Studies On Change Of Occurance Features And Control Techniques Of Main Pests In Wheat Field In Linwei District, Shaanxi

Historical data of occurance features and control techniques of main insect pests was colleted and analysed in wheat field in Linwei district, Shaanxi province in this paper. The kinds of wheat insect pests and their advantage species as well as kinds of natural enemy of wheat aphids, occurance features and population dynamics of main wheat insect pests in 4 ecological areas (including the cereal-cotton-oil crop growing area in irrigation area of Wei river (Area I), the cereal-cotton-vegetable crop growing area irrigated by Wei river and well irrigation (Area II), the cereal-oil-fruit plant growing area in southern plain (Area III), the summer-cereal and spring-herbage plant growing area in hilly, dried land of the Northern Qinling (Area IV)), effects of environmental factors on main insect pests, changes of control measures and so on, were cleared initially. On the basis of historical experiences and lessons obtained controlling insect pests for many years, a program of integrated pest management to wheat insect pests was proposed and extended in a large-area. A better economic benefit, society benefit and ecology benefit has been gained. The major result is as follows.(1) There are 77 kinds of insect and mite pests belonged to 10 orders 23 families of Insecta and Arachnida in wheat fields of Linwei district. Of which the underground insect pests, wheat mites and wheat aphids are the most seriously injurious pests in the locality. 28 kinds of natural enemy feeding the wheat aphids, belonged to 5 orders 8 families of Insecta, are reported also. Distribution characteristic of the underground insect pests, wheat mites and wheat aphids was investigated in 4 ecological areas. Results showed that there are of significant differences in individual number and injurious degree of the insect pests in various ecological areas owing to difference in the geography climate conditions and farm cultivating system.(2) Population dynamics of main insect pests was studied in local wheat fields. The results showed that the wheat blossom midges, underground insect pests, wheat aphids andwheat mites were main wheat pests. Specially, damage of the underground insect pests is more serious than any other pest. Petrokia latens (Muller) is advantage species of wheat mites in 1950's and 1960's. The wheat blossom midges and underground insect pests decreased and the wheat aphids and wheat mites increased year by year during 1970's. The individuals number of Penthaleus major (Duges) is over than that of Petrokia latens (Muller) and its occurring was of more frequency and injury was more serious than before. Since 1980's, the wheat aphids and the wheat mites still were advantage pests in wheat fields. The number of wheat blossom midges began to rise again in the part areas. Density of the underground insect pest had fallen to 0.5 /m2 or so and only cansed serious damage in a few areas and in particular years. The wheat mites and the wheat aphids had become common disaster pests of wheat field in the spring since the beginning of 21 century. Wheat production was greatly influenced by the wheat mites and the wheat aphids if control measures were not used in time.(3) Relationship between environmental condition and chief injurious pests in wheat field was researched and results indicated that there were more chafers in wheat fields of the northern platland and along the both banks of Wei river than in the side-hill field;more chafers were found in semi-sloping field, flatland by river and flood land than those in platland field;occurance of the insect pests is significantly more serious in the dried lands than that in the irrigated fields before the 1970's. But this difference was very unclear in recent years. During the 1970's, individuals of Penthaleus major (Duges) is more seen in wheat fields of the northern platland and along the both banks of Wei river and Petrokia latens (Muller) in the semi-dried plain and side-hill field. Generally, the mite is more serious in the semi-dried plain than in the irrigated field by Wei River. But, this situation was opposite since 1990, i.e. the irrigated wheat field by Wei river was of more mites than the semi-dried plain wheat fields. The occurring situation of wheat aphids, in which Schizaphis graminum (Rondani) and Macrosiphum avenae (F.) is advantageous species, was more serious in the wheat fields of semi-dried plain than in the irrigated platland in the 1970's. At present, advantageous species of wheat aphids are Macrosiphum avenae (F.) and Rhopalosiphcm padi (L.);there are more aphid individuals in the irrigated platland than in the semi-dried plain field.(4) Change of prevention and control technology to the major injurious pests was summaried in wheat field for many ten years. Results indicated agriculture measures such as land ploughing deeply and man-made means such as catching and killing insect pests were main methods used to control the underground insect pests in 1950-60's. Effects of thecontrolling actions also were very limited. Insecticide seed dressings used by Phorate, Demeton and BHC etc were commonly used during the autumn-sowing in 1970's and gained very good controlling effects. Both insecticide seed dressing and Furadan soil treating were chief methods since 1980's. In order to control the wheat mite and the wheat aphid, it is major method to construct water conservancy, strengthen the field management, protect natural enemy etc before 1970's. Organic phosphine pesticide was initially used to control the aphids and mites in part of wheat fields in 1980's. Since the 1990's, though IPM with many kinds of measures was emphasized in prevention and controlling practice of the wheat diseases and insect pests, many organic pesticides such as Dicofol, Pyridaben, Meothrin, Folimat, Cymbush, Imidacloprid and so on were still used by farmers in large-scale field. The large numbers of the pesticides were universally used and had largely killed and wounded the natural enemy, and destroyed the ecological balance. The wheat mite and the wheat aphid greatly occurred in the latest successive years.(5) On the basis of the change of occurance features and control techniques of main insect pests in wheat field and summary on historical experiences of insect pest controlling, a program of integrated pest management to wheat insect pests, including mainly agricultural measures and rational insecticide-spraying, was proposed and extended in a large-area in Linwei District, Shaanxi Province. A better economic benefit, society benefit and ecology benefit has been gained.