A Study on the Population Dynamics and Damage of Red Spider Mite (Tetranychus viennensis)

The result of the research which lasted for fifteen years indicate that growth and decline curve of Tetranychus viennensis Zacher population in orchards is one humped one.In the centre and south of Hebei Province, in the different or same years, in the different orchards, their occurrences are different.The peak occurs mainly from late June to mid July in the pear and peach orchards.The peak occurs mainly from mid June to early August in the apple orchards.The demarcation index of the temperature and relative humidity of the peak is the average of ten days which are 26.14±2.11℃ and 61.67%±8.92% respectively. Between the starting development temperature (9.2℃) and the temperature demarcation index, the rising of population is a straight line interrates with the total effective temperature.The spatial distribution patterns of population in crowns and orchards are all determined as a aggregate type.In apple, pear and peach trees, the lowest pest density to cause early leaf fall are respectively 31.79, 32.34 and 19.47 per leaf, the index of damage are respectively 61.27%、60.07% and 58.01%.