The light trap used to collect brown planthopper (BPH) in this study.

<p>It was placed adjacent to a rice field belonging to Bangladesh Rice Research Institute (BRRI).</p

The predicted daily catches of adult BPH (±SD) if minimum temperature increases with either 0°C, 1°C or 2°C, and daily precipitation either decreases or increases with 10%.

<p>The predicted daily catches of adult BPH (±SD) if minimum temperature increases with either 0°C, 1°C or 2°C, and daily precipitation either decreases or increases with 10%.</p

The predicted relative changes in daily catches of BPH under the various scenarios.

<p>The predicted relative changes in daily catches of BPH under the various scenarios.</p

Will Climate Change Affect Outbreak Patterns of Planthoppers in Bangladesh?

<div><p>Recently, planthoppers outbreaks have intensified across Asia resulting in heavy rice yield losses. The 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 speculate that global warming may increase outbreak risk of brown planthopper (<i>Nilaparvata lugens</i> Stål.). 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. 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.</p></div

The predicted mean daily catches of BPH averaged over a year if daily minimum temperature changes with either 0°C, +1°C or +2°C, and if daily rainfall changes with either 0%,

<p>−<b>10% or +10%.</b></p

Parameter values of the model that best describes the observed values of log(<i>N</i>+1), where <i>N</i> is the average number of BPH caught per day during a month.

<p><i>T</i> is the temperature and <i>R</i> the cubic root of the daily rainfall in month <i>i.</i> The predicted value of log(<i>N</i>+1) for month <i>i</i> is obtained as where <i>M_i</i> is the parameter associated with month <i>i</i>. <i>P</i> is the probability that the true parameter value is equal to 0.</p

Log (variance) plotted against log(average) for (a) daily rainfall and (b) daily catches of BPH adults.

<p>Each dot represents a month. The straight line for daily rainfall is described by <i>y = </i>1.3068<i>x</i>+0.1252 (<i>R</i>² = 0.9587) and for daily catches of BPH by <i>y = </i>2.0512<i>x</i>–0.2258 (<i>R</i>² = 0.9793).</p

Monthly averages (±SD) of (A) Minimum and maximum temperatures; (B) daily rainfall; and (C) daily catches of Brown Planthoppers (BPH).

<p>Data from Bangladesh Rice Research Institute (BRRI).</p

The effects of minimum temperature and rainfall on the predicted abundance of BPH (log(<i>N</i>+1)) (see Table 1 for further explanation).

<p>The effects of minimum temperature and rainfall on the predicted abundance of BPH (log(<i>N</i>+1)) (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0091678#pone-0091678-t001" target="_blank">Table 1</a> for further explanation).</p