Preliminary Analysis on Reasons of Population Crash of Paulownia Bagworm Clania variegata Snellen (Lepidoptera：Psychidae)

Data of Paulow nia bagw ormClania variegata Snellen (Lepidoptera: Psychidae) management, larval density and parasitism from 1985 to 1995 in Lankao County, Henan Province were analyzed. Results show ed that the development of the bagworm, on account of the area attacked by the pest, could be divided into spread stage (1985~1990) with average spread rate of 115% annually, peak stage (1991~1992) with spread rate of nearly zero and crash stage (1993~1995) during which the pest population perished sharply. Control operations of C. variegata were effective for foliage protection but it could not prevent the pest from expanding due to incomplete control of trees with living larvae, it was not the means to lead the population crash either. Reliable data also show ed that C. variegata cycles were more likely to be the result of interaction with parasitoids. Furthermore, parasitoids is one of the facilitation factors to promote the breakdown of bagworm population but not the key element. Population of C. variegata will extinct under condition of population crash threshold T_cr=355 of insect density or above, and spread rate should be or near zero because intensive high density caused severely inner -species competition and environmental carrying capacity was shortage to support the whole population.