Morphology And Ultrastructure Of Distal Femoral Gland And Abdominal Tubercles In Cicadas

There are many kinds of exocrine glands in insects,which play an important role in feeding,movement,courtship,mating and migration.Up to now,many studies have been conducted on the types and functions of the exocrine glands in social insects,but works on the exocrine glands in solitary insects are very limited.In the present study,the morphology and ultrastructure of the exocrine glands in the femurs of six representative cicada species and that of abdominal tubercles of two representative species were studied using light and electron microscopy.The main results are as follows:We discovered a novel gland at the apex of the fore,mid and hind femurs from all the six representative cicada species,which we propose to name as the epithelial femoral gland(EFG).The EFG is located between the paired apodemes and the articulation membrane within the apex of the femur,which faces the proximal articulation region of tibia.The EFG in the midlegs is less developed than that in the fore and hindlegs within a species.The glandular cells belong to class-1,which contain a large number of rough endoplasmic reticulum,secretory vesicles and Golgi bodies,indicating these cells may secrete proteinaceous exudates.Details of the EFG at the ultrastructural level suggest that it may function to produce nutrient substances to the joint between femur and tibia.The less developed EFG in the midleg and the slight difference in the EFGs between fore and hindlegs should be related to the morphological/functional differentiation of corresponding legs.In Meimuna opalifera,the tubercles were found in pairs on both sides of sterna III–VII of the abdomen.There were a large number of sensilla trichoid on the surface of tubercles as well as the cuticle around the tubercles.The sensilla trichoid on the surface of tubercles were longer than that on surrounding cuticle.N umerous waxes were secreted from the inner surface of the tubercles.The glandular cells existing in the tubercles belong to Class-1.There were a lot of rough endoplasmic reticulum,Golgi apparatus and secretory granules in the glandular cells.The tubercles may function to sense the temperature and humidity of the surrounding environment,e.g.,to receive stimulation and secrete waxes,which may play a role in preventing water loss and maintaining body temperature.In Tanna japonensis,a pair of tubercles were found on the sternum III of males,whereas they were absent in females.There were numerous sensilla trichoid on the sterna as well as the tubercles.Waxes were observed on the abdominal cuticle,but not from the tubercles.Ultrastructural observations reveal that there were no glandular cells in the tubercle,indicating that it is not a glandular structure.The presence of the tubercles only in male and the presence of a large number of sensilla trichoid on the surface of the tubercles indicate that the function of the tubercles in T.japonensis may be closely related to the activities associated with courtship and mating,or sensing the airflow pressure in flight.In summary,the ultrastructure of the EFGs of fore,mid and hind femurs in six representative species of Cicadidae provide a reference for future studies of the exocrine gland in legs of cicadas,which may be helpful for us to further understand the structural and functional divergence of legs in Cicadidae and other Cicadomorpha insects.The morphology and ultrastructure of the abdominal tubercles in two representative cicada species provide important information for us to further clarify the function of these structures in cicadas,which may be closely related to the activities of feeding,courtship and mating,etc.