Takeoff and emigration
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Key Words：Sogatella furcifera， takeoff behavior， caged observation， trajectory analysis
Abstract： The aerial migration of the whitebacked planthopper Sogatella furcifera (Horváth) (WBPH) was studied in the field and captivity in Suzhou in 2001 and 2002. The results indicate that WBPH immigrate into Suzhou in early July, and produce two generation in this area. A few adults were beginning to emigrate from the end of August but the peak of emigration occurred in mid September when the mass flight could be seen at dusk. When the population density was high, the mass flight of insects continued until 10 minutes after twilight. The daily emigration ratio was about 80% during the emigration peak in captive populations, but about 50% to 65% in paddy fields. We found that the emigration behaviour of WBPH has changed since the mid 1990’s. The offspring of immigrants would mostly emigrate when the macropterous adults emerged in 1980’s, but now very few hoppers depart in August which greatly prolongs the duration of damage to rice crops. Emigration trajectory analysis at altitudes of 500, 1 000 and 1 500 m indicates that in mid or late August about 40% of the migrating planthoppers from Suzhou arrive at the Yangtse and Huai River basin and the other 49% emigrate to the Yellow and East Seas, even crossing the sea to South Korea or Japan in a strong southerly low level jetstream. In September, these planthoppers return to rice planting areas south of the Yangtse and north of Nanling.