Superoxide dismutase in the anal gills of the mosquito larvae of Aedes aegypti: its inhibition by alpha-terthienyl.

The anal gills of the mosquito larvae of Aedes aegypti were shown to possess superoxide dismutase (EC 1.15.1.1) activity, which increased with the maturation of the larvae from instar 1 to instar 4. This enzyme was highly inhibited upon treatment of the larvae with alpha-terthienyl (2,2':5,2"-terthiophene) and subsequent exposure to long-wave ultraviolet light. Inhibition also occurred with treatment of the crude enzyme extract in a similar fashion. Exposure of the enzyme to the ultraviolet light alone or the treatment of the enzyme with alpha-terthienyl in darkness could not manifest this inhibition. This finding adds a new dimension to the complex mechanism(s) proposed for the photodynamic toxicity of alpha-terthienyl.     

Linkage of the genes for DDT and dieldrin resistance in larvae of the mosquito Aedes aegypti.

The DDT resistance gene RDDT1, and the dieldrin resistance gene Rd1 have been mapped on linkage group II with respect to visible markers, in the mosquito Aedes argypti L. The best interpretation of the data gives the order wa - Rdl - ds RDDT1 - s - y but was - Rdl -ds - y - s - RDDT1 is also possible. h is very loosely linked with RDDT1. The length of the linkage group has been considerably extended from previous studies.     

Infection sites of the entomopathogenic fungus Beauveria bassiana in the larvae of the mosquito Aedes aegypti

A series of experiments were conducted to determine the infection sites of the entomopathogenic fungus Beauveria bassiana after ingestion by the larvae of Aedes aegypti. The timing of the host death in relation to larval molting, the principle sites of fungal infection and development in host tissues were studied. Fungal conidiospores (CS) and blastospores (BS) were used separately for treatment of mosquito larvae. Although in most instances CS germinated and developed within the host, in others there was a premature abortion of the fungal development cycle. On the other hand, BS ingested by the larvae showed differences in the fungal development stages in the larval tissues. While the two primary infection sites were the head and the anal region, the most preferred site for fungal development was the larval gut. No more than two cycles of fungal development can occur in the host. Although both CS and BS are effective as larvicides, BS is far more pathogenic.

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Résumé Une série d'expériences a été menée afin de déterminer les emplacements d'infection du fongus entomopathogénique Beauveria bassiana (souche GK 2016) lequel avait été ingesté des larves d'Aedes aegypti. On a étudié le moment de la mort des hôtes en relation des mues des larves, les emplacements principaux où se conduit l'infection fongale et le développement du fongus dans des tissus divers d'hôte. On a utilisé les conidiospores (CS) et les blastospores (BS) séparément pour traitement des larves des moustiques. Bien que dans la plupart des cas CS ait germiné et se soit développé chez l'hôte, en d'autres cas, CS a germiné mais n'avait pas produit du BS évidemment grâce à l'avortement prématuré du cycle de développement des fongus chez l'hôte. Le BS qui avait été ingesté dans les larves présentait des stages différents de développement du fongus dans les tissus des larves. Quoique les deux emplacements placements principaux étaient la tête et la région anale, l'emplacement préféré pour le développement du fongus était l'intestin des larves. Nous montrons qu'il n'y a plus de deux cycles de développement du fongus chez l'hôte. Bien que CS et BS soient efficaces comme larvicides, BS est de loin plus pathogène.

     

Activation of vitellogenin synthesis in the mosquito Aedes aegypti by ecdysone

Injected β-ecdysone was found to induce the synthesis of yolk protein (vitellogenin) in adult female Aedes aegypti without a blood meal. After injection of 5 μg ecdysone per mosquito, vitellogenin constituted 80 per cent of the total protein secreted by explanted fat body, a proportion comparable to that produced by fat body from blood-fed females. Moreover, the time course of induction of vitellogenin synthesis in ecdysone-injected mosquitoes was similar to that triggered by a blood meal. Response to ecdysone is dosedependent: 0·5 μg per female was required to stimulate synthesis to 50 per cent of the level found 18 hr after a blood meal. Ecdysone was effective in decapitated or ovariectomized mosquitoes, and also when applied directly to fat body preparations in vitro. Thus it appears that ecdysone acts directly on the fat body to induce specific protein synthesis, as does the vitellogenin stimulating hormone (VSH) from the ovary of blood-fed mosquitoes. These results suggest that ecdysone can replace VSH in inducing vitellogenin synthesis in the unfed mosquito.     

Linkage of a gene for DDT-resistance in adults of the mosquito Aedes aegypti.

The gene RDDT2, which gives resistance to DDT in the imago of Aedes aegypti L. has been mapped on linkage group III with respect to six visible markers. The best interpretation of the order of the genes is:- blp - blt - co - fz - wi -RDDT2 - min, but the order blp - blt - co - fz -RDDT2 - wi - min is also possible.     

Assessment of diet choice by the yellow fever mosquito Aedes aegypti

To investigate feeding‐related decisions in Aedes aegypti (L.), adults are presented with simple diets of paired gustatory stimuli conveying information concerning energy content, nutrient richness, osmotic balance and food toxicity in a two‐diet matrix assay. Assessment of mosquito gut contents indicates that both sexes accept single sugar diets in a dose‐dependent manner. When presented with a choice between two different yet equimolar sugar solutions, more individuals of both sexes accept the disaccharides, sucrose and trehalose, than the monosacharrides, fructose and glucose. The combination of pyranose and furanose sugars in solution, either physically associated (as in sucrose) or present as monomers (as glucose and fructose), is accepted over solutions containing a single sugar moiety. Using the two‐diet matrix assay, mosquito diet‐choice is also tested between two equimolar sucrose ‘driver’ solutions in which one is presented with various concentrations of another potential feeding cue ‘test’ compound (i.e. each of the 20 naturally‐occurring amino acids, sodium chloride, quinine or caffeine). Diet‐choice between the ‘driver’ sucrose‐only solution and the solution of the ‘driver’ sucrose containing a ‘test’ amino acid is influenced by sex, amino acid concentration and sucrose concentration. There is also an example of synergism between the diet components, leucine and sucrose. Mosquitoes demonstrate a dose‐dependent acceptance of sucrose‐only diets over sodium chloride‐containing sucrose when presented together. Interestingly, the sucrose‐only diet is accepted by more mosquitoes than all concentrations of the saline‐containing sucrose diets except those approximately isotonic to mosquito haemolymph, at which concentration mosquitoes show no clear choice between the diets. More individuals of both sexes accept sucrose‐only diets than the diets of caffeine‐containing sucrose in a dose‐dependent manner. Only females, however, respond to quinine‐containing sucrose diets and modulate this behaviour in relation to the energetic reward: more females imbibed quinine‐containing sucrose at the higher sucrose concentration (1 m ). A systematic characterization of diet selection behaviour of A. aegypti is presented for 27 putative feeding cues potentially involved in nectar/honeydew feeding. This study will be used as a basis from which to investigate further the mosquito's assessment of food quality and ultimately host choice.     

Genetic transformation of the mosquito Aedes aegypti by micro-injection of DNA

We report the successful introduction of heterologous DNA sequences into embryos of the mosquito Aedes aegypti (L.) by microinjection. The injected DNA carried P transposable element sequences, derived from and known to facilitate transformation in Drosophila melanogaster. Two plasmids, one of which carried a dominant selectable marker, were introduced into the posterior of embryos prior to pole cell formation and subsequently taken up into the germ line of transformed individuals. Stable transfer of the selectable marker (G418 resistance) was demonstrated over two generations. The precise nature of these putative P mediated integration events is currently being investigated. However, the results presented here establish the technique of DNA transformation for the genetic manipulation of Aedes aegypti.     

Population structure of the mosquito Aedes aegypti (Stegomyia aegypti) in Pakistan

Eleven microsatellite markers were used to determine the genetic population structure and spread of Aedes aegypti (Stegomyia aegypti) (Diptera: Culicidae) in Pakistan using mosquitoes collected from 13 different cities. There is a single genetic cluster of Ae. aegypti in Pakistan with a pattern of isolation by distance within the population. The low level of isolation by distance suggests the long‐range passive dispersal of this mosquito, which may be facilitated by the tyre trade in Pakistan. A decrease in genetic diversity from south to north suggests a recent spread of this mosquito from Karachi. A strong negative correlation between genetic distance and the quality of road connections shows that populations in cities connected by better road networks are less differentiated, which suggests the human‐aided passive dispersal of Ae. aegypti in Pakistan. Dispersal on a large spatial scale may facilitate the strategy of introducing transgenic Ae. aegypti or intracellular bacteria such as Wolbachia to control the spread of dengue disease in Pakistan, but it also emphasizes the need for simple measures to control container breeding sites.     

A genetical study of DDT resistance in the mosquito Aedes aegypti.

Crosses have been carried out to determine the relationship between adult DDT resistance and the three linkage groups of the mosquito Aedes aegypti. Two linkage groups were implicated in the control of DDT resistance. In the Bangkok-HR strain resistance derived mainly from linkage group III, probably with the maor effect from the gene R-DDT2. When resistance was transferred into a susceptible background, by outcrossing Bangkok-HR to strain 64 and reselecting, resistance in the resulting Bangkok-MR strain came from both linkage groups II and III.     

Susceptibility and alterations by diflubenzuron in larvae of Aedes aegypti

Benzoylphenyl ureas inhibit chitin synthesis and interfere with the molting process in arthropods. In this study, the effect of diflubenzuron on third‐instar larvae of Aedes aegypti was evaluated. The susceptibility to the product was determined, and the alterations generated were shown through light and electron microscopy. LC₅₀ and LC₉₀ were 0.23 and 0.47 ppm, respectively. The main alterations observed were the incapacity to complete the molt, a reduction of mobility, the fragmentation of the old cuticle, a division of the body segments that was not evident, and the deformation of the caudal structures. Images of the ultrastructure are included, where breaking zones in the cuticle were observed, separation of the cuticle, the epidermis and the muscles, and these latter with a disorganized arrangement. In low concentrations, from 0.15 ppm, diflubenzuron causes alterations in the behavior and morphology of Ae. aegypti.     

The effect of DDT and rearing temperature on pecten spine number in larvae of the mosquito Aedes aegypti L.

Pecten spine number has been studied in larvae of Aedes aegypti exposed during development to low temperatures or to DDT at the fourth instar, both of which caused substantial mortality. But neither contingency caused stabilising selection for spine number, in contrast to what was observed in a previous study when larvae were exposed to scum on the surface of the rearing medium. — Two larval colour morphs, yellow and brown, did not differ in spine number.     

Lipophorin as a yolk protein precursor in the mosquito, Aedes aegypti

We examined expression of the lipophorin (Lp) gene, lipophorin (Lp) synthesis and secretion in the mosquito fat body, as well as dynamic changes in levels of this lipoprotein in the hemolymph and ovaries, during the first vitellogenic cycle of females of the yellow fever mosquito, Aedes aegypti. Lipophorin was purified by potassium bromide (KBr) density gradient ultracentrifugation and sodium dodecyl sulfate–polyacrylamide gel electrophoresis (SDS–PAGE). Polyclonal antibodies were produced against individual Lp apoproteins, apolipoprotein-I (apoLp-I) and apolipoprotein-II (apoLp-II), with molecular weights of 240 and 75 kDa, respectively. We report here that in the mosquito A. aegypti, Lp was synthesized by the fat body, with a low level of the Lp gene expression and protein synthesis being maintained in pre- and postvitellogenic females. Following a blood meal, the Lp gene expression and protein synthesis were significantly upregulated. Our findings showed that the fat body levels of Lp mRNA and the rate of Lp secretion by this tissue reached their maximum at 18 h post-blood meal (PMB). 20-Hydroxyecdysone was responsible for an increase in the Lp gene expression and Lp protein synthesis in the mosquito fat body. Finally, the immunocytochemical localization of Lp showed that in vitellogenic female mosquitoes, this protein was accumulated by developing oocytes where it was deposited in yolk granules.     

Insulin stimulates ecdysteroid production through a conserved signaling cascade in the mosquito Aedes aegypti.

Selective activators and inhibitors of insulin signaling cascades in mammalian cells were tested for their effects on insulin stimulated steroidogenesis by ovaries of Aedes aegypti. Bovine insulin in the concentration range of 1.7 microM to 85 microM stimulated ecdysteroidogenesis in vitro. Pervanadate, an inhibitor of tyrosine kinase phosphatase, stimulated ecdysteroid production at concentrations of 250 microM to 1 microM. Okidaic acid, a serine/threonine phosphatase inhibitor, stimulated steroidogenesis with an ED50 of 77.39 nM. A selective inhibitor of tyrosine kinase activity, HNMPA-(AM3), inhibited ecdysteroid production with an IC50 of 14.2 microM. Two selective inhibitors of phosphatidylinositol 3-kinase, wortmannin and LY294002, inhibited ecdysteroid production at low concentrations (IC50 = 1.6 nM and 30 nM, respectively). These concentrations are similar to those inhibiting insulin action in mammalian cells. A selective inhibitor of mitogen-activated protein kinase, PD098059, had no effect on ecdysteroid production even up to 100 microM. Thus, insulin stimulation of ecdysteroid production by ovaries in vitro appears to be controlled by the tyrosine kinase activity of the mosquito insulin receptor and the signaling cascade involving phosphatidylinositol 3-kinase and protein kinase B.     

Multiple functions of an odorant-binding protein in the mosquito Aedes aegypti

To prevent spreading of deadly diseases, populations of mosquitoes can be controlled by interfering with their chemical communication system. Odorant-binding proteins, recently shown to be required for olfaction, represent interesting targets for such purpose. Here we describe the ligand-binding properties and the unusual tissue expression of odorant-binding protein 22 from the repertoire of Aedes aegypti. Best ligands are molecules with two aromatic rings connected by a short rigid chain. The protein is expressed not only in sensory organs, such as the antennae and proboscis, but also in the male reproductive apparatus and transferred to the spermathecs of females. This suggests an additional function for this protein as pheromone carrier, analogously to vertebrates’ urinary and salivary proteins as well as some insect chemosensory proteins. Antiserum against odorant-binding protein 22 also stained the edges and sensilla of spiracles, indicating a third, still unknown, role for this protein.