Viability of Culex pipiens pipiens eggs affected by nutrition and aposymbiosis

Raisins were a better source of carbohydrate than sucrose for reproduction by autogenous Culex pipiens. A blood meal increased the number of eggs per raft from 49 autogenously to 114. Eggs of aposymbiotic females produced autogenously did not hatch, but 34% of the eggs were viable if the mosquitoes fed on chickens. With repeated blood meals the number of eggs per raft and the rate of embryonation and hatching declined in each successive gonotrophic cycle. In about $\text{1}\text{4}$ of the unhatched eggs of normal females there were no fully developed embryos, while many more of the unhatched eggs of aposymbiotic females contained no evidence of embryonic development. After the fifth blood meal, neither normal nor aposymbiotic insects oviposited. The ovaries of the nulliparous females contained approximately 10% of the potential number of mature terminal oocytes. Proximally in the ovarioles there were dilatations and coiled tracheoles indicating egg resorption. There were fewer parous follicles in aposymbiotic than in normal females. Larval rearing water, i.e., infusion in which larvae had been reared, was more attractive than fresh infusion for oviposition by normal, autogenous mosquitoes. The degree of embryonation of the eggs was lower and the hatching success rate was poorer in fresh infusion than in larval rearing water.     

Ovipositional and ovicidal effects of the microbial agent Bacillus thuringiensis israelensis on Culex quinquefasciatus say (Diptera: Culicidae).

The magnitude of oviposition as well as the size, shape and the number of eggs per of egg rafts egg raft were determined after gravid Culex quinquefasciatus Say oviposited on water treated with water dispersible granules (WDG) of Bacillus thuringiensis ssp. israelensis (Bti) and on untreated water. The mean number of eggs/raft was lower in the treated than in the untreated water. Bti concentrations from 0.5 to 2.0mg/L affected the shape of egg rafts and number of eggs in each raft. As the concentration of Bti increased from 0.5 to 2.0 mg/L the shape of egg rafts became more irregular with fewer eggs in each raft. Exposure to Bti at 2- and 26-h reduced the hatching rates, and fewer eggs hatched at 26-h of exposure to Bti. As the concentration of Bti WDG increased from 0.5 to 2.0 mg/L, the hatching rate decreased. Eggs exposed for 2-h to 2.0mg/ L Bti had a hatch of 30% after 24 h, the rate increasing to 57% after 72 h. In contrast, in 26-h exposed eggs to 2.0 mg/L Bti, the hatching rate after 24 h was only 12% and this rate increased to 39% after 72 h. In larvae from eggs exposed for 2 h, the survival rate was 40% at 2.0 mg/L Bti and 87% in untreated controls. In contrast, the survival rates of larvae from 26-h exposed eggs was 91% in controls while it was 30% at 2.0 mg/L Bti. As the concentration of Bti increased from 0.5 to 2.0 mg/ 1 the survival rates of larvae decreased. The combined effects of reductions of egg rafts, low number of eggs per egg raft, and reduced hatching and survival rates could have significant cumulative effects on the yield of adult mosquitoes, and this could result in a greater control potential of this microbial agent.     

Variation in morphology and morphometrics of eggs of Culex quinquefasciatus mosquitoes from different ecological regions of India

Variation in egg surface morphology and morphometrics of Culex quinquefasciatus mosquitoes of the Jodhpur, Bikaner, Jamnagar, and Bathinda strains were correlated with geographical distribution in different ecological regions of India. We report the geographic variation in Cx. quinquefasciatus based on 44 attributes of micropylar and conical‐shaped regions of eggs, including micropylar apparatus (corolla, disc, and mound), micropylar tubercles, and the exochorionic tubercle, pores, and network in anterior, middle, and posterior regions. No remarkable differences were observed in the surface morphology of eggs of these strains except the absence of small tubercles in the anterior and middle region of the JMN strain. However, a statistical analysis indicated significant morphometric variations in 66% of the attributes of the eggs. The cluster analysis of all egg attributes showed that the JD, BKN, and BTH strains are closer to each other than the JMN strain. The positive correlation (r = 0.95) also indicated an effect of geographical distribution on morphometry of various egg attributes of these strains. The present study suggests that ecological variation may have affected the morphometric attributes of the egg of four strains of Cx. quinquefasciatus from different geographical areas.     

STRUCTURE OF THE EGG-SHELL OF CULEX PIPIENS AND MANSONIA AFRICANA (CULICIDAE, DIPTERA)

Eggs of Culex pipiens L. are laid in rafts on the surface of still or slow moving water, whereas those of Mansonia africana (Theobold) are deposited beneath tho surface of the water on the undersides of floating leaves (Laurence & Smith 1958; Laurence 1959). The eggs of both species are surrounded by air, those of Culex pipiens are in direct contact with the external atmosphere, whereas those of Mansonia africana are partially surrounded by a bubble of air trapped between them. The anterior onds of the eggs of Mansonia africana project through the bubble of air into the surrounding water. This bubble of air is only found around living eggs and disappears if tho eggs die and shortly before they hatch. Iyengar (1935) has shown that the eggs of Ficalba minima Theo. although often deposited on the same leaf as those of Mansonioides , are laid above the water line and resemble in structure those of Culex and Coquillettidia . The structure of the egg-shell of both Culez pipiens and Mansonia africana is described and discussed.     

A quantitative analysis of underwater oviposition by the mosquito Mansonia titillans

ABSTRACT. Formation of the rosette-like egg mass of the neotropical mosquito Mansonia titillans Walker is described from video recordings of thirteen females ovipositing on the undersurfaces of water lettuce ( Pistia stratiotes ) leaves in the laboratory. The female abdomen executes symmetrical stroking behaviour to the right and left of centre line. Outstrokes consist solely of scratching, in which spines on the eighth tergite abrade the leaf surface preparatory to oviposition. A row of eggs is glued to the leaf only on instrokes, which are of longer duration than outstrokes, and may be interrupted by scratches and pauses. Scratching precedes oviposition of each of the first four eggs, which are laid without stroking behaviour. The egg mass is enveloped in an air bubble which is transported underwater on the hydrofuge female abdomen. The deposition of eggs on instrokes is homologous to the behaviour used by Culex and Culiseta mosquitoes in the construction of free-floating egg rafts.     

Direct evidence for aerial egg deposition in the burrows of the Malaysian mudskipper, <Emphasis Type="Italic">Periophthalmodon schlosseri</Emphasis>

The presence of mudskipper eggs in an air-filled chamber was confirmed by direct endoscopic observation of intact burrows of Periophthalmodon schlosseri in a mudflat in Penang, Malaysia. For all five burrows from which video images of egg chambers were successfully obtained, the presence of air was unequivocally demonstrated by the existence of an air–water interface inside the chambers. Of these burrows, eggs were found in two, but not in the others. Eggs were laid uniformly in a monolayer on the inner top surface of the chamber. The much brighter color of the surface mud of the egg chambers than the surrounding mud, irrespective of the presence or absence of the eggs, suggested that the surface mud had been oxidized by deposited air.     

Development of the bitterling,Tanakia tanago (cyprinidae), with a note on minute tubercles on the skin surface

The development of eggs and larvae and minute tubercles on the skin surface in larvae ofTanakia tanago were observed. The eggs began to hatch approximately 52 hours after insemination and the larvae reached free-swimming stage 19 days after hatching at water temperature of 22±1°C. The egg and larval development and minute tubercles on the skin surface in larvae of this species were similar to those ofAcheilognathus lanceolata andA. limbata. However,T. tanago was distinguishable in egg and larval development fromA. lanceolata andA. limbata by the following characters: the perivitelline space was narrower, embryonic and larval development was faster, and minute tubercles on the skin surface of the anteriormost parts of the yolk sac, and of the body and head were hemispheric in shape. From these characters,T. tanago is considered to be more specialized thanA. lanceolata andA. limbata.     

Sperm Incorporation Independent of Fertilization Cone Formation in the Danio Egg

The responses of the egg to insemination in a modified Fish Ringer's solution (FRS) were examined in eggs of the zebrafish ( Brachydanio rerio ) primarily by scanning electron microscopy. FRS is a physiological saline which temporarily inhibits parthenogenetic activation of the egg for 5–8 min. Spermatozoa were collected in a small volume of water and pipetted over eggs in FRS. Eggs inseminated in FRS typically incorporated the fertilizing sperm within 3–4 min. Inseminated cells showed an absence of a fertilization cone and no cortical granule exocytosis. The deep conical depression in the egg surface beneath the micropyle remained unaltered. Control eggs inseminated in tank water developed a large fertilization cone during sperm incorporation. Occasionally, eggs inseminated in water were observed to incorporate the entire sperm head prior to egg activation. Our results corroborate earlier findings showing that in the zebrafish, cortical granule exocytosis, fertilization cone formation and elevation of the sperm entry site are not triggered by the fertilizing sperm in experimental conditions (18, 19). Furthermore, sperm incorporation requires neither egg activation nor formation of a fertilization cone in this fish.     

Effects of Ca2+ ions on the formation of metaphase chromosomes and sperm pronuclei in cell-free preparations from unactivated Rana pipiens eggs

Nuclei transplanted into unactivated amphibian eggs are known to condense into metaphase chromosomes whereas those transplanted into activated eggs decondense and enlarge. We have made cell-free cytoplasmic preparations from Rana pipiens eggs which can induce demembranated Xenopus laevis sperm to undergo changes similar to those seen in intact eggs. Sperm chromatin which is incubated for 3 hr in unactivated egg preparations made using a buffer containing 3 mM EGTA is induced to form metaphase chromosomes. However, decondensed interphase nuclei are formed when chromatin is incubated in unactivated egg preparations made without EGTA as well as in activated egg preparations. When Ca2+ ions are added to unactivated egg preparations made with EGTA, the preparations lose the ability to induce metaphase chromosome formation and become capable of decondensing sperm chromatin. Once the ability to decondense chromatin has developed, either in unactivated or activated egg preparations, it cannot be suppressed by the addition of EGTA. However, decondensation of sperm chromatin in activated egg preparations can be suppressed by the addition of unactivated egg preparations made with EGTA. In this case, the incubated sperm chromatin is induced to form metaphase chromosomes. These results may indicate that the chromosome condensation activity of unactivated egg cytoplasm can be sustained in cell-free preparations when Ca2+ ion levels are kept low, but when Ca2+ ion levels increase this activity is lost and replaced by a new activity which can decondense chromatin. Since this change in cytoplasmic activities is comparable to that occurring in the intact egg following fertilization, these results suggest that Ca2+ ions play a crucial role during activation in altering the cytoplasmic activities which control nuclear behavior.     

Induced symmetry breaking in the egg of the frog Rana pipiens

Abstract. Unfertilized, unactivated eggs of the frog Rana pipiens were incubated in 10% Ringer solution containing 1.64 μ M 12-O-tetradecanoyl phorbol acetate (TPA). Under these conditions, the initially radially symmetric cells formed, within a few hours, a line of equatorial demarcation (IDL) which resembled the dorsal lip observed in fertilized eggs during gastrulation. Many IDLs went on to form structures which resembled lateral and ventral lips. The formation of the IDL broke the symmetry of the egg, converting it from a radially symmetric to a bilaterally symmetric object. It is suggested that such an increase in cellular organization is the result of a chemical reaction occurring in a far-from-equilibrium system of the class known as dissipative structures. It is assumed that TPA triggers this reaction as a result of its ability to stimulate protein kinase C.     

Sperm motility and fertilization time span in Atlantic salmon and brown trout—the effect of water temperature

The effect of water temperature on the duration of sperm motility, the time lapse after activation by fresh water and the fertility of eggs was studied in Atlantic salmon and brown trout. Eggs of both species were fully fertile in fresh water after 512 s. No interspecific differences were noted in egg fertility at the lower water temperatures, but the brown trout eggs showed a higher resistance to high temperatures, indicating a better physiological thermotolerance. A highly significant effect of temperature on the overall duration of sperm motility was found, with a marked peak at 3−4°C for salmon and a weaker one for trout. After freshwater activation the eggs of both species remained fertile for a longer time than the sperm were mobile.     

The alphaBbetaC integrin is expressed on the surface of the sea urchin egg and removed at fertilization

Integrins are expressed on the surface of some vertebrate eggs where they are thought to have a role in fertilization. The objective of this study is to determine if integrins are expressed on sea urchin eggs. The alphaB and betaC subunits were cloned using the homology polymerase chain reaction. Monoclonal and polyclonal antibodies were developed against bacterially expressed fragments of the extracellular domains of the betaC subunit and the alphaB subunit. As well, a monoclonal antibody was developed against a synthesized peptide corresponding to part of the cytoplasmic domain of betaC. Analysis of biotinylated egg cortex extracts immunoprecipitated with either anti-betaC or anti-alphaB yields bands of 130 and 225 kDa. Immunoblots confirm that betaC is part of the complex immunoprecipitated with anti-alphaB. Confocal immunofluorescence and immunogold electron microscopy show that betaC is present on the surface of the unfertilized egg at the tips of microvilli and in cortical granules. During the cortical reaction, immunoreactivity with antibodies to the extracellular domains of betaC and alphaB disappears from the egg surface, and microvillar casts on the fertilization envelope become immunoreactive. With antibodies to the cytoplasmic domain of betaC, immunoreactivity is lost from the surface of the egg, but the fertilization envelope does not immediately become immunoreactive. In immunoblots of egg cortex there are immunoreactive bands of the predicted sizes for alphaB and betaC. However, in fertilization envelopes, a second band that is slightly lower in molecular weight is also present. Eggs fertilized in the presence of soybean trypsin inhibitor have elongated microvilli that remain bound to the elevating fertilization envelope and immunoreactive to anti-betaC antibodies. Eggs fertilized in the presence of an ovoperoxidase inhibitor, 3-amino-1,2,4-triazole, have a patchy distribution of betaC immunoreactivity in fertilization envelopes. Together, these data suggest that alphaBbetaC integrins are expressed on the surface of unfertilized eggs and, during the cortical reaction, the extracellular domains are cleaved by proteases and cross-linked into the fertilization envelope by ovoperoxidase. The alphaBbetaC integrin receptors may have several potential functions prior to their removal at fertilization, including attachment of the vitelline envelope to the egg surface and anchoring the cortical cytoskeleton.     

Uptake and loss of water in diapause and non-diapause eggs of crickets

ABSTRACT. In laboratory-laid eggs of the striped ground cricket, Allonemobius fasciatus DeGeer (Gryllidae), water absorption occurs at an early stage of embryogenesis (stage II) at 30°C but is delayed until later stages at lower temperatures. This is related to the variation in diapause stage at different temperatures. No egg developed beyond stage VII (the end of anatrepsis) without water absorption.
A. fasciatus shows seasonal variation in the stage of water absorption. At 30°C, eggs collected in August absorb water at the early stage while many of those collected in September avert diapause and absorb water at a later stage.
Diapause also influenced the water absorption of eggs in A. socius Scudder. Eggs of short-day females enter diapause and absorb water at stage II, while those of long-day females develop without diapause and absorb water at a later stage (around stage IV).
The susceptibility to desiccation (r.h. 50%) was examined at 20°C with A. fasciatus eggs. The percentage water loss and mortality of eggs varied with the time and duration of exposure to desiccation. Eggs are most sensitive to desiccation during the first several days after being laid and during the period of water absorption.     

Rainbow trout egg quality determination by the relative weight increase during hardening: a practical standardization

The relative weight of fish eggs increases during water hardening; this increase is significantly correlated with egg viability in rainbow trout when determined after 120 min, providing an assay test for egg quality control. In the present paper, additional investigations on egg water uptake at different time intervals during the hardening process were performed to correlate these with egg viability and to improve the sensitivity of the assay while also reducing the handling time. Eggs of high quality had a significantly higher rate of water uptake than low quality eggs, with the highest rate occurring during the first 30 min of hardening. Bivariate correlation coefficients and regression models revealed that in addition to egg weight increase after 120 min of water hardening, the increases in weight after 30 min and 60 min were also significantly related to egg viability (P < 0.001). In contrast, the initial weight increase after 15 min of hardening revealed a lower correlation (P < 0.006) with egg viability. These results indicate the initial velocity of water uptake is not a valid criterion, but that the total amount of water imbibed during hardening provides the most reliable information on egg quality. The present study confirms the previously reported sensitivity of the assay, and also shows that a shorter incubation time of 30 min is adequate for reliable results. The shorter handling time is an improvement for testing large numbers of egg batches.     

The effect of temperature and water quality on the in vitro development and survival of Asellus aquaticus (Crustacea: Isopoda) eggs

The rate of development and degree of survival of Asellus aquaticus eggs outside the marsupium of ovigerous females are affected by water quality and temperature. Eggs were maintained in polluted river water and relatively clean canal water. Developmental rates increase with increased temperature, but survival decreases. Eggs from polluted site ovigerous females survive better in clean water than in polluted water. Eggs from clean site ovigerous females maintained in polluted water have significantly lower survival rates than eggs from the polluted site at all temperatures tested. The developmental rate of clean site eggs is increased significantly in polluted water at 10–25 °C, possibly as a response to the stress imposed upon them.It is suggested that the method outlined might form the basis of a useful bioassay technique for measuring water quality.     

Three new species of Huffmanela Moravec, 1987 (Nematoda: Trichosomoididae) from the gills of marine fish off New Caledonia

Three new species of Huffmanela, here described from eggs only, are reported from the gills of marine fish caught off Nouméa, New Caledonia. Eggs of Huffmanela branchialis n. sp., from Nemipterus furcosus (Nemipteridae), are 45-52 (mean 48) microm in length and 23-30 (mean 25) microm in width, with thin shells. Each egg is enclosed in a thin membrane forming a spindle-shaped envelope 53-85 (mean 63) microm in length. Eggs of H. filamentosa n. sp., from Gymnocranius grandoculis (Lethrinidae), are 48-53 (mean 50) microm in length and 25-30 (mean 27) microm in width, with thin shells. Each egg bears a few long (150 microm), thin filaments. Eggs of these two new species were compared to those of H. paronai Moravec & Garibaldi, 2000, which are redescribed. Eggs of H. ossicola n. sp. were found within the branchial arch bone of Bodianus loxozonus (Labridae) and also filled the spinal chord bone and other bones. This is the first species of Huffmanela reported from bone tissue. Eggs are large, 72-88 (mean 79) microm in length and 32-40 (mean 36) microm in width, with a very thick shell. Each egg is covered with numerous filaments enclosed in a thin envelope. Fresh eggs were unembryonated, but embryos were visible after incubation in seawater. The three new species can be distinguished from other species of Huffmanela by size and the nature of the egg covering. Egg morphology of and their location in the host suggest different life-cycles: those of the first two species (small eggs, thin shells, egg covering possibly favouring flotation) are released from the gill mucosa with the turnover of living tissues and immediately continue their life-cycle, but eggs of H. ossicola (large eggs, thick shell) are only available for the continuation of the life-cycle after the host's death.     

Synthesis and function of the fibrous layers covering the eggs of Siphlonurus lacustris (Ephemeroptera, Siphlonuridae)

Ultrastructural analysis (transmission and electron scanning microscopy) of the eggs of the mayfly Siphlonurus lacustris (Eaton) showed that they are wrapped in a thick coat composed of a network of tightly entwined filaments. Groups of twisted filaments form slightly uplifted buttons that are scattered on the coat surface. After experimentally induced egg deposition, egg–water interaction promotes marked cohesion of the eggs and their firm adhesion to the substrate. Egg masses include numerous gametes; the covering of those located close to the substrate greatly extends to anchor the whole mass. Eggs removed from the coat reveal a slightly punctuated smooth chorion and tagenoform micropyles (three to five). The coat increases egg size by about 20%. The lack of female reproductive accessory glands in Ephemeroptera transfers the synthesis of the adhesive coats to the follicle cells, which are typically competent for insect egg shell deposition (vitelline envelope and chorionic layers). This covering results from electron‐dense granules that give rise to filaments progressively organized to form superimposed layers variously orientated around the egg. In addition to egg adhesion to the substrate, a trophic function and protection from shear stress are postulated for this covering.     

The influence of light on egg buoyancy and hatching rate of the walleye pollock, Theragra chalcogramma

Changes in buoyancy in fertilized bathypelagic eggs of the walleye pollock, Theragra chalcogramma , collected from Shelikof Strait in the Gulf of Alaska were measured under controlled laboratory conditions in density gradient columns from 90 h post–fertilization through hatching. Eggs were incubated at 6° C and exposed to either diel light or constant dark. Eggs held under diel light conditions became more dense than eggs under constant dark beginning <10 h after exposure to light and remained so until 12 h before hatching. Eggs held under constant dark then became more dense than those under diel light. Hatching of eggs under both conditions began at the same time but eggs under diel light showed a delayed hatching rate. Light–induced changes in egg density indicate the ability of walleye pollock eggs to respond to external stimuli and thereby alter their position in the water column in an ecologically meaningful way.     

Male brooding behaviour of the giant water bugLethocerus deyrollei vuillefroy (Hemiptera: Belostomatidae)

The male brooding behaviour ofLethocerus deyrollei was investigated. Eggs were laid as masses on sticks above the water surface. Males did not leave the sticks until the eggs hatched. They mainly stayed at the bases of the sticks in water in the day, and frequently climbed up at night covering the egg-masses with their bodies. Eggs with male brooding had a 94.3% hatching rate. Eggs without male brooding failed to hatch and desiccated. Eggs with brooding considerably increased in wet weight in development; eggs without brooding decreased in wet weight. Eggs without male brooding and artificially supplied with water had a 93.2% hatching rate. Male brooding is considered to supply eggs with water.     

Egg size and composition in Ceratoserolis (Crustacea: Isopoda) from the Weddell Sea

Summary Samples of ovigerous female Ceratoserolis trilobitoides carrying newly spawned (stage A1) eggs in the marsupium were obtained from Borge Bay; Signy Island (South Orkney Islands), the continental shelf near Elephant Island (South Shetland Islands), and two sites in the inner Weddell Sea. The dry mass of a newly spawned egg was greater at the inner Weddell Sea sites even when the larger size of the females from the Weddell Sea and the positive relationship between egg size and female size were taken into account. Larger eggs contained more yolk, and there was a slight but significant tendency for larger eggs to have a lower percentage nitrogen content. Eggs from Ceratoserolis meridionalis were smaller in size than sympatric Ceratoserolis trilobitoides, but of similar composition. The reason for a greater investment per egg by females at higher latitudes is not clear, but it may be related to a slightly longer development period, itself associated with the lower water temperatures in the inner Weddell Sea.Data presented here were collected during the European Polarstern Study (EPOS) sponsored by the European Science Foundation