Germ cell cluster formation and ovariole structure in viviparous and oviparous generations of the aphid Stomaphis quercus

The developing ovaries of S. quercus contain a limited number of oogonial cells which undergo a series of incomplete mitotic divisions resulting in the formation of clusters of cystocytes. Ovaries of viviparous generations contain 6 to 9 clusters, containing 32 cystocytes each, whereas ovaries of oviparous generations contain 5 clusters containing 45-60 cystocytes. During further development, clusters become surrounded by a single layer of follicular cells, and within each cluster the cystocytes differentiate into oocytes and trophocytes (nurse cells). Concurrently, cysts transform into ovarioles. The anterior part of the ovariole containing the trophocytes becomes the tropharium, whereas its posterior part containing oocytes transforms into the vitellarium. The vitellaria of viviparous females are composed of one or two oocytes, which develop until previtellogenesis. The nuclei of previtellogenic oocytes enter cycles of mitotic divisions which lead to the formation of the embryo. Ovarioles of oviparous females contain a single oocyte which develops through three stages: previtellogenesis, vitellogenesis and choriogenesis. The ovaries are accompanied by large cells termed bacteriocytes which harbor endosymbiotic microorganisms.     

Structure of the ovaries of the primitive aphids Phylloxera coccinea and Phylloxera glabra (Hemiptera,Aphidinea: Phylloxeridae)

Ovaries of phylloxerids consist of short telotrophic ovarioles. Ovaries of wingless morphs contain four ovarioles whereas those of winged morphs contain one or two ovarioles. The individual ovariole of the adult female is differentiated into a terminal filament, trophic chamber (tropharium), vitellarium and short ovariole stalk (pedicel). The number of germ cells constituting ovarioles is not stable and ranges between 49 and 64. The tropharia enclose individual trophocytes and arrested oocytes. The vitellaria contain usually two oocytes, which develop through three stages: previtellogenesis, vitellogenesis and choriogenesis. Endosymbiotic microorganisms do not occur in the germ cells. In the light of the obtained results, the phylogenetic relationships between aphid families are discussed.     

Structure and development of the telotrophic ovariole in ensign scale insects (Hemiptera, Coccomorpha: Ortheziidae)

The paired ovaries of young larva of the 3rd instar of Orthezia urticae are filled with numerous germ cell clusters that can be regarded as ovariole anlagen. Germ cells (cystocytes) belonging to one cluster form a rosette, in the centre of which a polyfusome occurs. Staining with rhodamine-phalloidin has revealed that polyfusomes contain numerous microfilaments. The number of cystocytes per cluster is not stable and varies considerably. The ovaries of older larva become elongated with numerous young ovarioles protruding into the body cavity. The ovarioles are not subdivided into the tropharium and vitellarium. In this stage germ cells differentiate into oocytes and trophocytes (nurse cells). The ovaries of adult females are composed of about 20 (Newsteadia floccosa) or 30 (O. urticae) ovarioles. Their trophic chambers contain trophocytes and arrested oocytes. In the vitellarium, at the given moment, only one oocyte develops. It has been observed that after maturation of the first egg the arrested oocytes may develop.     

Structure of ovarioles in Adelges laricis, a representative of the primitive aphid family Adelgidae

The structure of ovaries has been analysed in advanced aphids only. In this paper we report the results of ultrastructural studies on the ovarioles of Adelges laricis, a representative of the primitive aphid family, Adelgidae. The ovaries of the studied species are composed of five telotrophic‐meroistic ovarioles that are subdivided into a terminal filament, tropharium (= trophic chamber) and vitellarium. The tropharium houses trophocytes (= nurse cells) and arrested oocytes. The vitellarium consists of one or two ovarian follicles. The total number of germ cells (trophocytes + oocytes) in the ovarioles analysed varies from 50 to 92 and is substantially higher than in previously studied aphids. The centre of the tropharium is occupied by a cell‐free region, termed a trophic core, which is connected both with trophocytes and oocytes. Trophocytes are connected to the core by means of cytoplasmic strands, whereas oocytes by nutritive cords. Both trophic core and nutritive cords are filled with parallel arranged microtubules. In the light of obtained results the anagenesis of hemipteran ovaries is discussed.     

Ultra- and microstructure of the female reproductive system of Matsucoccus matsumurae

The ultra- and microstructure of the female reproductive system of Matsucoccus matsumurae was studied using light microscopy, scanning and transmission electron microscopy. The results revealed that the female reproductive system of M. matsumurae is composed of a pair of ovaries, a common oviduct, a pair of lateral oviducts, a spermatheca and two pairs of accessory glands. Each ovary is composed of approximately 50 telotrophic ovarioles that are devoid of terminal filaments. Each ovariole is subdivided into an apical tropharium, a vitellarium and a short pedicel connected to a lateral oviduct. The tropharium contains 8–10 trophocytes and two early previtellogenic oocytes termed arrested oocytes. The trophocytes degenerate after egg maturation, and the arrested oocytes are capable of further development. The vitellarium contains 3–6 oocytes of different developmental stages: previtellogenesis, vitellogenesis and choriogenesis. The surface of the vitellarium is rough and composed of a pattern of polygonal reticular formations with a center protuberance. The oocyte possesses numerous yolk spheres and lipid droplets, and is surrounded by a mono-layered follicular epithelium that becomes binucleate at the beginning of vitellogenesis. Accessory nuclei are observed in the peripheral ooplasm during vitellogenesis.     

Structure of ovaries of scale insects: ii. margarodidae (INSECTA,hemiptera, COCCINEA)

The paired, spindle-shaped ovaries of the second instar of the Polish cochineal, Porphyrophora polonica (L.) (Hemiptera: Coccinea) are filled with cystocytes that are arranged into rosettes. In the centre of each rosette, there is a polyfusome. During the third instar, cystocytes differentiate into oocytes and trophocytes (nurse cells) and ovarioles are formed. Ovaries of adult females are composed of about 300 ovarioles of the telotrophic type. Each of them is subdivided into a tropharium (trophic chamber) and vitellarium. The tropharium consists of trophocytes and arrested oocytes that may develop. The number of germ cells in the trophic chambers varies from 11 to 18 even between the ovarioles of the same ovary. The obtained results seem to confirm the concept of a monophyletic origin of the primitive scale insects (Archaeococcoidea).     

Ovary structure and transovarial transmission of endosymbiotic microorganisms in Marchalina hellenica (Insecta,Hemiptera, Coccomorpha: Marchalinidae)

Szklarzewicz, T., Kalandyk‐Kolodziejczyk, M., Kot, M. and Michalik, A. 2011. Ovary structure and transovarial transmission of endosymbiotic microorganisms in Marchalina hellenica (Insecta, Hemiptera, Coccomorpha: Marchalinidae). —Acta Zoologica (Stockholm) 00 :1–9. The paired ovaries of Marchalina hellenica are composed of about 200 ovarioles of telotrophic type. In each ovariole, a trophic chamber, vitellarium and ovariolar stalk can be distinguished. The tropharia comprise trophocytes and early previtellogenic oocytes (termed arrested oocytes) or trophocytes only. The arrested oocytes are not capable of further development. In the vitellaria, single oocytes develop that are connected to the tropharium by means of broad nutritive cords. The number of germ cells (trophocytes and oocytes) constituting ovarioles is not constant and may range between 25 and 32. Numerous endosymbiotic bacteria occur in the cytoplasm of trophocytes. The endosymbionts are transported via nutritive cords to the developing oocyte. The obtained results are discussed in a phylogenetic context.     

Structure of ovaries and oogenesis in the snow scorpionfly boreus hyemalis (LINNE)(MECOPTERA : BOREIDAE)

The ovaries of the snow scorpionfly, Boreus hyemalis (Mecoptera : Boreidae) are panoistic and comprise 7–8 ovarioles. Each ovariole consists of a terminal filament, elongated vitellarium, and ovariole stalk (=pedicel) only ; in adult specimens, functional germaria are absent. Five consecutive stages of oogenesis i.e., early, mid- and late previtellogenesis, vitellogenesis, and choriogenesis have been distinguished in imagines. Oocyte nuclei (=germinal vesicles) of previtellogenic oocytes contain numerous polymorphic multiple nucleoli (or nucleolar masses), endobodies, and chromatin aggregations. Next to the nuclear envelope, large accumulations of nuage material are localized. The ooplasm of late previtellogenic oocytes is differentiated into transparent (perinuclear) and opaque (peripheral) regions. Ultrastructural investigations have revealed that within the latter, abundant ribosomes as well as mitochondria, elements of endoplasmic reticulum, Golgi complexes, annulate lamellae, symbiotic bacteroids, lipid droplets and distinctive accumulations of membrane-free clathrin-like cages are present. Early- and mid previtellogenic oocytes are invested with flat somatic cells that gradually transform into a follicular epithelium. In the vicinity of 3-cell junctions, neighbouring follicular cells are joined by narrow intercellular bridges. During late previtellogenesis, numerous microvilli develop on the oocyte surface. They interdigitate with morphologically similar but less frequent microvilli of the follicular cells. Concurrently, first endocytotic vesicles appear in the cortical ooplasm. In the context of presented results, the phylogenetic relationships between mecopterans (boreids) and fleas are discussed.     

Ultrastructural studies of the ovary of Palaeococcus fuscipennis (Burmeister) (Insecta, Hemiptera, Coccinea: Monophlebidae)

Ovaries of Palaeocoocus fuscipennis are composed of about 100 telotrophic ovarioles that are devoid of terminal filaments. In the ovariole a tropharium ( = trophic chamber) and vitellarium can be distinguished. The tropharium contains 7 trophocytes. A single oocyte develops in the vitellarium. The oocyte is surrounded by follicular cells that do not undergo diversification into subpopulations. The obtained results are discussed in a phylogenetic context.     

Heterologous gap junctions between oocytes and follicle cells of an insect,Dysdercus intermedius,and their potential role as ion current pathways

Summary In telotrophic insect ovaries, the oocytes develop in association with two kinds of supporting cells. Each ovary contains five to seven ovarioles. An ovariole consists of a single strand of several oocytes. At the apex of each ovariole is a syncytium of nurse cells (the tropharium), which connects by strands of cytoplasm (the trophic cords) to four or more previtellogenic oocytes. In addition, each oocyte is surrounded by an epithelium of follicle cells, with which it may form gap junctions. To study the temporal and spatial patterns of these associations, Lucifer yellow was microinjected into ovaries of the red cotton bug, Dysdercus intermedius. Freeze-fracture replicas were examined to analyze the distribution of gap junctions between the oocyte and the follicle cells. Dye-coupling between oocytes and follicle cells was detectable early in previtellogenesis and was maintained through late vitellogenesis. It was restricted to the lateral follicle cells. The anterior and posterior follicle cells were not dye-coupled. Freeze-fracture analysis showed microvilli formed by the oocyte during mid-previtellogenesis, and the gap junctions became located at the tips of these. As the microvilli continued to elongate until late vitellogenesis, gap junction particles between them and follicle cell membranes became arranged in long arrays. The morphological findings raise questions about pathways for the intrafollicular phase of the ion currents known to surround the previtellogenic and vitellogenic growth zones of the ovariole.Supported by the Deutsche Forschungsgemeinschaft (Schwerpunkt Differenzierung)     

Structure of the female reproductive system of the lac insect,Kerria chinensis (Sternorrhyncha,Coccoidea: Kerridae)

The ovaries of female lac insects, Kerria chinensis Mahd (Sternorrhyncha: Coccoidea: Kerridae), at the last nymphal stage are composed of several balloon‐like clusters of cystocytes with different sizes. Each cluster consists of several clusters of cystocytes arranging in rosette forms. At the adult stage, the pair of ovaries consists of about 600 ovarioles of the telotrophic‐meroistic type. An unusual feature when considering most scale insects is that the lateral oviducts are highly branched, each with a number of short ovarioles. Each ovariole is subdivided into an anterior trophic chamber (tropharium) containing six or seven large trophocytes and a posterior vitellarium harbouring one oocyte which is connected with the trophic chamber via a nutritive cord. No terminal filament is present. Late‐stage adult females show synchronized development of the ovarioles, while in undernourished females, a small proportion of ovarioles proceed to maturity.     

The ovaries of scale insects (Hemiptera, Coccinea). Morphology and phylogenetic conclusions

Coccoids (Coccinea, Coccoidea, Coccomorpha, scale insects, scales) are a highly diverse group of ectoparasitic insects. They comprise 2 subgroups: primitive archaeococcoids (= Orthezioidea sensu Koteja) and advanced neococcoids (= Coccoidea sensu Koteja). The ovaries of coccoids consist of numerous short telotrophic-meroistic ovarioles. The ovarioles of all investigated species share common characters (e.g. the same mechanism of ovariole development, lack of terminal filaments, occurrence of single oocytes in the vitellaria) supporting the concept of monophyletic origin of this group. Despite these characteristics, the ovaries of archaeococcoids and neococcoids differ in the number of germ cells (oocytes + trophocytes) constituting a single ovariole. In primitive families (Ortheziidae, Margarodidae), this number is relatively large (15-58), whereas in advanced ones (Pseudococcidae, Kermesidae, Eriococcidae, Cryptococcidae, Coccidae, Diaspididae) it is small and usually does not exceed 8. The comparative analysis of the ovary structure in the representatives of Coccinea and closely related Aphidinea (aphids) has revealed that: (1) the organization of archaeococcoid ovaries is more similar to those of aphids than to neococcoids and (2) during the evolution of Coccinea a gradual reduction in the number of germ cells in ovarioles took place.     

The ovaries of Mecoptera: basic similarities and one exception to the rule

Two entirely different types of ovaries (ovarioles) have been described in mecopterans. In the representatives of Meropeidae, Bittacidae, Panorpodidae and Panorpidae the ovarioles are of the polytrophic-meroistic type. Four regions: a terminal filament, germarium, vitellarium and ovariole stalk can be distinguished in the ovarioles. The germaria house numerous germ cell clusters. Each cluster arises as a result of 2 consecutive mitoses of a cystoblast and consists of 4 sibling cells. The oocyte always differentiates from one of the central cells of the cluster, whereas the remaining 3 cells develop into large, polyploid nurse cells. The vitellaria contain 7-12 growing egg chambers (= oocyte-nurse cell complexes). In contrast, the ovaries of the snow flea, Boreus hyemalis, are devoid of nurse cells and therefore panoistic (secondary panoistic). The ovarioles are composed of terminal filaments, vitellaria and ovariole stalks only; in adult females functional germaria are absent. Histochemical tests suggest that amplification of rDNA takes place in the oocyte nuclei. Resulting dense nucleolar masses undergo fragmentation into multiple polymorphic nucleoli. The classification of extant mecopterans as well as the phylogenetic relationships between Mecoptera and Siphonaptera are discussed in the context of presented data.     

Formation and structure of nutritive cords in telotrophic ovarioles of snake flies (Insecta: Raphidioptera)

Telotrophic ovariole of Raphidia spp. is composed of the anteriorly located terminal filament, tube-shaped tropharium, the vitellarium and the ovariole stalk. The tropharium consists of a central syncytial core surrounded by one cell thick layer of tapetum cells. Early previtellogenic oocytes differentiate at the base of tropharium. Both the oocytes and the tapetum cells are connected with the central syncytium by delicate intercellular bridges. At the onset of previtellogenic growth, the anterior parts of the oocytes become extended and form long cytoplasmic projections--nutritive cords. Each nutritive cord contains numerous microtubules that show no preferential orientation within the cord but diminishing anterior-posterior gradient of distribution. Irregular arrangement of microtubules indicates that this cytoskeletal scaffold does not play any role in directed transport within the ovariole but instead constitutes one of the elements of the structural framework of the nutritive cord. Besides microtubules, the stability of the nutritive cords in Raphidia ovarioles is maintained by the rim-shaped membrane foldings lined with microfilaments.     

The larval development of the telotrophic meroistic ovary in the bug Dysdercus intermedius (Heteroptera, Pyrrhocoridae)

Bug ovaries are of the telotrophic meroistic type. Nurse cells are restricted to the anterior tropharium and are in syncytial connection with the oocytes via the acellular trophic core region into which cytoplasmic projections of oocytes and nurse cells open. The origin of intercellular connections in bug ovaries is not well understood. In order to elucidate the cellular processes underlying the emergence of the syncytium, we analysed the development of the ovary of Dysdercus intermedius throughout the five larval instars. Up to the third instar, the germ cell population of an ovariole anlage forms a single, tight rosette. In the center of the rosette, phosphotyrosine containing proteins and f-actin accumulate. This center is filled with fusomal cytoplasm and closely interdigitating cell membranes known as the membrane labyrinth. With the molt to the fourth instar germ cells enhance their mitotic activity considerably. As a rule, germ cells divide asynchronously. Simultaneously, the membrane labyrinth expands and establishes a central column within the growing tropharium. In the fifth instar the membrane labyrinth retracts to an apical position, where it is maintained even in ovarioles of adult females. The former membrane labyrinth in middle and posterior regions of the tropharium is replaced by the central core to which nurse cells and oocytes are syncytially connected. Germ cells in the most anterior part of the tropharium, i.e. those in close proximity to the membrane labyrinth remain proliferative. The posterior-most germ cells enter meiosis and become oocytes. The majority of the ovarioles' germ cells, located in between these two populations, endopolyploidize and function as nurse cells. We conclude that the extensive multiplication of germ cells and their syncytial assembly during larval development is achieved by incomplete cytokineses followed by massive membrane production. Membranes are degraded as soon as the trophic core develops. For comparative reasons, we also undertook a cursory examination of early germ cell development in Dysdercus intermedius males. All results were compatible with the known basic patterns of early insect spermatogenesis. Germ cells run through mitotic and meiotic divisions in synchronous clusters emerging from incomplete cytokineses. During the division phase, the germ cells of an individual cluster are connected by a polyfusome rich in f-actin.     

The telotrophic ovary known from Neuropterida exists also in the myxophagan beetle <Emphasis Type="Italic">Hydroscapha natans</Emphasis>

The ovary structure of the myxophagan beetle, Hycdoscapha natans, was investigated by means of light and electron microscopy for the first time. Each of the two ovaries consists of three ovarioles, the functional units of insect oogenesis. The ovary type is telotrophic meroistic but differs strongly from the telotrophic ovary found among all polyphagous beetles investigated so far. All characters found here are typical of telotrophic ovaries of Sialidae and Raphidioptera. Both taxa belong to the Neuropterida. As in all telotrophic ovaries, all nurse cells are combined in an anterior chamber, the tropharium. The tropharium houses two subsets of germ cells: numerous nurse cell nuclei are combined in a central syncytium without any cell membranes in between, surrounded by a monolayer of single-germ cells, the tapetum cells. Each tapetum cell is connected to the central syncytium via an intercellular bridge. Tapetum cells of the posterior zone, which sufficiently contact prefollicular cells, are able to grow into the vitellarium and develop as oocytes. During previtellogenic and early vitellogenic growth, oocytes remain connected with the central syncytium of the tropharium via their anterior elongations, the nutritive cords. The morphological data are discussed in the light of those derived from ovaries of other Coleoptera and from the proposed sister group, the Neuropterida. The data strongly support a sister group relationship between Coleoptera and Neuropterida. Furthermore, several switches between polytrophic and telotrophic ovaries must have occurred during the radiation of ancient insect taxa.     

Morphology of the ovaries of Sphaerodema (Diplonychus) rusticum (Heteroptera,Belostomatidae)

The female reproductive system of Sphaerodema rusticum consists of a pair of ovaries, two lateral oviducts, a median common oviduct, and a median spermatheca. Accessory glands are absent. Each ovary has five free ovarioles branching from the oviduct. Each ovariole consists of a terminal filament, germarium, vitellarium, brown mass, and an exceptionally long pedicel. The terminal filament consists of a central core, interstitial cells, and an outer sheath. In the germarium, which consists of trophic and prefollicular regions, the trophic region or nurse cell chamber is divided into four histologically differentiated zones, distinguished as zones I–IV. Nutritive cords, originating from the posterior end of the trophic core in zone IV extend centrally and join the developing oocytes in the prefollicular chamber and the vitellarium. The compact prefollicular tissue at the base of the trophic core gives rise to prefollicular cells which, after encircling the young oocytes, become modified into follicular epithelial cells, the interfollicular plug, and epithelial plug. The young oocytes descend into the vitellarium and gradually develop into mature oocytes. A compound corpus luteum is observed simultaneously in all the ovarioles of both ovaries after ovulation. Below the epithelial plug there is an accumulation of material, the “brown mass,” which develops cyclically in correlation with the ovulation cycle. Each pedicel stores five mature chorionated eggs ready for oviposition. The epithelium of the anterior region of the pedicel secretes a PAS-positive material. General morphology and histology of the subdivisions of the ovarioles are described.     

Morphology,ultrastructure, and germ cell cluster formation in ovarioles of aphids

The structure of aphid ovaries, including ovipare and virginopare morphs of five species, was investigated by light and electron microscopy. Aphids contain telotrophic meroistic ovarioles. The amount and distribution of cytoplasmic components of nurse cells, nutritive cords, and young oocytes are nearly identical to those known from scale insects and heteropterans. Each ovariole has a constant number of nurse cells and oocytes. In ovaries of ovipare morphs, the nurse cell nuclei enlarge by endomitosis (n = 2⁸n?2¹⁰n), whereas in virginopare morphs the nurse cell nuclei remain small (n = 2²n?2⁴n). Furthermore, in virginoparae the previtellogenic growth of oocytes is highly reduced, and vitellogenesis and chorionogenesis are blocked totally. Embryogenesis starts immediately after the shortened previtellogenic growth. In each ovariole, all germ cell descendants belong to one germ cell cluster that follows the 2ⁿ rule. The cluster normally contains 2⁵ = (32) cells, but other mostly smaller numbers also occur. In contrast to polytrophic meroistic ovarioles, more than one cell of each cluster will develop into an oocyte. In Drepanosiphum platanoides, 16 (2^n?1) nurse cells and 16 (2^n?1) oocytes exist in each cluster, whereas, in Metopolophium dirhodum, 8 (2^n?2) oocytes and 24 (2^n?1 + 2^n?2) nurse cells are normally found. In many ovarioles of Macrosiphum rosae, 21 nurse cells nourish 11 oocytes. Models of germ cell cluster formation in aphid ovaries are discussed.     

Structure of ovaries in ensign scale insects,the most primitive representatives of Coccomorpha (Insecta,Hemiptera)

The ovaries of Orthezia urticae and Newsteadia floccosa are paired and composed of numerous short ovarioles. Each ovariole consists of an anterior trophic chamber and a posterior vitellarium that contains one developing oocyte. The trophic chamber contains large nurse cells (trophocytes) and arrested oocytes. The total number of germ cells per ovariole (i.e., cluster) is variable, but it is always higher than 32 and less than 64. This suggests that five successive mitotic cycles of a cystoblast plus additional divisions of individual cells are responsible for the generation of the cluster. Cells of the trophic chamber maintain contact with the oocyte via a relatively broad nutritive cord. The trophic chamber and oocyte are surrounded by somatic cells that constitute the inner epithelial sheath around the former and the follicular epithelium around the latter. Anagenesis of hemipteran ovarioles is discussed in relation to the findings presented. © 1995 Wiley-Liss, Inc.     

Structure of the ovaries and oogenesis in Cixius nervosus (Cixiidae), Javesella pellucida and Conomelus anceps (Delphacidae) (Insecta, Hemiptera, Fulgoromorpha)

Ovary organization in representatives of two families of Fulgoromorpha, Cixiidae (Cixius nervosus) and Delphacidae (Javesella pellucida and Conomelus anceps), was examined by light and transmission electron microscopy. Ovaries of studied fulgoromorphans consist of telotrophic ovarioles. From apex to base individual ovarioles have four well defined regions: a terminal filament, tropharium (trophic chamber), vitellarium and pedicel (ovariolar stalk). Tropharia are not differentiated into distinct zones and consist of syncytial lobes containing multiple trophocyte nuclei embedded in a common cytoplasm. Lobes are radially arranged around a branched, cell-free trophic core. Early previtellogenic (arrested) oocytes and prefollicular cells are located at the base of the tropharium. The vitellarium houses linearly arranged developing oocytes each of which is connected to the trophic core by a broad nutritive cord. Each oocyte is surrounded by a single layer of follicular cells that become binucleate at the beginning of vitellogenesis.