IJERD – International Journal of Environmental and Rural Development (2021) 12-1

Research articleerd

Effect of Temperature on the Cohort Life Table of Brown
Planthopper (Nilaparvata lugens Stål) (Homoptera:Delphacidae)
MAY THU HTET*
Yezin Agricultural University, Myanmar
Email:maythuyau91@gmail.com

MOE HNIN PHYU
Yezin Agricultural University, Myanmar

THI TAR OO
Yezin Agricultural University, Myanmar
Received 30 December 2020

Accepted 30 June 2021(*Corresponding Author)

Abstract We investigated the effect of constant temperatures (24, 28, 32, and 36 °C) and room
temperature on brown planthopper (BPH), Nilaparvata lugens, population dynamics; these data
are useful for forecasting BPH outbreaks. Eggs laid by gravid females were incubated in test
tubes at the treatment temperatures and observed for egg hatching. After hatching, first instarnymphs were collected using a camel-hair brush and incubated individually in new test tubes,
each with a rice plant. The number of hatched and unhatched eggs were recorded. Nymphs
were monitored daily for life table parameters until adult emergence; the longevity of adults
were also recorded. From life table analysis, the greatest mortality occurred in the first nymphal
instar, which resulted in type III survivorship curves. Moreover, at 36 °C, 100% mortality
occurred at the egg stage. Brachypterous and Macropterous forms achieved high net
reproductive rates at lower temperature regimes. The growth parameters of BPH decreased at36 °C; temperatures above 32 °C were detrimental to the development of BPH. Results indicatethat egg and nymphal stages were significantly affected by temperature. Egg hatch also
decreased drastically with increased temperatures, especially at 36 °C.
Keywords constant temperature, Nilaparvata lugens, life table parameters, rice

INTRODUCTION
Rice is an essential food crop and more than 90% of global production occurs in tropical and semitropical Asia (Food and Agriculture Organization, 2012). Each year, an additional 50 million riceconsumers will be added to the world population, meaning that rice production must increase markedly(Heong and Hardy, 2009). In Myanmar, rice is the single most important crop, both as a staple and as aforeign exchange earner (Ministry of Agriculture and Irrigation, 2003).
Rice is susceptible to pests and diseases. From sowing to harvest, all parts of the plant arevulnerable to insect-feeding (Grist and Lever, 1969). Eight hundred species of insects attack rice crops,
either in the field or during storage. Amongst these, one of the most economically important is thebrown planthopper (BPH), Nilaparvata lugens (Stal.) (Homoptera: Delphacidae). BPH has become
more problematic, posing a threat to rice production throughout South and South East Asia (Rao,1950). In Myanmar, the first outbreak of BPH happened in 1970 at the Kyaukse Central Farm(Mandalay Division) and in Upper Myanmar (Myint, 1975). The BPH has since become a major pestof rice in Myanmar (Win et al., 2011).
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BPH is present on rice during both dry and wet seasons. Biotic and abiotic factors affect survival,growth, development and multiplication of BPH; amongst these, temperature plays a significant role(abiotic factor). As a result of climate change, global mean temperatures are predicted to increase by1.5 - 6.0 ºC by the end of the 21st century (IPCC, 2001). This significant temperature increase willaffect insect physiology, behavior and development as well as species distribution and abundance;
there is already evidence for this in the increase in number of generations a year, increasing survival
rates in winter, and the earlier appearance of some insects (Huang, et al., 2010).
OBJECTIVE
This study aimed to investigate the effect of temperature on BPH life table parameters to provide thedata needed for forecasting BPH outbreaks.
METHODOLOGY
Study site:
The experiments have been done at the JICA – ELB 1 Laboratory, Department of Entomology andZoology, Yezin Agricultural University, Myanmar between August 2018 and January 2020.
Brown planthopper (BPH) rearing:
The initial population of BPH was collected from rice fields at Yezin Agricultural University. To
establish a colony adult was confined on 30-day old potted rice plants (susceptible variety Manawthukha) in aluminum rearing cages in a screen house.
Life table study:
There were four constant temperature treatments (24, 28, 32 and 36 °C), and a control maintained atroom temperature (26.8-30.7 °C) which was recorded daily. Individual rice plants (tillering stage) wereplaced in test tubes with four gravid female BPH for the collection of eggs and sealed with a cottonwool plug. Replicate test tubes (n=5) were placed at each of the treatment, control temperatures andoviposition allowed to proceed for 24 h. After this time adult females were removed and the groups ofeggs incubated at their allocated temperatures. Eggs were observed daily and, when they hatched, acamel-hair brush was used to transfer each first instar nymph individually into new test tubes, eachwith a new rice plant. Eggs continued to be observed and hatching first instars transferred into new test
tubes until hatching stopped; the number of hatched and unhatched eggs were recorded at this point.
The later instars were collected and transferred as the same way. Nymphs were monitored daily and thetime to moult to each life stage recorded; they were provided with fresh plant materials as required. We
recorded mortality (dx) daily until their death. As adults emerged, one male and one female were pairedand moved to a new rice plant. The total numbers of laid eggs were recorded daily until females died.
Age specific life table construction:
The life table was built by partitioning the life-cycle into distinct development stages (i.e. eggs,nymphs and adults) and recording the developmental time and survival or mortality of each stage. We
calculated the pivotal age for the age class in units of time (days) (X), number of alive at each life stage(nx), proportion of individuals surviving to the start of age interval x (l x), mean number of individuals
alive during the age interval x to x+1 (Lx), number dying during the age interval x to x+1 (dx), percent
apparent mortality (100 qx), total number of age X units beyond the age (Tx ), mean expectation of life
for individuals alive at the start of age x (ex), age-specific fertility, the number of living females born
per female in each interval class (mx), net reproductive rate (Ro), the innate capacity for an increase innumbers (rm), and the mean length of a generation (G) from these data.

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Data analysis:
ANOVA and comparison of means was done using LSD in the software program (SAS 9.1).
RESULTS AND DISCUSSIONLife Table
Life table analysis showed that a mean of 26.4% of 139.4 BPH eggs survived to adulthood whenincubated at room temperature (control); this was 45.2% (of 143.0 eggs) at 24 °C, and 49.2% (of 113.8eggs) at 28 °C. Win et al. (2011) found that 37.26% of 365 BPH eggs successfully emerged as adults ina field experiment where the temperature ranged between 23 °C and 33 °C.
Table 1 Mean number and percentage of BPH alive at each life stage when reared at different
constant temperatures
Mean ± SE

Control

24 °C

28 °C

32 °C

36 °C

Stages
nx%

nx%

nx%

nx%

nx%

Egg

139.4 ± 3.9

100.0

143.0 ± 3.2

100.0

113.8 ±1.1100.0132.4 ±1.6

100.0135.8 ± 2.7

100.0

First
instarnymph

102.4 ± 6.2

73.5

137.0 ± 3.2

95.8

96.8 ± 1.5

85.1

107.4 ± 2.5

81.1

0.0 ± 0.0

0.0

Secondinstarnymph

77.6 ± 4.8

55.7

112.2 ± 3.1

78.5

77.4 ± 1.1

68.0

76.6 ± 1.857.9

0.0 ± 0.00.0

Third
instarnymph

67.4 ± 3.8

48.4

99.0 ± 2.6

69.2

72.8 ± 0.9

64.056.4 ± 1.842.6

0.0 ± 0.0

0.0

Fourthinstarnymph

57.2 ± 3.1

41.0

90.4 ± 2.6

63.2

67.2 ± 0.9

59.1

44.8 ± 1.333.8

0.0 ± 0.0

0.0

Fifth
instarnymph

48.0 ± 2.7

34.4

80.0 ± 2.4

55.9

64.0 ± 0.8

56.2

22.6 ± 1.1

17.1

0.0 ± 0.0

0.0

Adult

36.8 ± 2.4

26.4

64.6 ± 2.2

45.2

56.0 ± 0.849.2

0.0 ± 0.0

0.0

0.0 ± 0.00.0In our study high mortality occurred during the early immature stages and at 32 °C and 36 °C
there was no survival to adulthood (Table 1). Begon and Mortimer (1981) reported that this low
survivorship at higher temperatures is common in most insect species.
The highest mortality of any life stage (135.8±2.7) was observed at 36 °C in the egg stage.
Greatest mortality in first, second, third, fourth and fifth instar nymph were found at 32°C. At 36 °C,
none of the nymphal instars survived (Table 2). Krishnaiah et al. (2005) reported that temperatures
ranging between 25 and 30 °C were most favorable for BPH multiplication, and that the insect could
not tolerate constant temperatures of 35 °C and higher. Rout and Jena (2012) found that BPH thrived
and multiplied well at a temperature of 30 ± 3 ºC, and that 33ºC and 35 ºC were unfavorable for insect
survival.

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Table 2 Mean number of BPH dying between age interval x and age interval x+1 (dx) whenreared at different constant temperatures
Mean ± SE
StagesControl

24°C

28°C

32°C

36°C

dxdx

dx

dxdx

Egg

37.0±2.4

6.0±0.7

17.0±0.9

25.0±1.7

135.8±2.7First instar nymph24.8±1.524.8±0.8

19.4±0.730.8±0.8

0.0±0.0

Second instar nymph10.2±1.1

13.2±0.5

4.6±0.3

20.2±0.6

0.0±0.0

Third instar nymph10.2±0.8

8.6±0.3

5.6±0.2

11.6±0.6

0.0±0.0

Fourth instar nymph

9.2±0.511.2±0.4

10.4±0.515.4±0.2

3.2±0.2
8.0±0.1

22.2±0.522.6±1.1

0.0±0.00.0±0.0

Fifth instar nymph

The highest net reproductive rate (175.6) of the brachypterous form was observed at room
temperature (control), followed by (168.2) at 24 °C, (166.8) at 28 °C and (74.6) at 32 °C, respectively.
The lowest net reproductive rate (32.6) was found at 36 °C. The intrinsic rate of natural increase (rm)
was 0.6, 0.5, 0.7, 0.9 and 0.8 for control, 24 °C, 28 °C, 32 °C and 36°C, respectively (Table 3). The net
reproductive rate of BPH was higher at lower temperature regimes. Manikandan et al. (2015) foundthat the net reproductive rate of BPH was greater at 30 °C (39.95) than at 36 °C (8.84).
Table 3 Life table parameters of brachypterous forms at different temperature
Brachypterous forms
Parameter

Mean length ofa generation (G)Instantaneousrate
Net reproductive
rate
Gross reproductive
rate

FormulaControl

24 °C

28 °C

32 °C

36 °C

𝑙𝑥 𝑚𝑥

8.5

9.8

7.4

4.7

4.4

𝑟𝑚 = log 𝑒 (𝑅𝑜 ) /𝐺

0.6

0.5

0.7

0.9

0.8

175.6

168.2

166.8

74.6

32.6

175.6

168.2

166.8

74.6

32.6

𝐺=

𝑙𝑥 𝑚𝑥 𝑋/𝑅𝑜 =𝑚𝑥𝑙𝑥 𝑚𝑥

The highest net reproductive rate (204.0) of macropterous forms was found at room temperature(control), followed by 142.6 at 28 °C, 102.4 at 24 °C and 93.6 at 32 °C. The lowest net reproductiverate (29.2) was found at 36°C. The intrinsic rate of natural increase (rm) was 0.6 in both the control andat 24 °C, 0.6 at 28 °C, 0.8 at 32 °C and 0.9 at 36 °C (Table 4). Similar results were reported for BPH
by Manikandan et al. (2015) who reported that the net reproductive rate was greater at lower
temperature regimes (30.0 °C) than at higher temperature regimes (36.0 °C).
Developmental stages of BPH varied in length and time at different temperatures. The mean
number of first instar nymph was highest at 24 °C with the value of (137.0 ± 3.2) and lowest at 28 °C(96.8 ± 1.5). The second instar nymph was highest at 24 °C (112.2 ± 3.1) and lowest at 32 °C (76.6 ±1.8). The third instar nymph was highest at 24 °C (99.0 ± 2.6) and lowest at 32 °C (56.4 ± 1.8). Thefourth instar nymph was highest at 24 °C (90.4 ± 2.6) and lowest at 32 °C (44.8 ± 1.3). The fifth instar
nymph was highest at 24 °C (80.0 ± 2.4) and lowest at 32 °C (22.6 ± 1.1). Adults had the highest at24 °C (64.6 ± 2.2) and no adults emerged adult at 32 °C. All eggs died at 36 °C (Table 5). This showsthat, overall, 24 °C is the most favorable temperature for development of each life stage. Bae andⒸ ISERD111

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Pathak (1970) reported that there was no apparent difference in rate of growth of nymphs when rearedat 25 °C or 29 °C but at 33 °C no nymphs survived beyond second instar.
Table 4 Life table parameters of macropterous forms at different temperature
Macropterous forms
Parameter
Mean length ofa generation (G)Instantaneousrate
Net reproductive
rate
Gross reproductive
rate

Formula𝐺=𝑙𝑥 𝑚𝑥 𝑋/

𝑙𝑥 𝑚𝑥

𝑟𝑚 = log 𝑒 (𝑅𝑜 ) /𝐺
𝑅𝑜 =

𝑙𝑥 𝑚𝑥

𝑚𝑥

Control

24 °C

28 °C

32 °C

36 °C

8.8

7.5

8.9

6.0

3.8

0.6

0.6

0.6

0.8

0.9

204.0

102.4

142.6

93.6

29.2

204.0102.4

142.6

93.6

29.2

Table 5 Life table of developmental stages of BPH at different temperature
Mean ± SE
Stages

P- value
control

24 °C

28 °C

32 °C

36 °C

Egg

139.4 ± 3.9

143.0 ± 3.2

113.8 ± 1.1

132.4 ± 1.6

135.8 ± 2.7<.0001First instar nymph102.4 ± 6.2

137.0 ± 3.2

96.8 ± 1.5

107.4 ± 2.5

0.0 ± 0.00<.0001

Second instar nymph

77.6 ± 4.8

112.2 ± 3.1

77.4 ± 1.1

76.6 ± 1.8

0.0 ± 0.00<.0001

Third instar nymph

67.4 ± 3.8

99.0 ± 2.6

72.8 ± 0.9

56.4 ± 1.8

0.0 ± 0.00<.0001

Fourth instar nymph

57.2 ± 3.1

90.4 ± 2.6

67.2 ± 0.9

44.8± 1.3

0.0 ± 0.00<.0001Fifth instar nymph

48.0 ± 2.7

80.0 ± 2.4

64.0 ± 0.8

22.6 ± 1.1

0.0 ± 0.00<.0001Adult

36.8 ± 2.4

64.6 ± 2.2

56.0 ± 0.8

0.0 ± 0.0

0.0 ± 0.00<.0001

CONCLUSION
This study showed that population growth parameters were positively correlated with temperature up
to 28 °C but negatively correlated at 32 °C and above. At 36 °C, survival of all growth stages
decreased. Thus, temperatures above 32°C are detrimental to the development of BPH and no adults
emerged at 32 °C and 36 °C. The most favorable temperature for BPH development was 24 °C for
every life stage. According to results, BPH's net reproductive rate was greater at lower temperature
regimes (control, 24 and 28 °C) than at higher temperature regimes (32 °C and 36 °C). No eggs
hatched into nymph at 36 °C. BPH development was good at control, 24 °C and 28 °C although fitness
was reduced at 32 and 36 °C. In the life table analysis, the highest mortality occurred in the firstnymphal instar. The survivorship curve indicated a modest rate of mortality during the early life stages
that gradually decreased as individuals reached adulthood; this followed a type III survivorship curve.
Temperature had a direct effect on development, survival and reproduction of BPH.
Brown planthopper have high reproductive rate, so critical monitoring and forecasting of thebrown planthopper is very necessary for timely control management. The research finding will provide
valuable information to take monitoring program for control of BPH population outbreak according tothe climate change.
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ACKNOWLEDGEMENTS
The authors would like to thank the generous financial and technical training support provided by theJapan International Cooperation Agency (JICA) Project for Capacity Development of Yezin
Agricultural University (YAU-JICA TCP).
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