Morphology And Actinomycetes Community Composition In The Infrabuccal Pocket Of The Ant Ectomomyrmex Javanus(Hymenoptera,Formicidae)

Ants are an extremely diverse group of insects in nature and highly evolved social insects.They are known as ‘engineers of ecosystems',the activities of their foraging and nesting also have an important impact on other biological groups and ecological environments in the ecosystem.Most of the ants are omnivorous,they can feed on solid foods such as plant seeds and insect corpses during foraging,and they can also feed on liquid foods such as plant juice,nectar and honeydew of Hemiptera insects.However,the specificity of the ant's digestive system indicates that they mainly use liquid food.At the anterior part of their mouth,there is a special structure called the infrabuccal pocket,which can filter solid food particles and ensure the smooth flow of the entire digestive tract.The results of previous studies on the morphology and microbial composition of the infrabuccal pocket in the omnivorous ant Camponotus japonicus showed that the type and quantity of microorganisms in the infrabuccal pocket were significantly higher than that of the digestive tract,the pocket has the function of filtration and storage of microorganisms from food,nests and the surface of ants.The main microorganisms of the infrabuccal pocket are actinomycetes.However,studies of the function and microbial composition of the infrabuccal pocket are limited to a few sporadic studies.In this study,we investigated the morphology and ultrastructure of the infrabuccal pocket,its actinomycete composition and antibacterial activity in workers of the ant Ectomomyrmex javanus,here are the main results:1.We observed the infrabuccal pocket with serial semithin sections,they show the infrabuccal pocket is a spherical sac-like extension of the ventral pharynx wall that occurs anteriorly in the head,underneath the pharynx.The size of the infrabuccal pocket is flexible according to the amount of its accumulated solid contents,the maximum diameter of the full pocket that we observed is 330 ± 30 ?m.The lower dorsal lip of the prepharynx forms a ventrally oriented flap that acts as a valve-like dorso-anterior lining of the infrabuccal pocket;at its ventro-anterior side,an upward extension of the labium forms the other part of the infrabuccal pocket's connection to the prepharynx,both valve-like structures work together to control the opening and closing of the infrabuccal pocket.There are not any muscle fibres surrounding the pocket,which indicates that the emptying of the pocket is achieved by changes in the hemolymph pressure in the head.The infrabuccal pocket of workers is always empty in the morning,whereas in the afternoon it is full.2.The result of SEM shows the external surface of the infrabuccal pocket looks like an irregular lattice,covered by regular hairs with hook-like curved terminal tips.The internal surface of the infrabuccal pocket is ornamented with an imbricate pattern of polygonal scales.Each scale displays a number of uniform finger-like denticulate hairs that are oriented toward the entrance of the pocket.The number and length of the hairs decrease posteriorly,in the most posterior part,the scales do not show any hairs anymore.They are related with the filtration function of the infrabuccal pocket.3.The result of TEM shows the pocket wall reaches a thickness of 24.45 ± 3.45 ?m in its anterior part,but elsewhere only measures 6.87 ± 1.12 ?m,this morphology increases the stability of the infrabuccal pocket with regard to the ants' feeding habit.The wall consists of an epidermal layer covered by three cuticular layers(endocuticle,exocuticle and epicuticle).The epidermis is formed by a single layer of cuboidal cells lining the anterior part of the pocket with a thickness of 10.18 ± 2.50 ?m,whereas it measures only 3.18 ± 0.97 ?m in the posterior part of the pocket.The apical cell membrane is differentiated into an irregular border with short microvilli.The intercellular membrane appears interdigitated in the apical part of the epithelium.The cytoplasm of the epidermal cells contains some mitochondria and glycogen.The lumen of the infrabuccal pocket contains numerous fungus particles.which looks like Saccharomycetes.4.The composition of actinomycetes in the infrabuccal pocket is determined isolated using a culture-dependent method and identified with DNA sequence analysis.We have isolated 9 actinobacterial strains from the infrabuccal pocket.Among the result of species of isolated strains and their distribution and separation frequency in different nests,Streptomyces form the dominant group,with a total of 6 strains(B1,A3,B4,B5,B3,A2),strain B1,A3 and B5 are distributed in all 3 nests,the average isolation frequencies are 93.3%,80.0% and 53.3%.C1 is Microbacterium,the average isolation frequency is 100.0%,we find it in all 3 nests.A1 is Tsukamurella,the average isolation frequency is 80.0%.B2 is Amycolatopsis,we only find it in 2 nests,the average isolation frequency is 26.7%.5.The result of the antibacterial activity of 9 strains of actinomycetes by using the plate confrontation method and the growth rate method shows strain B2 Amycolatopsis,strain B3 Streptomyces,B4 Streptomyces and B5 Streptomyces have antibacterial activity to 8 strains of tree pathogenic fungi.The fermentation liquor of strain B4 exhibits inhibitory activity for all the 8 strains of tree pathogenic,especially for Botryosphaeria dothidea,Thanatephorus cucumeris,Melanconium oblongum Berk and Valsa mali,the antibacterial rate is 100.0%,showing strong inhibitory activity which can be used in development and utilization.