| Apoidea has a very rich variety of species and biological characteristics,and plays an important role in the control of plant pollination,pest population and agriculture.The purpose of this study is to clarify the general rules of alimentary canal morphology and histology of species in Apoidea,Hymenoptera,and discuss its function and systematics,so as to supplement the blank of research on the whole structure of alimentary canal of Apoidea species.In this study,the alimentary canal of 30 species belonging to 9 families and 29 genera in Apoidea was observed and studied by stereomicroscope,scanning electron microscope and paraffin section and HE staining.The structure of oesophagus,crop,proventriculus,midgut,ileum and rectum of each species were described.The characteristics of alimentary canal of each species were compared and summarized.And discuss the relationship between histology and morphology of alimentary canal and biological characteristics,as well as systematic classification.The main results and conclusions of the study are as follows:1.In Apoidea,species of Anthophila are with well-developed oesophageal muscles,and the circular muscles are usually regularly densely arranged except for the kleptoparasitic species Nomada sp..In Spheciformes,a few species have densely arranged circular muscles,while other species are usually not densely arranged.The muscle tissue of crop is similar to oesophagus.The possible reason for the tendency of muscles characteristics of Anthophila and Spheciformes is that they feed on pollen and nectar,and the developed muscle layer of oesophagus and crop is required for pollen.Among them,the species of Nomada sp.provides a contrary example.The species of Spheciformes usually only feed on nectar or honeydew and other liquid food,and there is no adaptive condition for pollen grains,so the muscle tissue is diverse and has no significant regularity.2.In this study,the diverticulum crop that is usually found in adult of Lepidoptera and Diptera is found in Crabroninae,that is a caecum with lateral openings.The diverticulum crop is significantly different from the normal crop in other species of Apocrita.The muscle bundle of circular muscle in diverticulum crop is centered on the proventriculus and radiates laterally.The lips of the proventriculus is wrapped by the foregut wall and the hairs usually become vestigial.There is a functional difference between the diverticulum crop and the normal crop,the proventriculus of the diverticulum crop configuration opens in the foregut cavity,and the solid is hard to be discharged from the diverticulum.Therefore,the change to the diverticulum crop can be regarded as to weaken the ability to handle pollen grains in Crabroninae,which belongs to the specialization of structure and function.The structure of diverticulum crop is similar to that of Lepidoptera and Diptera,but different from that of Hemiptera,which indicates that diverticulum crop can adapt to intermittent feeding of pure liquid food,and the mechanism of diverticulum crop may be similar to that of Lepidoptera and Diptera.Compared with some Diptera species,the diverticulum crop of the subfamily Crabroninae are more simple and primitive,and seem to have only the function of storage.The existence of other degenerated structures also indicates that this transition is short-lived.However,the dominant status of the subfamily Crabroninae,which accounts for nearly half of the Spheciformes species,indicates that this change may have a competitive advantage,which is second only to the absolute number advantage of pollen nectar feeding habits of the bees.There is no exception of diverticulum crop configuration in the subfamily Crabroninae,which can be regarded as a stable morphological feature and can be used for the morphological classification of the subfamily.In addition,it remains to be studied whether the sister group of the subfamily Dinetinae belongs to the diverticulum crop configuration.3.The proventriculus is considered to be the most valuable in the morphological study of insect alimentary canal.The whole body is usually cylindrical.The proventriculus bulb extends into the crop(except for Crabroninae),which is divided into four parts,with hairs on the lip of each part.In the Apoidea,the proventriculus lips of Xylocopa tranquabarorum,Andrena sp.,Colletes sp.and Hylaeus sp.is not prominent,and the division is not significant.In addition to the poly-hairs of the Macropis hedini,the rest of the Anthophila are single-hairs,and the other two species Xylocopa tranquabarorum and Hylaeus sp.are of pectinate-hairs.Most of the species Spheciformes are poly-hairs,and a few of them,such as Ampule x dissector and Alysson harbinensis,are single-hairs.The proventriculus hairs of the Crabroninae species is degenerated or invisible due to the diverticulum crop configuration.The structure of the proventriculus lips of Apoidea changed from prominent to not prominent,and from the poly-hairs to the single-hairs,which may be related to feeding habits,but there are many exceptions.There are no inducible features that can be distinguished at the family or subfamily level.4.The midgut of Apoidea species is usually cylindrical,ellipsoidal or fusiform.The midgut of Anthophila is usually cylindrical,with dense and obvious ring folds,while that of Spheciformes is usually nearly cylindrical or ellipsoidal,with a few fusiform.The midgut is the main place of digestion,and the epithelium of the posterior segment of the midgut has vesicae in some species.Regenerative crypts,which are common in Coleoptera species,appear in the midgut epithelium of Xylocopa tranquabarorum and Hylaeus sp..In addition,the epithelium of Andrena sp.and Gorytes sp.protrudes slightly from the muscle layer,but is not regenerative crypts.At present,regenerative crypts and regenerative cells are considered to have the function of replacing damaged epithelial cells,and there is a negative correlation between them and the development of peritrophic matrix(PM),which may mean that the PM of the midgut of these two species is underdeveloped,or some of their habits cause greater damage to the epithelium.The hammer like protrusion in the anterior part of midgut may also enhance the digestive function of midgut.The specific reasons need more research to explain.5.The ileum of Apoidea species is similar to that of Apis mellifera,with welldeveloped circular muscles and longitudinal folds of epithelial tissue,without ileocolic division.However,in some species,the epithelium of the posterior segment of the ileum is less developed than that of the anterior segment.In some species,longitudinal muscle is attached to the ring muscle in the posterior segment of ileum,but it is significant in Spheciformes,but not significant in Anthophila.There were single-or poly-hairs on the inner surface of pylorus in the anterior segment of ileum,which were arranged side by side or slightly radially.Its function may be to prevent the retrogradation of the food pellets during ileal contraction.It was found that there were more than ten protrusions in a circle behind the Malpighian tubes,which were obviously derived from the lengthening of epithelial tissue,called pylorus pads.Its function may be to reabsorb nutrients from excrement of Malpighian tubules,or to compensate for the weakening or loss of the resorption capacity of Malpighian tubules.Or have sex-related endocrine function,Further studies on TEM are needed.6.The rectum of Apoidea species is saccate,the outer longitudinal muscles are arranged in 6 rows and alternate with the rectal pads.The number of rectal pads is usually 6,which is 3 in Nomada sp..The rectal pads are in parallel or alternate arrangement,and they are basically arranged in parallel in Spheciformes.The shapes of rectal pads vary from oval to long strip.In Anthophila,they can be divided into two types:one is long strip psds and parallel arrangement represented by honeybee and Andrena sp.,and the other is round to oval pads and alternate arrangement.The rectal mats are nearly round to oval.From mud wasps to flower wasps,they showed a trend of parallel to alternate arrangement,the pads shapes are diversity to polarization.There was no functional difference between the two groups.The alimentary canal morphology of the Apoidea has a certain tendency in two different feeding groups,Spheciformes and Anthophila,but there are exceptional species in both groups.Except for the diverticulum crop configuration of Crabroninae.There are no other strongly related morphological characteristics of the same group. |
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