Abstract:

The soft scale, Eulecanium gigantea (Shinji) (Homoptera: Coccoidea; Coccidae) was an important pest in cities of northern China in recent years. During 1998—1999, five experimental districts with different degrees of air pollution in Taiyuan City and one clean area as the contrast district at campus of Shanxi Agricultural University located in Taigu County were selected. The nutriological relationship between the soft scale population increase and its host plant was studied. The results showed that (1) In the pollution districts, the quantity of reductive sugar, general sugar, soluble protein and amino acids in twigs and leaves of the host tree, Sophora japonica, were much more than those in the clean district. (2) In the sample districts, the soft scale population densities increased as the air pollution deteriorated. At the same time, the contents of reductive sugar and soluble protein in twigs were positively correlated to the population density of the scale insect significantly. The regression equations were made out respectively in Y₁=87.602 8X₁-117.825 0, with correlation coefficient r₁=0.98, and Y₂=2.893 6X₂-142.152 3, with r₂=0.84. (3) During March to October, two peaks and one valley were appeared in the content fluctuation of the nutrition substances in host tree twigs. That echoed respectively to the two feeding stages and one egg stage of the soft scale in its life cycle. It was concluded that a higher content of nutrition substances in the host tree in polluted urban environment may be one of the important factors which make the scale insect greatly propagating. An nutriological evidence was provided by this research in the trend of scale insect population to increase in polluted urban environment.

Key words: Urban pollution, Coccidae, Scale insect, Eulecanium gigantea (Shinji), Nutriology