Dynamics of pest and natural enemy community in wheat field

Community dynamics of major insects in winter wheat fields were investigated for the period of March 15 to May 29 in 2008 in accordance with the theory and method of community ecology. Data collected on pest and natural enemy communities and temporal niches were analyzed based on factors such as relative richness, dominance index, dominant concentration index, diversity index and evenness. Results show a rich insect community composition in winter wheat fields, with 11 orders, 39 families and 59 species. Dominant species are Macrosiphum avenae, Penthaleus major, Propylea japonica and Ephedrus plagiator. Individual population and abundance change with investigation time. Diversity index and evenness of communities are relatively low during wheat early growth stage. However, both are high during the mid and late stages, with the same variation trend. The change of dominant concentration index is inversely related to evenness and diversity index. Among the natural pest population, intra-species competition is fiercest for Helicoverpa armigera and weakest for Psammotettix striatus. On the other hand, inter-species competition is fiercest for H. armigera and M. avenae, followed by P. major and Dolerus tritici. Among the enemy population, intra-species competition is fiercest for Coccinella septempunctata and weakest for E. plagiator. In terms of time, competition between P. japonica and C. septempunctata or Leis axyridis is relatively fierce. However, that between E. plagiator and P. japonica, C. septempunctata or L. axyridis is weaker. Based on overlaps between the pest and natural enemy populations, L. axyridis and C. septempunctata have a strong control effect on H. armigera. E. plagiator and P. japonica have a stronger control effect on main pests such as M. avenae, P. striatus and Phytomyza nigra in winter wheat fields.