Antagonistic effects of energy status on meal size and egg-batch size of Aedes aegypti (Diptera: Culicidae).

The effect of sugar feeding on egg-batch size in Aedes aegypti was examined in a way that would distinguish between the roles of a recent sugar meal (full vs. empty crop) and of repeated sugar feeding and digestion (high vs. low energy reserves). Egg numbers of females representing the four combinations of these characteristics (full crop/high reserves, full crop/low reserves, empty crop/high reserves, empty crop/low reserves) were counted during their first gonotrophic cycle. In addition, the sizes of their replete sugar meals and human blood meals were measured to understand the interactions between them. Results demonstrated that blood-fed mosquitoes with full crops and low energy reserves produced the fewest eggs (mean = 56.2); those with empty crops and high energy reserves produced the most eggs (mean = 84.6); and those with the opposite combinations (full/high and empty/ low) had an intermediate fecundity (mean = 75.2 and 76.9, respectively). This ranking of fecundities did not correspond to blood-meal size ranks, owing to direct and indirect effects of energy reserves on meal sizes and egg number. Full-crop females with low reserves ingested the smallest blood meals (mean = 0.62 mg) and had the lowest fecundities. Full-crop females with high reserves ingested more blood (mean = 0.82 mg) and produced more eggs. But empty-crop females with low reserves ingested the largest blood meals (mean = 1.19 mg), yet produced significantly fewer eggs than their high-reserve counterparts, which took smaller blood meals (mean = 0.99 mg). These results demonstrate extremes in the reproductive penalty of crop sugar and the reproductive reward of digested sugar. Energy reserves and an empty crop are similarly valuable in promoting fecundity at the time blood is taken.     

Energy metabolism during diapause in Culex pipiens mosquitoes

Diapause in overwintering adult female Culex pipiens mosquitoes plays an important role in the transmission of West Nile and other encephalitis-inducing flaviviruses. To investigate the dynamic metabolic processes that control Cx. pipiens diapause, we used radioactive tracer techniques with [¹⁴C]-glucose to investigate the metabolic fate and flux of glucose in adult mosquitoes reared under diapause (18 °C, short day) and non-diapause (27 °C, long day) conditions. We found that by 72 h post-¹⁴C-labeling of 1-day-old mosquitoes, the diapause-destined mosquitoes had converted 46% more ¹⁴C-labled glucose into ¹⁴C-labled lipid than mosquitoes reared under non-diapausing conditions. When 5-day-old mosquitoes were fed [¹⁴C]-glucose, and then switched to water only, the non-diapausing mosquitoes oxidized nearly three times more ¹⁴C-labled glycogen and lipid by day 7 than diapausing-mosquitoes. This increased energy expenditure in non-diapausing mosquitoes is most likely due to temperature- and light-dependent increases in the basal metabolic rate. Amongst the diapausing-mosquitoes we analyzed over a subsequent 7-week period, we found that the amount of ¹⁴C-labeled glycogen decreased steadily for the first month of diapause, whereas, ¹⁴C-labeled-lipid levels were not significantly decreased until after day 35 of diapause, indicating that flux through glycogenolysis is higher than lipolysis during the first month of diapause. Lastly, our analysis revealed that 38% of the initial ¹⁴C-labled lipid that was synthesized during the adult pre-diapause phase was still present following the first gonotrophic cycle. About 33% of this remaining ¹⁴C-labeled lipid was localized to the newly developed eggs, suggesting that lipid sparing processes during a minimal 7-week long diapause may enhance egg production.     

The effect of larval and adult nutrition on successful autogenous egg production by a mosquito

Females of most mosquito species require a blood meal to provision eggs and can be medical problems because of this dependency. Autogenous mosquitoes do not require blood to mature an initial egg batch and, instead, acquire nutrients for egg provisioning as larvae. We studied the importance of larval and adult nourishment for Ochlerotatus atropalpus which is obligatory autogenous for its first egg cycle but may ingest blood for subsequent cycles. Larval nourishment strongly influenced autogenous egg production: female larvae that were nutritionally stressed emerged as smaller adults, produced fewer eggs and emerged with less protein, lipid and glycogen stores. Female Oc. atropalpus are 100% autogenous, regardless of larval diet quality or whether females are fed sugar or water at emergence. Upon completion of the first egg batch, only females emerging from a poor larval diet ingested blood and produced a second egg batch.     

Metabolic fate of [14C]-labeled meal protein amino acids in Aedes aegypti mosquitoes

We developed a method to follow the metabolic fate of [(14)C]-labeled Euglena gracilis protein amino acids in Aedes aegypti mosquitoes under three different adult nutritional regimes. Quantitative analysis of blood meal protein amino acid metabolism showed that most of the carbon of the amino acids was either oxidized to CO(2) or excreted as waste. Under the three different adult nutritional regimes, no significant differences in the metabolism of amino acids were found, which indicated that the female A. aegypti mosquitoes possess a substantial capacity of maintaining metabolic homeostasis during a gonotrophic cycle. The amount of maternal glycogen and lipid after egg laying were significantly lower in the mosquitoes that underwent a partial starvation before a blood meal and/or starvation after the blood meal. The content of egg lipid or protein or the number of eggs laid did not show a significant difference among the three different regimes, which indicates that stable fecundity of A. aegypti under the partial starvation before a blood meal and/or starvation after the blood meal seemed to result from a trade-off between current fecundity and future survival after the eggs laid. The methods described in this paper can be applied to a wide range of questions about the effects of environmental conditions on the utilization of blood meal amino acids.     

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.     

Effect of body size on energy reserves in Culex pipiens pallens females (Diptera: Culicidae)

We examined the relationship between body size and energy reserves of female Culex pipiens pallens under laboratory conditions. Small and large‐sized adult mosquitoes were obtained from larvae reared at different densities. There was a significantly positive relationship between pupal body weight and adult wing length depending on body sizes. Studies showed large females contained significantly higher contents of glycogen and lipid but lower protein stores in comparison to small females. Large sized mosquitoes accumulated higher percentages of glycogen (21.2% vs 15.9%) and lipid (45.8% vs 30.7%) but lower levels of protein (33.0% vs 53.4%) than small females. This result suggests that larval‐derived glycogen and lipid stores may be important in determining the body size of female Cx. pipiens pallens.     

Feeding strategies of anthropophilic mosquitoes result in increased risk of pathogen transmission

Vector-borne disease specialists have traditionally assumed that in each egg-laying cycle mosquitoes take a single bloodmeal that is used for egg development and feed on plant sugars for flight and production of energy reserves. Here we review research showing that for two of the most important vectors of human pathogens (Anopheles gambiae and Aedes aegypti) imbibing multiple bloodmeals during a gonotrophic cycle while foregoing sugar feeding is a common behaviour, not an exception. By feeding preferentially and frequently on human blood these species increase their fitness and exponentially boost the basic reproduction rate of pathogens they transmit. Although the epidemiological outcome is similar, there are important differences in processes underlying frequent human contact by these species that merit more detailed investigation.     

Physiological aspects of multiple blood feeding in the malaria vector Anopheles tessellatus

The malaria vector Anopheles tessellatus is able to take several blood meals in a gonotrophic cycle. The fecundity is largely dependent on the first blood meal and is not generally increased by subsequent blood meals during a gonotrophic cycle. Larval rearing densities influenced adult body size. There is an inverse relationship between wing length and larval rearing densities. Smaller mosquitoes produced from larvae reared at higher densities had reduced body reserves of protein, lipid and carbohydrates. At emergence, ovarian development in An. tessellatus is in the previtellogenic stage and it remained at this stage until the intake of a blood meal. The number of ovarian follicles is related to wing length and, irrespective of adult body size, An. tessellatus developed oocytes to maturity with a single blood meal. This is attributed to the availability of metabolic reserves above the threshold level required for further development of oocytes. Mosquitoes that took more than one blood meal had largely digested their previous blood meal and had ongoing vitellogenesis. Blood meals subsequent to the first one apparently contribute mainly to increasing metabolic reserves. The stimulus for a second and third blood meal in An. tessellatus appears to be completion of the digestion of the previous blood meal. There was no evidence that multiple blood meals taken in the first gonotrophic cycle influenced fecundity significantly in the second cycle.     

Effects of Plasmodium yoelii nigeriensis infection on Anopheles stephensl egg development and resorption

Abstract It has been shown previously that infection with Plasmodium yoelii nigeriensis reduces the number of eggs produced by female Anopheles stephensi. Here we examine the mechanism underlying fecundity reduction. Ovaries from infected and uninfected (control) female mosquitoes were examined12, 24 or 36 h after blood-feeding during the first gonotrophic cycle (replicated) or the second gonotrophic cycle (unreplicated). Follicular development was assessed according to Christophers' stages and the proportions of developing and resorbing follicles per ovary were determined. Resorption of some follicles commenced within 12h of blood-feeding, affecting significantly more follicles in the infected females: 1.1% v. 3.2%. The difference was greatest 36h after blood-feeding: 25% reduction (10 v. 35%) in the first cycle; 16% reduction (9 v. 25%) in the second gonotrophic cycle. The mean speed of oogenesis was also found to be significantly retarded in infected mosquitoes. During the second gonotrophic cycle, for example, only 92–94% of follicles reached stage III by 24 h and stage IV by 36 h in infected females, whereas all the developing follicles of uninfected females reached these stages more or less synchronously in the time specified.     

Quantitative seasonal changes in the protein, lipid and energy content of the carcass, ovaries and liver of adult female plaice, Pleuronectes platessa L.

A detailed study was made of the seasonal changes in energy reserves in adult female plaice, Pleuronectes platessa L. The weights of lipid, protein, glycogen and ash in the carcass, liver and ovaries were measured in females approximately 35 cm long on ten occasions during one year. These data were converted to data for a'real'growing female by using a growth curve to take account of increasing length during the year. Growth of the whole body and of the body components was assumed to be isometric.
Plaice show a marked seasonal cycle of body weight and energy content. A six year old female plaice of 330 g, 32.6 cm long and with an energy content of 406 kcal in May, assimilates 560 kcal before December when it ceases to feed. Of this, 234 kcal is used to produce eggs, 159 kcal is used for metabolism during starvation, and the remainder 167 kcal, is used in growth. There is an increase in length to 35.9 cm and in weight to 462 g over the year. From December until March, when plaice do not feed but grow large ovaries, 40% of the protein in the body is utilised, 33% is devoted to egg production and 7% is metabolised to provide energy; 64% of the lipid is used, only 14% being used for egg production but 50% is metabolised for energy. Lipid supplies 75% of the energy for metabolism and so forms the major reserve; 42% of the energy assimilated during the year is devoted to reproduction. The main source of lipid and protein reserves is the carcass.     

Two stages of juvenile hormone-mediated growth of secondary follicles in Culex pipiens

To investigate the effect of juvenile hormone deprivation on the growth of secondary follicles during the second gonotrophic cycle, female mosquitoes, Culex pipiens L., were allatectomized daily after the first blood meal. Allatectomy on days 1–3 suppressed growth of secondary follicles indicating that juvenile hormone was required for a second gonotrophic cycle. When allatectomy was performed 4 days or more after the first blood meal, secondary follicles grew, indicating the presence of juvenile hormone. However, if mosquitoes were allatectomized before oviposition, only 25% developed a second batch of eggs after a second blood meal.Allatectomies performed 1 and 24 h after oviposition indicated that additional juvenile hormone was released after deposition of the first batch of eggs, and that this second release was needed for secondary follicles to complete previtellogenic growth. Thus, in C. pipiens, secondary follicles undergo two periods of juvenile hormone-mediated growth-one before and one after oviposition.     

Nectar feeding by the early-spring mosquito Aedes provocans

Abstract. Nectar feeding by males and females of the mosquito Aedes provocans was studied at a site near Belleville, Ontario, Canada. Canada plum, Prunus nigra , and especially pin cherry, P. pensylvanica , bloomed contemporaneously with the emergence of Ae. provocans and were important nectar sources for adult mosquitoes during their first week of life. Blossoms of P. pensylvanica shielded for 24 h from foragers produced an average of 0.14 mg of sugar (≅ 2.3 J). This nectar was avidly sought by both sexes of Ae.provocans; > 97% of the blossoms were visited by mosquitoes in the first few days of blooming. Young adult mosquitoes were found on blossoms at all hours of the day and night; feeding on P. nigra was strongly eocrepuscular, whereas on P.pensylvanica feeding was much less strongly periodic. Adults foraged for nectar in an energy-conserving, pedestrian strategy, devoting 56% (females) and 68% (males) of their time on blossoms to nectar feeding during foraging bouts that lasted a median of 5.3min. Both sexes sought nectar soon after emergence - males before they had completed hypopygial rotation or swarmed, and females before mating or host seeking. Female Ae.provocans sought nectar in all stages of oogenesis, but primarily at the initiation of a gonotrophic cycle. Energy stores in the crop averaged 18 J per female, with a distribution that depended on gonotrophic age and parity.     

Coordinated changes in JH biosynthesis and JH hemolymph titers in Aedes aegypti mosquitoes

Juvenile hormone III (JH) is synthesized by the corpora allata (CA) and plays a key role in mosquito development and reproduction. A decrease in JH titer during the last instar larvae allows pupation and metamorphosis to proceed. As the anti-metamorphic role of JH comes to an end, the CA of the late pupa once again synthesizes JH, which plays an essential role in orchestrating reproductive maturation. In spite of the importance of Aedes aegypti as a vector, a detailed study of the changes of JH hemolymph titers during the gonotrophic cycle has never been performed. In the present studies, using a high performance liquid chromatography coupled to a fluorescent detector (HPLC–FD) method, we measured changes in JH levels in the hemolymph of female mosquitoes during the pupal and adult stages. Our results revealed tightly concomitant changes in JH biosynthesis and JH hemolymph titers during the gonotrophic cycle of female mosquito. Feeding high sugar diets resulted in an increase of JH titers, and mating also modified JH titers in hemolymph. In addition these studies confirmed that JH titer in mosquitoes is fundamentally determined by the rate of biosynthesis in the CA.     

Juvenile hormone connects larval nutrition with target of rapamycin signaling in the mosquito Aedes aegypti

Anautogenous mosquitoes require blood meals to promote egg development. If adequate nutrients are not obtained during larval development, the resulting "small" sized adult mosquitoes require multiple blood meals for egg development; markedly increasing host-vector contacts and the likelihood of disease transmission. Nutrient-sensitive target of rapamycin (TOR) signaling is a key signaling pathway that links elevated hemolymph amino acid levels derived from the blood meal to the expression of yolk protein precursors in the fat body. Here we report that the blood-meal-induced activation of the TOR-signaling pathway and subsequent egg maturation depends on the accumulation of adequate nutritional reserves during larval development. We have established well-nourished, "standard" mosquitoes and malnourished, "small" mosquitoes as models to address this nutrient sensitive pathway. This regulatory mechanism involves juvenile hormone (JH), which acts as a mediator of fat body competence, permitting the response to amino acids derived from the blood meal. We demonstrate that treatment with JH results in recovery of the TOR molecular machinery, Aedes aegypti cationic amino acid transporter 2 (AaiCAT2), TOR, and S6 kinase (S6K), in fat bodies of small mosquitoes, enabling them to complete their first gonotrophic cycle after a single blood meal. These findings establish a direct link between nutrient reserves and the establishment of TOR signaling in mosquitoes.     

Size‐dependent insect flight energetics at different sugar supplies

Under most circumstances, large body size confers a higher fitness and is positively selected, whereas selection against large size is empirically poorly documented. Physiologically, according to the ¾ power law, larger animals have lower relative but higher absolute energy demands, such that large body size may become disadvantageous, particularly under fast locomotion in food‐limited environments. After a period of initial feeding on different sugar concentrations, we investigated size‐dependent energy content (reserves) at baseline and of females unflown (i.e. resting) or flown for 18 h in two (replicate) insect species: the yellow dung fly Scathophaga stercoraria and the yellow fever mosquito Aedes aegypti. Tethered adults of various sizes were tested in a flight mill. In both species, teneral glycogen, sugar, and lipid content increased with sugar availability, and isometrically or even hyper‐allometrically (slope > 1) with body size. Activity treatment also revealed the expected consumption effects. Both species increased their flight distance with sugar supply, although only larger mosquitoes flew longer. Crucially, larger females of both species disproportionately exhausted more glycogen and sugars (but not lipid) during flight. The mosquitoes appeared to adjust their flight more finely to their size‐dependent energy reserves at all sugar availabilities, whereas, in the dung flies, size‐dependent energy demands were detectable only with a low but not with an overly high sugar supply. Although we found a greater absolute and relative locomotory energy demand for the larger flies, which is in agreement with interspecific patterns in insects, this was (more than) compensated by their greater baseline energy reserves, resulting in the greater net flying capacity of larger individuals. Consequently, we found no evidence for energetic mechanisms limiting the performance of large flying insects under food limitation. The differences between the two species presumably relate to mosquitoes inherently being long distance flyers and dung flies being short distance flyers. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, ●● , ●●–●●.     

Changes in lipid and carbohydrate metabolism during starvation in adult Manduca sexta

Summary Adult Manduca sexta feed very irregularly in the laboratory, and many adult males never feed. Feeding adults live longer and feeding females lay many more eggs; however, in both feeding (sugar water) and starving adults a decrease of metabolic reserves is observed. Carbohydrates disappear from hemolymph and from fat body. Fat body lipid also decreases, while hemolymph lipid concentration increases strongly in starving adults. The activity of fat body glycogen phosphorylase increases strongly in starving adult M. sexta. The activity of glycogen phosphorylase is correlated inversely with hemolymph sugar concentration. Injected trehalose inactivates glycogen phosphorylase within 2 h, and lowers the hemolymph lipid level within 6 h. In starving adult M. sexta, neither the activation of glycogen phosphorylase nor the increase of hemolymph lipid concentration depends on adipokinetic hormone, since cardiacectomy does not prevent the activation of glycogen phosphorylase nor the increase of hemolymph lipid level.Abbreviations AKH adipokinetic hormone - EDTA ethylenediamine tetraacetate Present address: Department of Biochemistry and Center for Insect Science, The University of Arizona, Tucson, AZ 85721, USA     

Multiple blood meals in Anopheles darlingi (Diptera: Culicidae)

Anopheles darlingi is an important vector of human malaria in the Amazon. Adult females of this mosquito species require a blood meal to develop eggs, preferring humans to other blood sources. Although gonotrophic concordance has been described as the norm for An. darlingi, here we report An. darlingi female mosquitoes taking two or more blood meals within their first gonotrophic cycle. Only half of field‐captured adult females fed one blood meal developed follicles to Christophers' stage V. This outcome is dependent on larval nutrition, as 88% of laboratory‐raised well‐nourished females completed the first gonotrophic cycle with only one blood meal, while less nourished females needed additional blood meals. Half of the field‐captured blood‐seeking An. darlingi females had follicles in intermediate (IIIa and IIIb) and final (V) stages of the gonotrophic cycle, supporting the conclusion that An. darlingi blood feed more than once during a gonotrophic cycle. Additionally, we observed females attempting to blood feed a second time during the same day. Additional studies of An. darlingi biting behavior are necessary to accurately estimate Plasmodium sp. entomologic inoculation rates throughout the An. darlingi vast geographical distribution.     

登革Ⅱ型病毒经白纹伊蚊滞育卵的传递

采用C6/36细胞培养分离病毒的方法检测感染登革Ⅱ型病毒的白纹伊蚊Aedes albopictus滞育卵孵化的F₁代蚊虫感染率,从第一个生殖营养周期子代蚊虫中未分离到病毒,第二与第三生殖营养周期子代蚊虫最低感染率没有显著性差异（χ²=0.01,P＞0.0 5）,感染子代的批阳性率为9.1%,最低感染率为1∶330;间接免疫荧光检测结果表明感染登革Ⅱ型病毒的白纹伊蚊滞育卵孵化的子代成蚊能通过叮咬将登革病毒传播给敏感乳鼠。这些研究结果表明登革病毒能在媒介滞育卵内存活并传至子代,子代蚊虫能通过叮咬敏感宿主水平传播病毒。