Advances in Environmental Biology Culex pipiens (Diptera: Culicidae) Mosquito

Advances in Environmental Biology, 8(4) March 2014, Pages: 1169-1174
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Advances in Environmental Biology
ISSN:1995-0756 EISSN: 1998-1066
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Comparative Toxicological Evaluation between Different Formulations of Two
Selected Neonicotinoid Pesticides on Culex pipiens (Diptera: Culicidae) Mosquito
1
1
2
Mohamed A.I. Ahmed and 2Reda M. Saba
Plant Protection Department, Faculty of Agriculture, Assiut University, Assiut 71526. Egypt.
Plant Protection Department, Faculty of Agriculture, Al-Azhar University, Assiut. Egypt.
ARTICLE INFO
Article history:
Received 11 April 2014
Received in revised form 21 April
2014
Accepted 25 April 2014
Available online 5 May 2014
Keywords:
Culex
pipiens,
Imidacloprid,
Acetamprid, Formulations, Mosquito
Control
ABSTRACT
Background: Culex pipiens mosquito considered one of the dangerous pest not only in
Egypt but also all over the world for their ability to transmit many vector-borne
diseases such as West Nile virus (WNV), Rift valley fever (RVF), Saint Louis
encephalitis (SLE), and Eastern Equine encephalitis (EEE). Objective: to evaluate the
toxicity of different formulations of two selected neonicotinoid pesticides (Imidacloprid
and Acetamprid) on Culex pipiens larvae. Also, to shed light on their control. Results:
Imidacloprid (20% SL) is the most potent Imidacloprid formulations whereas
Acetamprid (20% SL) is the most toxic Acetamprid formulations. The toxicity
increased after 48 h and continues increased after 72 h comparing to 24 h data. In
contrast, the lowest toxicity index which is observed dramatically was Imidacloprid
(35% SC) and Acetamprid (20% SP) after 24 h and the toxicity index were 2.24% and
0.06% respectively, however, the same tendency was observed after 48 and 72 h
exposure. Conclusion: Given results of different formulations of Imidacloprid and
Acetamprid should be directed to the potential efficient and effective control of Culex
pipiens especially under field conditions. Also, further biochemical and molecular
biological investigation should be done in order to understand the unique mechanism of
the two selected neonicotinoids pesticides in Culex pipiens mosquito.
© 2014 AENSI Publisher All rights reserved.
To Cite This Article: Mohamed A.I. Ahmed and Reda M. Saba., Comparative Toxicological Evaluation between Different Formulations of
Two Selected Neonicotinoid Pesticides on Culex pipiens (Diptera: Culicidae) Mosquito. Adv. Environ. Biol., 8(4), 1169-1174, 2014
INTRODUCTION
Culex pipiens mosquito is become a serious health problem to human in that it transmits many diseases
[1,2,3,4]. In Egypt, Culex pipiens is the key vector pest of Western Nile virus (WNV) and Rift Valley Fever virus
(RVFV) [5,6,7]. However, globally, insecticide application is considered the most important aspect in the
mosquito vector control effort [2,8]. Furthermore, conventional insecticides are known for their fast action but,
on the other side, their application is non-selective and could be harmful to other beneficial organisms, animals,
human beings, and the whole environment [9,10]. Further, Insecticide resistance considered a major problem and
posed a severe threat to our efforts in controlling the insect vectors of many human and animal diseases [11,12].
Regardless to all these restrictions on the using of the conventional insecticides, it is very important to rely on
other strategies, especially the new trends in controlling pests, to avoid the development of resistance among
major pest insects. Neonicotinoid pesticides are a comparatively considered a new class of insecticides which
belong to the fastest-growing class of insecticides in the world especially in the field of plant protection following
the common pyrethroids group [13]. Interestingly, neonicotinoids have a unique mode of action as compared to
other classes of insecticides in that they act as the agonists to the nicotinic acetylcholine receptor (nAChRs) [14].
As a result of their selective mode of action, so far there have not been any major cases of cross-resistance to
conventional long-established insecticide classes, and therefore, the neonicotinoids have been replacing
chlorinated hydrocarbons, organophosphates, carbamates and several other chemical classes of insecticides
frequently used to control insect pests, also, their mammalian toxicities are generally low and also show low acute
toxicities to birds, and fish, but display significant toxicities to bees [15,16]. Thus, in this study, we conducted a
comparative toxicological study using different formulations, soluble liquid (SL), wettable granules (WG),
soluble concentrate (SC), emulsifiable concentrate (EC), and soluble powder (SP) of two selected neonicotinoid
pesticides (Imidacloprid and Acetamprid) on 4th instar larvae of Culex pipiens mosquito.
Corresponding Author: Mohamed Ahmed, Plant Protection Department, Faculty of Agriculture, Assiut University, Assiut
71526, Egypt.
Phone: +201113991177; Fax: +20882331384; E-mail: [email protected]
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Mohamed A. I. Ahmed and Reda M. Saba, 2014
Advances in Environmental Biology, 8(4) March 2014, Pages: 1169-1174
MATERIALS AND METHODS
Mosquito:
The 4th instar larvae of Culex pipiens was collected from Arab-Almadabegh area in Assiut City then directly
transfer to the central laboratory at Faculty of Agriculture, Al-Azhar University, Assiut for conduct the
experiments.
Pesticides:
The formulations of Imidacloprid (20% SL, 70% WG, and 35% SC) and Acetamprid (20% SL, 10% EC, and
20% SP) were used in the toxicity test (Figure 1). These materials were obtained from Central Agricultural
Pesticides Laboratory (CAPL) in Dokki, Giza, Egypt as gifts.
Fig. 1: Chemical structures of Imidacloprid and Acetamprid
Toxicity test method:
The toxicity test method was conducted on 20 fourth instar larvae placed in glass cups each containing 100
ml of tap water. Each test was conducted in three replicates per each concentration (n = 60). Each container with
20 larvae was treated with 1 ml of tap water containing pesticides to give varying concentrations of technical
grade of Imidacloprid and Acetamprid. Controls received only tap water, and were run concurrently with each
series of tests. At least five concentrations were used for each test. Every test was held at 25 oC (≈60% RH). The
observation of larvae mortalities were made after 24, 48, 72 h of treatment, and corrected according to Abott’s
formula [17]. Larvae were considered dead if they were unresponsive to touching with a probe or if they could
not reach the surface of the water.
The toxicity test data were pooled and analyzed (LC50, LC90, and 95% CL values) by using Proban probit
analysis program version 1.1 [18]. Figures were done by using GraphPad Prism 6 software (San Diego, CA,
USA).
RESULTS AND DISCUSSION
Toxicity of different formulations of Imidacloprid and Acetamprid on fourth instar larvae of Culex pipiens
after 24 h is shown in Table 1. Imidacloprid (20% SL) was the most toxic pesticide formulation (LC 50 was 1.89
ppm) among all Imidacloprid formulations whereas Acetamprid (20% SL) was the most potent (LC50 was 2.46
ppm). However, Imidacloprid (70% WG) and Acetamprid (10% EC) are shown a modest toxicity and
Imidacloprid (35% SC) and Acetamprid (20% SP) shown the lowest toxicity among the all pesticide
formulations.
All the LC50 values decreased after 48 and 72 h when compared with the 24 h data (Table 2 and 3),
however, this trend was particularly noticeable among Imidacloprid and Acetamprid formulations.
The toxicity of all formulations of Imidacloprid was increased after 72 h, for example, Imidacloprid (20%
SL) increased in toxicity from 1.90-fold after 48 h to 3.32-fold after 72 h compare to the toxicity after 24 h
(Figure 2). Furthermore, this trend was shown strongly in Acetamprid formulations toxicity (Figure 3).
Moreover, the toxicity index of the most toxic pesticides after 24 h which are Imidacloprid (20% SL) and
Acetamprid (20% SL) was 100% and for Imidacloprid (70% WG) and Acetamprid (10% EC) which is moderate
in toxicity index was (54.94% and 49.30% respectively) whereas the lowest toxicity index which is observed
dramatically was Imidacloprid (35% SC) and Acetamprid (20% SP) and the toxicity index for these pesticides
were 2.24% and 0.06% respectively. However, the same trend was observed for the toxicity index after 48 and
72 h (Figure 4).
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Mohamed A. I. Ahmed and Reda M. Saba, 2014
Advances in Environmental Biology, 8(4) March 2014, Pages: 1169-1174
Table 1: Toxicity of selected neonicotinoid pesticides on 4th instar larvae of Culex pipiens after 24 h exposure.
Pesticides
LC50 (ppm)
LC90 (ppm)
(95% CL)
(95% CL)
Imidacloprid (20% SL)
1.89 (1.51-2.28)
5.34 (4.22-7.56)
Imidacloprid (70% WG)
3.44 (2.86-4.08)
10.23 (8.03-14.70)
Imidacloprid (35% SC)
84.37 (71.91-100.29)
213.64 (166.05-316.23)
Acetamprid (20% SL)
2.46 (1.87-2.99)
6.81 (5.50-9.49)
Acetamprid (10% EC)
4.99 (4.12-6.05)
12.87 (10.00-18.72)
Acetamprid (20% SP)
4078.38 (3400.33-4879.72)
8728.05 (6947.54-12533.88)
Table 2: Toxicity of selected neonicotinoid pesticides on 4th instar larvae of Culex pipiens after 48 h exposure.
Pesticides
LC50 (ppm)
LC90 (ppm)
(95% CL)
(95% CL)
Imidacloprid (20% SL)
0.99 (0.77-1.20)
2.12 (1.72-2.96)
Imidacloprid (70% WG)
1.70 (0.09-2.84)
4.79 (2.87-16.14)
Imidacloprid (35% SC)
51.46 (44.19-59.22)
110.89 (91.51-149.07)
Acetamprid (20% SL)
1.63 (1.09-2.05)
4.01 (3.27-5.50)
Acetamprid (10% EC)
3.13 (1.57-5.68)
8.12 (4.66-46.18)
Acetamprid (20% SP)
3122.91 (2403.71-3899.08)
7175.86 (6811.24-15349.28)
Table 3: Toxicity of selected neonicotinoid pesticides on 4th instar larvae of Culex pipiens after 72 h exposure.
LC50 (ppm)
LC90 (ppm)
Pesticides
(95% CL)
(95% CL)
Imidacloprid (20% SL)
0.57 (0.22-0.76)
1.27 (0.99-2.07)
Imidacloprid (70% WG)
1.34 (0.98-1.59)
2.63 (2.23-3.54)
Imidacloprid (35% SC)
36.88 (30.43-42.74)
78.54 (65.43-105.46)
Acetamprid (20% SL)
1.29 (0.67-1.74)
3.52 (2.79-5.00)
Acetamprid (10% EC)
2.60 (2.13-3.15)
6.66 (5.22-9.42)
Acetamprid (20% SP)
2698.19 (2057.27-3350.76)
6493.52 (5675.14 -12076.62)
Slope ± SE
2.84 (0.37)
2.71 (0.33)
3.17 (0.40)
2.90 (0.44)
3.12 (0.39)
3.87 (0.56)
Slope ± SE
3.90 (0.67)
2.58 (0.94)
3.84 (0.51)
3.29 (0.62)
3.09 (0.70)
2.73 (0.54)
Slope ± SE
3.67 (1.11)
4.38 (0.91)
3.90 (0.61)
2.93 (0.64)
3.13 (0.37)
2.88 (0.49)
Fig. 2: Times fold increase in toxicity of different formulations of Imidacloprid on 4th instar larvae of Culex
pipiens after 24, 48, and 72 h exposure.
Fig. 3: Times fold increase in toxicity of different formulations of Acetamprid on 4th instar larvae of Culex
pipiens after 24, 48, and 72 h exposure.
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Mohamed A. I. Ahmed and Reda M. Saba, 2014
Advances in Environmental Biology, 8(4) March 2014, Pages: 1169-1174
Fig. 4: Toxicity index of Imidacloprid formulations (A, B, and C) and Acetamprid formulations (D, E, and F) on
4th instar larvae of Culex pipiens after 24, 48, and 72 h exposure. Toxicity index = [(LC50 of the most
toxic tested pesticide formulation / LC50 of the tested pesticide formulation) ×100].
In general, neonicotinoid pesticides are agonists of the nAChRs and have low toxicity to mammals, birds,
and fish [14]. Regardless of whether they are acting as stomach poisons, many of them have low contact toxicity
on insect pests and are most effective against piercing-sucking insects such as mosquitos [19]. Ahmed and
Matsumura [20] evaluated six neonicotinoid pesticides on Aedes aegypti mosquito and they demonstrated that
Imidacloprid was more toxic than Acetamprid after 72 h which is agreed with our results. Corbel et al. [19]
evaluated dinotefuran, neonicotinoid pesticide commercialized by Mitsui Chemicals (Tokyo, Japan), against
three different species of mosquitoes and reported that dinotefuran was less toxic than most of the commonly
used pesticides (e.g., deltamethrin, carbosulfan, and temephos) but he concluded that neonicotinods were useful
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Mohamed A. I. Ahmed and Reda M. Saba, 2014
Advances in Environmental Biology, 8(4) March 2014, Pages: 1169-1174
candidates for public health and disease vector control, particularly in areas where pesticides resistance to other
pesticides is high. However, Allan [21] stated that imidacloprid was highly effective neonicotinoid pesticide and
as toxic as certain pyrethoid pesticides such as deltamethrin and permethrin for Culex quinquefasciatus,
furthermore, it was one of the most toxic pesticides for Anopheles quadrimaculatus and Aedes taeniorhynchus.
However, the known tolerance and safety of Imidacloprid in some insect predators, such as Coccinella
septempunctata (Coleoptera: Coccinellidae) is powerful advantages with respect to non-target organism
concerns and for environmental impact issues [22].
To sum up, these results indicate that there are two neonicotinoid pesticides with different formulations,
especially Imidaclprid 20% SL and Acetamprid 20% SL, that are effective in eliciting high levels of Culex
pipiens mosquito mortality. However, one of important and primary factor determining efficacy of a pesticide is
the type of the pesticide formulation. Meanwhile, these two neonicotinoid pesticides are a promising tool for
insect resistance management (IRM), integrated pest management program (IPM), and integrated mosquito
control program (IMC). On the other side, further biochemical and molecular biological investigation should be
done in order to understand the unique mechanism of the two selected neonicotinoids pesticides in Culex pipiens
mosquito; also, further semi-field or field tests, on larvae and adults, are required to measure their real effect
under field conditions.
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