Study On Regulatory Effect Of Predatory Insects On Aphids In Agroforestry System

An integrated research aimed on regulatory effect of predatory insects on aphids in agroforestry system was carried out in daxing county, Beijing. from April,2009 to October,2010. Investigation was accomplished in a typical hedgerows-winter wheat field system, using methods of net and vison to monitor aphids and their predatory insects population dynamics, dominant predatory insect habitat selection and assess on natural enemy efficiency. Complicated effects of "crop growth-habitat-pest-natural enemy"were taken into consideration integratedly.Conclusions of this research shows:1. Harmonia axyridis, Coccinella septempunctata and Propylea japonica are the main predatory insects of wheat aphids in farmland, which are belong to Coccinellidae;2. Harmonia axyridis is the main predatory insects in the wheat field and on the hedgerows including hedgerows of Hippophae rhamnoides and poplar coppice shoot (Populus sp.);3. Hedgerow is the primary habitat for H. axyridis in the early period of wheat growth(period of seedling establishment to early heading period), bridging this species from overwintering sites to crop field. Moreover, it acts to some extent like " reservoir " for this creature in wheat field and successive crop field;4. Through entire wheat growth stages, H. axyridis has an obvious preference on habitat selection. Movement among habitat patches is significant. H. axyridis appears to favour hedgerow in original stages of wheat growth (period of seedling establishment to initial heading stage), while it prefers wheat field in the medium term and later period of wheat growth (later heading stage to full ripe stage) and moves totally to nearby hedgerow and early seeded maize field after harvest of wheat;5. During mid-term and later stage of wheat growing period, wheat aphids and coccinellids will appear aggregated distribution,and coccinellids distinctly follow wheat aphids at horizontal space, distribution pattern between coccinellids and wheat aphids overlaps at space-time to enhance predatory role of coccinellids;6.Predatory insects have certain impact on regulatory effect on wheat aphids, however, evaluation of their effectiveness shows that coccinellids have bigger influence in this system;7.This study indicates that hedgerow, a non-crop habitat in a agroforestry system, affects insect natural enemy in two aspect:on the one hand, in the early period of crop growth,when natural enemy's prey is lacking,non-crop habitat can provide natural enemy with food, habitat, ovipositing site,which plays a bridge role for natural enemy'population development,so non-crop habitat is a species pool for natural enemy; on the other hand,in the period of crop harvest, a stable shelter for predatory insect to escape from fierce chaneges in cropland landscape, becomes a important source of natural enemy for reconstructing its population in succedent crop field.