Analysis Of Feeding Habits Of Harmonia Axyridis Adults On Plant Pollens By DNA Molecular Tracking Technology

Harmonia axyridis(Pallas)is a common predatory ladybird in China.In the farmland ecosystem,it is effective in the control of sucking pests such as aphids,aleyrodids and mites.As a predator,H.axyridis can also feed on nectar,pollen and other plants food.The comprehensive understanding of the nutritional relationship between H.axyridis and pollen,nectar or other plant parts will contribute to the rational application of the corresponding nectar crops in farmland,to promoting population establishment and proliferation of H.axyridis and to play its greatest control function in farmland.In this study,DNA tracking technology was used to investigate feeding habits of H.axyridis adults on pollens.The results were shown as follows:In order to evaluate the predation preference of H.axyridis different pray spacies,and ingest the main source of plant DNA through prey.population survey and predation assessment were carried out in cotton field.Field population survey showed that the population density of Aphis gossypii and Bemisia tabaci was significantly higher than that of Helicoverpa armigera and Tetranychus cinnabarinusc.The acquired detection rates of A.gossypi,H.armigera,B.tabaci,and T.cinnabarinus was 65.83%,2.5%,0.67% and 0.67%,respectively in H.axyridis.In the field,A.gossypii dominated the preys of H.axyridis.The relation of H.axyridis,A.gossypii,and G.hirsutum was studied to assess the residual time of plant DNA in H.axyridis accurately.Cotton DNA in H.axyridis was detected by PCR technology after feeding on the A.gossypii from cotton leaves or cotton pollen.The effects of intaking method and digestion time on DNA detection rate were also analyzed.The results demonstrated that the maximum detection rate of cotton DNA in H.axyridis adults preying on A.gossypii was 16.7% at 4 h after feeding,and cotton DNA could not be detected after feeding 8 h.The detection rates of cotton DNA in H.axyridis feeding on cotton pollen were 70.4% after 4 h,51.9% after 12 h,and 39.3% after 16 h.No cotton DNA was detected after 20 h.To clarify the habit of pollen utilization of H.axyridis in multi-crop farmland ecosystem,H.axyridis was trapped at Langfang Experimental Station.And the plant DNA extracted from gut of H.axyridis starved for 12 h was then cloned and sequenced in the laboratory.In total,DNA from 13 plant families were detected including Malvaceae,Umbelliferae,Brassicaceae,and Leguminosae.The main DNA were from G.hirsutum and Petroselinum in above families,the detection rates were 56.06% and 21.21% respectively.In July,the detected plant DNA from the ladybirds' guts were mainly from G.hirsutum,Petroselinum,Ulmus,Brassica.In August,the DNA from 9 plant families were detected including G.hirsutum,Humulus scandens,Prunus salicina,Ambrosia artemisiifolia,Petroselinum,Populus,Brassica.In September,the detectionrates of G.hirsutum and Petroselinumwere higher than Suaeda glauca,Glycine willd,Chenopodium and other plants.During the years of 2014-2015,H.axyridis adults were trapped at Changdao Experimental Station and were conducted the same analysis described above in the laboratory.The results showed that DNA from 22 plant families were detected.In June,DNA from 13 plant families were detected including Amorpha,Citrus,Robinia pseudoacacia,accounting for 17.86%,14.29%,10.71%.There were also detection of plant DNA from Quercus,Triticum aestivum.In July,DNA from 12 plant families were detected from Gossypium,Albizia julibrissin,accounting for 29.03% ? 12.90%.There were also detection of plant DNA from Salsola,Vitex.In August,DNA from 13 plant families were detected including Artemisia,G.hirsutum,Suaeda,accounting for 33.33%?13.33%?13.33%.The DNA of Albizia julibrissin were also detected.The results above illustrated the main plant pollen species feeded on by H.axyridis.The plant preference of H.axyridis in different seasons were also demonstrated.The study will provide important scientific theoretical basis for promoting the regional protection natural enemies and further study on the different habitat transformation of H.axyridis.