Nghiên cứu tính kháng thuốc của quần thể rầy nâu (nilaparvata lugens stal) hại lúa ở một số vùng trồng lúa tại việt nam tt tiếng anh

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:
1. Assoc. Prof. Dr. Ho Thi Thu Giang
2. Assoc. Prof. Dr. Michael Kristensen

Reviewer 1: ………………………………………………
…………………………………………………………….

Reviewer 2 ………………………………………………
…………………………………………………………..
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


1
INTRODUCTION
1. 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 ha was damaged by planthoppers nationwide, of which 34,287
ha were badly damaged and 179 ha 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 ha 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 ha. 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-


2
growing areas in Vietnam”.
2. 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.
3. 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.
4. 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.
5. 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.


3
Chapter 1. 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 2. 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 1 (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


4
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, 5 provinces are selected, including 3 districts in
each province, 2 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


5
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 3
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 3. 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
1 Growth regulators
4.17
2.50
6.67
3.33
2 Phenylpyrazole
2.50
0.83
0.83


6
3
4
5
6
7
8
9
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 2 to 3
insecticides in one spray. Specifically, the percentages of farmer households using the
mixture of 2 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 3 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 2 to 3 insecticides in one spray. The percentages of
farmer households using the mixture of 2 to 3 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 2 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 3 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 3 times in a rice crop. However, in Hung Yen, Nam Dinh, Nghe An and Phu Yen
provinces, there are no farmers spraying 4 times/rice crop but popularly spraying 2 to 3
times/rice crop. In particular, the percentages of farmer households spraying 2 times in a rice
crop in Hung Yen, Nam Dinh, Nghe An and Phu Yen provinces are 44.17%, 45.83%, 40.83%


7
and 43.33%, respectively. The percentages of farmer households spraying 3 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
1
7.50
9.17
6.67
30.83 45.00
Number
of
insecticides
2
59.17 60.00 57.50 49.17 41.67
used in 1 spray
3
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 1 spray
recommended
2 times higher than
8.33
6.67
10.00 12.50 20.00
recommended
1

5.83
7.50
12.50 11.67
8.33
2
44.17 45.83 40.83 43.33 30.00
Number
of
sprays in 1 crop
3
50.00 46.67 46.67 45.00 57.50
4-7
0
0
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. 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


8

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


9

2017

PY
AG
HY
ND
NA
PY
AG

3.996 (2.677 - 5.029)
9.013 (5.847 - 11.600)
2.474 (1.735 - 3.062)
2.448 (1.645 - 3.107)
2.806 (1.801 - 3.579)

4.426 (3.093 - 5.526)
11.412 (7.214 - 14.632)

3.194 ± 0.516
1.374 ± 0.218
5.668 ± 0.762
5.454 ± 0.807
4.443 ± 0.725
3.178 ± 0.435
1.105 ± 0.173

8.448
19.054
5.230
5.175
5.932
9.357
24.112

Note: HY: Hung Yen; ND: Nam Dinh; NA: Nghe An; PY: Phu Yen; AG: An Giang; RR: resistance rate; LC50
of susceptible brown planthoppers: 0.473 (0.308 – 0.606) mgl

3.2.1.3. Resistance of brown planthopper populations in some provinces to active
ingredient fenobucarb
Results of determination of resistance levels of brown planthopper populations to the
active ingredient fenobucarb in Hung Yen, Nam Dinh, Nghe An, Phu Yen and An Giang
show that two brown planthopper populations in Hung Yen and Nam Dinh have a moderate
resistance over the years 2015 - 2017 with the resistance rates ranging from 37.232 - 39.827
and 23.441 - 28.319, respectively. Brown planthopper populations in Nghe An, Phu Yen
and An Giang have a high resistance to the active ingredient fenobucarb with the resistance

rates ranging from 41.499 - 46.052; 52.296 - 58.301; and 82.571 - 89.461, respectively over
the years 2015 - 2017 (table 3.10).
Table 3.10. Resistance levels of brown planthopper populations to active ingredient
fenobucarb in some rice-growing provinces from 2015 - 2017
Year

2015

2016

2017

Planthopper
origin
HY
ND
NA
PY
AG
HY
ND
NA
PY
AG
HY
ND
NA
PY
AG

LC50 (mgl) and 95% confidence
intervals
168.365 (108.034 - 214.719)
106.054 (66.574 - 136.705)
208.250 (134.792 - 269.612)
263.638 (176.611 - 338.542)
404.542 (253.921 - 523.810)
180.096 (117.671 - 227.099)
128.059 (83.128 - 164.935)
199.472 (127.607 - 258.367)
253.291 (162.313 - 329.643)
373.385 (242.435 - 477.619)
171.651 (111.005 - 221.072)
122.247 (78.865 - 154.810)
187.658 (130.059 - 234.762)
236.484 (149.678 - 308.289)
386.724 (246.648 - 498.823)

Angular
coefficient
0.074 ± 0.012
0.110 ± 0.020
0.059 ± 0.010
0.052 ± 0.007
0.028 ± 0.005
0.074 ± 0.011
0.106 ± 0.015
0.060 ± 0.010
0.052 ± 0.008
0.032 ± 0.005

0.073 ± 0.012
0.111 ± 0.016
0.063 ± 0.012
0.053± 0.008
0.028 ± 0.006

RR
37.232
23.441
46.052
58.301
89.461
39.827
28.319
44.111
56.013
82.571
37.959
27.034
41.499
52.296
85.521

Note: HY: Hung Yen; ND: Nam Dinh; NA: Nghe An; PY: Phu Yen; AG: An Giang; RR: resistance rate; LC50
of susceptible brown planthoppers: 4.522 (2.765 – 5.958) mgl

3.2.1.4. Resistance of brown planthopper populations in some provinces to active
ingredient sulfoxaflor
Active ingredient sulfoxaflor is the first product of the new generation insecticides,
which is registered for use in 2012 for brown planthopper control in our country. At present,

there are very few published domestic and foreign studies on the resistance of brown


10
planthoppers to the active ingredient sulfoxaflor. The results of the study show that the
resistance levels of brown planthopper populations in Hung Yen, Nam Dinh, Nghe An, Phu
Yen and An Giang are still susceptible to the active ingredient sulfoxaflor. The resistance
rates of these brown planthopper populations to the active ingredient sulfoxaflor range from
1.447 - 1.943; 1.226 - 1.563; 1.426 - 2.353; 1.493 - 2.091; and 1.694 - 2.868, respectively
over the years 2015 - 2017. In particular, the resistance rate of the brown planthopper
population in An Giang to the active ingredient sulfoxaflor is the highest.
Resistance rates of brown planthopper populations in Nam Dinh, Nghe An, Phu Yen
and An Giang to the active ingredient sulfoxaflor tend to increase slightly over the years
2015 - 2017. The resistance of brown planthopper populations in Hung Yen to this active
ingredient shows signs of increase and decrease over the years 2015 - 2017 (Table 3.11).
Table 3.11. Resistance levels of brown planthopper populations to active ingredient
sulfoxaflor in some rice-growing provinces from 2015 - 2017
Year

2015

2016

2017

Planthopper
origin
HY
ND
NA

PY
AG
HY
ND
NA
PY
AG
HY
ND
NA
PY
AG

LC50 (mgl) and 95% confidence
intervals
0.571 (0.400 - 0.717)
0.455 (0.240 - 0.627)
0.529 (0.358 - 0.669)
0.554 (0.354 - 0.718)
0.629 (0.387 - 0.823)
0.537 (0.326 - 0.710)
0.511 (0.271 - 0.703)
0.640 (0.416 - 0.825)
0.650 (0.442 - 0.825)
0.829 (0.480 - 1.106)
0.721 (0.490 - 0.911)
0.580 (0.383 - 0.740)
0.873 (0.590 - 1.101)
0.776 (0.496 - 1.005)
1.064 (0.656 - 1.394)

Angular
coefficient
22.216 ± 3.647
21.626 ± 4.304
22.488 ± 3.837
21.700 ± 3.704
21.124 ± 3.043
21.346 ± 3.992
21.029 ± 3.990
21.265 ± 3.029
21.405 ± 3.038
13.465 ± 2.441
21.943 ± 3.412
21.928 ± 3.603
14.088 ± 2.307
15.500 ± 2.646
10.842 ± 1.940

RR
1.539
1.226
1.426
1.493
1.694
1.447
1.377
1.725
1.752
2.2345

1.943
1.563
2.353
2.091
2.868

Note: HY: Hung Yen; ND: Nam Dinh; NA: Nghe An; PY: Phu Yen; AG: An Giang; RR: resistance rate; LC50
of susceptible brown planthoppers: 0.371 (0.195 – 0.511) mgl

3.2.1.5. Resistance of brown planthopper populations in some provinces to active
ingredient pymetrozine
Results of determination of resistance levels of brown planthopper populations to the
active ingredient pymetrozine in Hung Yen, Nam Dinh, Nghe An, Phu Yen and An Giang
over the years 2015 - 2017 show that three brown planthopper populations in Hung Yen,
Nam Dinh and Nghe An have a mild resistance to the active ingredient pymetrozine with the
resistance rates ranging from 2.762 - 3.435; 3.872 - 4.762; 4.139 - 4.896, respectively.
Brown planthopper populations in Phu Yen and An Giang have a moderate resistance to the
active ingredient pymetrozine with the resistance rates ranging from 11.263 - 16.321 and
15.946 - 25.664, respectively over the years 2015 - 2017 (Table 3.10).


11
Table 3.12. Resistance levels of brown planthopper populations to active ingredient
pymetrozine in some rice-growing provinces from 2015 - 2017
Planthopper
LC50 (mgl) and 95% confidence
Angular
Year
RR
origin

intervals
coefficient
HY
57.061 (36.068 - 73.158)
0.221 ± 0.035
2.762
ND
79.810 (46.208 - 106.038)
0.136 ± 0.025
3.872
2015
NA
85.516 (56.127 - 108.743)
0.139 ± 0.025
4.139
PY
232.724 (160.286 - 290.823)
0.057 ± 0.008
11.263
AG
329.482 (213.036 - 421.386)
0.037 ± 0.006
15.946
HY
60.745 (41.560 - 75.665)
0.224 ± 0.033
2.939
ND
86.819 (56.105 - 111.064)
0.139 ± 0.024

4.202
2016
NA
92.862 (61.463 - 117.451)
0.139 ± 0.021
4.494
PY
293.588 (186.756 - 378.835)
0.037 ± 0.007
14.209
AG
420.221 (271.316 - 539.587)
0.028 ± 0.005
20.338
HY
70.976 (48.367 - 89.074)
0.187 ± 0.027
3.435
ND
98.389 (65.329 - 125.323)
0.137 ± 0.019
4.762
2017
NA
101.165 (70.088 - 127.263)
0.136 ± 0.019
4.896
PY
337.224 (224.241 - 427.879)
0.037 ± 0.006

16.321
AG
530.270 (332.872 - 638.529)
0.022 ± 0.004
25.664
Note: HY: Hung Yen; ND: Nam Dinh; NA: Nghe An; PY: Phu Yen; AG: An Giang; RR: resistance rate; LC50
of susceptible brown planthoppers: 20.662 (10.385 – 28.864) mgl

3.2.1.6. Resistance of brown planthopper populations in some provinces to active
ingredient buprofezin
Results of determination of resistance levels of brown planthopper populations to the
active ingredient buprofezin in Hung Yen, Nam Dinh, Nghe An, Phu Yen and An Giang
over the years 2015 - 2017 show that the brown planthopper population in Nghe An has a
mild resistance to the active ingredient buprofezin with the resistance rate ranging from
4.733 to 5.321. Meanwhile, two brown planthopper populations in Hung Yen and Nam
Dinh have a low resistance to the active ingredient buprofezin with the resistance rates
ranging from 6.487 - 7.256 and 7.357 - 8.390, respectively. The two brown planthopper
populations in Phu Yen and An Giang had a moderate resistance to the active ingredient
buprofezin with the resistance rates ranging from 10.203 - 11.422 and 11.607 - 14.114,
respectively. The rate of increase in resistance levels of 5 brown planthopper populations in
Hung Yen, Nam Dinh, Nghe An, Phu Yen and An Giang to the active ingredient buprofezin
is slow and unstable over the years 2015 - 2017 (Table 3.13).
Table 3.13. Resistance levels of brown planthopper populations to active ingredient
buprofezi in some rice-growing provinces from 2015 - 2017
Planthopper
LC50 (mgl) and 95% confidence
Angular
Year
RR
origin

intervals
coefficient
HY
125.641 (82.445 - 160.310)
0.092 ± 0.017
6.487
ND
142.507 (96.615 - 179.332)
0.079 ± 0.016
7.357
2015
NA
91.678 (62.772 - 115.880)
0.138 ± 0.023
4.733
PY
197.631 (133.893 - 249.373)
0.056 ± 0.012 10.203
AG
224.816 (149.494 - 285.253)
0.055 ± 0.009 11.607
2016
HY
140.532 (94.164 - 179.006)
0.092 ± 0.014
7.256


12

2017

ND
NA
PY
AG
HY
ND
NA
PY
AG

148.030 (101.209 - 186.305)
103.058 (71.327 - 129.084)
221.242 (149.108 - 279.240)
273.367 (194.569 - 338.227)
133.455 (93.516 - 166.313)
162.508 (107.560 - 205.539)
94.961 (63.454 - 221.094)
211.471 (144.584 - 266.150)
254.736 (174.731 - 321.271)

0.080 ± 0.015
0.138 ± 0.018
0.056 ± 0.009
0.055 ± 0.006
0.095 ± 0.015
0.079 ± 0.012
0.136 ± 0.021
0.056 ± 0.010

0.055 ± 0.007

7.657
5.321
11.422
14.114
6.890
8.390
4.903
10.918
13.152

Note: HY: Hung Yen; ND: Nam Dinh; NA: Nghe An; PY: Phu Yen; AG: An Giang; RR: resistance rate; LC50
of susceptible brown planthoppers: Buprofezin 19.369 (9.948 – 26.878) mgl

3.2.1.7. Resistance of brown planthopper populations in some provinces to active
ingredient dinotefuran
The active ingredient dinotefuran belongs to Neonicotinoid insecticides, which is
registered in the list of permissable insecticides in Vietnam in 2004. Results of determination
of resistance levels of brown planthopper populations in Hung Yen, Nam Dinh, Nghe An, Phu
Yen and An Giang to the active ingredient dinotefuran over the years 2015 - 2017 show that
brown planthopper populations in Hung Yen, Nam Dinh, Nghe An, and Phu Yen do not show
resistance to the active ingredient dinotefuran with the resistance rates ranging from 2.354 2.568; 2.096 - 2.678; 2.150 - 2.446; 2.336 - 2.857, respectively. As for the brown planthopper
population in An Giang, there is a mild resistance to the active ingredient dinotefuran with the
resistance rate ranging from 3.686 to 4.600. The rate of increase in resistance levels of brown
planthopper populations in Hung Yen, Nam Dinh, Nghe An, Phu Yen and An Giang to the
active ingredient dinotefuran is slow over the years 2015 - 2017 (Table 3.14).
Table 3.14. Resistance levels of brown planthopper populations to active ingredient
dinotefuran in some rice-growing provinces from 2015 - 2017
Planthopper LC50 (mgl) and 95% confidence

Angular
Year
RR
origin
intervals
coefficient
HY
0.659 (0.426 - 0.843)
18.273 ± 3.200
2.354
ND
0.587 (0.374 - 0.758)
18.220 ± 3.737
2.096
2015
NA
0.602 (0.394 - 0.771)
18.488 ± 3.529
2.150
PY
0.654 (0.446 - 0.821)
18.691 ± 3.275
2.336
AG
1.032 (0.689 - 1.308)
11.064 ± 2.163
3.686
HY
0.674 (0.448 - 0.856)
18.482 ± 2.990

2.407
ND
0.644 (0.434 - 0.815)
18.544 ± 3.259
2.300
2016
NA
0.630 (0.407 - 0.809)
18.427 ± 3.263
2.250
PY
0.742 (0.521 - 0.918)
18.894 ± 2.540
2.650
AG
1.158 (0.807 - 1.441)
11.248 ± 1.807
4.136
HY
0.719 (0.491 - 0.902)
18.538 ± 2.723
2.568
ND
0.750 (0.520 - 0.943)
18.390 ± 2.489
2.678
2017
NA
0.685 (0.480 - 0.860)
18.513 ± 3.039

2.446
PY
0.800 (0.560 - 1.006)
18.138 ± 2.124
2.857
AG
1.288 (0.892 - 1.614)
11.060 ± 1.423
4.600
Note: HY: Hung Yen; ND: Nam Dinh; NA: Nghe An; PY: Phu Yen; AG: An Giang; RR: resistance rate; LC50
of susceptible brown planthoppers: Dinotenfuran 0.280 (0.158 – 0.377) mgl


13
3.2.2. Study results explaining resistance mechanism of brown planthoppers
All brown planthopper populations in different localities are resistant to the active
ingredient Imidacloprid. The Cytochrome P450 enzyme activities of the brown planthopper
populations in Hung Yen, Nghe An and An Giang are higher and different to that of
susceptible brown planthopper population. However, the results show that there is no
difference in the Cytochrome P450 enzyme activities between the brown planthopper
populations collected in Hung Yen and Nghe An; the enzyme activities are 3.60 and 3.57
(mOD/min/mg protein), respectively. However, the Cytochrome P450 enzyme activity of
the brown planthopper population in An Giang is stronger than that of the two brown
planthopper populations in Hung Yen and Nghe An; the enzyme activity of the brown
planthopper population in An Giang reaches 5.70 (mOD/min/mg protein). This is also
appropriate when the brown planthopper population in An Giang has significantly higher
resistance to the active ingredient imidacloprid than the two brown planthopper populations
in Hung Yen and Nghe An.
Esterase enzyme activities of brown planthopper populations in Hung Yen, Nghe An
and An Giang are also higher and different to that of susceptible brown planthoppers.

However, Esterase enzyme activities of brown planthopper populations in Hung Yen, Nghe
An and An Giang vary. Esterase enzyme activity of brown planthopper population in An
Giang (6.75 mOD/min/mg protein) > that of brown planthopper population in Hung Yen
(4.92 mOD/min/mg protein) > that of brown planthopper population in Nghe An (3.69
mOD/min/mg protein).
The results show that there is no difference in Glutathione enzyme activities between
two brown planthopper populations in Hung Yen and An Giang; the enzyme activities are
1.25 and 1.28 (mOD/min/mg protein), respectively. However, Glutathione enzyme activities
of two brown planthopper populations in Hung Yen and An Giang are higher than that of
brown planthopper population in Nghe An (1.19 mOD/min/mg protein). Glutathione
enzyme activities of brown planthopper populations in Hung Yen, Nghe An and An Giang
are higher and different to that of susceptible brown planthopper population (Table 3.15).
Table 3.15. Activities of detoxifying enzymes in brown planthopper populations
collected in some provinces in 2016
Brown
planthoppe
Cytochrome P450
Glutathione
Esterase
r
(mOD/min/mg protein) (mOD/min/mg protein) (mOD/min/mg protein)
populations
Hưng Yên
3.60b ± 0.011
1.25a ± 0.051
4.92b ± 0.176
Nghệ An
3.57b ± 0.037
1.19b ± 0.021
3.69c ± 0.079

An Giang
5.70a ± 0.039
1.28a ± 0.036
6.75a ± 0.040
c
c
Mẫn cảm
1.67 ± 0.0087
0.77 ± 0.142
1.51d ± 0.0086
Note: The letters are usually the same in the column range with no difference at confidence level p ≤ 0.05

The results show a close correlation between the activity enhancement degree of
Esterase, Glutathione, Cytochrome P450 enzymes and the resistance levels of brown
planthopper populations to active ingredients. The more resistant the brown planthopper
populations are, the higher the enzyme activities.


14
3.2.3. Cross-resistance of brown planthopper populations which are resistant to active
ingredient imidacloprid to some other active ingredients against brown planthoppers
Resistance rates of brown planthopper populations (already resistant to the active
ingredient imidacloprid) to the active ingredients fenobucarb, sulfoxaflor, and pymetrozine,
buprofezin all decrease after 12-generation selective pressure with the active ingredient
imidacloprid. Resistance rates of brown planthopper populations to these active ingredients
decrease from 89.461 to 43.307; 1.694 to 1.493; 15.946 to 8.031; and 11.607 to 6.166,
respectively. Thus, brown planthopper populations which are resistant to the active
ingredient imidacloprid do not have cross-resistance to the active ingredients fenobucarb,
sulfoxaflor, pymetrozine, and buprofezin.
Brown planthopper populations which are resistant to the active ingredient

imidacloprid exhibit unclear cross-resistance to the active ingredients dinotefuran and
nitenpyram (these 2 active ingredients belong to the same group - Neonicotinoids). After the
selective pressure of 12 generations of brown planthoppers with the active ingredient
imidacloprid, resistance rates of brown planthopper populations to these two active
ingredients increase slightly. The resistance rates increase from 3.686 to 4.207 and from
16.552 to 17.139, respectively (Table 3.16).
Table 3.16. Cross-resistance of An Giang brown planthoppers which are resistant to
active ingredient imidacloprid to some other active ingredients against brown
planthoppers, 2015 - 2016
After 12 selective
LC50 susceptible
Prior to selection
generations with active
Active
brown
ingredient Imidacloprid
ingredient
planthoppers
(mg/l)
LC50 (mg/l)
RR
LC50 (mg/l)
RR
0.207
26.490
43.821
Imidacloprid
127.971
211.69
(0.097 - 0.294)

(16.72 - 34.23)
(31.524 - 55.071)
0.473
7.829
8.107
Nitenpyram
16.552
17.139
(0.308 - 0.606)
(4.980 - 10.102)
(5.614 - 10.166)
4.522
404.542
195.835
Fenobucarb
89.461
43.307
(2.765 - 5.958)
(253.921 - 523.810)
(132.954 - 246.962)
0.371
0.629
0.554
Sulfoxaflor
1.694
1.493
(0.195 - 0.511)
(0.387 - 0.823)
(0.354 - 0.718)
20.662

329.482
165.931
Pymetrozine
15.946
8.031
(10.385 - 28.864) (213.036 - 421.386)
(111.831 - 209.429)
19.369
224.816
119.437
Buprofezin
11.607
6.166
(9.948 - 26.878) (149.494 - 285.253)
(82.466 - 148.168)
0.280
1.032
1.178
Dinotefuran
3.686
4.207
(0.158 - 0.377)
(0.689 - 1.308)
(0.812 - 1.471)
Note: RR: resistance rate; Values in brackets are 95% confidence interval values

3.2.4. Effect of insecticide active ingredients on some biological characteristics of
brown planthoppers after exposure to insecticides
3.2.4.1. Effect of active ingredients nitenpyram and imidacloprid on reproductive
capacity of long-winged and short-winged brown planthoppers

Study results show that long-winged brown planthoppers, after exposure to 2 active


15
ingredients nitenpyram and imidacloprid, have egg-laying capacity affected. However, the
effect of active ingredient nitenpyram on egg-laying capacity of adult brown planthoppers is
stronger than that of active ingredient imidacloprid. After exposure to nitenpyram and
imidacloprid, the total numbers of eggs laid by brown planthoppers are 190.13
(eggs/female) and 226.85 (eggs/female), respectively. When compared to non-insecticidal
formula which is 322.76 (eggs/female), this result has a reliable difference at the probability
P <0.05. Thus, the egg-laying capacity of long-winged brown planthoppers after exposure to
nitenpyram and imidacloprid is reduced to 58.91% and 70.28%, respectively, when
compared to that of non-treated brown planthoppers.
Results show that the two active ingredients nitenpyram and imidacloprid have an
effect on egg-laying rate of adult females. The egg-laying rates are 74.44% and 75.56%,
respectively. Compared to non-insecticidal formula which is 83.33%, this result has a
significant difference with the confidence at the probability P <0.05. However, the effect of
these two active ingredients on egg-laying rate of adult females has no difference. (Table
3.18).
Table 3.18. Effect of active ingredients nitenpyram and imidacloprid on reproductive
capacity of long-winged brown planthoppers, 2016
Egg-laying capacity
Egg-laying rate of
Test
Ratio compared to control
adult females (%)
Eggs/female
(%)
Nitenpyram
74.44b ± 2.22

190.13c ± 8.94
58.91
Imidacloprid
75.56b ± 1.11
226.85b ± 13.09
70.28
a
a
Control
83.33 ± 1.93
322.76 ± 15.19
100
Note: in columns, different letters indicate reliable difference at probability P <0.05

For short-winged brown planthoppers, the results in Table 3.19 show that the effects
of the two active ingredients nitenpyram and imidacloprid on egg-laying capacity of adult
females are similar to those of long-winged brown planthoppers. The egg-laying capacities
of short-winged brown planthoppers after exposure to nitenpyram and imidacloprid are
210.77 (eggs/female) and 249.19 (eggs/female), respectively, which are reduced to 52.88%
and 62.52% compared to that of brown planthoppers in control formula without insecticides.
The two active ingredients nitenpyram and imidacloprid affect the egg-laying rate of
adult females with the rate of 75.56% and 76.67%, respectively. Compared to noninsecticidal formula which is 84.44%, this result has a significant difference with the
confidence at the probability P < 0.05. (Table 3.19).
Table 3.19. Effect of active ingredients nitenpyram and imidacloprid on reproductive
capacity of short-winged brown planthoppers, 2016
Egg-laying capacity
Egg-laying rate of
Test
Ratio compared to control
adult females (%)

Eggs/female
(%)
b
c
Nitenpyram
75.56 ± 2.94
210.77 ± 9.18
52.88
b
b
Imidacloprid
76.67 ± 1.93
249.19 ± 11.00
62.52
Control
84.44a ± 1.11
398.59a ± 17.25
100.00
Note: in columns, different letters indicate reliable difference at probability P<0.05


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<0.05

In short-winged brown planthoppers, the effect of the active ingredients nitenpyram
and imidacloprid on the wing formation of brown planthoppers is more noticeable than that
in long-winged brown planthoppers. The rates of female and male long-winged brown
planthoppers are 32.83% and 29.94%, respectively, after exposure to the active ingredient
nitenpyram. The rates of female and male long-winged brown planthoppers affected by the
active ingredient imidacloprid are 53.44% and 46.56%, respectively. The active ingredients
nitenpyram and imidacloprid increase the rates of female and male long-winged brown
planthoppers. This increase is significant when compared to the control formula which is
11.71% (rate of female long-winged brown planthoppers) and 18.40% (rate of male longwinged brown planthoppers) (Table 3.21).


17

Table 3.20. Effect of active ingredients nitenpyram and imidacloprid on short-winged
brown planthoppers in An Giang, 2016
Female brown planthoppers
Male brown planthoppers
Test
Long-winged
Short-winged
Long-winged
(%)
(%)
(%)
b
b
b
Nitenpyram
32.83
67.17
29.94
70.06b
Imidacloprid
53.44c
46.56a
46.56c
53.44a
Control
11.71a
88.29c
18.40a
81.60c
Note: in columns, different letters indicate reliable difference at probability P<0.05

The study results show that the active ingredients nitenpyram and imidacloprid both
reduce the egg-laying capacity of adult female brown planthoppers and the rate of formation
of long-winged brown planthoppers is higher than that of the control formula. However, the
active ingredient nitenpyram reduces the egg-laying capacity of adult female brown
planthoppers more strongly than the active ingredient imidacloprid, and makes the rate of
long-winged brown planthoppers lower than the active ingredient imidacloprid. Thus, for
the active ingredient imidacloprid, it needs to be restricted from production, while the active
ingredient nitenpyram can still be used in brown planthopper control; however; management
measures are needed to reduce the level of use.
3.3. Study on reasonable solutions to manage insecticide resistance of brown
planthoppers
3.3.1. Study on method of use of resistant varieties in management of insecticide
resistance of brown planthoppers
3.3.1.1. Resistance of common rice varieties in An Giang to brown planthopper
Nilaparvata lugens (Stål) population in An Giang
Out of 14 rice varieties assessed for their susceptibility to brown planthopper
population in An Giang, 1 rice variety has moderate resistance level (OM6976); 8 rice
varieties react at moderate infection level (OM8017, OM7347, OM10041, OM16976,
OM5451, OM8108, OM6162, OM4900); 3 rice varieties react at infection level (IR50404,
OM4218, IR504) and 2 rice varieties react at serious infection level (Jamie85, VD20). From
the above results, the thesis has selected the OM6976 rice variety (having the highest
resistance level among the rice varieties collected in An Giang) and the infected TN1 rice
variety for studies on assessment of effect of brown planthopper-resistant rice varieties on
resistance level of brown planthopper population in An Giang to the active ingredient
imidacloprid.
3.3.1.2. Effect of rice varieties on resistance level of An Giang brown planthopper
population after a number of generations not exposed to active ingredient
imidacloprid
An Giang brown planthopper population is collected in the field and raised in the

laboratory on two rice varieties TN1 and OM6976. After one generation, the resistance level
of An Giang brown planthopper population to the active ingredient imidacloprid is
determined. An Giang brown planthopper population has high resistance to the active
ingredient imidacloprid with the resistance rates (RR) of 127.98 on TN1 rice variety and


18
125.27 on OM6976 rice variety.
An Giang brown planthopper population reared on 2 rice varieties TN1 and OM6976
is not exposed to the active ingredient imidacloprid for 12 generations in the laboratory. The
results show that the resistance level of the planthopper population to the active ingredient
imidacloprid decreases as the number of generations increases. On TN1 variety, the
resistance rate of brown planthoppers to the active ingredient imidacloprid decreases rapidly
from 127.98 in the first generation (G1) to 32.63 in the 12th generation (G12). The resistance
rate of brown planthoppers to the active ingredient imidacloprid decreases rapidly from G3 G9 and decreases slowly after 9 generations. When brown planthoppers are continuously
reared on OM6976, the resistance rate of brown planthoppers to the active ingredient
imidacloprid decreases faster than that of brown planthoppers reared on TN1. The resistance
rate decreases from 125.27 in G1 to 18.96 in G12. The resistance rate of brown
planthoppers to the active ingredient imidacloprid decreases rapidly after G1 - G6 and
decreases slowly after 6 generations (Table 3.23).
Table 3.23. Resistance level of An Giang brown planthopper population after a
number of generations not exposed to active ingredient imidacloprid, 2015 - 2016
Rice
Confidence interval
Resistance rate
Generation LC50 (mgl)
variety
(95%)
(RR)
G1

26.491
16.715 - 34.234
127.98
G3
24.931
15.748 - 32.363
120.44
TN1
G6
12.610
8.213 - 16.228
60.92
G9
7.063
3.203 - 10.072
34.12
G12
6.754
3.504 - 9.262
32.63
G1
25.931
14.854 - 34.088
125.27
G3
11.722
5.483 - 16.520
56.63
OM6976
G6

6.551
3.610 - 8.899
31.65
G9
4.292
2.396 - 5.736
20.73
G12
3.925
1.951 - 5.370
18.96
Note: LC50 of susceptible brown planthoppers: 0.207 (0.097 - 0.294); G: generation

3.3.1.3. Effect of rice varieties on resistance level of An Giang brown planthopper
population after a number of generations exposed to active ingredient imidacloprid
An Giang brown planthopper population which is reared on TN1 and OM6976 rice
varieties in the laboratory and created selective pressure exposed to the active ingredient
imidacloprid through generations has the resistance increased to this active ingredient.
Brown planthoppers reared on TN1 have the resistance rate to the active ingredient
imidacloprid increased from 127.98 in G1 to 211.69 in G12. The resistance rate of brown
planthoppers to the active ingredient imidacloprid increases slowly from G1 - G6 but
increases rapidly from 136.66 in G6 to 211.69 in G12.
When brown planthoppers are reared on OM6976 rice variety, the resistance rate of
brown planthoppers to the active ingredient imidacloprid increases more slowly than that of
brown planthoppers reared on TN1 with the resistance rate increased from 125.27 in G1 to
179.69 in G12. The resistance rate of brown planthoppers to the active ingredient


19
imidacloprid increases slowly after G1 - G9 but increases rapidly from 146.42 in G9 to

179.69 in G12 (Figure 3.8).

Figure 3.8. Changes in resistance rate of An Giang brown planthopper population after a
number of generations of selective pressure exposed to active ingredient imidacloprid
The study results show that after 12 generations of brown planthoppers not exposed
to the active ingredient imidacloprid in the laboratory, the resistance rate of brown
planthoppers reared on OM6976 rice variety (RR = 18.96) to the active ingredient
imidacloprid decreases faster than that of brown planthoppers reared on TN1 rice variety
(RR = 32.63). However, the resistance rate of brown planthoppers to the active ingredient
imidacloprid on OM6976 rice variety (RR = 179.69) increases more slowly than that of
brown planthoppers reared on TN1 rice variety with the resistance rate (RR = 211.69) after
12 generations of selective pressure to the active ingredient imidacloprid. The combined use
of OM6976 in rice variety structure and the limited use of the active ingredient imidacloprid
for about 12 generations of brown planthoppers will reduce the resistance of brown
planthoppers to the active ingredient imidacloprid.
3.3.2. Study on method of use of chemical insecticides in management of insecticide
resistance of brown planthoppers
3.3.2.1. Effect of some insecticides commonly used in brown planthopper control
* Laboratory effect of some insecticides commonly used in production on brown
planthoppers
- Effect of some insecticides on 1- to 2-year-old nymphs of brown planthoppers
After 72 hours of treatment, the insecticides still have a strong effect on brown
planthoppers when the efficacy of the insecticides is increased. Highly effective insecticides
for 1- to 2-year-old nymphs of brown planthoppers include Oshin 20WP, Elsin 10EC, and
Closer 50WG, reaching the efficacy of 91.16 - 94.67%. Applaud 10WP, Bassa 50EC, and
Chess 50WG have lower efficacy reaching 79.77 - 83.66%. And Admire 50 EC has the
lowest efficacy for 1- to 2-year-old nymphs of brown planthoppers which is only 67.22%.
- Effect of some insecticides on 3- to 4-year-old nymphs of brown planthoppers

20
After 72 hours of treatment, the efficacy of these insecticides on 3- to 4-year-old
nymphs of brown planthoppers increases compared to the first 24 hours of treatment. In
particular, the effect of Applaud 10WP increases the most from 13.62% to 79.39%, while
the effect of Bassa 50EC increases the slowest from 72.27% to 78.78% (Bassa 50EC has the
highest effect among the insecticides after 24 hours of treatment). Bassa 50EC, Applaud
10WP, Chess 50WG, Closer 50WG, Elsin 10EC, and Oshin 20WP have a quite high
efficacy on 3- to 4-year-old nymphs of brown planthoppers which is 77.60 - 85.45% (Oshin
20WP has the highest efficacy of 85.42%). Admire 50EC has the lowest efficacy on 3- to 4year-old nymphs of brown planthoppers which is 65.12%.
- Effect of some insecticides on adult brown planthoppers
Like other insects, the more brown planthoppers grow up, the lower their
susceptibility to insecticides; therefore, the efficacy of the insecticides on adult brown
planthoppers is lower than that on nymphs of brown planthoppers. After 72 hours of
treatment, the efficacy of Oshin 20WP, Closer 50WG, Elsin 10EC, Chess 50WG, and Bassa
50EC on adult brown planthoppers reaches 60.35 - 66.85%. Applaud 10WP and Admire
50EC have low efficacy on adult brown planthoppers, reaching 28.59% and 47.39%,
respectively. Applaud 10WP has the lowest efficacy on adult brown planthoppers compared
to other experimental insecticides right after 24 hours of treatment.
* Field effect of some insecticides commonly used in production on brown
planthoppers
Results show that out of 7 insecticides selected for assessment of their efficacy on
field brown planthoppers, Oshin 20WP has the highest efficacy on brown planthoppers,
reaching 80.15% after 5 days of treatment. Closer 50WG and Elsin 10EC have lower
efficacy on brown planthoppers than Oshin 20WP, reaching 76.82% and 77.72%,
respectively. These insecticides have a high efficacy on brown planthoppers from the first
day of treatment and have the highest efficacy after 5 days of treatment.
Bassa 50EC, Chess 50WG, and Applaud 10WP are effective against brown
planthoppers ranging from 62.07 to 70.32%. In particular, Bassa 50EC has the highest
efficacy after 3 days of treatment, reaching 66.98%. Chess 50WG and Applaud 10WP have
the highest efficacy on brown planthoppers after 10 days of treatment, reaching 70.32% and

62.07%, respectively.
Among the 7 experimental insecticides, Admire 50EC is the lowest effective against
brown planthoppers in the field. Its highest efficacy is found at 55.58% after 7 days of
treatment.
After 10 days of treatment, most of the insecticides reduce their efficacy against
brown planthoppers. However, Applaud 10WP (the active ingredient is Buprofezin which
has the action mechanism for inhibition of insect chitin synthesis during molting process)
and Chess 50WG (the active ingredient is Pymetrozine which has the action mechanism for
causing anorexia in insects) are effective slowly, reaching the highest efficacy after 10 days
of treatment (Table 3.27).


21
Table 3.27. Efficacy of some insecticides on field brown planthopper population in An
Giang
No.
1
2
3
4
5
6
7

Name of
insecticide
Admire 50 EC
Applaud 10WP
Bassa 50EC
Chess 50WG

Closer 50WG
Elsin 10EC
Oshin 20WP

Dose (kg,
l/ha)
0.4
1.0
1.0
0.3
0.2
0.9
0.1

1 NSP
17.34d
16.16 e
40.62b
24.91c
39.91b
40.82b
43.16a

Post-spray efficacy (%)
3 NSP
7 NSP
c
25.45
55.58f
45.02b

60.33e
66.98a
64.63d
44.99b
68.95c
68.65a
76.82b
65.32a
77.72b
67.09a
80.15a

10 NSP
52.62d
62.07b
56.97c
70.32a
55.05c
57.10c
60.82b

Note: Different letters in columns indicate reliable difference at probability P<0.05; NSP: day(s) after
spraying

The efficacy assessment results of some insecticides against brown planthoppers
show that when brown planthoppers have a high level of resistance to insecticide active
ingredients, the efficacy of the insecticides on brown planthoppers is lower than the active
ingredients showing low and no resistance to brown planthoppers. An Giang brown
planthopper population has a high level of resistance to the active ingredient imidacloprid
(resistance rate of 118.294 - 161.768). Experimental results showed that Admire 50EC

(active ingredient imidacloprid) has low efficacy on brown planthoppers (reaching 55.58%
in the field). With active ingredient showing low and no resistance to brown planthoppers
such as dinotefuran and sulfoxaflor, Oshin 20WP and Closer 50WG are highly effective
against brown planthoppers (reaching 76.82 - 80.15% in the field). These results serve as a
basis for production recommendations on rational use of insecticides to increase economic
efficiency and reduce the ability to form and develop resistance of rice brown planthoppers.
3.3.2.2. Effect of insecticide rotation in brown planthopper control
The assessment results of effect of insecticide rotation on the change in LC50 value of
Admire 50EC to laboratory brown planthopper population show that in formulas 1, 2 and 3,
LC50 value of Admire 50EC to brown planthopper population after rotation is increased
compared to the initial LC50 value of Admire 50EC. In formula 1 (imidacloprid imidacloprid - imidacloprid), when the rotation formula only uses Admire 50EC for
spraying, LC50 value of Admire 50EC to brown planthopper population increases the most
from 15.293 to 16.143 (mg/l). LC50 value of Admire 50EC to brown planthopper population
in formula 2 (imidacloprid - sulfoxaflor - imidacloprid) increases from 15.293 to 15.859
(mg/l) when the rotation formula repeats Admire 50EC twice. And LC50 value of Admire
50EC to brown planthopper population in formula 3 (dinotefuran - imidacloprid sulfoxaflor) increases slightly from 15.293 to 15.397 (mg/l) when the rotation formula
repeats Admire 50EC only once (Table 3.28).


22
Table 3.28. Effect of insecticide rotation to the change in LC50 value of Admire 50EC to
brown planthopper population, 2017
LC50 (mg/l) after 3-times
ForName of
Active ingredient
rotating spray
mula
insecticide
1

2

3

4

5

6
7

Admire 50EC
Admire 50EC
Admire 50EC
Admire 50EC
Closer 500WG
Admire 50EC
Oshin 20WP
Admire 50EC
Closer 500WG
Closer 500WG
Oshin 20WP
Chess 500WP
Elsin 10EC
Applaud 10WP
Closer 500WG
Applaud 10WP
Oshin 20WP
Closer 500WG

Imidacloprid
Imidacloprid
Imidacloprid
Imidacloprid
Sulfoxaflor
Imidacloprid
Dinotefuran
Imidacloprid
Sulfoxaflor
Sulfoxaflor
Dinotefuran
Pymetrozine
Nitenpyram
Buprofezin
Sulfoxaflor
Buprofezin
Dinotefuran
Sulfoxaflor

Water

Water

16.143
(9.309 - 21.651)
15.859
(10.574 - 20.153)
15.397
(10.200 - 19.636)
9.024

(6.331 - 11.180)
9.302
(6.695 - 11.444)
9.119
(6.412 - 11.291)
8.107
(5.614 - 10.166)

Note: LC50 (mg/l) and 95% confidence interval before spray: 15.293 (9.975 - 19.555) mgl

When the rotation formulas do not use Admire 50EC, LC50 value of Admire 50EC to
brown planthopper population after rotating spray is decreased compared to initial LC50
value of Admire 50EC. LC50 value of Admire 50EC to brown planthopper population in
formula 4 (sulfoxaflor - dinotefuran - pymetrozine), formula 5 (nitenpyram - buprofezin sulfoxaflor), and formula 6 (buprofezin - dinotefuran - sulfoxaflor) is decreased from 15.293
to 9.024 mg/l, from 15.293 to 9.302 mg/l, and from 15.293 to 9.119 mg/l, respectively.
Study results show that the use of active ingredients with different action mechanism
according to rotation formulas: sulfoxaflor - dinotefuran - pymetrozine; nitenpyram buprofezin - sulfoxaflor; and buprofezin - dinotenfuran - sulfoxaflor, is an important
measure to restore the properties and delay the development of resistance of brown
planthopper populations to the active ingredient imidacloprid.
3.3.3. Toxicity of some insecticides against brown planthoppers to green stink bugs
3.3.3.1. LC50 value of some insecticides to green stink bugs, brown planthoppers
LC50 value of 7 insecticides against brown planthoppers to green stink bugs after 24
hours of treatment is in the order of: Applaud 10WP (12.323 mgl) > Elsin 10EC (8.276 mgl)
> Closer 500WG (5.293 mgl) > Chess 50WP (3.345 mgl) > Oshin 20WP (2.689 mgl) >
Admire 50EC (0.300 mgl) > Bassa 50EC (0.150 mgl). Out of the 7 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 7 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 7 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 7 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 > 1. Admire 50EC, Chess 50WP, Bassa 50EC, and Applaud 10WP are more
toxic to green stink bugs than to brown planthoppers with selective index < 1 (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.