MINISTRY OF EDUCATION AND TRAINING MINISTRY OF AGRICULTURE AND RURAL DEVELOPMENT VIETNAM ACADEMY OF AGRICULTURAL SCIENCES BUI XUAN THANG STUDY ON INSECTICIDE RESISTANCE OF RICE BROWN PLANTHOPPER (Nilaparvata lugens Stal) POPULATIONS IN SOME RICE-GROWING AREAS IN VIETNAM Specialization: Plant protection Code: 9620112 SUMMARY OF DOCTORAL THESIS HANOI, 2019 The thesis is completed at: Vietnam Academy of Agricultural Sciences Supervisors: Assoc Prof Dr Ho Thi Thu Giang Assoc Prof Dr Michael Kristensen Reviewer 1: ……………………………………………… …………………………………………………………… Reviewer ……………………………………………… ………………………………………………………… Reviewer 3: ……………………………………………… …………………………………………………………… The thesis will be defended in front of the Academy-level Thesis Evaluation Council At Vietnam Academy of Agricultural Sciences On 2019, a.m./p.m The thesis can be found at the following libraries: - National Library of Vietnam - Library of Vietnam Academy of Agricultural Sciences - Library of PhD candidate's agency INTRODUCTION Rationale of the study Rice is one of the most important food crops and a major source of food for one third of the world's population (Jena and Kim, 2010) In Vietnam, the population is over 90 million people and most of them use rice as their staple food Therefore, rice production plays an important role in agricultural production However, rice production is affected by many pests and diseases Among them, brown planthopper, Nilaparvata lugens (Homoptera: Delphacidae) is the most dangerous pest (Dyck and Thomas, 1979) In recent years, brown planthopper has been causing significant losses in some countries such as China, Japan, Korea, Thailand and Bangladesh In Vietnam, brown planthopper is also the most dangerous pest which causes the most damage to rice production From 1999 to 2003, an annual average of 408,908 was damaged by planthoppers nationwide, of which 34,287 were badly damaged and 179 were completely lost (Nguyen Van Dinh and Bui Sy Doanh, 2010) In 2016, an outbreak of brown planthoppers occurred in the Southern provinces and some provinces in the Red River Delta with an area of nearly 150,000 ha, of which over 20,000 were seriously infected (Plant Protection Department, 2016) Brown planthopper has become more and more dangerous when it is a vector of rice grassy stunt virus (RGSV) and rice ragged stunt virus (RRSV) and has been causing widespread damage recently In the Southern provinces, although the disease has been controlled, brown planthopper still causes damage on an area of 332,941 In the Northern provinces, brown planthopper has always been a direct threat to rice and a potential threat to the spread of RRSV virus (Plant Protection Department, 2012) Chemical insecticides are still the first choice in the current brown planthopper control measures The fact shows that this measure is highly effective against brown planthoppers and quickly quells outbreaks on a large scale However, an increase in the area affected by brown planthoppers will lead to an increase in the use of plant protection insecticides against planthoppers (Nguyen Thi Me et al., 2002) An increase in the number of plant protection insecticides against planthoppers will lead to an increased risk of resistance of brown planthoppers and cross-resistance between insecticides In addition, different crop seasons among regions combined with the migratory ability of brown planthoppers is one of the factors that increase the risk of resistance of brown planthoppers One of the reasons that make many brown planthopper insecticides not as effective as before is the developed and increased resistance of brown planthoppers When the brown planthoppers have become resistant to such insecticides, it will cause difficulties for the management of brown planthoppers in rice production The study and monitoring of resistance of brown planthoppers to common plant protection insecticides that are currently used to control brown planthoppers become very urgent and require systematic and continuous implementation for many years, thereby, serving as a basis for proposing solutions to limit the formation and development of resistance of brown planthoppers Based on the above points of view, we have choosen the topic: “Study on insecticide resistance of rice brown planthopper (Nilaparvata lugens Stal) populations in some rice- growing areas in Vietnam” Study objectives To determine the current status of use of plant protection insecticides and the resistance of brown planthopper populations in some rice-growing provinces, serving as a scientific basis for proposing solutions to manage the resistance of brown planthoppers Scientific and practical significance 3.1 Scientific significance - Providing data on resistance levels and resistance development of brown planthoppers to some active ingredients in some provinces, contributing to the recommendation and selection of effective insecticides against brown planthoppers - Providing data on effect of active ingredients such as imidacloprid, nitenpyram on some biological characteristics of brown planthoppers and on toxicity of some active ingredients on green stink bug which is an important natural enemy of brown planthoppers 3.2 Practical significance - The thesis contributes to the application of solutions of use of plant protection insecticides and resistant rice varieties to effectively control brown planthoppers, thereby reducing the resistance of brown planthoppers in production - The thesis is a reliable reference, providing scientific data for professional training on the management of resistance of brown planthoppers Subject and scope of the study 4.1 Subject of the study Resistance of brown planthopper (Nilaparvata lugens) populations in some typical rice-growing provinces: Hung Yen, Nam Dinh, Nghe An, Phu Yen and An Giang for some plant protection active ingredients used in brown planthopper control 4.2 Scope of the study - Resistance levels of brown planthopper populations in some typical rice-growing provinces: Hung Yen, Nam Dinh, Nghe An, Phu Yen and An Giang - Effect of chemical active ingredients on biological characteristics of brown planthoppers - Study and recommendation of strategies for management of plant protection substance resistance of brown planthoppers New contributions of the study - Supplementing new scientific data on the resistance of brown planthoppers to some active ingredients of Neonicotinoids, Carbamates, growth regulators, Pyridine azomethines, Sulfloximines - Providing new scientific data on the effect of plant protection insecticides on some biological characteristics, the effect of rice varieties on the development of resistance of brown planthoppers and the toxicity of such insecticides to green stink bugs - Proposing some measures to effectively prevent brown planthoppers and reduce the resistance of brown planthoppers Chapter LITERATURE REVIEW AND SCIENTIFIC BASIS OF THE THESIS 1.1 International study situation Brown planthoppers have formed and developed resistance to many insecticides of Carbamates, Neonicotinoids, growth regulators and Pyridine azomethines Some authors outside the country have studied the resistance of rice brown planthoppers such as: Zewen et al (2003), Masumura et al (2008, 2013), Wang et al (2008), Catindig et al (2009), Wen et al (2009), Shao et al (2011), Basanth et al (2013), Xiaolei Zhang et al (2014), Padmakumari et al (2002), Srivastava et al (2009), Mu et al (2016), Ping et al (2001), Jie Zhang et al (2010), He YuePing et al (2011), and Wang Peng et al (2013) Study results of these authors show that brown planthopper populations are resistant to active ingredients such as imidacloprid, fenobucar, buprofezin, dinotefuran, nitenpyram, and pymetrozine 1.2 Domestic study situation Some authors in the country have studied the resistance of rice brown planthoppers such as Luong Minh Chau (2007), Nguyen Pham Hung (2009), Nguyen Thi Hong Van (2010), Nguyen Thanh Hai (2011), Le Thi Kim Oanh et al (2011), Le Thi Dieu Trang (2012), Phan Van Tuong et al (2013, 2014), Phung Minh Loc et al (2016, 2017), Dao Bach Khoa et al (2018), Huynh Thi Ngoc Diem et al (2017), and Nguyen Hong Phong et al (2012) Study results of these authors show that brown planthopper populations are resistant to most of active ingredients commonly used for brown planthopper control However, these studies still lack continuity with sporadic resistance management measures Chapter MATERIALS, CONTENTS AND METHODS OF STUDY 2.1 Duration and place of study - Duration of study: The thesis is made from 2014 - 2018 - Place of study: Study on insecticide resistance of brown planthopper populations is conducted in Hung Yen, Nam Dinh, Nghe An, Phu Yen and An Giang and has the results gathered at laboratories, net houses of Vietnam National University of Agriculture and Plant Protection Research Institute 2.2 Study materials and instruments - Taichung Native (TN1) rice variety, susceptible brown planthoppers originated from the National Agricultural Research Institute in Okinawa - Kyushu (Japan) - Experimental insecticides: Carbamates, Neonicotinoids, Pyridine azomethines, Sulfloximines, growth regulators - Planthopper pipette, tube, plastic cup, cotton, magnifying glass, pipette, volumetric flask, measuring cylinder, planthopper cage, seedling tray, seedling rack - Na/K phosphate buffer, acetone, ELISA plate, NADPH, oxidized glutathione, acetonitrile, TRIZMA-base, 1-naphthyl acetate, Tris-HCl 2.3 Contents of study - Determining the current status of use of plant protection insecticides against rice brown planthoppers in some rice-growing areas in Vietnam - Studying the resistance of brown planthopper populations to some groups of plant protection insecticides in some rice-growing areas in Vietnam - Proposing reasonable solutions to manage insecticide resistance of brown planthoppers 2.4 Methods of study 2.4.1 Method of determination of current status of use of plant protection insecticides against rice brown planthoppers in some rice-growing areas in Vietnam By face-to-face interview method, provinces are selected, including districts in each province, communes in each district, 20 surveyed farmers/household in each commune 2.4.2 Method of study of resistance of brown planthopper populations to some groups of plant protection insecticides in some rice-growing areas in Vietnam - Method of determination of resistance levels of brown planthopper populations in some rice-growing areas in Vietnam: Zhuang and Shen's rice-stem dipping method (2000) - Study and explanation of insecticide resistance mechanism of brown planthoppers: Assessment of activity of Cytochrome P450-dependent monooxygenase enzyme according to the method of Puinean et al (2010), Esterase enzyme according to the method of Wen et al (2009), Glutathione S-transferase enzyme according to the method of Ralf Nauen and Natascha Stumpf (2002) - Cross-resistance of brown planthopper populations which are resistant to active ingredient imidacloprid to some other active ingredients against brown planthoppers: Using LC50 insecticide dose for brown planthoppers in the previous generation as selective pressure dose for the next generation After 12 generations of selective pressure on the active ingredient imidacloprid, redetermining the resistance of brown planthopper populations to active ingredients - Effect of insecticide active ingredient on some biological characteristics of brown planthoppers after exposure to insecticide: According to the method of Jie Zhang et al (2010) 2.4.3 Method of study of reasonable solutions to manage insecticide resistance of brown planthoppers - Study of method of use of resistant rice varieties in management of insecticide resistance of brown planthoppers + Assess the resistance levels of some rice varieties to brown planthopper Nilaparvata lugens (Stål) populations according to the method of IRRI (1996) + Effect of rice varieties on resistance levels of An Giang brown planthopper population after a number of generations not exposed to the active ingredient imidacloprid: The planthopper population is reared on two rice varieties TN1 and OM 6976 without exposure to insecitide After every two generations, determine the resistance level of brown planthopper population + Effect of rice varieties on resistance level of An Giang brown planthopper population after a number of generations exposed to the active ingredient imidacloprid: The brown planthopper population is reared on two rice varieties TN1 and OM 6976, through each selection, use determined LC50 dose of the previous generation as the selective pressure dose for the next generation - Study of method of use of chemical insecticides in management of resistance of brown planthoppers: + Assess the effect of some insecticides according to the national technical regulations on effect testing of rice planthopper insecticides (QCVN 01 - 29 : 2010/BNNPTNT) + Rotationally use insecticides in brown planthopper control: Spray insecticides in turn in a rotation formula for 2-3-year-old larvae of brown planthoppers After each spray, select healthy living individuals to continue breeding Each spraying formula rotates times Determine LC50 value of brown planthopper population to insecticides after alternating spray of insecticides + Toxicity of some brown planthopper insecticides on green stink bugs according to the method of Preetha et al (2010) 2.4.4 Data processing method Data is processed using IBM SPSS 20, StatView and Excel software Chapter STUDY RESULTS AND DISCUSSION 3.1 Current situation of use of plant protection insecticides against rice brown planthoppers in some rice-growing areas Survey results show that there are 11 groups of insecticides commonly used by farmers in Hung Yen, Nam Dinh, Nghe An, Phu Yen and An Giang to control rice brown planthoppers In particular, farmers in Hung Yen, Nam Dinh, Nghe An and Phu Yen provinces mainly use Neonicotinoids (insecticide group with many different active ingredients) to control brown planthoppers The percentage of farmer households in these provinces using Neonicotinoids for brown planthopper control ranges from 74.17 to 98.34% In addition to Neonicotinoids, farmers in Phu Yen province use Pyridine azomethines (active ingredient pymetrozine) to control brown planthoppers at a quite high rate with the percentage of 52.50% For other insecticide groups, the percentage of use for brown planthopper control by farmer households in Hung Yen, Nam Dinh, Nghe An and Phu Yen provinces is lower, ranging from 0.83 to 21.67% However, in An Giang province, farmers mainly use Pyridine azomethines to control brown planthoppers with the percentage of use by households of 89.17% The Neonicotinoids are also used by farmers in An Giang with a fairly high percentage of 58.97% For other insecticide groups, the percentage of use for brown planthopper control by farmer households in An Giang is lower than 14% (Table 3.6) Table 3.6 Current situation of use of plant protection insecticides by groups in the studied provinces in 2014 Pct (%) of use by farmer households by groups No Insecticide group HY ND NA PY AG Growth regulators 4.17 2.50 6.67 3.33 Phenylpyrazole 2.50 0.83 0.83 6 10 11 12 13 14 15 16 Neonicotinoids Carbamates Pyridine azomethines Avermectins Organophosphates Sulfloximines Nereistoxin analogue Organophosphates; Pyrethroids Carbamates; Pyrethroids Pyrethroids; Neonicotinoids Trifluoromethylnicotinamid; Neonicotinoids Growth regulators; Neonicotinoids Organophosphates; Growth regulators Neonicotinoids; Pyridine azomethines 83.33 5.83 3.33 2.50 1.67 74.17 4.17 5.83 - 98.34 7.50 21.67 - 78.33 7.50 52.50 - 58.97 5.83 89.17 1.67 7.50 4.17 - 6.67 4.17 5.00 - 5.83 - - 3.33 17.50 - - - - - - 6.70 12.50 15.00 - - 13.14 15.83 13.33 7.36 9.17 - - - - - 2.50 Note: HY: Hung Yen; ND: Nam Dinh; NA: Nghe An; PY: Phu Yen; AG: An Giang Survey results on producers' perceptions of plant protection insecticide use in Hung Yen, Nam Dinh and Nghe An provinces show that most farmers use a mixture of to insecticides in one spray Specifically, the percentages of farmer households using the mixture of insecticides in one spray in Hung Yen, Nam Dinh and Nghe An provinces are 59.17%, 60% and 57.50%, respectively The percentages of farmer households using the mixture of insecticides in one spray in these provinces are 33.33%, 30.83% and 35.83%, respectively However, the survey results in Phu Yen and An Giang provinces show that there are still many farmers using a single insecticide in one spray The percentages of farmer households using a single insecticide in one spray in Phu Yen and An Giang provinces are 30.83% and 45%, respectively However, farmers in Phu Yen and An Giang provinces still mainly use the mixture of to insecticides in one spray The percentages of farmer households using the mixture of to insecticides in one spray farmers in Phu Yen and An Giang provinces are 69.17% and 55%, respectively In parallel with the mixture of many insecticides in one spray, farmers in the surveyed provinces also increase the dose in one spray from 1.5 to times higher than the recommended dose The percentages of farmer households in Hung Yen, Nam Dinh, Nghe An, Phu Yen and An Giang provinces using the dose higher than the recommended dose in one spray are 35,00%, 31.67%, 33.33%, 40% and 49.17%, respectively In An Giang, farmers commonly spray times in a rice crop with the percentage of 57.50% Furthermore, in An Giang, there is still 4.17% of farmer households spraying more than times in a rice crop However, in Hung Yen, Nam Dinh, Nghe An and Phu Yen provinces, there are no farmers spraying times/rice crop but popularly spraying to times/rice crop In particular, the percentages of farmer households spraying times in a rice crop in Hung Yen, Nam Dinh, Nghe An and Phu Yen provinces are 44.17%, 45.83%, 40.83% and 43.33%, respectively The percentages of farmer households spraying times in a rice crop in these provinces are 50%, 46.67%, 46.67% and 45% respectively (Table 3.7) Table 3.7 Farmers' habit of using plant protection insecticides in the studied provinces in 2014 Percentage of responding farmer households (%) Applied technique HY ND NA PY AG 7.50 9.17 6.67 30.83 45.00 Number of insecticides 59.17 60.00 57.50 49.17 41.67 used in spray 33.33 30.83 35.83 20.00 13.33 According to 65.00 68.33 66.67 60.00 50.83 recommendation Insecticide dose 1.5 times higher than 26.67 25.00 23.33 27.50 29.17 in spray recommended times higher than 8.33 6.67 10.00 12.50 20.00 recommended 5.83 7.50 12.50 11.67 8.33 44.17 45.83 40.83 43.33 30.00 Number of sprays in crop 50.00 46.67 46.67 45.00 57.50 4-7 0 0 4.17 Note: HY: Hung Yen; ND: Nam Dinh; NA: Nghe An; PY: Phu Yen; AG: An Giang 3.2 Resistance of brown planthoppers to some major insecticide groups in some ricegrowing areas 3.2.1 Resistance of brown planthopper populations to common active ingredients against rice brown planthoppers 3.2.1 Resistance of brown planthopper populations in some provinces to active ingredient imidacloprid Results show that both brown planthopper populations in Hung Yen and Nam Dinh have moderate resistance to the active ingredient imidacloprid The resistance rates of these two planthopper populations to the active ingredient imidacloprid vary from 31.575 to 41.082 over the years 2015-2017 However, brown planthopper populations in Nghe An, Phu Yen and An Giang have high to very high resistance to the active ingredient imidacloprid The resistance rates of these brown planthopper populations to the active ingredient imidacloprid vary from 51.415 from 161.768 (Table 3.8) Table 3.8 Resistance levels of brown planthopper populations to active ingredient imidacloprid in some rice-growing provinces from 2015 - 2017 Year 2015 2016 Planthopper origin HY ND NA PY AG HY LC50 (mgl) and 95% confidence intervals 8.504 (5.852 - 10.749) 7.642 (5.242 - 9.638) 12.065 (7.627 - 15.598) 17.241 (11.338 - 22.216) 26.490 (16.72 - 34.23) 7.818 (4.794 - 10.099) Angular coefficient 1.581 ± 0.208 1.829 ± 0.235 1.089 ± 0.150 0.769 ± 0.102 0.440 ± 0.085 1.560 ± 0.265 RR 41.082 36.918 58.285 83.289 127.971 37.681 2017 ND NA PY AG HY ND NA PY AG 7.189 (4.905 - 9.019) 11.199 (6.870 - 14.658) 15.406 (9.128 - 20.428) 33.486 (19.890 - 44.596) 6.748 (4.070 - 8.853) 6.536 (4.461 - 8.205) 10.643 (6.564 - 13.940) 14.351 (8.991 - 18.581) 24.487 (16.643 - 31.083) 1.854 ± 0.272 1.081 ± 0.178 0.766 ± 0.127 0.353 ± 0.064 1.540 ± 0.328 1.869 ± 0.327 1.084 ± 0.194 0.781 ± 0.149 0.499 ± 0.088 34.729 54.101 74.425 161.768 32.599 31.575 51.415 69.328 118.294 Note: HY: Hung Yen; ND: Nam Dinh; NA: Nghe An; PY: Phu Yen; AG: An Giang; RR: resistance rate; LC50 of susceptible brown planthoppers: 0.207 (0.097 – 0.294) mgl 3.2.1.2 Resistance of brown planthopper populations in some provinces to active ingredient nitenpyram Results of determination of resistance levels of brown planthopper populations to the active ingredient nitenpyram in Hung Yen, Nam Dinh, Nghe An, Phu Yen and An Giang show that two brown planthopper populations in Hung Yen and Nam Dinh begin to form a mild resistance in 2015-2016 with the resistance rates ranging from 4.087 to 4.896 However, in 2017, the resistance of the two brown planthopper populations develops to a low resistance to the active ingredient nitenpyram The resistance rates of the two brown planthopper populations to the active ingredient nitenpyram in Hung Yen and Nam Dinh vary from 5.175 to 5.230 From 2015 to 2017, brown planthopper populations in Nghe An and Phu Yen have a low resistance to the active ingredient nitenpyram with the resistance rates ranging from 5.418 to 9.357 However, the brown planthopper population in An Giang has a moderate resistance to the active ingredient nitenpyram with the resistance rate ranging from 16.552 to 24.112 Resistance rates of brown planthopper populations to the active ingredient nitenpyram in Hung Yen, Nam Dinh, Nghe An, Phu Yen and An Giang all increase over the years 2015 - 2017 Resistance rates of these brown planthopper populations to the active ingredient nitenpyram increased from 2015 to 2017 are 4.087 - 5.230; 4.607 - 5.175; 5.418 5.932; 7.867 - 9.357; 16.552 - 24.112, respectively (Table 3.9) Table 3.9 Resistance levels of brown planthopper populations to active ingredient nitenpyram in some rice-growing provinces from 2015 - 2017 Year 2015 2016 Planthopper origin HY ND NA PY AG HY ND NA LC50 (mgl) and 95% confidence intervals 1.933 (1.258 - 2.473) 2.179 (1.487 - 2.735) 2.563 (1.605 - 3.318) 3.721 (2.399 - 4.779) 7.829 (4.980 - 10.102) 2.115 (1.446 - 2.661) 2.316 (1.614 - 2.881) 2.713 (1.753 - 3.471) Angular coefficient 5.515 ± 1.162 5.607 ± 0.982 4.372 ± 0.834 3.125 ± 0.572 1.371 ± 0.280 5.594 ± 1.019 5.624 ± 0.903 4.433 ± 0.752 RR 4.087 4.607 5.418 7.867 16.552 4.471 4.896 5.736 16 The results show that the effect of the two active ingredients nitenpyram and imidacloprid on egg-laying capacity of short-winged brown planthoppers (reduced to 52.88% and 62.52%, respectively) is more noticeable than that of long-winged brown planthoppers (reduced to 58.91% and 70.28%, respectively) Of the two active ingredients used for testing, the active ingredient nitenpyram has more noticeable effect than the active ingredient imidacloprid in both long-winged and short-winged brown planthoppers As a result, it is still possible to continue to use the Neonicotinoid insecticides for brown planthopper control and the active ingredient nitenpyram is recommended as more effective in brown planthopper control 3.2.4.2 Effect of active ingredients nitenpyram and imidacloprid on wing shape of brown planthoppers Lethal concentrations LC30 of the active ingredients nitenpyram and imidacloprid affect the wing formation of brown planthoppers The effect of the active ingredient imidacloprid on the wing formation of brown planthoppers is stronger than that of the active ingredient nitenpyram in both long-winged and short-winged brown planthoppers In long-winged brown planthoppers, the rates of female and male long-winged brown planthoppers are 56.73% and 60.58%, respectively, after exposure to the active ingredient nitenpyram The lethal concentration LC30 of the active ingredient imidacloprid affects the female and male long-winged brown planthoppers with the rates of 74.52% and 71.80%, respectively The lethal concentrations LC30 of nitenpyram and imidacloprid affect the increase in the female and male long-winged brown planthoppers This increase is significant when compared to the control formula which is 43.16% (rate of female longwinged brown planthoppers) and 51.84% (rate of female long-winged brown planthoppers), respectively (Table 3.20) Table 3.20 Effect of active ingredients nitenpyram and imidacloprid on long-winged brown planthoppers in An Giang, 2016 Female brown planthoppers Male brown planthoppers Test Long-winged Short-winged Long-winged Short-winged (%) (%) (%) (%) b b b Nitenpyram 56.73 43.27 60.58 39.42b Imidacloprid 74.52c 25.48a 71.80c 28.20a Control 43.16a 56.84c 51.84a 48.16c Note: in columns, different letters indicate reliable difference at probability P Chess 50WP (3.345 mgl) > Oshin 20WP (2.689 mgl) > Admire 50EC (0.300 mgl) > Bassa 50EC (0.150 mgl) Out of the insecticides against brown planthoppers, Bassa 50EC is the most toxic one to green stink bugs with LC50 value 23 to green stink bugs after 24 hours and 48 hours of 0.150 mgl and 0.100 mgl, respectively Applaud 10WP is the least toxic to green stink bugs with LC50 value to green stink bugs after 24 hours and 48 hours of 12.323 mgl and 10.574 mgl, respectively Out of the insecticides against brown planthoppers, Oshin 20WP has the highest toxicity to brown planthoppers with LC50 value to brown planthoppers after 24 hours and 48 hours of 2.281 mgl and 1.377 mgl, respectively Bassa 50EC has the lowest toxicity to brown planthoppers with LC50 value to brown planthoppers after 24 hours and 48 hours of 298.376 mgl and 258.895 mgl, respectively LC50 value of these insecticides to brown planthoppers is in the order of: Bassa 50EC (258.895 mgl) > Applaud 10WP (115.861 mgl) > Chess 50WP (51.337 mgl) > Admire 50EC (15.667 mgl) > Elsin 10EC (4.275 mgl) > Closer 500WG (2.679 mgl) > Oshin 20WP (1.377 mgl) at 48 hours after treatment (Table 3.29) Table 3.29 LC50 value of some insecticides to green stink bugs and brown planthoppers, 2017 LC50 to green stink bugs (mgl) LC50 to brown planthoppers (mgl) Name of insecticide 24 hours 48 hours 24 hours 48 hours 0.300 0.171 18.775 15.667 Admire 50EC (0.205 - 0.381) (0.119 - 0.214) (13.238 - 23.499) (10.636 - 19.757) 3.345 1.894 88.774 51.337 Chess 50WP (2.271 - 4.256) (1.276 - 2.396) (62.189 - 110.241) (34.366 - 64.896) 5.293 3.345 4.800 2.679 Closer 500WG (3.619 - 6.686) (2.151 - 4.297) (3.445 - 5.949) (1.701 - 3.458) 8.276 4.785 6.677 4.275 Elsin 10EC (5.695 - 10.405) (3.280 - 5.962) (4.455 - 8.524) (2.536 - 5.653) 0.150 0.100 298.376 258.895 Bassa 50EC (0.104 - 0.189) (0.070 - 0.123) (208.269 - 374.936) (170.113 - 330.227) 2.689 1.595 2.281 1.377 Oshin 20WP (1.890 - 3.398) (1.042 - 2.036) (1.549 - 2.902) (0.915 - 1.751) 12.323 10.574 154.587 115.861 Applaud 10WP (8.029 - 15.844) (7.229 - 13.308) (106.990 - 193.626) (69.273 - 150.344) Note: Values in brackets are 95% confidence interval values 3.3.3.2 Toxicity index of some insecticides against brown planthoppers to green stink bugs Out of the insecticides against brown planthoppers, Closer 500WG, Elsin 10EC, and Oshin 20WP are less toxic to green stink bugs than to brown planthoppers with selective index > Admire 50EC, Chess 50WP, Bassa 50EC, and Applaud 10WP are more toxic to green stink bugs than to brown planthoppers with selective index < (Table 3.31) However, when used at the recommended dose in the field, Chess 50WP, Closer 500WG, Elsin 10EC, Oshin 20WP, and Applaud 10WP are quite safe to green stink bugs (toxicity index < 50) although Chess 50WP and Applaud 10WP are more toxic to green stink bugs than to brown planthoppers (selective index < 1) The assessment results of toxicity of some insecticides to green stink bugs show that Chess 50WP, Closer 500WG, Elsin 10EC, Oshin 20WP, and Applaud 10WP, when used to control brown planthoppers at the recommended dose, are quite safe to green stink bugs 24 Bassa 50EC and Admire 50EC, when used at the recommended dose in the field, are not safe to green stink bugs Table 3.31 Selective index of some insecticides against brown planthoppers which are less toxic to green stink bugs after 24 hours of treatment, 2017 No Name of insecticide Active ingredient Recommended dose (g a.i/ha) Selective index Admire 50EC Imidacloprid 20 0.016 Chess 50WP Pymetrozine 150 0.038 Closer 500WG Sulfoxaflor 100 1.103 Elsin 10EC Nitenpyram 180 1.239 Bassa 50EC Fenobucarb 500 0.001 Oshin 20WP Dinotefuran 20 1.179 Applaud 10WP Buprofezin 100 0.080 3.3.4 Some proposed solutions to manage insecticide resistance of brown planthoppers The management of insecticide resistance of brown planthoppers should be based on the principle of application of Integrated Pest Management (IPM) on rice (Technical advance 01- 88: 2018/BNNPTNT): * Cultivation method - Clean weeds, ratoon rice along the edges of fields, irrigation ditches Field land must be thoroughly plowed, harrowed, and flattened Before sowing and transplanting of seedlings, it is necessary to comply with the crops as recommended by specialized organizations - Use rice varieties with clear origin, give priority to rice varieties that are resistant to brown planthoppers - Do not apply too high nitrogen fertilizer of over 150 kg N/ha, use rice leaf color chart to adjust the amount of nitrogen fertilizer * Biological method Do not use chemical insecticides when not needed, grownectar flowers on rice field edges to attract and protect natural enemies such as blue stink bugs (Cyrtorhinus lividipennis), wolf spider (Lycosa pseudoannulata), lynx spider (Oxyopes javanus), etc * Chemical method - Control time: If, before flowering, the planthopper density reaches 1,000 head/m2 or more, and after flowering, the same reaches 2,000 head/m2 or more, use plant protection insecticides for control This density threshold is applied when young planthoppers (nymphs aged 1-3 years) are common - Insecticides to be used: Priority is given to insecticides that brown planthoppers have not shown resistance The chemicals that brown planthoppers have shown to have resistance must be used alternately with other insecticides in the following rotation formula: Sulfoxaflor - Dinotefuran - Pymetrozine Buprofezin - Dinotefuran - Sulfoxaflor 25 Nitenpyram - Buprofezin - Sulfoxaflor Each insecticide should be used only once per crop and no more than consecutive crops, then it must switch to another insecticide - Dosage and concentration: According to the manufacturer's instructions, spray suffient amount of insecticides as prescribed (400 - 600 liters/ha) - Spraying technique: When rice is grown well, before spraying, create bands so that insecticides can be sprayed close to the rice roots where planthoppers reside and raise the water level - 5cm high to increase the effectiveness (if water is always available) Use standard spray pumps After spraying for - days, it is necessary to check the field if the planthoppers' density still increases If so, it is necessary to re-spray to meet the requirements CONCLUSIONS AND RECOMMENDATIONS Conclusions 20 active ingredients belonging to 11 insecticide groups are identified for brown planthopper control in the studied provinces In particular, in Hung Yen, Nam Dinh, Nghe An and Phu Yen, the Neonicotinoid insecticides are most commonly used by farmers (74.17 - 98.34% of respondents) In An Giang, the Pyridine azomethine insecticides are widely used by farmers (up to 89.17% of respondents) for brown planthopper control Most farmers spray - times/rice crop, with some farmers spraying up to - times/rice crop in An Giang Only 50.83 - 68.33% of farmers spray according to the recommended dose, while the remainder sprays 1.5 to times higher than the recommended dose, and most farmers mix 2-3 insecticides in a spray In 2015 - 2017, the brown planthopper populations in the studied provinces have low to very high levels of resistance to the active ingredients dinotefuran, buprofezin, nitenpyram, pymetrozine, fenobucarb, and imidacloprid The resistance rates of brown planthoppers to the above active ingredients are 2.096 - 4.600; 4.733 - 14.114; 4.087 24.112; 2.762 - 25.664; 23.441 - 89.461; and 31.575 - 161.768, respectively The brown planthopper populations are still susceptible (RR is only 1.226 - 2.868) to the active ingredient sulfoxaflor The higher the resistance levels of brown planthopper populations, the higher the activities of Cytochrome P450, Glutathione and Esterase enzymes Brown planthopper populations which are resistant to the active ingredient imidacloprid are not cross-resistant to the active ingredients buprofezin, pymetrozine, fenobucarb, and sulfoxaflor When exposed to the active ingredients nitenpyram and imidacloprid at LC30 concentrations, the egg-laying capacity and egg-laying rate of adult female brown planthoppers are significantly reduced For long-winged type, compared to the control, the egg-laying capacity reaches 58.91% and 70.28%, respectively, and the egg-laying rate of adult females reaches 74.44% and 75.56%, respectively For short-winged type, compared to the control, the egg-laying capacity reaches 52.88% and 62.52%, respectively, and the egg-laying rate of adult females reaches 75.56% and 76.67%, respectively In contrast, the 26 active ingredients nitenpyram and imidacloprid increase the long-winged adult rate in the next generation, respectively reaching 56.73 - 60.58% and 71.80 - 74.52% compared to 43.16 - 51.84% in the control where female long-winged adults are treated; when female short-winged are treated, the long-winged adult rates in the next generation are respectively 29.94 - 32.83% and 46.56 - 53.44% compared to 11.71 - 18.40 % in the control Thus, the active ingredient nitenpyram reduces the egg-laying capacity of brown planthoppers more strongly, and makes the rate of long-winged brown planthoppers lower, than the active ingredient imidacloprid All common rice varieties in An Giang are assessed to be infected with brown planthoppers, except for OM6976 rice variety with a moderate resistance After 12 generations not exposed to the active ingredient imidacloprid, the resistance rate of brown planthoppers decreases faster when nourished on OM6976 rice variety (RR is 18.96) compared to brown planthoppers on infected TN1 variety (RR is 32.63) In contrast, under the selective pressure of the active ingredient imidacloprid, the resistance rate of brown planthoppers cultivated on the infected TN1 variety to the active ingredient imidacloprid increases faster than that of brown planthoppers living on brown planthopper-resistant OM6976 rice variety (resistance rates are 211.69 and 179.69, respectively) At the recommended dosage, the effect of Oshin 20WP, Closer 50WG, Elsin 10EC, and Chess 50WG on brown planthoppers is quite high (68.95 - 80.15%) and safe for green stink bugs Insecticide rotation (sulfoxaflor - dinotefuran - pymetrozine; nitenpyram buprofezin - sulfoxaflor; buprofezin - dinotefuran - sulfoxaflor) slows the development of insecticide resistance of brown planthoppers Recommendations Use the results of the thesis as a reference for research, teaching, and production direction Limit the use of insecticides containing active ingredients imidacloprid and fenobucarb in brown planthopper control 27 THESIS-RELATED PUBLICATIONS Bui Xuan Thang, Ho Thi Thu Giang, Ho Thu Trang, Le Ngoc Anh (2017), “Level of resistance to active ingredient Imidacloprid of brown planthoppers Nilaparvata lugens (Stål) on some rice varieties”, Journal of Agriculture and Rural Development, No 21/2017, p 56-60 Bui Xuan Thang, Ho Thi Thu Giang (2018), “Effects of active ingredients Imidacloprid and Nitenpyram on some biological characteristics of brown planthoppers Nilaparvata lugens (Stål), Journal of Agriculture and Rural Development, No 3+4/2018, p 120-124 Ho Thi Thu Giang, Nguyen Duc Khanh, Le Ngoc Anh, Nguyen Thi Kim Oanh and Bui Xuan Thang (2017), “Study on insecticide susceptibility of brown planthoppers Nilaparvata lugens (Stål) (Homoptera: Delphacidae) in some rice-growing areas in Vietnam”, Plant Protection Journal, No 2/2018, p 31-41 Bui Xuan Thang, Ho Thi Thu Giang (2018), “Toxicity of some insecticides used for brown planthopper control to green stink bugs”, Vietnam Journal of Agricultural Science and Technology, No 4/2018, p 83-87 ... “Study on insecticide resistance of rice brown planthopper (Nilaparvata lugens Stal) populations in some rice- growing areas in Vietnam” Study objectives To determine the current status of use... planthoppers Nilaparvata lugens (Stål), Journal of Agriculture and Rural Development, No 3+4/2018, p 120-124 Ho Thi Thu Giang, Nguyen Duc Khanh, Le Ngoc Anh, Nguyen Thi Kim Oanh and Bui Xuan Thang... 4.1 Subject of the study Resistance of brown planthopper (Nilaparvata lugens) populations in some typical rice-growing provinces: Hung Yen, Nam Dinh, Nghe An, Phu Yen and An Giang for some plant