Study On Oviposition Site Selection And Overwinter Strategy Of Chrysopids (Neuroptera: Chrysopidae) In Agroforestry Environment

Chrysopids is one kind of important natural enemy in the agricultural areas, and is considered to be a common predator of the environment for a long time. From November 2006 to December 2007, the study was carried out by recording the individual numbers and distribution sites of lacewings and pests in crop fields, forest belts and peach orchard at North China Plain agricultural area. The aim was to investigate the selection behavior of Chrysopids for different environmnents such as habitats, oviposition sites, overwintering areas and so on, and evaluate the function that Chrysopidae controlled the major pests of crops. The main results of study as follows:1. Chrysopids adults had siginificant preference for habitats and ovipostion sites in different corps. In the five crops, Chrysopids adults had a significantly higher preference for peanut and maize fields to inhabit and for peanut and soybean fields to oviposit. The mainly influencing factors was crop species, extent of plants damage, richness of food resources, farming activities and so on.2. Being influenced by food, temperature and humidity, etc., Chrysopids adults had preference for ovipostion sites at vertical directions and vegetative organs sites of plants, weaker preference at level directions. In the vertical directions, Chrysopids eggs mainly distributed in upper and middle positions of crops, and in middle and lower positions of peaches. There were significantly difference in the level directions of peanut and hot pepper(P<0.01), while others had no difference(P>0.05). In the vegetative organs, Chrysopids eggs mainly distributed on leaves of plants.3. As four types forest belt which near crop fields were different, Chrysopids adults had stronger preference for forest belt 4 which have thinning slashs (new branches) to inhabit, for forest belt 1 (arabayashi) to oviposit. In forest belt, Chrysopids adults had selectivity for tree, stump (new branches) and weed, they had a significantly higher preference for thinning slashs (new branches) to inhabit, for weeds to oviposit.4. Chrysopids larvals chose the forest belts nearly corp fields to inhabit, and presented an aggregating distribution in the forest belt. The numbers and distributions of Chrysopids larvals related to coarse intensity of bark of different plants species (t=3.669 , P<0.01), and not related to diameter(F=1.604,P>0.05).5. Chrysopids overwintering in cocoon as prepupa usually, it often selected crack of barks, topsoil, litters to cocooning in forest belts and peach orchard.. It had no significantly preference for three cocooning places above. The forest belt offered the habitats for Chrysopids larva before overwintering, and guaranteed the recovery of the population in the next year.6. Based on the variety population dynamics of Chrysopids and Aphids in corps fields, the results shown that there were an indicated obvious hysteresis between the occurrence period of Chrysopids and Aphids, and the control period was relatively short. According to the relevant analysis of population's density between Chrysopids and Aphids, it had certain control function to Aphids by using Chrysopids adults. But the control function was relatively weak, and lasting time was relatively short. On the basis of appetite and emergence amount of Chrysopids adults in crops, it was conjectured Aphids could be controlled by Chrysopids adults at a certain extent in theory. From the results of temporal and spatial niche of Chrysopids eggs and Aphids, it was showed that both had a wide niche overlap.