Comparative Study On The Ultrastructure And Chemical Composition Of The Mandibular Gland Of Males Of Camponotus Japonicus Mayr(Hymenoptera: Formicidae) At Different Ages

Ants are not only the most successful social insects in evolution,but also the most diverse and abundant insect groups in terrestrial ecosystems,with complex chemical communication patterns and social organizations.The exocrine glands throughout the whole body of ants can synthesize and release abundant chemical information substances,forming a complex chemical communication network and regulating its social behaviors such as nest development,foraging,parental recognition and caste differentiation,and playing important functions such as tracking,defense,recruitment and reproduction.The mandibular gland is one of the main exocrine gland in the head of ants,which can secrete,store and release a variety of chemicals and play an important role in the production of various pheromones.Its ultrastructure and chemical composition change correspondingly between different castes of the same ant species and different age stages of the same caste.Comparative studies on morphology and chemical composition of different castes of Camponotus japonicus Mayr showed that the mandibular glands of males were significantly more developed than those of other castes,and its volatile components were different among different castes.However,the function of the mandibular glands in the soial life of males was still unknown.Combined with the male ant’s survival time in the ant nest for up to 10 months,the mandibular glands may play a more important role in the male ant’s chemical communication.With the increase of age,how the morphology,ultrastructure and chemical composition of mandibular gland of male ant will change,and whether it is closely related to its mating and reproduction is worth further study.In order to reveal the changes of mandibular gland morphology and volatile components in secretions of male ants of C.japonicus at different ages,in this study light microscope（LM）,scanning electron microscope（SEM）,Transmission Electron Microscope（TEM）were used to compare the overall morphology and ultrastructure of mandibular glands of males of different ages after emergence.The volatile components of mandibular gland and accessory glands in reproductive system were identified by Gas chromatography-mass spectrometer（GC-MS）.Electroantennogram（EAG）was used to determine the potential response of different castes of C.japonicus to the main volatile substances in the mandibular gland of males,and the behavioral response categories of castes with strong antennal potential response were determined with laboratory behavioral test.The main results of this study are as follows:1.Morphological observation of mandibular gland of male C.japonicus at different agesMandibular gland consists of reservoir and secretory unit,and reservoir wall is made up by a layer of uniform thickness of cuticle.Secretory cell is round,and its cytoplasm full of organelles such as smooth endoplasmic reticulum,rough endoplasmic reticulum,Golgi body,rich and developed at the end apparatus,mitochondria,and various kinds of secretion.The length of mandibular gland,the length of reservoir and the diameter of secretory cells decreased with the increase of age.The secretory cells gradually dry and shrinked,and the degree of intercellular extrusion decreased and the gap increased.The position of mitochondria in the cytoplasm of secretory cells changed,and the secretory vesicles became abundant and then disappeared.The density of secretory granules increased,and the cell volume decreased gradually.Overall,the mandibular glands gradually decline and lose their vitality.2.Chemical constituents of mandibular gland and accessory gland in male ants at different agesThere are 23 kinds of volatile chemical constituents in the mandibualr gland.2-hydroxy-6-methyl-,methyl ester Benzoic acid is the dominant chemical,with 50.89%～62.48%relative content,and followed by Methyl anthranilate,（-）-Mellein and3-methyl-Phenol.The relative contents of other substances were low and dispersed in the mandibular gland secretions of male ants at different ages.The volatiles were the most abundant at 7^th and 8^th months of emergence,and the total peak area of GC-MS was the smallest at 3^rd months of eclosion and highest in 9^th month（prepare to mating）.There were 39 volatile components in the accessory glands of reproductive system,mainly hydrocarbons,esters and alcohols.The relative content of squalene in the accessory gland was significantly higher than that in the mandibular gland.3.Observation of antennae potential response and behaviorThe minor workers of C.japonicus reacted strongly to 1μg/μL and 100μg/μL2-hydroxy-6-methyl-,methyl ester Benzoic acid and 1μg/μL Methyl anthranilate.These two substances can regulate the behavior of minor workers and make them produce excitatory reactions.In conclution,through morphological observation,chemical composition detection and behavioral test,this study shows that the mandibular gland of males of C.japonicus gradually declined with age,and the secretions were mainly lipid substances,which had certain regulation effect on the minor workers.The results provided a theoretical basis for the further study of the mandibular gland function.