marine sediments in offshore and far sea areas of the East China Sea, including the Hangzhou Bay and the area along the Zhejiang Province coast, and measured the concentrations of nine commercialized neonicotinoids. The total concentration of neonicotinoids was 11.9 ± 6.22 ng/g (dry weight) (range: 4.77–29.9 ng/g), which was higher than other regions reported in previous studies. Neonicotinoid residues found in far sea areas were statistically lower than those in offshore areas. Nitenpyram and dinotefuran were the dominant compounds, contributing to >75 % of the total residue. It is thought that the flux of the Yangtze River is the main source of the neonicotinoid pollution in the East China Sea and the sediment is the sink of neonicotinoid residue from mainland China. Neonicotinoid residues were found to be negatively correlated with sediment pH, and positively correlated with microbial diversity and nitrate content. Based on structural equation modeling, we also illustrated the associations between neonicotinoid residues and different factors, suggesting that the change in sediment pH and microbial diversity were related to the degradation of neonicotinoid residues. Actinobacteriota, Chloroflexi, and Nitrospirota were found to be the key bacterial community at the phylum level on the degradation of neonicotinoids. Our findings provide new insights into the understanding of spatial distribution, source, and migration of neonicotinoids and their impacts on marine microorganisms.
... For example, only 1.6 to 28% of NNIs could be directly absorbed by plants after being applied through seed treatment, and the remaining NNIs will migrate into other environmental media (e.g., air, soil, and water) (Sur and Stork 2003). Meanwhile, NNIs can accumulate in the food chain and subsequently threaten human and ecosystem health (Pastor-Belda et al. 2016;Wu et al. 2020). ...
Article
Full-text available
Neonicotinoid insecticides (NNIs) have been widely used to control insect pests, while their environmental residues and associated hazardous impacts on human and ecosystem health have attracted increasing attention worldwide. In this study, we examined the current levels and associated spatial and temporal patterns of NNIs in multiple environmental media across China. Concentrations of NNIs in surface water, sediment, and soil were in the range of 9.94–755 ng·L⁻¹, 0.07–8.30 ng·g⁻¹ DW, and 0.009–356 ng·g⁻¹ DW, respectively. The high levels of NNIs in surface water, such as in Yangtze River (755 ng·L⁻¹), North River (539 ng·L⁻¹), Nandu River (519 ng·L⁻¹), and Minjiang River (514 ng·L⁻¹), were dominated by imidacloprid, thiamethoxam, and acetamiprid due to their extensive use. The levels of NNIs in sediments were relatively low, and the highest concentration (8.30 ng·g⁻¹ DW) was observed in Dongguan ditch. Sediment–water exchange calculated from fugacity fraction indicated that NNIs in sediment can be released back into the water due to their high solubility and low KOW. Soils from agricultural zones contained the largest residual NNIs, with imidacloprid concentrations in cultivated soil reaching 119 ng·g⁻¹ DW. The calculated leaching potential showed that clothianidin has the highest migration potential to deep soil or groundwater. The monitored data of NNIs presented a decreasing trend from 2016 to 2018, which might be caused by the implementation of relevant control policies for NNI applications. The high levels of NNIs mainly occurred in southern China due to frequent agricultural activities and warm and humid meteorological conditions. The results from this study improve our understanding of the pollution levels and environmental behavior of NNIs in different environmental media across China and provide new knowledge that is needed for making future control policies for NNIs production and application. Graphical abstract
Article
Trace analysis method is a reliable basis for studying the translocation and metabolism of imidacloprid used as an insecticide in wheat, and it clarifies whether biologically active metabolites including residual imidacloprid, have long‐lasting insecticidal potency against wheat aphids under seed treatment during the entire growth period. In this study, a highly sensitive analytical method was established to determine the residues of imidacloprid and its six metabolites (5‐hydroxy imidacloprid, imidacloprid olefin, imidacloprid guanidine, imidacloprid urea, 6‐chloronicotinic acid and imidacloprid nitrosimine) in wheat–soil systems, such as in wheat leaves, wheat ears, wheat grains, roots and soil. All the compounds were extracted using an ACN:water (8:2, v/v) mixture and purified by dispersive solid‐phase extraction. The average recoveries ranged from 74.4 to 109.5% for all matrices, with intra‐ and inter‐day variations of less than 14.9%. The limit of quantitation was in the range of 0.001 to 0.005 mg/kg. The method is demonstrated to be sensitive and accurate for monitoring imidacloprid and its metabolites at trace levels during the entire growth period under field conditions. This article is protected by copyright. All rights reserved
Article
The objective of this work is to study the toxicological effect of the imidacloprid (IMD) on common bean plants (Phaseolus vulgaris L) when used at high doses and its quantification by electrochemical method. Common bean plants were exposed to increasing concentrations of IMD and the different plant tissues were subjected to various analyses. The IMD detection in different tissues of the bean plant was performed after extraction on the metallic silver electrode using square wave voltammetry. The analytical and calibration parameters (Slope, correlation coefficient, linear range, detection limit and relative standard deviation) were calculated for the different plant tissues. The effect of different doses (5.0 × 10−3 to 5.0 × 10−2 mol L−1) of IMD was evaluated on germination, seedling (vigour, growth) and photosynthetic pigments in the bean plant. The results indicate that germination rate and seed vigour index reduced significantly (p ≤ 0.05) only in the applied concentrations above the recommended dose. A similar effect of IMD was observed on seedling development in term of roots length, plant length, number of leaves and number of nods. Concerning pigments content, chlorophyll a, b and total chlorophyll maximally decreased by 95.26%, 80.44% and 82.15% respectively at high applied dose. The bioaccumulation and translocation behaviour of IMD in bean plant was investigated, revealing that the IMD can be bioaccumulated in roots and can easily be translocated into stems and leaves.
Article
Full-text available
Honeybees foraging in crop plants seed-dressed with imidacloprid may be exposed to imidacloprid and imidacloprid plant me-tabolites. Metabolism studies on a large variety of crop plants were reviewed to identify plant metabolites which have a potential toxicological relevance to honeybees. Three different bioassays were conducted to characterize the pharmacological and toxico-logical profile of imidacloprid and these potentially relevant plant metabolites in the honeybee. The nicotinic acetylcholine receptor (nAChR) was identified as the molecular target of [ 3 H]imidacloprid and some of the tested plant metabolites in honeybee head membrane preparations. IC 50 -values for the displacement of [ 3 H]imidacloprid of 2.9, 0.45, 24, 6600, >100000, and >100000 nM were recorded for imidacloprid and the plant metabolites olefine, 5-OH-imidacloprid, 4,5-OH-imidacloprid, urea metabolite and 6-chloronicotinic acid (6-CNA), respectively. These values indicate a potential toxicological relevance only for the olefine and the 5-hydroxy metabolite. Whole cell voltage clamp electrophysiology revealed that imidacloprid, the olefine and the 5-hydroxy metabolite act agonisti-cally on the nAChR of neurons isolated from the antennal lobe of Apis mellifera. All other metabolites did not induce inward cur-rents at test concentrations up to 3 mM. As for the parent compound, the electrophysiology data of the active metabolites revealed Hill coefficients of approximately 1, thus indicating a single binding site responsible for an activation of the receptor and no direct cooperativity or allosteric interaction with a second binding site, respectively. In standard toxicity assays following the EPPO guideline 170 LD 50 values between 40 and 104 ng/bee were determined for the oral and contact toxicity of imidacloprid to honeybees. No indications were found for significant differences in sensitivity to imi-dacloprid between honeybees from different apiaries. The acute oral toxicity of the potentially relevant plant metabolites of imi-dacloprid to honeybees were well correlated with their receptor binding affinity and receptor activation potential. Only the olefine and the 5-hydroxy metabolite were identified as toxicologically relevant. The results from the current studies suggest that residue investigations aiming to define the field exposure of honeybees to imi-dacloprid applied as seed dressing should not only include a detection method sensitive for the parent compound but should also be sensitive to the presence of the olefine and 5-hydroxy-imidacloprid.
Chapter
Following the discovery of the insecticidal properties of the heterocyclic nitromethylenes (Soloway et al. 1978), chemists of Nihon Bayer Agrochem started in 1979 to optimize these structures. In 1985 the coupling of the chloropyridyl moiety to the N-nitro substituted imidazolidine ring system enabled the synthesis of the highly active insecticide imidacloprid (Fig. 1). Imidacloprid is the first commercial example of the chloronicotinyl insecticides acting on nicotinic acetylcholine receptors (Leicht 1993). It is now registered in more than 60 countries as a compound with a new or non-conventional mode of action to combat highly resistant insect pests (Elbert et al. 1991; Elbert et al. 1996; Nauen et al. 1996a). Chloronicotinyl insecticides will grow in importance in the coming years because other close analogues of imidacloprid, such as Takeda’s and Nippon Soda’s open chain derivatives nitenpyram and acetamiprid, respectively, have been described (Tomizawa et al. 1995; Yamamoto et al. 1995). During recent years several studies have demonstrated the excellent activity of imidacloprid on pest species of different orders. The present chapter gives an overview of the biological activity of imidacloprid on different target pests, its selectivity even at the molecular level, its physicochemical properties which led to good systemicity and its agricultural importance.
Article
It is known from laboratory studies that tobacco-associated forms of Myzus persicae (Sulzer) and the closely related tobacco aphid Myzus nicotianae (Blackman) are often somewhat less susceptible to imidacloprid than non-tobacco strains of M. persicae. Choice tests (floating leaf technique) showed that tobacco aphids were also less susceptible to the antifeedant potential of imidacloprid in contact bioassays. Synergists like piperonyl butoxide or DEF did not enhance the susceptibility of tobacco-associated morphs of Myzus ssp. to imidacloprid, thus providing evidence that neither oxidative detoxication nor hydrolytic metabolization took place. However, in an attempt to study the influence of endosymbiotic bacteria on the efficacy of imidacloprid, we allowed small populations of tobacco aphids to feed on diets containing the antibiotic chlortetracycline prior to imidacloprid treatment. While the effectiveness of imidacloprid, i.e. lower LC50 values, could be improved in all strains, including the susceptible reference strain, there was no change in overall tolerance factors. In order to investigate any possible alteration of the target site, the affinity of imidacloprid and nicotine to nicotinic acetylcholine receptors in whole-aphid homogenates was measured. All strains (and clones) showed the same high-affinity binding sites and no detectable difference.Studies using the FAO dip method revealed that the lower susceptibility of M. nicotianae is not restricted to chloronicotinyls like imidacloprid or acetamiprid, because other insecticides with different modes of action such as pymetrozine and fipronil were also affected in laboratory studies. It is considered that the observed tolerance to chloronicotinyls in certain strains of Myzus ssp. is a natural variation in response, probably not coupled with any known mechanism of resistance in this species complex. © 1998 SCI
Article
Nitromethylenes and their analogues are a novel class of insecticidally active molecules of commercial importance. Here we describe the actions of a novel nitroguanidine analogue, l-(6-chloro-3-pyridylmethyl)-N-nitroimidazolidin-2-ylideneamine (imidacloprid; NTN 33893) and a nitromethylene, l-(3-pyridylmethyl)-2-nitromethylene-imidazolidine (PMNI) on the cockroach fast coxal depressor motor neurone Df and their effectiveness in displacing [125I]α-bungarotoxin binding to cockroach nerve cord preparations. When tested on the cell body of this identified neurone both imidacloprid and PMNI induce slow depolarizations, which are sensitive to nicotinic receptor antagonists, such as dihydro-β-erythroidine (1.0 × 10−5 M) and mecamylamine (1.0 × 10−4 M). Lower concentrations of imidacloprid (1.0 × 10−8 −1.0 × 10−6 M) and PMNI (1.0 × 10−8 M) show no antagonist action on nicotine-induced depolarization. At concentrations in the range 1.0 × 10−7 −5.0 × 10−7 M, PMNI partially and reversibly blocks nicotine-induced depolarization. Both compounds are more effective displacers of specific [125I]α-bungarotoxin binding than nicotine, with imidacloprid (IC50 = 2.0 × 10−7 M) about tenfold more potent than PMNI (IC50 = 1.3 × 10−6 M).
Article
The uptake by roots from solution, and subsequent translocation to shoots in barley, of two series of non-ionised chemicals, O-methylcarbamoyloximes and substituted phenylureas, were measured, Uptake of the chemicals by roots was greater the more lipophilic the chemical, and fell to a lower limiting value for polar chemicals. Translocation to the shoots was a passive process, and was most efficient for compounds of intermediate polarity. Both processes had reached equilibrium within 24h of treatment. The reported behaviour of many pesticides in various plant species agrees with the derived relationships, but the detailed mechanisms of these processes are unknown.
Article
Acute oral and contact toxicity tests of imidacloprid, an insecticide acting agonistically on nicotinic acetylcholine receptors (nAChR), to adult honeybees, Apis mellifera L var carnica, were carried out by seven different European research facilities. Results indicated that the 48-h oral LD50 of imidacloprid is between 41 and >81 ng per bee, and the contact LD50 between 49 and 102 ng per bee. The ingested amount of imidacloprid-containing sucrose solution decreased with increasing imidacloprid concentrations and may be attributed to dose-related sub-lethal intoxication symptoms or to antifeedant responses. Some previously reported imidacloprid metabolites occuring at low levels in planta after seed dressing, ie olefine-, 5-OH- and 4,5-OH-imidacloprid, showed lower oral LD50 values (>36, >49 and 159 ng per bee, respectively) compared with the concurrently tested parent molecule (41 ng per bee). The urea metabolite and 6-chloronicotinic acid (6-CNA) exhibited LD50 values of >99 500 and >121 500 ng per bee, respectively.
Article
In a greenhouse metabolism study, sunflowers were seed-treated with radiolabelled imidacloprid in a 700 g kg−1 WS formulation (Gaucho® WS 70) at 0.7 mg AI per seed, and the nature of the resulting residues in nectar and pollen was determined. Only the parent compound and no metabolites were detected in nectar and pollen of these seed-treated sunflower plants (limit of detection <0.001 mg kg−1). In standard LD50 laboratory tests, imidacloprid showed high oral toxicity to honeybees (Apis mellifera), with LD50 values between 3.7 and 40.9 ng per bee, corresponding to a lethal food concentration between 0.14 and 1.57 mg kg−1. The residue level of imidacloprid in nectar and pollen of seed-treated sunflower plants in the field was negligible. Under field-growing conditions no residues were detected (limit of detection: 0.0015 mg kg−1) in either nectar or pollen. There were also no detectable residues in nectar and pollen of sunflowers planted as a succeeding crop in soils which previously had been cropped with imidacloprid seed-treated plants. Chronic feeding experiments with sunflower honey fortified with 0.002, 0.005, 0.010 and 0.020 mg kg−1 imidacloprid were conducted to assess potential long-term adverse effects on honeybee colonies. Testing end-points in this 39-day feeding study were mortality, feeding activity, wax/comb production, breeding performance and colony vitality. Even at the highest test concentration, imidacloprid showed no adverse effects on the development of the exposed bee colonies. This no-adverse-effect concentration of 0.020 mg kg−1 compares with a field residue level of less than 0.0015 mg kg−1 ( = limit of detection in the field residue studies) which clearly shows that a sunflower seed dressing with imidacloprid poses no risk to honeybees. This conclusion is confirmed by observations made in more than 10 field studies and several tunnel tests.
Uptake of NTN 33893 in Phacelia and Summer Rape
CLARK T., 1997.-Uptake of NTN 33893 in Phacelia and Summer Rape.-Unpublished report no. 4293, Bayer CropScience AG, Metabolism/Environmental Fate, Monheim, Germany.