~ 150 ~ Journal of Entomology and Zoology Studies 2018; 6(2): 150-156 E-ISSN: 2320-7078 P-ISSN: 2349-6800 JEZS 2018; 6(2): 150-156 © 2018 JEZS Received: 01-01-2018 Accepted: 03-02-2018 Milagros M Greif Biology Department, Cebu Normal University, Cebu, Philippines Correspondence Milagros M Greif Biology Department, Cebu Normal University, Cebu, Philippines Study on mosquito ovary using transmission electron microscopy Milagros M Greif Abstract The study focuses on the ovaries of mosquito using transmission electron microscopy. Mosquito that were used comprised of six different strains, namely: Culex pipiens Complex, Aedes aegypti, Aedes vexans, Ochlerotatus cantans, Ochlerotatus rusticus collected from the Philippines and Germany. A meal of blood in the mosquito can alter a series of changes in the cell structure that leads to the formation of a mature egg. After the mosquito has taken a blood meal, some prominent changes occur in the epithelial follicles. The very prominent changes that occur are the development of large inter-cellular spaces and a decrease in desmosomal connections. Several numbers of microvilli covered the area of the oocyte facing the epithelial follicles of which during seven hour after blood meal, push towards the extra-cellular spaces created by the separation of the epithelial follicle cells. The microvilli vary in length and are not regularly distributed like those of the typical intestinal epithelium. A unit membrane is seen which later fuses to form a yolk. A meal of blood or controlled diet leads to a series of changes in cell structures in the reproductive organ of female mosquitoes that quickly results to the formation of matured eggs. Another prominent changes observed in the ovary of mosquitoes having blood meal is the presence of various un-oriented microvilli in the area of the oocyte which is adjacent to the epithelial follicles. These microvilli can also be observed in ovary of mosquitoes having no blood meal but they are smaller in size. Furthermore, pits or vesicular bodies are developed after a mosquito has taken a blood meal. Keywords: mosquito, ovary, oogenesis, transmission electron microscopy Introduction Most of the insects including mosquitoes reproduce sexually. Adult mosquitoes, typically obtain nutrients for survival and reproduction from three sources [1, 2] : (1) teneral reserves from larval feeding on the microbiota and detritus in water, (2) nectar or other plant juices for energy, and (3) blood taken only by females for egg production. Mosquito ovaries are classified as meroistic type because they contain nurse cells as well as oocytes. Furthermore, they are categorized as polytrophic because groups of nurse cells are enclosed with an oocyte in each ovarian follicle. In contrast to other insects, like for instance mayflies (Ephemeroptera) and cockroaches (Blattodea), no nurse cells are present within the oocytes. This ovary is classified as telotrophic meroistic type. In these insects, the follicle cells are equipped to carry out secretion and protein synthesis [3] . A central chamber or calyx is present in each paired ovary. The calyx is lined by an epithelium which contains muscle filaments that are also present in the lateral oviduct. Two tracheae enter each ovary and branch into the tracheoles within the ovarioles. Each paired ovary consists of variable numbers of tubular epithelial ovarioles where the oocytes are placed in a linear sequence according to their stage of growth [3] . The number of ovarioles ranges from 50 to 500 depending on the species, physiological stages as well as the size of the individual female [1] . Each of the ovariole is enclosed by a sheath which consists of cells forming a thin squamous mesothelium. Proximally, the ovarian sheath forms the long suspensory ligament which inserts into the 4 th abdominal tergite. The ovariole contains a germarium as well as a maturing and presumptive follicle. In the anterior part of each ovariole, are the differentiated cells of germarium through which the mitotic divisions of germ cells takes place resulting in the formation of the oocytes. In mosquitoes, these are accompanied by other cells which later perform the task of nursing or supplying nutrients to the developing gametes. In other insects, however, special nurse cells are absent and instead the nutritional responsiblity falls upon the epithelium of the oocyte follicles [3] . In the posterior portion of the ovariole, approaching to the oviduct, lies the