Conservation Effect Of Suaeda Strip On The Hippodamia Variegata In Adjacent Cotton Fields

In our previous study,we found that the population density of Hippodamia variegata on suaeda strip was more abundant,and H.variegata preferred to lay eggs and establish populations on suaeda strip.However,the conservation effect of suaeda strip on the H.variegata in cotton fields and the management of H.variegata on Aphis gossypii were not clear.Therefore,our study through systematic investigation of the populations of various natural enemies,aphids and other pests on suaeda strip and cotton fields,combined with DNA molecular detection technology and evaluation of natural enemy control,in order to clarify the transfer habits of H.variegata between suaeda strip and cotton fields and the effect of suaeda strip on its biological control in cotton pest management.The main results are as follows:1?The species of arthropods on suaeda strip are more abundant than that on cotton fields.The arthropod community included 40 different species,which was divided into phytophagous,predacious,parasitic and neutral sub-communities,and the number of species of three sub-communities was 18,11 and 11.The proportion of species in phytophagous,predacious,parasitic and neutral sub-communities was 45%,27.5%and 27.5%,respectively.The proportion of individuals in each sub-communities accounted for 90%,2.12%,7.88%of the total number of individuals.The dominant species of the predacious sub-community were Hippodamia variegata,Orius similis,Campylomma diversicornis,respectively.The dominant species of parasitic and neutral sub-communitiy were Eulophidae and Aphidiidae.The dominant species of the phytophagous sub-community were Clypeoaphis suaedae and Orthotylus sp.The diversity index and evenness index in the cotton field with suaeda strip were higher than that in the cotton field without suaeda strip,and its seasonal dynamics were smaller.In the cotton field without suaeda strip,the diversity index ranged from 0.074 to 1.207,the evenness index ranged from 0.038 to 0.620,and its range of seasonal variation was larger.However,the dominant concentration index of the cotton field with suaeda strip was lower than that of cotton field without suaeda strip.2?We used the specific primers of suaeda and cotton?Aphis gossypii and Clypeoaphis suaedae to test the H.variegata collected in fields.Molecular detecting results showed that cotton DNA can be clearly detected in 4.88%of H.variegata adults collected in suaeda strip,16.67%of the adults contained A.gossypii DNA,4.44%of the adults had the target DNA of Clypeoaphis suaedae,but there are no target DNA of suaeda was detected in H.variegata.Clypeoaphis suaedae DNA can be detected 2.14%of H.variegata adults collected in cotton fields,6.45%of the adults contained A.gossypii DNA,but there are no target DNA of cotton and suaeda in H.variegata collected in cotton fields.The results indicated that H.variegata transferred from suaeda strip to the cotton fields for feeding.3?H.variegata is the dominant natural enemy in cotton fields.The population density of H.variegata and the ratio of enemy to aphids in cotton field with suaeda strip were higher than that in the cotton field without suaeda strip.The average population density of H.variegata in cotton field with suaeda strip was 1.9 times than that in the cotton field without suaeda strip and the ratio of enemy to aphid was 8.8 times than that in the cotton field without suaeda strip.Exclusive cage experiment indicated that the relative growth rate of A.gossypii in caged treatment?i.e.,without predators?are significantly higher than those in the open treatment?i.e.,with predators?on the 7^thh and 14^th days after trial.In addition,the biocontrol services index of predators to cotton aphid in two cotton fields reached the maximum on the 14^th days after trial,which were 0.93 and 0.74respectively,the biocontrol services index of predators to cotton aphid in cotton field with suaeda strips was significantly higher than that in cotton field without suaeda strips.But the biocontrol effect of predators to cotton aphid at difference distances have no significant difference.This study clarified the transfer habits of H.variegata in suaeda strip to cotton fields and the effects of suaeda strip on its biological control in cotton pest management,which also explained the the conservation effect of suaeda strip on the H.variegata from the perspective of landscape.So,it is more important to protect the non-crop habitats around the cotton fields and leave plant suaeda strips around cotton field as banker plant for the biological control in cotton pest management.This study provided an important theoretical basis for constructing farmland ecosystems benefited to the conservation and pest control of the ladybeetles.