KUNMING -- Planthopper insects have invaded 5.28 million mu (352,000 hectares) of paddy fields in southwest China's Yunnan province since April, more than four times as much as the same period last year, local authorities said on Tuesday.

A spokesman with the Yunnan Provincial Department of Agriculture said 32,500 mu (2,167 hectares) of paddy fields have been ruined by the pests, which have a predilection for rice plants.

The insects have been reported in 42 counties of the province.

The province has sent 91 working teams and 52 groups of plant-protection professionals to the pest-stricken areas, and has invested 25 million yuan (3.3 million U.S. dollars) on sprayers, the spokesman said.

The department vowed on Tuesday to allocate more funds, buy more sprayers and keep a close eye on the situation with the number of counties threatened by the pests likely to increase.

Planthoppers had invaded 1.2 million hectares of paddy field in southern China regions by the end of last month, up 40 percent on the same period in 2006, the Ministry of Agriculture has said.

The pests flew from overseas to the rice-rich southern areas 10 to 15 days earlier than last year, the ministry said.

By May 30, the pests had attacked fifteen cities and provinces in south China.

The China National Climate Center had estimated the planthopper would become more fertile as a result of high temperatures and excessive rain in June.