Comparative Toxicity of Selected Insecticides to ...

Journal of Agricultural Science and Technology A 4 (2014) 514-520 Earlier title: Journal of Agricultural Science and Technology, ISSN 1939-1250

D DAVID

PUBLISHING

Comparative Toxicity of Selected Insecticides to Phytoplasma Transmitted Leafhopper Cicadulina bipunctata (Melichar) Mahmoud Massoud Abo-El-Saad1, Khalid Abdullah Alhudaib2 and Abdulaziz Mohamed Al Ajlan2 1. Date Palm Research Center of Excellence, King Faisal University, Alahsa 31982, Saudi Arabia 2. College of Agriculture and Food Science, King Faisal University, Alahsa 31982, Saudi Arabia

Received: April 15, 2014 / Published: June 20, 2014. Abstract: Leafhopper Cicadulina bipunctata is represented the main insect as a pathogen for phytoplasma disease occurring by insect-transmitted plant viruses in date palm orchards. Therefore, it is important to investigate the potential effect of some insecticides against such insect. The adults of leafhopper C. bipunctata were collected from date palm orchards in Alhasa, Eastern province, Saudi Arabia. Three insecticides from different classes—beta-cyfluthrin (pyrethroids), imidacloprid (neonicotinoids) and abamectin (natural compounds)—have been evaluated in vivo against adults C. bipunctata. This stage was exposed to residual film of various concentrations of each insecticide on transparent plastic cups using a Potter precision laboratory spray tower. Bioassay test showed that both beta-cyfluthrin and imidacloprid caused 100% mortality by 500 ppm at 24 h after treatment, whereas abamectin gave the same mortality by 50 ppm at the same time. Toxicity values revealed that abamectin was the most potent insecticide compared with beta-cyfluthrin and imidacloprid, where the lethal concentrations LC50 and LC95 were 24.58 ppm and 116.73 ppm at 3 h after treatment, respectively. Therefore, abamectin can be a possible candidate to be applied on date palm or ground grass by the Ministry of Agriculture after successful field experiments. Key words: Abamectin, imidacloprid, beta-cyfluthrin, leafhopper, insecticides, phytoplasma, bioassay.

1. Introduction Date palm (Phoenix dactylifera L.) has been affected by a disease called Al-Wijam in Saudi Arabia. The main symptoms are leaf stunting, yellow streaking and a marked reduction in fruit and stalk size, which leads to failure in fruit production at harvest [1]. Phytoplasmas are prokaryote organisms of the class Mollicutes, which affect more than 700 plant species from tropical to temperate countries [2]. They cannot be cultivated in vitro and are mainly transmitted by leafhopper or planthoppers of the order Hemiptera [3]. Phytoplasmas have been associated with diseases in date palm such as white tip die-back (WTD), slow Corresponding author: Mahmoud Massoud Abo-El-Saad, professor, research field: insect toxicology. Email: [email protected].

decline in Sudan in North Africa [4, 5], yellowing in Kuwait [6], and lethal decline in Texas [7]. A phytoplasma pathogen was suspected to cause Al-Wijam affected palms following histopathology and antibiotic therapy studies [8]. This was further supported by El-Zayat et al. [9], who reported a phytoplasma similar to that causing lethal yellow of coconut palm in Florida. The 16S rDNA sequences of the phytoplasma identified in date palm (DQ913090) and Cicadulina bipunctata (Melichar) (DQ913091) were 100% identical in between and 98% with that of Aster yellows phytoplasma (AF322644) from 16SrI, Candidatus Phytoplasma asteris group [10]. The control of phytoplasma diseases is always difficult because the vectors are generally small and mobile, and so it is hard to prevent crop colonisation.

Comparative Toxicity of Selected Insecticides to Phytoplasma Transmitted Leafhopper Cicadulina bipunctata (Melichar)

515

Hoppers and psyllids can transmit phytoplasmas with short feeding periods so that insecticides must act very rapidly and persist in their activity to provide satisfactory protection [11]. The variable nature of the diseases and the sporadic way they spread make their control difficult. Control requires integrated management, combining early detection and monitoring, eradication of infected plant material and control of the aster leafhoppers [12]. The use of insect-proof nets can prevent access of infective leafhoppers to the crop [13]. The objective of the study was to investigate the potential effect of some insecticides against phytoplasma transmitted Leafhopper Cicadulina bipunctata, subsequently providing satisfactory protection of date palm orchards from phytoplasma diseases.

Arabia. Insects were collected in 1,000 mL cylindrical plastic cups with a hand-trap, and placed in an icebox until arrival at the lab for bioassay test.

2. Materials and Methods

to preserve the plant life in order to provide the

2.1 Insecticides Insecticides are as follows: Beta-cyfluthrin emulsifiable concentrate (EC) 2.5%; cyano-(4-fluoro -3-phenoxy-phenyl) methyl 3-(2,2-dichloroethenyl)2,2-dimethyl cyclo propane carboxylate, Vermectin 1.8% EC (abamectin); C48H72O14 (avermectin B1a) + C47H70O14 (avermectin B1b) and Imidacloprid EC 20%; (2E)-1-[(6-chloro-3-pyridinyl)methyl]-N-nitro2-imidazolidinimine. All insecticides used in the bioassay test were generous gifts from the Ministry of Agriculture, Saudi Arabia. Preliminary susceptibility test of each insecticide has been conducted to assess effective range of the selected insecticides. Therefore, five concentrations of each insecticide were used as follows: 100, 200, 300, 400 and 500 ppm for imidacloprid and beta-cyfluthrin, while 10, 20, 30, 40, and 50 ppm were used for abamectin. 2.2 Collecting Insects The adults of leafhopper Cicadulina bipunctata, an insect-transmitted plant virus, were collected from date palm orchards in Alhasa, Eastern province, Saudi

2.3 Bioassay Test against Adults Bioassay test was carried out against adults C. bipunctata (Melichar) as described by Abo-El-Saad et al. [14, 15] as a residual film method under laboratory conditions. This method is recommended by the FAO against insects in laboratory conditions. A series of concentrations for each insecticide mentioned above were prepared. Each concentration was sprayed using a Potter precision laboratory spray tower to produce a residual film of the insecticide. This insecticidal film was established on the vegetative part of the host plant green foxtail, Setaria viridis, while the root was immersed in an Eppendorf tube containing 1 mL water appropriate environment for insects to suck their food from the plant. Ten insects were exposed to each concentration in three replicates, while the control was run with water. In order to assess the effect of the insecticides, the insects were examined at 0.24, 0.5, 1, and 2 h. An insect was considered dead if it neither moved nor responded by reflex movement, when gently touched with a brush. The percentages of mortality, normal equivalent deviates: chi square, 50% and 95% lethal concentrations, and their fiducial limits, were calculated according to Finney [16] using MINITAB Statistical Software, Ver. 13.30, Copyright 2000, Minitab Inc.

3. Results and Discussion The effect of beta-cyfluthrin against leafhopper C. bipunctata with various concentrations 100, 200, 300, and 500 ppm at different periods of time is clearly shown in Fig. 1, which obviously indicated that beta-cyfluthrin exhibited less effect until 30 min after treatment. When the concentration increased progressively to 500 ppm, mortality reached 100% at 120 min after treatment. The results in Tables 1 and 2

516


100.00

120 min

Mortality (%)

80.00

60.00

60 min

40.00 30 min

20.00

15 min

0.00 0.00

100.00

200.00 300.00 400.00 Concentration (ppm)

500.00

Fig. 1 Effect of beta-cyfluthrin at different concentrations against leafhopper, Cicadulina bipunctata (Melichar) after exposing for various time periods. Table 1 LC50 and LC95 values of certain insecticides against leafhopper, Cicadulina bipunctata (Melichar) after exposing for various periods. Insecticide

Time (min) 60

Beta-cyfluthrin 120 60 Imidacloprid 120 60 Abamectin 120

LC50 (ppm) (95% fiducial limits) 259.9 (123.4-444.1) 146.1 (57.9-201.2) 320.4 (202.9-571.5) 180.6 (110.1-231.1) 24.58 (11.34-39.17) 16.13 (7.3-22.13)

LC95 (ppm) (95% fiducial limits) 1260.5 (613.4-1574.5) 506.1 (348.0-1789.3) 1224.8 (636.15-4129.5) 464.19 (345.1-1000.5) 116.73 (59.27-648.5) 56.94 (38.8-183.89)

revealed that the LC50 and LC95 values of beta-cyfluthrin were 146.1 ppm and 506.1 ppm at 120 min after treatment, whereas LT50 and LT95 were 130.7 and 518.8 min at 100 ppm. By increasing the concentration to 500 ppm, these values were decreased to reach 35.7 min and 99.3 min, respectively. On the other hand, the data in Fig. 2 obviously shows the effect of imidacloprid against leafhopper C.

Chi square (χ )

Degrees of Slope ± SE freedom

P

0.07

2

0.93 ± 0.36

0.96

2.7

2

1.18 ± 0.37

0.26

0.62

2

1.10 ± 0.39

0.74

1.9

2

1.50 ± 0.42

0.39

0.16

2

0.94 ± 0.35

0.93

0.08

2

1.16 ± 0.34

0.96

2

bipunctata with various concentrations 100, 200, 300, and 500 ppm at different periods of time, 15, 30, 60 and 120 min. The results indicated that the percentage of mortality increased by increasing of both concentrations and exposure time, where 500 ppm caused 100% mortality at 120 min after treatment. Tables 1 and 2 show that LC50 and LC95 were 180.6 ppm and 464.19 ppm at 120 min after treatment, respectively; whereas LT50 and LT95 reached 161.6


517

Table 2 LT50 and LT95 values of certain insecticides against leafhopper, Cicadulina bipunctata (Melichar) after exposing for various periods. insecticide

LT50 (min) (95% fiducial limits) 130.7 (78.6-1228.6) 101.4 (58.5-810.2) 58.8 (33.8-101.4) 35.7 (22.9-47.6) 161.6 (99.7-3050.9) 130.7 (78.64-1228.6) 55.5 (29.8-98.3) 30.5 (15.3-43.4) 455.8 (294.0-5397.8) 276.3 (200.1-456.5) 216.2 (156.8-293.3) 157.9 (115.6-199.0)

Conc. (ppm) 100 200

Beta-cyfluthrin 300 500 100 200 Imidacloprid 300 500 10 20 Abamectin 30 50

LT95 (min) (95% fiducial limits) 518.8 (200.6-3201.5) 590.8 (201.7-1710.3) 288.4 (143.7-398.2) 99.3 (70.4-215.6) 445.0 (193.9-4473.0) 518.77 (200.6-3201.5) 307.5 (145.4-6669.3) 120.4 (77.3-407.8) 1201.5 (556.5-4603.9) 727.0 (445.1-3658.8) 547.3 (375.9-1411.1) 353.8 (269.2-607.6)

Chi square (χ )

Degrees of freedom

Slope ± SE

0.003

2

1.06 ± 0.41 0.99

0.158

2

0.83 ± 0.33 0.92

0.230

2

0.92 ± 0.29 0.89

1.56

2

1.43 ± 0.34 0.46

0.67

2

1.44 ± 0.59 0.72

0.003

2

1.06 ± 0.41 0.99

0.009

2

0.86 ± 0.28 0.99

3.16

2

1.06 ± 0.29 0.21

2.12

2

1.51 ± 0.61 0.35

3.28

2

1.51 ± 0.44 0.19

3.64

2

1.57 ± 0.39 0.16

2.90

2

1.81 ±0 .39 0.23

2

P

100.00

Mortality (%)

80.00

120 min

60.00 60 min

40.00

30 min

15 min

20.00

0.00 0.00

100.00

200.00

300.00

400.00

500.00

Concentration (ppm) Fig. 2 Effect of imidacloprid at different concentrations against leafhopper, Cicadulina bipunctata (Melichar) after exposing for various time periods.

min and 445 ppm at 100 min, respectively. However, it was decreased by insecticide concentration to reach 30.5 min and 120.4 min at 500 ppm, respectively.

These results are consistent with those reported by Saracco et al. [17] who noted the insecticide imidacloprid was the most important insecticide that

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has the capacity to limit the transmission of chrysanthemum yellows phytoplasma (CYP) by the leafhopper vector Macrosteles quadripunctulatus to potted daisy plants, Chrysanthemum carinatum. In addition, many studies have been conducted to investigate the effect of some organophosphates (OPs) and a neonicotinoid insecticide on transmission of CYP to its herbaceous host under controlled conditions. For insect-transmitted plant viruses, insecticide activity is commonly evaluated in terms of reduced transmission, both in the laboratory [18-20] and in the field or greenhouse [21-23], while for phytoplasma diseases, the available data are based on vector mortality. The OPs were used in Italian vineyards against Scaphoideus titanus Ball, vector of “flavescence doree” phytoplasma (FDP) [24, 25]. A neonicotinoid insecticide, imidacloprid, was also included in the study since this insecticide class has good activity in preventing persistent transmission of arthropod-borne plant pathogens [19, 21, 22, 26]. Besides its economic importance, CYP is a useful experimental model system to investigate the efficiency of insecticides in preventing phytoplasma

transmission because of the high transmission efficiency of M. quadripunctulatus [27], and the clear symptoms developed by infected daisies. These findings are also in agreement with those reported by Alhudaib [10] showing that leafhopper C. bipunctata is the main insect acting as a pathogen for phytoplasma disease, which occurred by insect-transmitted plant viruses in date palm orchards in Saudi Arabia. In addition, the results presented in Fig. 3 show the effect of abamectin (a natural insecticide derived from fermentation of Streptomyces avermitilis) on leafhopper C. bipunctata at laboratory condition with various concentrations 10, 20, 30 and 50 ppm for different exposure times, 1, 2, 3, 6 and 24 h, which obviously indicated that abamectin possesses less effect until 2 h after treatment. When the concentration increased progressively to 50 ppm, mortality reached 93% and 100% at 6 h and 24 h after treatment. Tables 1 and 2 show that the toxicity values, LC50 and LC95, were 24.58 ppm and 116.73 ppm at 180 min after treatment, respectively; whereas, LT50 and LT95 reached 157.9 min and 353.8 min at 50 ppm, 24 hours

100.00

Mortality (%)

80.00

6 hours

60.00 3 hours

40.00

20.00

2 hours

1 hour

0.00 0.00

10.00

20.00

30.00

40.00

50.00

Concentration (ppm) Fig. 3 Effect of abamectin at different concentrations against leafhopper, Cicadulina bipunctata (Melichar) after exposing for various time periods.


respectively. These data are consistent with those reported by Weintraub [28] who indicated the effectiveness

of

abamectin

against

Liriomyza

huidobrensis.

4. Conclusions

519

Acknowledgements The authors would like to thank the King Abdulaziz City for Science and Technology, Saudi Arabia for kindly providing financial support for the Project No. AT-28-111, and King Faisal University’s Pests and Plant Diseases Unit.

Three insecticides from different classes have been chosen in the experimental bioassay, as it possesses

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