Identification Of A Aggregation Pheromone In Megalurothrips Usitatus(Bagnall)and Its Biological Activity Verification

Megalurothrips usitatus(Bagnall)is an important leguminous pest in South China,which has caused enormous losses to cowpea planting industry.Currently,the control of M.usitatus in China still highly relies on chemical control.However,overuse of pesticides leads to pesticides resistance,agricultural ecosystem imbalance,environmental pollution as well as food safety problems.Consequently,it is urgent to develop green control methods.Thrips aggregation pheromone could attract both male and female conspecifics.As an environmentally friendly method,aggregation pheromone could be an alternative control method with great potential for M.usitatus management.In this study,the presence of aggregation pheromone in M.usitatus was confirmed by laboratory behavioral tests.The natural active compound was extracted by two extraction methods,isolated and identified by two chemical analysis techniques and three spectral analysis methods.The chemical structure of the active compound was also predicted.The biological activity of synthetic aggregation pheromone was verified by laboratory behavioral tests and field trapping experiments.These results could provide theoretical and practical basis for management of M.usitatus by using aggregation pheromone.The results are as follows:1.The responses of female and male adults to male-or female-produced volatiles were tested using Y-tube olfactometer.The results showed that male and female adults showed significant preference to the odor of male adults,but no significant preference to the odor of female adults when compared with the control odor.These results indicate that M.usitatus males could produce semichemicals that are attractive to both sexes.Those semichemicals might function as aggregation pheromone.2.Headspace volatiles of male and female M.usitatus were extracted by head space solid-phase microextraction(HS-SPME).In addition,hexane extracts of both sexes were obtained by soaking thrips in hexane.The total ion current(TIC)of both headspacevolatiles and hexane extracts were analyzed by gas chromatography-mass spectrometry(GC-MS).GC-MS analyses of both headspace volatiles and hexane extracts revealed one major peak in the male profiles that was absent from female profiles,of which the retention time was 23.85 min.This indicated that males could synthesize,store and release this compound,but females could not.3.By comparing the mass spectrum of natural compound of M.usitatus with the standard mass spectrum library of GC-MS,we found that the target compound was closely matched with a compound with CAS No.4128-17-0(the matching degree is above 90).Moreover,the fragment ion peaks of mass spectrum of natural compound were highly consistent with that of CAS 4128-17-0 in the mass spectrum library,in NIST on-line mass spectrum library,and in published literature.The aggregation pheromone compound of M.usitatus could be preliminarily considered as(E,E)-Farnesyl acetate.4.The TIC and MS charts of natural compound,(E,E)-Farnesyl acetate standard and mixture of natural compound and(E,E)-Farnesyl acetate standard were compared by three spectrometry methods: chromatography,mass spectrometry.The chemical structure of the compound was analyzed by mass spectrometry and infrared spectroscopy.The results show that natural compound-chemical standard mixture gave one single peak and the peak appearance and retention time were consistent with that of single compound;the fragment ion peaks of natural compound,chemical standard and mixture of natural compound and chemical standard were identical,with approximately the same relative abundance.Structure analysis results from mass spectrometry and infrared spectroscopy were consistent.The above results confirmed that the aggregation pheromone compound of M.usitatus is(E,E)-Farnesyl acetate.5.Y tube olfactometer experiments and field trapping trials were conducted to test the attraction activity of synthetic(E,E)-Farnesyl acetate.Olfactometer results showed that male and female adult thrips showed significant preference to(E,E)-Farnesyl acetate at certain doses,and the dose range of significant preference for female thrips was wider than that for male thrips.The results of field trapping trials showed that(E,E)-Farnesyl acetate at certain doses could greatly increase trap catches of blue sticky cards.In addition,the attractive dose range for male and female adults in the field were also different.