The Ecological Mechanisms Of Chemical Communication In The Preference Of Harmonia Axyridis (Coleoptera:Coccinellidae) To Sophora Japonica Flowers

Harmonia axyridis(Coleoptera:Coccinellidae)is a common natural enemy insect in North China farmland ecosystem.By field investigation,we found that H.axyridis adult preferred to Sophora pendula in flowering phase.In this work,the ecological mechanisms of H.axyridis preference for Chinese pagoda tree flowers were comprehensively studied.The main results were summarized as follows:We investigated the effect of Chinese pagoda tree flowers on the longevity of H.axyridis adult using indoor and outdoor life table method.The results revealed male and female adults provided with flowers had longer longevity than those only with branches in laboratory condition.In addition,the longevity of adults living on branches with flowers was significantly higher than that living on branches in field.The nutrient substances(sugars and amino acids)analysis in branches and flowers indicated that branches and flowers all contained glucose,fructose,sucrose and maltose and their contents in flowers were all higher than that in branches.17 and 19 kinds of amino acids were identified from branches and flowers,respectively.Among them,12 amino acids had significant lower contents in flower than that in branches.In the test of the influence of four kinds of sugar in flowers on longevity of coccinellid adults,the longevity of adult feeding on tampons soaked in 20μg/mL sugar liquor were higher compared to that feeding on tampons soaked in rinsing.In addition,adults feeding on tampons soaked in fructose liquor had the longest longevityWe tested the behavioral responses of H.axyridis to Chinese pagoda tree branches and flowers by Y-tube olfactometer,the results revealed that male and female adult observably had a preference to flowers.Nonanal from the volatile substances of Chinese pagoda tree flowers could induce the antenna electrophysiological activity of coccinellid adults through coupled gas chromatography-electroantennography(GC-EAD)and gas chromatography-mass spectrometer(GC-MS)analysis.EAG dose-dependent responses revealed that EAG amplitude of adults increased as the concentration increased and maximized at the concentration of 10 mg/mL.The results of H.axyridis behavioral responses to two different concentrations(10 mg/mL and 100 mg/mL)of nonanal standard compounds revealed female adults showed observably higher EAG response to 10 mg/mL nonanal compared to that in control and there were no significant difference between females and males.There was no significant difference in EAG response to 10 mg/mL nonanal,while male showed significantly higher EAG response to 100 mg/mL nonanal.In the trail of behavioral choices of H.axyridis adult to different plant volatiles by using Y-tube olfactometer,the females showerd significant preferences for 10 mg/mL indole,methyl salicylate,leaf alcohol butyrate,anisic aldehyde,1-octene and dihydrogen jasmone acid.However,there was no difference in the behavioral choices of female to 2-methyl butyric acid glycol ester,4-ethylbenzaldehyde and linalool.Males had similar behavioral choices to the nine different plant volatiles.In the laboratory,we found that female and male showed avoidance for N,N-diethyl-3-methyl benzoic acid and menthol.In this study,we explored ethological and ecological mechanisms of H.axyridis adult preference for S.pendula flowers and identified multiple candidate volatile substances which provides scientific evidence for the development of behavior regulation techniques,protection and utilization of H.axyridis.