Preliminary studies on population dynamics of the scale insect Parasaissetia nigra on rubber trees and influencing factors in Xishuangbanna

Investigations on population dynamics of the rubber tree scale insect Parasaissetia nigra were carried out from April 2005 to March 2008 in Xishuangbanna rubber plantation.The results showed that this scale insect occurred in this region year by year.The population density of the scales at the same month was significantly different among different years(One-Way ANOVA,p0.05).The density reached highest in July and October in 2007,at 108.5±11.9 and 107.2±5.5 individuals per branch,respectively.There were three density peaks for the scales of various stages.As for the nymphs,the first peak appeared in early April,and the second in the middle of July,and the third in October(December in 2006).The density peaks of the adult scales occurred in January,June and October,respectively.Analysis combined with climatic factors demonstrated that the temperature was the main factor affecting the population dynamics of the scale insects in dry seasons,and the intensity and frequency of rainfall was the key factor restricting the growth of scale populations in wet seasons.