Rice planting systems, global warming and outbreaks of Nilaparvata lugens (Stål)

Brown Planthopper (BPH, Nilaparvata lugens (Stål)) is one of the most serious pests of rice in both temperate and tropical regions of East and South Asia and has become especially problematic over the past few years. In order to analyze the effect of the change of rice cropping system on the population dynamics of BPH, field surveys of the occurrence and distribution of BPH were performed and other relevant data, including light trap data and ovary dissection data were collected in nearly 40 Chinese counties encompassing six provinces (or municipalities), including Hainan, Guangxi, Anhui, Shanghai, Fujian and Guangdong from April to October in 2007.The mixed planting areas of single- and double-cropping rice in China include Hubei, South and Central Anhui, North Hunan, and North Jiangxi. In these areas, double-cropping rice has now been greatly reduced and single-cropping rice has been rapidly increasing since 1997. The surveys revealed that when the immigration peak of BPH occurred in June and July, the single-cropping rice was at the tillering to booting stage and fit for BPH, but early rice had already matured and most of late rice had not yet been transplanted. BPH immigrants from southern rice areas prefer to inhabit and breed in single-cropping rice paddies. Moreover, farming activities between early rice and late rice interrupted the continuous growth of BPH populations in double-cropping rice paddies. As a result, in comparison with data collected 30 years ago, the spatiotemporal dynamics and migration patterns of BPH have dramatically changed in the lower-middle reaches of the Yangtze River. In the mixed planting areas, due to their high suitability, the BPH population in single-cropping rice grew so quickly that it caused serious local damage and there was mass emigration of macropterous progeny to the Yangtze River Delta in late August and early September.Global warming may also affect BPH populations, where results suggest steadily warmer autumns have occurred from the 1990s on, with such conditions gradually the norm. The combination of 'cooler summer' and 'warmer autumn' are conditions known to promote outbreaks of BPH in the lower-middle reaches of the Yangtze River. Immigrant BPH arrivals in late August and September now cause serious damage to late-maturing mid-season rice and late rice in the lower-middle reaches of the Yangtze River.