Changing patterns of the East Asian monsoon drive shifts in migration and abundance of a globally important rice pest

Numerous insects including pests and beneficial species undertake
windborne migrations over hundreds of kilometers. In East Asia,
climate-induced changes in large-scale atmospheric circulation systems are
affecting wind-fields and precipitation zones and these, in turn, are
changing migration patterns. We examined the consequences in a serious
rice pest, the brown planthopper (BPH, Nilaparvata lugens) in East China.
BPH cannot overwinter in temperate East Asia, and infestations there are
initiated by several waves of windborne spring or summer migrants
originating from tropical areas in Indochina. The East Asian Summer
monsoon, characterized by abundant rainfall and southerly winds, is of
critical importance for these northward movements. We analyzed a 42-year
dataset of meteorological parameters and catches of BPH from a
standardized network of 341 light-traps in South and East China. We show
that south of the Yangtze River during summer, southwesterly winds have
weakened and rainfall increased, while the summer precipitation has
decreased further north on the Jianghuai Plain. Together, these changes
have resulted in shorter migratory journeys for BPH leaving South China.
As a result, immigration levels of pest outbreaks of BPH in the key
rice-growing area of the Lower Yangtze River Valley (LYRV) have declined
since 2001. We show that these changes to the East Asian summer monsoon
weather parameters are driven by shifts in the position and intensity of
the Western Pacific subtropical high (WPSH) system that have occurred in
the last 20 years. As a result, the relationship between WPSH intensity
and BPH immigration that was previously used to predict the size of the
immigration to the LYRV has now broken down. Our results demonstrate that
migration patterns of a serious rice pest have shifted in response to the
climate-induced changes in precipitation and wind pattern, with
significant consequences for the population management of migratory pests.