Studies On Function Of Protecting Natural Enemies By Habitat Regulation

This research investigates the insect species and the occurrences in the vegetation of apple orchard in Huangling, Shaanxi, and then selects the certain kind of weeds and crops to be the inducing species. Via analyzing the diversity index of the community of natural enemies, it finds out the function of different habitat for insect to avoid the adverse condition and enhances its ability to resistance and regeneration of insect population. The main conclusion shows below:1. In the investigation of habitats of around or inside orchard, in terms of living habitat of natural enemies, this research concludes that there are some of the ruderals can be proper inducing species for the natural enemies, such as: alfalfa, Setaria viridis,Amaranthus retroflexus,Bidens pilosa,Imperata cylindrical+Echinochloa crusgalli etc. Bidens pilosa shows the strongest abilities to induce lacewings, so does Imperata cylindrical+Echinochloa crusgalli to spiders. And some other kind of weeds have the functions to aphid,soybean can induce a lot of Riptortus linearis and Cowpea weevil etc.2. The index of diversity in the orchards which grows much weed is more than the orchards which have been furrowed, seeding the weeds to the orchard benefit the natural enemies'development. Mixed growing is good for increase the index of natural enemies. Alfalfa will lead a good aggregating effect for the natural enemies.3. There are dynamics showed on the diversity index between orchard and its surrounding habitat: if orchard is disturbed by human activities, natural enemies will move into the around habitat, then go back when the disturbance stopped. For example, human activities such as the harvest, will disturb the community structures of the natural enemies.4. The comparability index of natural enemies in orchard to the weeds such asMedicago sativa+Setaria viridis and Medicago minimach+Hemistepta lyrata, can approximately be 0.853, and rational mixed grows can enlarge the capacity of natural enemies and protection effect. For mixed grows, the best mixed type can be legume, the worst can be shallot.5. To the extent of habitat character, the diversity index from more to less can right be from the less chaos orchard to the ordinary chaos orchard in the sample pool of 7 different trial plot: Wujiaodi, Kouhe, Zhaojiayuan, Guoyejidi, Nanmao, Houzhuang and Tuqiao, etc.6. The main pest in the apple orchard includes Tetranychus viennensis,Aphispomi DeGeer,Myzus malisutus,Lithocolletis ringoniella,Carposina niponensis,Grapholitha molesta .The Aphispomi DeGeer,Myzus malisutus break out in June, and Tetranychus viennensis breaks out during July to August. The main natural enemies include Chrysopa sinica,C.formosa and C.septempunc. The predominant species of Ladybugs can be Coccinella septempunctata and Propylaea Japonica, and the Erigonidium graminicolum to spiders. The value of Niche overlap shows the strong effect of following and preying on Coccinella septempunctata and Chrysopa sinica. During September, parasiting natural enemies show high parasite rate which more than 0.8 for the main pest.