Response Of Male Guava Fruit Fly Bactrocera Correcta To Methyl Eugenol And Environmental Health Risk Assessment Of Methyl Eugenol

Guava fruit fly(Bactrocera correct)is an important agricultural pest in the world.It severely harms more than 70 fruits and vegetables such as mango,guava,and citrus,and has caused huge losses to the fruit and vegetable industry and import and export trade of Asian countries including China.Methyl engenol(ME)is the main biological attractant for monitoring and control of fruit flies,and it has a good effect on monitoring and controlling of the invading pest guava fruit fly.However,some basic issues such as the response mechanism of guava fruit fly to methyl eugenol and the environmental impact of the widespread use of methyl eugenol are still unclear.To clarify these problems has important scientific guiding significance and practical production value for optimizing and improving the trapping efficiency of methyl eugenol and clarifying the environmental health risks of methyl eugenol.The results of the study are as follows:1)It was discovered that male guava fruit fly could capture and detect methyl eugenol through their antennae and Maxillary palpus,but the antennae played a major role.It was further discovered that the right antennae of Bactrocera guava is better than the left antennae in processing methyl eugenol odor information,which is manifested as the lateralization of the right antennae-dependent methyl eugenol olfactory.These results indicate that guava fruit fly mainly uses the antennal mechanism and the lateralization mechanism of the right antennae to process the odor information of methyl eugenol.2)For the first time,the diversity of the olfactory structure types of the antennal flagellum and their unique 3D organization architecture are analyzed with high precision from the perspective that the fruit fly antennae are structurally adapted to quickly capture and process the inestimable odor information in the air.There are 5types of olfactory sensillum including trichoid I sensillum,trichoid Ⅱ sensillum,basiconic I sensillum,basiconic Ⅱ sensillum,grooved sensillum and 1 type of nonsensory microtrichia on the surface of the antennal flagellum of guava fruit fly.In the horizontal dimension,they are distributed on the inner and outer surfaces,and have their own distribution pattern.Basiconic Ⅱ sensillum is firstly found to be clustered in the ventral region of the flagellum.Microtrichia and the five olfactory sensillum form a forest-like hierarchical organization structure in the vertical dimension.Trichoid I sensillum is at the top position,which exceeds the other organs in height by 10 μm,so it can touch air freely,but the other 4 types of sensillum are covered by a dense“canopy”,which formed by the upper part of microtrichia.They live in a relatively closed space,and the interior is hairy from high to low.Trichoid Ⅱ,basiconic I,basiconic Ⅱ and grooved sensillum form a "multi-stage odor molecular sieve system" integrating an open and relatively closed structure in the vertical space.In summary,this experiment found for the first time that the antennae of guava fruit fly are not only a cluster of olfactory sensillum with 5 types of a total number of about 2800,but also a multi-stage odorous molecular sieve system with a unique 3D organization structure.Combined with the related research of other insects,the guava fruit fly uses the unique structure of the antennae surface to adapt to accurately and efficiently screening in an air-flowing environment with trace odors.3)Independently developed the nickel chloride and cobalt chloride nerve tracing visualization technology of fruit fly antennae,enabling people to examine the olfactory nerve fiber bundles of fruit fly antennae without slicing(which can cause structural damage).The internal structure was observed,and then the number,distribution,trajectory and source of the olfactory nerve bundles of the antennae of guava fruit fly were analyzed for the first time.The details are as follows: The olfactory nerve fiber bundle is the structure that transmits odor information to the brain.Antennae flagellum sends out two bundles of nerve fibers FO1 and FO2 into the infarct,where FO1 is composed of three bundles,which comes from the nerve fiber bundle DF that travels along the dorsal path of the whiplash,and from the ventral to the back at the proximal end of the flagellum.PF traveling sideways and ATF traveling inside the antennae.FO1 will go down slightly through the dorsal micro foramen between the flagellum and pedicel and continue along the route of the middle area of the pedicel.FO2 is derived from the nerve fiber bundle VF that travels proximally from the distal ventral side of the flagellum segment.It suddenly turns from the ventral side to the dorsal side at the proximal end of the flagellum,passing through the microporous in the joint into the pedicel and then travel on the ventral route.According to the high-precision sensor level distribution map,the DF,VF and PF of the flagellum are formed with trichoid I sensillum,trichoid Ⅱ,basiconic I,Basiconic Ⅱ,Grooved sensillum,but the VF nerve bundle is directly related to the basiconic Ⅱ sesillum distributed on the ventral side.ATF is the specialized nerve bundle of the arista.FO1 traveling along the midline of the pedicel and FO2 traveling along the ventral line of the pedicel,and JO1 and JO2 issued by the Johnston’s organ in the pedicel converge into a bunch at the joints of the pedicel and scape and then enter the scape,finally the scape sends out a large bundle of mixed nerve bundles(AN)into the forebrain.These results are the first time to obtain a map of the olfactory nerve fiber bundles of the antennae flagellum of the guava fruit fly through the visual tracing technology of the insect antennae(opaque),which will lay the anatomical foundation for the study sensory nerve pathway mechanism of processing of the odor molecules of the guava fruit fly and other Tephritidae insects in the future.4)Through electrophysiological techniques,it was found that methyl eugenol can induce the EAG response of male guava fruit flies(10ng/μl-100000ng/μl)in a dosedependent manner.However,mechanical damage to the sensilla trichome type I,which is at the highest position in the vertical structure,resulted in a decrease in the EAG response to methyl eugenol.These results suggest the electrophysiological mechanism of guava fruit fly antennae response to methyl eugenol,and the important role of sensilla trichome type I in it.5)Through antenna RNA-seq and transcriptomics analysis techniques,it was found that there are 1964 unigenes in male guava fruit fly induced by methyl eugenol,of which 794 genses were up-regulated and 1170 genes were down-regulated.29 candidate important receptor genes in response to methyl eugenol in the olfactory pathway are found,including 4 odorant binding protein genes,19 olfactory receptor genes and 4 ionotropic receptors gene,1 odorant receptor co receptor genes and 1sensory neuron membrane protein gene.These results show the response of guava fruit fly antennae to methyl eugenol at the molecular level,which also provides a candidate target gene for solving the molecular mechanism of methyl eugenol in attracting male guava in the future.6)It is the first time that low-dose methyl eugenol exposure can cause damage to the central nervous system of mice at the behavioral,cellular and molecular levels.The details are as follows: at the behavioral level,methyl eugenol can not only damage the formation of fear memories in the hippocampus-dependent spatial scene,but also enhance depression-like behavior in mice,showing that low-dose methyl eugenol exposure can lead to impairment of cognitive function and increase of negative emotions in animals.At the cellular level,methyl eugenol inhibits the basic synaptic transmission of the hippocampal CA1 circuit with dose-dependent manner,inhibits long-term potentiation and facilitates long-term inhibition,showing low-dose methyl eugenol exposure can cause damage to the function of brain cells.At the molecular level,methyl eugenol reduces the expression of the learning-dependent synaptic protein Glu A1 phosphorylation sites Ser831 and Ser845,showing that low-dose methyl eugenol exposure can damage molecule function of synaptic protein in the brain.Combined with the carcinogenic risk of high-dose methyl eugenol exposure earlier,our experimental results at low dose levels have further improved its potential environmental risk level.In summary,this work systematically explored the response mechanisms of guava fruit fly to methyl eugenol from the perspective of information capturing and processing,and also assessed the potential environmental health risks of methyl eugenol from the perspective of the application of methyl eugenol technology.The research results are of great significance for understanding the relationship between methyle ugenol and guava fruit fly,optimizing the technology of methyl eugenol,and preventing the environmental health risks of methyl eugenol.