Conservation Functions Of Non-cotton Habitat On Predatory Natural Enemies In Northern Xinjiang

Cotton agroecosystems included cotton habitat and non-cotton habitat, non-cotton habitat is the main place of natural enemies to avoid adverse environment and look for alternative host. Systematic investigation of several years found cotton aphids were vulnerable to predators at most years, but the transfer routes of natural enemies at non-cotton fields is not clear. In the present study,the relationship between the number of prey aphids and the population abundance of lady beetles、lacewings、hoverflies on different plants were studied through systematic investigation in cotton and non-cotton fields during 2013-2014. The host preference and transfer of various natural enemies were studied from the the relationship between the cotton pests,enemy and plants period. The main results were summarized as follows.6224 predatory insects(adult and larval of lady beetles、lacewings and hoverflies) were captured during 2014-2015, 3301 of them were lady beetles,and 2607 of them were lacewings, 316 of them were hoverflies.The proportion of three kinds of predator species were analyzed in the region. For predatory lady beetles, Adonia variegata(Goeze) and Propylaea quatuordecimpunctata( Linnaeus) were dominant species, Hippodamia tredecimpunctata(Linnaeus) in a small number,Adonia variegata(Goeze),Propylaea quatuordecimpunctata(Linnaeus),Oenopia conglobata Linnaeus play an important role in the control aphid. Chrysopa carnea(Stepnens)and Chrysopa phyllochroma Wesmael were dominant species,Chrysopa formosa Brauer and Chrysopa pallens(Rambur) were common species, Chrysopa albolineata Killington)and Chrysopa yatsumatsui Kuwayara was rare species. Sphaerophoria,Paragus and Syritta were the dominant genus, Sphaerophoria scripta,Sphaerophoria rueppelli, Paragus compeditus, and Syritia pipiens were the dominant species,Episyrphusbalteatus was the common species.The transfer rules of the lady beetles between different host were analyzed. Host selection preferences of predatory lady beetles is closely related to the density of aphid on hosts. Meanwhile,the transfer of lady beetles were determined during three successive periods: in spring,adult ladybug leaved hibernation location and transferred to the host of high abundance aphids,such as Alhagi sparsifolia Shap.,Acroptilon repens(L.)DC.,Sophora alopecuroides L.,Leymus secalinus(Georgi) Tzvel.,Lepidium chalepensis(Linnaeus) Hand.-Mazz.; Then due to the change of aphid’s quantity,a large number of lady beetles transferred to Gossypium hirsutum Linn.,Triticum aestivum L.,Glycyrrhiza uralensis Fisch.,Medicago sativa L.,Phragmites australis(Cav.) Trin. ex Steud,Suaeda glauca(Bunge) Bunge,Apocynum venetum L.;Finally,The number of natural enemies was decline in cotton,but Medicago sativa L.,Sophora alopecuroides L.,Glycyrrhiza uralensis Fisch. and other plants can still maintain a high number of lady beetles. Furthermore,the influence of plant growth stage to the population dynamics of lady beetles were examined. The results indicated that even if the population abundance of aphids were very low or none on Medicago sativa L.and Phragmites australis during the flowering growth stage,there are still higher population abundance of lady beetles. These results demonstrated that sugar source play a certain extent role in the habitat searching and preferring behavior of predatory lady beetles.Green lacewing habitat selection and transfer behavior were analyzed. Chrysopa host choice preference and aphid density is closely related by correlation analysis of aphid population density and chrysopids adults,eggs. Lacewings showed selection bias to different host plants habitat and spawning. In the fields found,aphids peak on Cynanchum sibiricum Willd,Alhagi sparsifolia Shap.,Kareliniacaspia(Pall.)Less.,Cirsium setosum(Willd.) MB.,Peganum harmala L.,Phragmites australis(Cav.) Trin. ex Steud,wheat etc. occurred earlier than on the cotton,which have certain attract to lacewing. Aphids peak on Alfalfa,Cynanchum sibiricum Willd, Suaeda glauca(Bunge) Bunge, Alhagi sparsifolia Shap.,Phragmites australis(Cav.) Trin. ex Steud,Sophora alopecuroides L.,Peganum harmala L. Ect. are the the same period of cotton aphids. These plants have certain reserve function for lacewings.The species composition and habitat selection characteristics of the hoverflies were analyzed. All species of hoverflies preferred to the plants with flowers or aphids. For example,Sphaerophoria rueppelli,Sphaerophoria scripta,Paragus compeditus,Posthosyrphus Latilunulatus,Syritia pipiens preferred to the plants infested by aphids.The article also puts forward the strategy to protect the lady beetles、lacewings and syrphids. Sophora alopecuroides L. Phragmites australis(Cav.) Trin. ex Steud、Alhagi sparsifolia Shap.、Suaeda glauca(Bunge) Bunge、Atriplex patens(Litv.) Iljin、Sisymbrium loeselii Linn.、Acroptilon repens(L.)DC.、Lepidium chalepensis(Linnaeus) Hand.-Mazz., these plants surrounding cotton field was conducive to conservation natural enemies and provided theory basic for further developing the approach of cotton aphid control by the natural enemy population in northern Xinjiang.