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Will Climate Change Affect Outbreak Patterns of Planthoppers in Bangladesh?

M. P. Ali
SSO
Entomology Division BRRI, Gazipur 1701

Dingcheng Huang
Researcher
International Affairs Office, University of Chinese Academy of Sciences, Beijing, China

G. Nachman
Researcher
Department of Biology, University of Copenhagen, Copenhagen, Denmark

Nur Ahmed
CSO(C.C)
Head, Entomology Division BRRI, Gazipur 1701

Mahfuz Ara Begum
SSO
Entomology Division BRRI, Gazipur 1701

M. F. Rabbi
CSO (Ex.)
Entomology Division BRRI, Gazipur 1701

Abstract/ Executive Summary:

The planthopper problem has been widely reported as being induced by insecticides while other factors such as global warming that could be potential drivers have been neglected. Here, We present data that demonstrate the relationship between climate variables (air temperature and precipitation) and the abundance of brown planthopper (BPH) during 1998–2007. Data show that BPH has become significantly more abundant in April over the 10-year period, but our data do not indicate that this is due to a change in climate, as no significant time trends in temperature and precipitation could be demonstrated. The abundance of BPH varied considerably between months within a year which is attributed to seasonal factors, including the availability of suitable host plants. On the other hand, the variation within months is attributed to fluctuations in monthly temperature and precipitation among years. The effects of these weather variables on BPH abundance were analyzed statistically by a general linear model. The statistical model shows that the expected effect of increasing temperatures is ambiguous and interacts with the amount of rainfall. According to the model, months or areas characterized by a climate that is either cold and dry or hot and wet are likely to experience higher levels of BPH due to climate change, whereas other combinations of temperature and rainfall may reduce the abundance of BPH.

Keywords: BPH, Climatic variables, Population

Location: BRRI farm, Gazipur

Start Date: 01-01-1998

End Date: 31-12-2007

Program Area: Pest Management

Commodity: Insects

Objectives:

In this paper, we use concurrent information on air temperatures, precipitation and abundance of BPH, recorded in Bangladesh over a 10-years period, to analyze the complex relationship between the climate variables and the dynamics of BPH. The aim of the present study is to provide a better understanding of the role of global warming in eliciting destructive outbreaks of BPH during the recent years as well as predicting its future role.

Methodology:

The BPH population was monitored daily by a light trap which was placed close to rice fields. The trap used a 100-watt tungsten light bulb positioned at 2 m height. Lighting hours were set for 12 h (from evening to dawn) and a strip with dichlorvos (or Vapona) was put in each collecting cage to kill the insects when caught. A steel drum was placed below the cages to collect all insects including minute ones and to allow for their easy removal from the cages. The bulb and Vapona were changed when needed. The insects in the cages were removed every morning and preserved temporarily in paper bags dated daily before processing. Trapped insects were identified, counted and deposited in the Entomology Division of Bangladesh Rice Research Institute. There were no other lights near the trap. Monthly BPH catches from January to December from 1998 through 2007 were then calculated and used in this study. We analyzed whether the climate data showed any long-term trends with respect to monthly temperatures and precipitation. For this purpose, we applied three climatic variables for every month through the 10 years period: Min Temp and Max Temp which represent the average of the daily minimum and maximum temperatures during a month, and Rain which is the average amount of rain falling per day during the month. The three dependent variables were analyzed by a general linear model (PROC GLM in SAS with Month as a classification variable and Year (number of years since 1998) as a quantitative variable. The model also included the interactions between Month and Year to test whether trends differed among months. In the following, this model is termed the ‘‘null-model’’. Overall, the model included 12 month parameters, 1 year parameter, and 12 Month X Year interaction terms, to a total degree of freedom of 23. The monthly variation in BPH was analyzed in the same way as the climate variables, using the dependent variable N calculated as the average number of adult BPH caught per day during a month. Prior to the analysis we checked the dependent variables for normality and variance homogeneity. Variables that did not meet these requirements were transformed with the appropriate transformation obtained by means of Taylor’s power law. We used the general linear model identified above to simulate what will happen to the BPH if climate change results in higher temperatures in combination with a changing pattern of rain. We applied the following scenarios: Daily average temperatures were assumed to increase with 0ºC, 1ºC or 2ºC and daily precipitation was either increased or decreased with 10%. The relative change in abundance of BPH for each month was calculated as R= 100 (N-N0) /N0%, where N is the predicted catch of BPH for a given scenario and N0 is the corresponding value in the status quo scenario (i.e. the scenario with no climate change).

Source of Information: PLoS ONE 9(3); 2014; e91678. doi:10.1371/journal.pone.0091678

Article Link (Online Journal):

Funding Source:

1. Government

Budget:

Total Budget (Tk.) :

Achievement/Findings:

The analysis indicates that global warming may have contributed to the recent outbreaks of BPH in some rice growing areas of Asia, and that the severity of such outbreaks is likely to increase if climate change exaggerates. Our study highlights the need to consider climate change when designing strategies to manage planthoppers outbreaks.

Knowledge Management: Journal