Demographic Variation And Habitat Selection Of Coccinellidae And Chrysopidae In Central Hebei Province

Predator insect is an important group of natural enemies. From March 2005 to March 2007, temporal variation and habitat selection predator insect were studied, the results are shown as following:Aphids were the main pests of crops such as pumpkin, cucumis melon, corn and so on. There were three dominant predators: Coccinella septempunctata, Propylaea japonic and Chrysopa septempunctata. The two ladybird beetles which had a tracking action to aphids in the early period were the dominant natural enemies in spring and summer, and C.septempunctata mainly occured in summer and autumn. Air temperature and raining did not effected directly on the predator population in corn fields. Discharging insecticide played a negative role in the distribution of C. septempunctata. Predator population began to rebuild about seven days after discharging insecticide.Predators were effected by different seeding dates: predators occurred about ten days after aphids in early-seeding corn field, and they had a concurrence with aphids in delayed-seeding and late-seeding corn field(P=0.001). Corns in late-seeding field were harmed most seriously, which had a aphid infestation of 47.5%. Corns in delayed-seeding field had the lowest aphid infestation of 16.6%.C.septempunctata has high activity and transferring behavior between different habitats. C. septempunctata was inclined to the weed habitats, the distribution of C. septempunctata in the weeds was affected directly by the width of weed, 1m width of weed had larger density of C. septempunctata; Forest belt played a positive role in the distribution of C. septempunctata, the function extents of forest belt was different along with the structure of forest belt: maximum effecting range of forest belt II (mature shelter belt) was about 20 meters, the range of forest belt I (neglected forest belt) and IV (mid-aged shelter belt) was about 10 meters; Road condition played a negative role in the distribution of C. septempunctata: the district near the road had lower density of C. septempunctata. The maximum effecting range was about 50 meters.The function of forest belts varied between different types of forest belts and in different periods. Mature shelter belt had largest effecting range in crop-growing season, and mid-aged shelter belt was best habitat for surviving-in-winter of predators, and neglected forest belt played a positive role in the population rebuilding of predators.