Close encounters: contributions of carbon dioxide and human skin odour to finding and landing on a host in Aedes aegypti

In a wind‐tunnel study, the upwind flight and source location of female Aedes aegypti to plumes of carbon dioxide (CO₂) gas and odour from human feet is tested. Both odour sources are presented singly and in combination. Flight upwind along the plumes is evident for both CO₂ and odour from human feet when the odours are presented alone. Similarly, both odour sources are located by more than 70% of mosquitoes in less than 3 min. When both CO₂ and odour from human feet are presented simultaneously in two different choice tests (with plumes superimposed or with plumes separated), there is no evidence that females orientate along the plume of CO₂ and only a few mosquitoes locate its source. Rather, the foot odour plume is navigated and the source of foot odour is located by over 80% of female Ae. aegypti. When a female is presented a plume of CO₂ within a broad plume of human foot odour of relatively low concentration, the source of CO₂ is not located; instead, flight is upwind in the diffuse plume of foot odour. Although upwind flight by Ae. aegypti at long range is presumably induced by CO₂ and the threshold of response to skin odours is lowered, our findings suggest that, once females have arrived near a prospective human host, upwind orientation and landing are largely governed by the suite of human odours, whereas orientation is no longer influenced by CO₂.     

Aedes aegypti: model for blood finding strategy and prediction of parasite manipulation

Aedes aegypti mosquitoes salivate during intradermal probing of vertebrate prey before ingesting blood (Griffiths and Gordon 1952). Nonsalivating mosquitoes locate blood more slowly; this difference was ascribed to an anti-platelet activity found in the mosquito's saliva (Ribeiro et al. 1984). Mosquitoes infected with Plasmodium gallinaceum suffer pathology that specifically impairs saliva anti-hemostatic activity but without reducing volume of output (Rossignol et al. 1984). The complexity of the feeding apparatus of mosquitoes provides opportunity for a variety of strategies in which pathogens may produce specific lesions that enhance their transmission, but the variables that affect the duration of probing by mosquitoes have not been defined. We sought to resolve this complexity by identifying and quantifying relevant parameters of probing behavior. Mosquitoes thrust their mouthparts repeatedly through their host's skin while searching for blood. Female A. aegypti thrust at 7-sec intervals. If this search results in success, feeding ensues. Alternatively, the mosquito "desists," the mouthparts stylets are withdrawn, and the mosquito attempts to feed at another site. Even after previous desistance, the probability of finding blood remains undiminished. Functions for the probability of feeding success and desistance over time were derived using data from observations on 300 mosquitoes. The probability of feeding success was interpreted as being a function of the density of vessels in the skin, their geometric distribution, and the conditions locally affecting hemostasis. During each probe, the probability of desisting increased linearly with time, and after desisting once, mosquitoes tended to desist more rapidly. A model was developed incorporating Monte Carlo simulation which closely fit observed data. By changing values for the several parameters of the probability functions, we predicted modes in which parasites may manipulate their hosts to enhance transmission, both to and from the vector. In particular, parasite strategies in the vector would include induced salivary pathology; increased duration of probing thrusts; decreased desistance time; and inhibited phagoreception. Predicted parasite strategies in the reservoir host would include increased skin vascular volume and impaired host hemostasis. Our model supports the hypothesis of a mutualistic interaction of malaria and mosquitoes.     

Renewal of sexual receptivity in mated female mosquitoes, Aedes aegypti

ABSTRACT. Females of Aedes aegypti (L.) (Diptera, Culicidae) were not receptive to mating 1 h after the initial insemination or at later times throughout the first gonotrophic cycle. A significant proportion of these females (75–90%) were inseminated again prior to the second gonotrophic cycle. Insemination was determined by the detection in females of sperm labelled with ³ H(G)-adenine or ³²PO₄ after matings with radiolabeled males. Females deprived of males after the first insemination displayed an abnormal reduction in fertility throughout successive gonotrophic cycles.     

Modelling distributions of Aedes aegypti and Aedes albopictus using climate,host density and interspecies competition

Florida faces the challenge of repeated introduction and autochthonous transmission of arboviruses transmitted by Aedes aegypti and Aedes albopictus. Empirically-based predictive models of the spatial distribution of these species would aid surveillance and vector control efforts. To predict the occurrence and abundance of these species, we fit a mixed-effects zero-inflated negative binomial regression to a mosquito surveillance dataset with records from more than 200,000 trap days, representative of 53% of the land area and ranging from 2004 to 2018 in Florida. We found an asymmetrical competitive interaction between adult populations of Aedes aegypti and Aedes albopictus for the sampled sites. Wind speed was negatively associated with the occurrence and abundance of both vectors. Our model predictions show high accuracy (72.9% to 94.5%) in validation tests leaving out a random 10% subset of sites and data since 2017, suggesting a potential for predicting the distribution of the two Aedes vectors.     

Precocene is not a specific antigonadotropic agent in adult female Aedes aegypti

ABSTRACT. In the mosquito, Aedes aegypti , other workers have shown that prior to blood-feeding a pre-vitellogenic period ensues manifested by the growth and differentiation of ovarian follicles. This results in resting stage follicles which will then complete ovarian development after the blood-meal. Allatectomy of newly emerged females prevents follicles from reaching their resting stage and such follicles do not undergo subsequent vitellogenesis after blood-feeding. Precocene II, a plant substance which effectively prevents ovarian development in Oncopeltus fasciatus by causing the irreversible degeneration of the corpus allatum, was applied to newly emerged mosquitoes, and at various times after blood-feeding. Sublethal doses of precocene applied 1 h after adult emergence had no effect on pre-vitellogenic follicular development and did not prevent yolk deposition after the blood-meal. Precocene applied after blood-feeding had two major effects. When administered early, it inhibited trypsin synthesis and retarded ovarian maturation. Animals exposed to it later, exhibited abnormal oviposition. It is proposed that precocene II does not act as an antigonadotropic agent in adult Aedes aegypti , but that it does induce a general toxic state in treated animals.     

Contribution of triglyceride-rich lipoproteins to plasma free fatty acids.

Free fatty acids are the major lipid fuel of the body. Dysregulation of adipose tissue lipolysis results in increased plasma free fatty acid concentrations, and via that mechanism contributes to insulin resistance in obesity and type 2 diabetes mellitus. Adipose tissue hormone sensitive lipase is thought to be responsible for the production of the majority of free fatty acids. However, a separate contribution comes from the action of endothelial lipases, especially lipoprotein lipase, on triglyceride-rich lipoproteins via a process known as spillover. The primary substrate for spillover appears to be chylomicrons derived from dietary fat. The spillover of fatty acids into the free fatty acid pool varies from one tissue to another. For example, spillover is low ( approximately 14%) in the forearm of healthy volunteers, suggesting that triglyceride fatty acid storage is relatively efficient in skeletal muscle. In contrast, spillover appears to be higher in adipose tissue and may also be higher in the splanchnic bed, based on preliminary data. If systemic spillover is increased in insulin resistant states such as diabetes, this could represent a mechanism contributing to the abnormal increases in plasma concentrations of free fatty acids in that condition.     

Toward a description of the sialome of the adult female mosquito Aedes aegypti

To describe the set of mRNA and protein expressed in the salivary glands (sialome) of Aedes aegypti mosquitoes, we randomly sequenced a full-length cDNA library of this insect and performed Edman degradation of PVDF-transferred protein bands from salivary homogenates. We found 238 cDNA clusters which contained those coding for 10 of the 11 proteins found by aminoterminal degradation. All six previously described salivary proteins were found in this library. Full-length sequences of 32 novel cDNA sequences are reported, one of which is the product of a transposable element. Among the 31 novel protein sequences are 4 additional members of the D7 protein family; 4 novel members of the antigen 5 family (a protein family not reported in Aedes); a novel serpin; a novel member of the 30-kDa allergen of Ae. Aegypti; a secreted calreticulin; 2 proteins similar to mammalian angiopoietins; adenosine deaminase; purine hydrolase; lysozyme; a C-type lectin; 3 serine proteases, including one with high similarity to Bombyx prophenoloxidase activating enzyme; 2 proteins related to invertebrate immunity; and several sequences that have no significant matches to known proteins. The possible role of these proteins in blood and sugar feeding by the mosquito is discussed.     

Ultrastructural changes in the fat body of adult female Aedes aegypti in relationship to vitellogenin synthesis

Summary The ultrastructure of the fat body of Aedes aegypti was followed from emergence through a blood meal. Changes in the volume of protein granules and lipid droplets were also examined. The relationship of these events to the known endocrinology of vitellogenin synthesis in mosquitoes is discussed.Massachusetts Experiment Station Paper No. 2130. Supported by the Massachusetts Agricultural Experiment Station, Project n° 356, and by NIH grant n° AI-11909     

The Gr family of candidate gustatory and olfactory receptors in the yellow-fever mosquito Aedes aegypti

The gustatory receptor (Gr) protein family contains most of the diversity in the insect chemoreceptor superfamily, including within it not only taste receptors but select olfactory receptors as well. Manual annotation of the Gr family in the genome sequence of the yellow-fever mosquito, Aedes aegypti, yielded a total of 114 potential proteins encoded by 79 genes. In the sequenced genome, 23 of these genes and protein isoforms are pseudogenic, leaving 91 putatively functional Grs. Comparison with our previously published set of 76 Grs encoded by 52 genes in the distantly related Anopheles gambiae mosquito revealed 13 new AgGrs encoded by 8 genes. Phylogenetic analysis reveals the conservation of carbon dioxide, sugar, and several orphan receptors in these 2 mosquitoes and Drosophila flies. On the other hand, most of these Grs are unique to mosquitoes and many are specific to the Aedes or Anopheles lineages, indicating their involvement in mosquito-specific aspects of both gustatory and olfactory perception. In particular, most instances of alternative splicing in orthologous loci appear to have evolved after the culicine-anopheline split +/-150 million years ago.     

Aedes aegypti oviposition in response to NPK fertilizers

Fertilizers are mineral associations intended to bring to the plants nutritive complements necessary to their growth. Modern fertilizers (NPK) combine the three basic elements which are the nitrogen (N), phosphorus (P) and potassium (K). In this study, we investigated in tunnel apparatus the influence of aqueous solutions containing low, moderate and high concentrations of NPK on the oviposition of Aedes aegypti. The results showed that the solutions containing moderate concentrations (NK = 17-33 mg/l and P = 23-47 mg/l) attracted significantly more gravid females than distilled water (P < 0.001). Conversely, the solutions containing either low or high concentrations of NPK (NK = 8 mg/l and P = 12 mg/l; NK = 50 mg/I and P = 70 mg/l) did not induce significant attraction (P > 0.05). These findings suggest that NPK fertilizers may influence the egg-laying behaviour of Ae. aegypti in field situations.     

Lipid metabolism during sequential gonotrophic cycles in large and small female Aedes aegypti

The lipid metabolism was investigated during six gonotrophic cycles of Aedes aegypti. Females of constant body size were analyzed for their total lipid content: large females with a body size of 41.06 (wing length cubed) and small females with 15.63. Their lipid contents at eclosion were compared to lipid values after two days of sugar-feeding, shortly before a blood meal, after oviposition, of their total egg batches, and again before the next blood meal, with intermittent access to sugar for two days for six gonotrophic cycles.Large females transferred most of their pre-blood meal lipid into the ovaries. Their low lipid content after oviposition was restored by synthesis from intermittent sugar meals. After the third gonotrophic cycle, they withheld more and more of the resynthesized lipid in their fat body, thus gradually reducing their fecundity. Since blood consumption was not altered significantly during these six cycles, age-related reduction of fecundity was clearly caused by limitations of yolk lipid.Small females transferred a considerably smaller, but constant segment of sugar-derived lipids to the ovaries. In both size classes, lipid content per oocyte was constant throughout all cycles with 9 mcal/oocyte in large and 7 mcal/oocyte in small females. Total fecundity reached 450 eggs in large and 280 eggs in small females. Large females that were maintained on water without sucrose took large blood meals from which part of the yolk lipid was synthesized. Extrapolations suggest that only one or two additional gonotrophic cycles would be possible without additional carbohydrate sources, despite lipogenesis from blood protein.     

白纹伊蚊和埃及伊蚊对基孔肯雅病毒的易感性和传播性的研究

用４株基孔肯雅病毒经口感染白纹伊蚊和埃及伊蚊,进行了易感性和传播性的研究。结果表明,这两种蚊虫对基孔肯雅病毒易感。无论白纹伊蚊或埃及伊蚊,感染后第５－６天即可通过吸血将病毒传播给乳鼠,至第８－１３天,传播率可高达５５．５５％－１００％。感染蚊亦可经叮咬将病毒传播给小鸡。埃及伊蚊的易感性和传播率高于白纹伊蚊。实验还发现,不同来源毒株之间存在一定差异,如分离自云南白纹伊蚊的Ｍ８１株的感染率和传播率均高于其它毒株。这些结果表明,白纹伊蚊和埃及伊蚊在基孔肯雅病毒的保存和传播中起重要作用。