Mosquito Aedes Atropalpus Research Articles

Gut bacteria differentially affect egg production in the anautogenous mosquito Aedes aegypti and facultatively autogenous mosquito Aedes atropalpus (Diptera: Culicidae).

BackgroundAedes aegypti and A. atropalpus are related mosquitoes that differ reproductively. Aedes aegypti must blood-feed to produce eggs (anautogenous) while A. atropalpus always produces a first clutch of eggs without blood-feeding (facultatively autogenous). We recently characterized the gut microbiota of A. aegypti and A. atropalpus that were reared identically in the laboratory. Here, we assessed the effects of specific members of the gut microbiota in A. aegypti and A. atropalpus on female fitness including egg production.MethodsGnotobiotic A. aegypti and A. atropalpus larvae were colonized by specific members of the gut microbiota. Survival, development time, size and egg production for each treatment was then compared to axenic and conventionally reared larvae.ResultsMost species of bacteria we tested supported normal development and egg production by A. aegypti but only one betaproteobacterium, a Comamonas, supported development and egg production by A. atropalpus to equivalent levels as conventionally reared females. Aedes atropalpus females colonized by Comamonas contained similar stores of glycogen and protein as conventionally reared females, whereas females colonized by Aquitalea did not. Small differences in bacterial loads were detected between gnotobiotic and conventionally reared A. aegypti and A. atropalpus, but this variation did not correlate with the beneficial effects of Comamonas in A. atropalpus.ConclusionsSpecific members of the gut microbiota more strongly affected survival, size and egg production by A. atropalpus than A. aegypti.Electronic supplementary materialThe online version of this article (doi:10.1186/s13071-016-1660-9) contains supplementary material, which is available to authorized users.

In Memoriam

In Memoriam

Targeting gene expression to the female larval fat body of transgenic Aedes aegypti mosquitoes

As the fat body is a critical tissue for mosquito development, metamorphosis, immune and reproductive system function, the characterization of regulatory modules targeting gene expression to the female mosquito fat body at distinct life stages is much needed for multiple, varied strategies for controlling vector-borne diseases such as dengue and malaria. The hexameric storage protein, Hexamerin-1.2, of the mosquito Aedes atropalpus is female-specific and uniquely expressed in the fat body of fourth instar larvae and young adults. We have identified in the Hex-1.2 gene, a short regulatory module that directs female-, tissue-, and stage-specific lacZ reporter gene expression using a heterologous promoter in transgenic lines of the dengue vector Aedes aegypti. Male transgenic larvae and pupae of one line expressed no Escherichia coli β-galactosidase or transgene product; in two other lines reporter gene activity was highly female-biased. All transgenic lines expressed the reporter only in the fat body; however, lacZ mRNA levels were no different in males and females at any stage examined, suggesting that the gene regulatory module drives female-specific expression by post-transcriptional regulation in the heterologous mosquito. This regulatory element from the Hex-1.2 gene thus provides a new molecular tool for transgenic mosquito control as well as functional genetic analysis in aedine mosquitoes.

Lactic acid sensitive receptors in the autogenous mosquito Aedes atropalpus

Host seeking behavior is not observed during the first gonotrophic cycle in Aedes atropalpus. The objectives of this study were to examine the possible role of the peripheral sensory system in this phenomenon. The results show that the rate of maturation of the lactic acid sensitive neurons is relatively rapid in this species so the absence of host-seeking during the first gonotrophic cycle cannot be attributed to delayed development of the peripheral sensory system. Furthermore, lactic acid receptors of high sensitivity are present on the antennae of females that are gravid and in the early stages of egg development. These results support the conclusion that a humoral mechanism of host-seeking inhibition is not operative in this species, at least during autogenous egg development, and show that receptors for at least one host attractant are fully mature early in the first autogenous gonotrophic cycle.

Host-seeking behavior in the autogenous mosquito Aedes atropalpus

The absence of host-seeking behavior during the first gonotrophic cycle in Aedes atropalpus is not due to hemolymph-borne factors. The removal of all developing eggs from nulliparous, gravid individuals by ovariectomy did not result in host-seeking. Furthermore, hemolymph transfers from non-host-seeking, nulliparous, gravid females into host-seeking, parous, non-gravid females did not inhibit host-seeking in the recipients. Circumstantial evidence supports the hypothesis that distention inhibits host-seeking during the first gonotrophic cycle in this species. Host-seeking can only be elicited after oviposition of the first egg clutch. Although the frequency of sugar feeding is high, particularly in the parous, non-gravid population, host-seeking is not correlated with the presence of sugar in the crop. Host-seeking and non-host-seeking individuals were equally likely to have recently fed on sugar. The control of host-seeking behavior during the first gonotrophic cycle in Ae. atropalpus is thus very different from that in the anautogenous mosquito Aedes aegypti, in which host-seeking is inhibited by hemolymph-borne factors associated with egg development.

Thiophenes as mosquito larvicides: Structure-toxicity relationship analysis

The phototoxicity and non-light-mediated toxicity of 41 naturally occurring and synthetic tricyclic thiophenes was assessed against larvae of the mosquito Aedes atropalpus. Seventeen of the tested compounds were extremely potent, with LC 50 values for phototoxicity in the nanomolar range. The role of the thiophenes' physicochemical properties, such as hydrophobicity and ability to produce singlet oxygen, with regard to their larvicidal activity was investigated using quantitative structure-activity analysis. It was found that 84% of the variation in phototoxicity could be explained by a combination of the logarithm of octanol/water partition coefficients and the rate of singlet oxygen production. Comparison of this model with one derived for phototoxicity to nauplii of the brine shrimp ( Artemia salina) suggests the possibility of achieving some degree of species selectivity by manipulation of the lipophilic character of the tricyclic thiophenes.

In vivo induction of ovarian development in decapitated Aedes atropalpus by physiological levels of 20‐hydroxyecdysone

AbstractThe Bass Rock strain of the mosquito Aedes atropalpus is autogenous for the first gonadotropic cycle; i.e. adult females will undergo normal oocyte maturation without the benefit of a blood meal. Yolk deposition can be completely inhibited if these animals are decapitated within 6 hours or abdominally ligated within 8 hours of adult emergence. Injection of 4.8 ng of 20‐hydroxyecdysion into 12‐hour‐old adult females that had been decapitated soon after eclosion restored vitellogenesis in 100% of the treated insects. With this dosage of hormone 50% of the oocytes appeared mature 72 hours after injection. When the amount of hormone administered was increased to 4.8 × 103 ng all of the follicles in 100% of the animals contained yolk, but the average follicle length was 35% less than the vitellogenic follicles of either the non‐decapitated controls or the decapitated females that had received 4.8 ng of hormone.Yolk deposition was not restored in isolated abdomens by 4.8 ng of 20‐hydroxyecdysone. When the dosage was increased to 5 × 103 ng, 100% of the abdomens injected had follicles with yolk, and almost all the follicles contained yolk, but the average follicular length was reduced by 42% compared to intact controls.The vitellogenic activity induced by μg quantities of 20‐hydroxyecdysone in decapitated females or in isolated abdomens is no doubt nonphysiological. However the fact that a single injection of only 4.8 ng of 20‐hydroxyecdysone was capable of inducing in vivo vitellogenesis in decapitated females suggests that this hormone is normally required for this process to occur. Since isolated abdomens did not respond to this amount of 20‐hydroxyecdysone, the possibility that the presence of a thoracic factor, perhaps juvenile hormone, may also be necessary for normal ovarian development in A. atropalpus is discussed.

Endocrine regulation of ovarian development in the autogenous mosquito, Aedes atropalpus

The mosquito Aedes atropalpus is autogenous, i.e., normal ovarian development proceeds in adult females without any exogenous source of protein. Using a radioimmunoassay (RIA) for ecdysone, it was found that the titer of antigen-positive material in whole-body extracts of adult females rose from about 150 pg equiv of β-ecdysone per female at eclosion to an average peak value of 323 pg 32 hr later. The titer then dropped to approximately 100 pg over the next 16 hr. A comparison of the RIA titer with follicle size, vitellin deposition into oocytes, and total extractable soluble proteins from ovaries suggested a causal relationship between the hormone titer and normal ovarian development. Preliminary data also suggest that the ovary is a source of ecdysteroid in these adult animals. Decapitation of adult females from 0 to 4 hr after eclosion completely prevented ovarian development. Animals decapitated 30 min after eclosion and then assayed for ecdysteroid content 32 hr later revealed a hormonal titer 75% less than normal intact controls. An analysis of the 32-hr RIA-positive material by high-pressure liquid chromatography confirmed the presence of β-ecdysone but did not detect any α-ecdysone. Ovarian deficiencies incurred by decapitation were partially restored by injection with β-ecdysone or by topical application of juvenile hormone.

Photoinhibition of Diapause in Field Populations of Aedes atropalpus12

A one-h light pulse, which occurred between 7 and 9 h after the beginning of a short-day scotophase, inhibited diapause in a laboratory colony of the mosquito Aedes atropalpus . Tests were conducted to see if induction of diapause in the field is also inhibited by nighttime light pulsing. It was determined that the natural light intensities at which A. atropalpus experiences the start of the scotophase occur shortly before sunset. Therefore, a one h pulse of light, at 8 h post sunset, was used to simulate the conditions which inhibited diapause in the laboratory. This prevented induction of diapause both in field cages and at a natural breeding site for A. atropalpus . The observation, made during this study, that the natural scotophase for A. atropalpus ends at much lower light intensities than those at which it begins is discussed.

The required day number and timely induction of diapause in geographic strains of the mosquito Aedes atropalpus

Diapause is triggered in A. atropalpus from 14°N lat when 9 or more short-day photoperiod cycles occur during the photosensitive 4th instar and pupa. Temperatures of 22°C and higher cause part or all of this population to complete the photosensitive period in less than 9 days thereby avoiding diapause. In contrast, 4 short-day cycles during the photosensitive period are sufficient to trigger diapause in A. atropalpus from 45°N lat. This population experiences the 4 required days at temperatures as high as 28°C. A strain from an intermediate location of 34°N lat must “see” 7 short days during the photosensitive stages for induction of diapause. This requirement is met at temperatures of 24°C and less. These results suggest that southern strains of A. atropalpus have evolved a means of avoiding short-day induced diapause if temperatures are high and other requirements for growth are available. A correlation between critical daylength for induction of diapause and geographic origin has been shown for several insect species. The evolution of a requirement for different numbers of diel cycles during the photosensitive period is another means of modifying the diapause response in populations from different latitudes and geographic areas.

Night length measurements by the circadian clock controlling diapause induction in the mosquito Aedes atropalpus

Night interruption experiments were used to investigate the behavior of the clock controlling diapause induction in the mosquito, Aedes atropalpus. The data from these experiments indicated that the clock included a circadian oscillator which was phase set at dusk. Following this event the oscillator proceeded to drive a nightly rhythm of sensitivity to light. This rhythm included a photoinducible phase where light interruption inhibited diapause. The photoinducible phase was fixed, occurring 7 to 9 hr after dusk in all photoperiod regimens tested. The photoinducible phase was followed by a refractory phase, which continued until dawn. During the refractory period light did not inhibit diapause. These observations indicated that the circadian clock behaved like an interval timer which was set at dusk. The rhythm of sensitivity to light, an inherited time scale, limited the induction of diapause to seasonal periods when nights were longer than 9 hr. As a result, diapause was induced only when the daylength dropped below the critical photoperiod of L15:D9 (hours of light:hours of dark). A ‘T’ experimental design was used to confirm the importance of the length of the night in clock controlled induction of diapause in this mosquito.

The chemistry of egg maturation in the unfed mosquito Aedes atropalpus

The mosquito Aedes atropalpus, maintained without a blood meal and without sugar, matures 150 to 200 eggs. The gradual accumulation of protein and triglyceride in the maturing eggs could be entirely accounted for by the gradual disappearance of protein and lipid from the abdomen (fat body).