Antennal Sensilla And Aggregation Behavior In Euplatypus Parallelus(F.)(Coleoptera: Curculionoidea,Platypodidae)

Euplatypus parallelus(F.)(Coleoptera: Curculionoidea)is one of the most invasive species of all the Platypodinae.E.parallelus is a greatly polyphagous insect that attacks over 82 host-tree species of 25 distinct families,which include mainly coniferous or broad-leaved trees.They penetrate the xylem and oviposit in their host trees,thereby weakening the trunk causing them to break under extreme conditions,eventually resulting in trees wilting and dying,and it has been a quarantine pest of imported plants in China.It was first record of this beetle in Hainan,China,in 2017 and has been successfully colonized in Hainan and Yunnan.Traditional physical control and biological control have low control efficiency,and overuse of pesticides leads to environmental pollution as well as food safety problems.Bark beetles aggregation pheromone could attract both male and female conspecifics,becomes a new method for controlling these beetles.In order to develop an attractant based on aggregation pheromone for the prevention and control E.parallelus,the external morphology of antennae and mouthparts,aggregation behavior and semiochemials of hindgut were investigated in this study.The main results are summarized as follows:1.We used a field emission scanning electron microscopy(FESEM)to study the external morphology of antennae and the type,distribution,number of the sensilla of the beetle.The result showed that E.parallelus have a geniculate antenna(sensory appendage on either side of the rostrum)composed of 6 segments,namely the scape,4-segmented funicle and club.Ninety-seven percent of the antennal sensors were distributed in the club,and 3% were distributed in the scape and funicle.We observed 6 types of sensilla on the antennae,including sensilla trichodea(subtypes: ST Ⅰ,ST Ⅱ and ST Ⅲ),sensilla basiconica(subtypes: SBⅠ,SBⅡ,SBⅢ,and SBⅣ),sensilla chaetica(subtypes: SChⅠ,SChⅡ and SChⅢ),as well as sensilla coeloconica,sensilla campaniform and sensilla furcatea.There was no significant difference in the type,distribution and number of sensilla in males and females.We observed no significant differences between the shape and distribution of antennae in males and females,but the length of antennae and the number of SChⅠ,SChⅡ,STⅠ,SBⅠ,SBⅢ,and SBⅣ in the females were significantly larger than in males.These results showed that females may play a greater role in chemoreception and mechanoreception than males.2.We used a field emission scanning electron microscopy to describe the sexual difference in mouthparts and forelegs morphology of the beetle.E.parallelus has chewing type mouthparts composed of a labrum,a pair of mandibles,a pair of maxillae,and a labium.In females,the size of maxillary palpi,submentum,prementum,and labial palpi are significantly larger than males.E.parallelus forelegs were walking type composed of procoxa,protrochanter,profemur,protibia,protarsus,and propretarsus.We observed no significant differences between the forelegs of males and females,but the procoxa of the males was slightly larger than that of females.The structural differences in mouthparts and forelegs between females and males indicated that females invest more time in gallery excavation than males,while the difference in forefoot indicates that male adults may assisted in smoothening and cleaning the tunnel.Possible functional relationships of these structures are discussed.3.Spatial distribution pattern of E.parallelus on rubber tree was determined by spatial distribution pattern indices.Spatial distribution pattern indices satisfies C > 1.This result showed that E.parallelus presented a pattern of aggregation distribution.According to the statistical analysis of the number of penetration holes of 0-4 m rubber trees,the vertical distribution of the penetration holes of long cockles is shown.The results show that it is the largest at 1-2 m,and the number gradually decreases upward or downward.4.Using the solvent extraction to extract the hindgut volatiles from adults of E.parallelus,and then imported into the GC-MS analysis.From the hindgut of the female adult in the flying period,37 kinds of conpositions were detected,which were divided into amides,alkanes,esters and alkenes;from the hindgut of the male adult in the flying period,27 kinds of conpositions were detected,which were divided into amides,alkanes,fatty acids,esters,nitriles and alkenes;from the hindgut of male adult before mating,21 kinds of conpositions were detected,which were divided into amides,alkanes,alcohols,alkenes,fatty acids,esters,etc;from the hindgut of male adult after mating,15 kinds of conpositions were detected,which were divided into amides,alkanes,alcohols,nitriles,esters and alkenes;from the frass before mating,46 kinds of conpositions were detected,which were divided into alkanes,amides,fatty acids,alcohols,alkenes,esters,etc;from the frass after mating,37 kinds of conpositions were detected,which were divided into alkanes,amides,fatty acids,alkenes,esters,alcohols,etc.