Different plant habitats provide different shelters and prey or host for natural enemies, thereby influencing the maintenance and propagation of the population of enemies. Therefore, which kind of crops to plant in the field is vital to the conservation of natural enemies. Presently, there have been lots of studies concerning the effect of crop diversity on community structure and population dynamics of arthropods, but the chill conservation effect of post-crop habitats on the natural enemies has rarely been reported. Sweet corn, a neonatal variety, has been planted on a large scale in south China. To make full use of biological control on the insect pests of sweet corn, it's necessary to study the conservation effect of natural enemies in different post-crop habitats.
In this paper, investigation was conducted to study the community structure and the time dynamics of natural enemy in maize field with different plant habitats (corn-stalk, leafy vegetable, sweet potato or weed) after autumn corn harvest by means of netting method and visual observation. The different chill conversation effects on natural enemies among different habitats were also discussed with cluster analysis. Results showed that the corn-stalk was listed as the habitat with the largest number of natural enemies, i.e. as many as 555, which was about twice of the leafy vegetable habitats (Brassica oleracea, Brassica campestris or Lactuca sativa), and 4.5 times of weed habitat or sweet potato habitat. Spiders, which took up eighty percent of the total natural enemies in B.oleracea, sweet potato or weed habitat, were the main group of natural enemies. Nevertheless, the dominant species of natural enemies in corn stalks habitat was Micraspis discolor (Fabricius), with more than 30 individuals per hundred plants. The magnitude of number of natural enemy species or diversity index was as "corn stalks habitat>leafy vegetables habitats≥ weed habitat> sweet potato habitat", while dominant concentration index of natural enemy community was to the contrary.
Results also indicated that all the six plant habitats could be classified into 3 groups, i.e. the corn stalk habitat group, the leafy vegetable habitat group and the weed and sweet potato habitat group. Both the total number and the species of natural enemies were the mostplentiful in the corn stalk habitat. In the leafy vegetable habitat, dynamics of the characteristic of community structure of natural enemies was steady, with a great number of enemy individuals but less species. On the contrary, neither enemy individuals nor species number was abundant in the weed and sweet potato habitat.
In conclusion, the corn stalk habitat had the best chill conservation effect on natural enemies in maize field. In south China, the leafy vegetables are often planted after autumn corn harvest. Researches suggested that during the period of vegetable production at winter, the corn stalk should be reserved between crop rows in order to protect the natural enemies to the most.