| Apis cerana cerana is a kind of fully abnormal insect with both sociality and economy,which not only maintains the ecological balance of animals and plants,but also brings significant economic benefits to beekeepers.Its alimentary canal mainly has the functions of food intake,digestion,nutrition absorption and excretion,but in the process of growth and development,the alimentary canal is easy to be violated and make the bee colony sick,which brings great economic losses for bee farmers.In addition,the alimentary canal of holometabolic insect is remodeled in the process of metamorphosis.At present,the morphological characteristics and ultrastructure of honeybee alimentary canal in the process of metamorphosis have not been systematically described.Therefore,the study on the morphological characteristics and ultrastructure of alimentary canal in different ages of honeybee is helpful for us to understand the development process of alimentary canal and provide morphological basis for treating alimentary canal diseases and guiding the development of modern apiculture.In this study,scanning electron microscopy(SEM)and transmission electron microscopy(TEM)were used to analyze the 6th instar larval stage,prepupa stage,white eye stage,pink eye stage,red eye stage and black eye stage of worker A.c.cerana.The morphological structure of the whole alimentary canal and the ultrastructure of the midgut were studied,and the significant changes of the alimentary canal in 6 stages were summarized,and the adaptive relationship between the structure and function of the alimentary canal of the worker bee during the development was discussed.The main results of the study were as following:1.In different developmental stages,the morphological ultrastructure of the alimentary canal components(foregut,midgut and hindgut)of A.c.cerana was different.2.The morphological characteristics of foregut in worker A.c.cerana at different ages were as follows.The 6th instar larval stage and the prepupa stage of the foregut included only the oesophagus,which was a short tubular structure,and the circular muscles of the foregut part of both were well developed.Starting from the white eye stage,the foregut differentiated into crop and proventriculus,and the overall length increased.With the increase of age,the circular muscles and longitudinal muscles on the crop of the pupal stage continued to develop,and the oesophagus nerves appeared on the oesophagus and extended on the crop to regulate the crop extension.The overall shape of the foregut in the pupal stage was getting closer to that of the adult,and the function was also becoming more perfect.3.The morphological characteristics of midgut in worker A.c.cerana at different ages were as follows.The midgut of the 6th instar larval stage and pupal stage were enlarged,and the circular muscle and longitudinal muscle were developed.The arrangement of the midgut muscles in the pupal stage was the same as that of the larval stage.With the change of the pupal stage,the muscle layer became more and more developed.The shape of the midgut at the black eye stage was similar to that of the adult.However,the midgut was elongated in the prepupa stage,and only the longitudinal muscles were outside.There are differences in the inner wall of the anterior and posterior region of the midgut during the pupal stage.In addition,in the larva and prepupa stages,the developed tracheole involved in respiration attached to the outside of the midgut,and the malpighian tubules involved in excretion was located at the junction of the midgut and hindgut,and the morphology changed with the development ages.4.The morphological characteristics of hindgut in worker A.c.cerana at different ages were as follows.The hindgut was not differentiated at the 6th instar larvae and the prepupa stage.The longitudinal and circular muscles of the hindgut developed in these two stages,and the hindgut differentiated into the ileum and rectum during the pupa stage.The ileum was curved and slender,with only circular muscles distributed,and the inner wall of the ileum was distributed with "grooves";The rectum was thick and short,the circular muscles and longitudinal muscles were aligned,and the epithelial layer was specialized into 6 rectal pads inside the rectum.As the age increases,the muscles on the ileum and rectum continued to develop,and the"grooves" on the inner wall of the ileum and the folds on the rectal pads deepen.5.The anterior and posterior region of the midgut showed different ultrastructural characteristics at different ages.And the zonulae adherens was the connection mode of the epithelial cells of the midgut.(1)At the stage of 6th instar larvae,there were cytoplasmic vacuoles and few organelles in the anterior midgut,and there were no cytoplasmic vacuoles and two kinds of epithelial cells in the posterior midgut.There were a large number of mitochondria,rough endoplasmic reticulum and electron-dense materials in the epithelial cells,and there was no significant difference in microvilli between the anterior midgut and the posterior midgut.(2)At the stage of prepupa,the plasma membrane folded in both the anterior and posterior region of the midgut,the exocytosis occurred in the microvilli in the anterior region of the midgut,and similar apoptotic bodies were excreted into the lumen,and the density of microvilli in the anterior region was higher than that in the posterior region,and the number of tracheole in the posterior region was more than that in the anterior region.(3)At the stages of white eye and pink eye,the cytoplasmic vacuoles in the anterior region became larger,and the microvilli arranged densely and distributed with bubble-like structure,in addition,the microvilli in the posterior region were longer than those in the anterior region,and there was no vesicular structure excreted of the midgut.But the cytoplasmic vacuoles began to appear in the posterior region of the midgut in the white eye stage.(4)At the stages of pink eye and red eye,there were a large number of different electron-dense materials in the midgut.(5)At the stage of the red eye,there continued to be cytoplasmic vacuoles in the anterior region of the midgut,with a large number of endoplasmic reticulum and no bubble-like structure in the microvilli;the number of cytoplasmic vacuoles and electron-dense materials in the posterior region of the midgut decreased,and the number of microvilli was more than that in the anterior region.(6)At the stage of black eye,there were no cytoplasmic vacuoles in the anterior and posterior region of the midgut,a large number of spherocrystals and different electron-dense materials were distributed in the anterior region,the microvilli were arranged densely,and similar apoptotic bodies were excreted to the lumen through microvilli;the length of microvilli in the posterior region was longer than that in the anterior region and there was no apoptotic body.Therefore,in the larval stage and prepupa stage,the anterior region of midgut is the place of digestion,the pupa stage is the place of secretion,and the posterior region of the midgut is the place of absorbing nutrients and enzyme secretion. |
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