The influence of mating on autogenous egg development in the mosquito, Aedes taeniorhynchus

In several strains of Aedes taeniorhynchus, the presence of males increased the levels of autogeny. To stimulate autogenous egg production, the males had to mate with the females. Ageing further enhanced the rates of autogeny in mated females but not in virgins. Males did not influence the size of the autogenous egg batch. Even after the sixth day following emergence some females still possessed the capacity to respond to the male stimulus. With regard to ovarian maturation in A. taeniorhynchus, there appeared to be 3 types of females: (1) those that did not require a mating stimulus to be autogenous, (2) those that needed this stimulus and (3) those that remained anautogenous whether mated or not.     

Development of monoclonal antibodies for monitoring Aedes atropalpus vitellogenesis

Monoclonal antibodies to a mixture of Aedes atropalpus and A. aegypti soluble yolk proteins were produced by hybridomas between the fusion of P3X63.653 myeloma cells and splenocytes of immunized BALB/c mice. Ascites fluid collected from mice innoculated with cloned hybridoma cells contained high specificity and affinity to the soluble yolk proteins of both Aedes species. Seven different hybridoma lines produced antibodies with specificity to both A. atropalpus and A. aegypti and one cell line produced antibodies monospecific to A. aegypti soluble yolk proteins. Monoclonal antibodies specific to A. atropalpus vitellin and vitellogenin were characterized by a combination of gel electrophoresis, western blotting and immunohistochemical staining. An indirect double antibody sandwich enzyme-linked immunosorbent assay was developed using a mixture of the seven hybridoma antibodies to A. atropalpus vitellin for monitoring vitellogenin levels in individual mosquito haemolymph samples. With this procedure, the peak period of vitellogenin synthesis in A. atropalpus was found to be 18 to 30 h after adult eclosion.     

The role of factors from the head in the regulation of egg development in the mosquito Aedes aegypti

The relationships between the release of factors from the head after blood-feeding, subsequent levels of ecdysteroids and vitellin, and the ultimate maturation of eggs in Aedes aegypti were investigated. Females were decapitated at various times after a blood meal, at 20 or 48 h after feeding the animals were dissected and divided into two groups, those with arrested oöcytes (yolk length < 100 μm) and those with maturing oöcytes (yolk length > 100 μm). These yolk lengths correspond with the levels of oöcyte growth believed to accompany the proposed initiation and promotion phases of egg development. Animals dissected at 20 h were assayed for ecdysteroid by radioimmunoassay; those dissected at 48 h were assayed for vitellin by rocket immunoelectrophoresis.Non-blood-fed unoperated females contained 8% as much ecdysteroid as blood-fed controls and no measurable vitellin. Females with arrested oöcytes (< 100 μm) were obtained only if decapitations were performed before 8 h; these females had about 20% of the ecdysteroids and 8% of the vitellogenin normally found in blood-fed animals. Females decapitated between 2 and 8 h with maturing oöcytes contained 50–60% as much ecdysteroid and vitellin as blood-fed unoperated controls. Normal ecdysteroid and vitellin levels were reached only when decapitations were delayed for 12 and 24 h, respectively. The number of developing oöcytes was also decreased by early decapitation and was closely correlated with vitellin levels.We conclude that the egg development neurosecretory hormone is released twice, once before 8 h and once after 8 h, to control ecdysteroid levels. We also suggest the presence of other factors from the head that control vitellin levels, the number of developing oöcytes, and the early growth of the oöcyte (initiation).     

Female-dependent stenogamy in the mosquito, Aedes taeniorhynchus

A female-dependent stenogamous condition was found in the mosquito, Aedes taeniorhynchus. When confined in cages, males attempted with similar frequencies to mate with wild and colony females. Wild females remained uninseminated because they actively prevented firm genital union. During simulated sunsets, swarming flights of colony males began at higher light intensities than those of wild males, and throughout these sunsets many more colony males participated in swarming than did wild males. Nevertheless, wild and colony males did not differ in their mating effectiveness. Both kinds of males were highly successful in transferring sperm to colony females, yet most of their attempted matings with wild females ended in failure. Autogeny occurred in stenogamic colony females and in eurygamic wild females.     

Circadian control of permethrin-resistance in the mosquito Aedes aegypti

Daily fluctuation of permethrin-resistance was found in adult mosquito Aedes aegypti, the major vector of dengue viruses in Taiwan. We hypothesized there is a relationship between resistance and the circadian clock. To test our hypothesis we correlated changes in the knock-down time (KT₅₀) response to permethrin with the expression of the pyrethroid-resistant gene CYP9M9 and the clock gene period (per) during a 12:12 h photoperiodic cycle. Rhythmic expression of per peaked at early scotophase of the light-dark cycle and at early subjective night in constant darkness. The values of KT₅₀ and the expression of CYP9M9 also exhibited circadian rhythms in both susceptible and permethrin-resistant mosquito strains, from which we inferred a link to the circadian clock. The KT₅₀ was significantly longer in the light than in the dark phase, and the level of CYP9M9 mRNA was maximal in early scotophase, dropped to a minimum in the midnight and then slowly increased through the photophase. Existence of a clock control over mosquito sensitivity to permethrin was further indicated by reduced expression of CYP9M9 and reduced mosquito resistance to permethrin after temporal silencing of the per gene. These data provide the first evidence on the circadian control of insect resistance to permethrin.     

Response of the antennal receptors of the male Aedes aegypti mosquito

Extracellular recordings of the spike discharge patterns of single chemoreceptor neurons in the antennae of male Aedes aegypti mosquitos were obtained and compared with similar recordings made from homologous sensilla on the antennae of female A. aegypti. In both male and female mosquitos, the grooved-peg sensilla were associated with two types of neurons sensitive to lactic acid—one excited by lactic acid and the other one inhibited by lactic acid. The short, blunt-tipped sensilla trichodea Type II (A2-II) of the male mosquito house chemosensory neurons sensitive to volatile chemical substances associated with sources of plant nectar, whereas in the female this information is provided by the long, sharp-tipped sensilla trichodea and the female A2-II sensilla respond to oviposition-site attractants.     

Release of egg development neurosecretory hormone in Aedes aegypti and Aedes taeniorhynchus induced by an ovarian factor

Ovariectomized Aedes aegypti do not synthesize vitellogenin after a blood meal, unless an ovary from a blood-fed donor is implanted. Decapitation, however, prior to implantation inhibits vitellogenin synthesis. A female ovariectomized and decapitated 6 hr after a blood meal, synthesizes vitellogenin if an ovary from a blood-fed donor is implanted. On the other hand, females that are fed on blood and immediately decapitated can not be stimulated to synthesize vitellogenin with implanted ovaries removed from blood-fed donors. These experiments led to the hypothesis that the blood meal stimulates the ovary to secrete a corpus cardiacum stimulating factor, that in turn promotes release of egg development neurosecretory hormone stored in the corpus cardiacum.Injection of 20-hydroxy-ecdysone or ovarian extract prepared from ovaries removed from unfed females does not release egg development neurosecretory hormone. Thus corpus cardiacum stimulating factor is not 20-hydroxy-ecdysone, and ovaries removed from unfed females do not store it.The rate of inactivation of egg development neurosecretory hormone released from the corpus cardiacum after a blood meal was investigated by implanting an ovary into females that were blood fed for various intervals than decapitated and ovariectomized. Seventy per cent of implants grow when the operation is done 18 hr after feeding, and 30% when the operation is done between 18 and 24 hr after feeding, indicating that egg development neurosecretory hormone is stable for the first 18 hr after a blood meal.Aedes taeniorhynchus females ovariectomized 24 hr after adult emergence do not synthesize vitellogenin. When such a female is implanted with an ovary removed from a sugar-fed or blood-fed Aedes aegypti donor vitellogenin synthesis is initiated, and the implant grows. Decapitation prior to implantation inhibit vitellogenin synthesis and implants do not grow. These results indicate that corpus cardiacum stimulating factor is not species specific.     

Proteomic analysis of the mosquito Aedes aegypti midgut brush border membrane vesicles

We analyzed brush border membrane vesicle proteins from isolated midguts of the mosquito Aedes aegypti, by two proteomic methods: two-dimensional gel electrophoresis (isoelectric focusing and SDS-PAGE) and a shotgun two-dimensional liquid chromatographic (LS/LS) approach based on multidimensional protein identification technology (MudPIT). We were interested in the most abundant proteins of the apical brush border midgut membrane. About 400 spots were detected on 2D gels and 39 spots were cored and identified by mass spectrometry. 86 proteins were identified by MudPIT. Three proteins, arginine kinase, putative allergen and actin are shown to be the most predominant proteins in the sample. The total number of 36 proteins detected by both methods represents the most abundant proteins in the BBMV.     

Stochastic eco-epidemiological model of dengue disease transmission by Aedes aegypti mosquito

We present a stochastic dynamical model for the transmission of dengue that takes into account seasonal and spatial dynamics of the vector Aedes aegypti. It describes disease dynamics triggered by the arrival of infected people in a city. We show that the probability of an epidemic outbreak depends on seasonal variation in temperature and on the availability of breeding sites. We also show that the arrival date of an infected human in a susceptible population dramatically affects the distribution of the final size of epidemics and that early outbreaks have a low probability. However, early outbreaks are likely to produce large epidemics because they have a longer time to evolve before the winter extinction of vectors. Our model could be used to estimate the risk and final size of epidemic outbreaks in regions with seasonal climatic variations.     

The cardiacal neurosecretory system and associated organs of an adult mosquito, Aedes aegypti

Unlike most other insects, mosquitoes do not possess discrete corpora cardiaca composed of neuropile, intrinsic neurosecretory cells and glial cells. Cells homologous with the intrinsic neurosecretory cells of other insects are located at the junction of the neck and thorax of mosquitoes, close to the corpora allata. These cells are named cardiacal neurosecretory cells. Axons run forwards from the cardiacal neurosecretory cells into the allatal nerves. Neurosecretory release sites occur over almost the whole of the nervi corporum cardiacorum, allatal nerves and oesophageal nerves, and these nerves constitute a very extensive neurohaemal organ for many of the cerebral neurosecretory cells. The neurosecretory release sites of the cardiacal neurosecretory cells appear to be in the allatal nerves and possibly also on the perikarya of these cells.     

Distention-mediated egg maturation in the mosquito,Aedes aegypti

Abdominal distention accelerates the release of a factor from the head of blood-fed Aedes aegypti mosquitoes. The critical period during which the head is required for oögenesis following blood ingestion is approx 6 h with a 5 μl meal, but small blood meals of 1 μl require the head to be present for significantly longer. Increasing the abdominal distention by supplementing the 1 μl meal with saline results in a critical period similar to that with 5 μl of blood. The information from the distended abdomen appears to travel via the ventral nerve cord. Transection of the ventral nerve cord prevents oögenesis from occurring after small blood meals, but not with larger blood volumes. Topical application of 100 pg of juvenile hormone III can substitute for the distention message.     

Humoral inhibition of host-seeking in Aedes aegypti during oöcyte maturation

Female Aedes aegypti mosquitoes were given 1 μl blood enemas, and their subsequent host-seeking behaviour determined in an olfactometer. Those females failing to develop eggs consistently responded to a host stimulus whenever tested, but inseminated mosquitoes developing eggs were inhibited from host-seeking during the period of egg development. Gravid uninseminated mosquitoes were also inhibited, but not to the same degree as inseminated mosquitoes. Experiments involving surgical manipulations and haemolymph transfusions indicate that a haemolymph-borne substance, present during egg development, inhibits the response toward a host.     

Development and fine structure of Pleistophora sp. (Cnidospora: Microsporida) in the mosquito, Aedes sierrensis

The development and fine structure of a Pleistophora sp. from larvae of Aedes sierrensis was investigated. The usual site of infection was the posterior midgut epithelium, and small uni- and binucleate forms were the first stages observed. There was no evidence of autogamy or the production of uninucleate sporonts. Binucleate sporonts produced prosporoblasts with two and four nuclei. Cellularization of the prosporoblasts resulted in sporoblasts which matured into spores. Heavily infected larvae have less fat body than healthy hosts and usually die when infected in the first or second instar. The pathogen could remain chronic and be carried into the adult host. Although natural infections were low, the pathogen could serve as a biological control agent.     

A new cytoplasmic polyhedrosis virus from the salt-marsh mosquito, Aedes cantator (Diptera: Culicidae)

The ultrastructure, development, and histopathology of a new cytoplasmic polyhedrosis virus of Aedes cantator are described. Virus particles measure 70 nm in diameter, are icosahedral in shape, and consist of a central electron-dense core surrounded by a capsid with six projections. Occlusion bodies are irregular in size (0.5–3.0 μm) and shape and contain several virus particles. Virus particles are assembled within an interconnecting network of fine filaments and are occluded by the deposition of a proteinaceous crystal around groups of mature virus particles within a virogenic stroma. Infections are confined to cells of the cardia, gastric ceca, and posterior portion of the midgut, which hypertrophy and frequently lyse. Infected larvae die during the fourth larval instar or as pupae. The prevalence of infection in natural field populations is less than 1%.     

Life cycle,epizootiology, and horizontal transmission of Amblyospora (Microspora: Amblyosporidae) in a univoltine mosquito, Aedes stimulans

Amblyospora infections in Aedes stimulans are transovarially transmitted by females infected in the previous year. Pathogen development in progeny is dimorphic and host sex dependent. In males, the pathogen invades fat body tissue and undergoes an extensive developmental sequence which kills the host and results in the formation of eight haploid spores enclosed in an accessory membrane that are not infectious to other larvae. In females, the pathogen invades host oenocytes and undergoes a simple developmental sequence which has no detrimental affect on longevity, fecundity, oviposition, or egg hatch, and results in the formation of binucleated spores that infect the ovaries and ensure transmission to the next generation. Transovarial transmission is continuous and is the major way in which these microsporidia are maintained from year to year, but is incapable of maintaining infections in breeding populations because of low transmission rates and is not sufficient to account for the types and levels of infection observed in the field. Horizontal transmission is reported for the first time. It occurs sporadically during the early stages of larval subsequently disseminated to oenocytes of adult hosts and are transovarially transmitted by females to filial host generations. This pathway of transmission provides the necessary mechanism whereby these microsporidia can reenter the mosquito population and thus perpetuate themselves.     

The first stage larva of brugia pahangi in Aedes togoi: An ultrastructural study

Lehane M. J. 1978. The first stage larva of Brugi pahangi in Aedes togoi: an ultrastructural study. International Journal for Parasitology8: 207–218. The ultrastructure of the first stage larva in the mosquito is described up to the onset of the first cuticular moult. The following structural changes from the microfilarial stage have been noted at this time; the numbers of muscle cells have increased, usually to four with a maximum of six in each intercordai quadrant ; part of the pharyngeal thread has formed into a knot ; the intestinal lumen has developed and is surrounded in any given transverse section by up to four intestinal cells and the inner body has largely been lost; the anal apparatus has enlarged and developed; the excretory apparatus has largely degenerated. The functional morphology of the various organ systems described is discussed.     

Fine structure of the male accessory glands in Aedes triseriatus

The paired accessory glands of the male mosquito, Aedes triseriatus, consisted of a single layer of columnar epithelial cells enclosed by a richly-nucleated circular muscle layer. Each accessory gland is divided into an anterior gland (AG) with one type of secretory cell, and a posterior gland (PG) with two types. The cells of the AG and those of the anterior region of the PG showed macroapocrine secretion. The mucus secreting cells located at the posterior region of the PG, however, released their contents into the lumen of the gland by rupturing the apical membrane of the cell. The secretion from all cells was in the form of membrane-bound granules which had distinct electron-dense and electron-lucent areas.