Nitrogen partitioning and blood meal utilization by Aedes aegypti (Diptera Culicidae)

The utilization of the blood meal by mosquitoes was investigated by first feeding females quantities of blood ranging from 1 to 5 mg, and then analyzing the faeces for the various by-products of protein catabolism that were subsequently eliminated. The nitrogeneous waste products in order of importance were uric acid, histidine, ammonia and arginine. Only traces of the other amino acids were excreted.The total amount of each faecal substance varied linearly with the quantity of blood ingested, however their relative proportions did not change. Regardless of blood meal size the quantily of uric acid and ammonia produced indicates that about 80% of the non-histidine and arginine amino acids are deaminated and utilized for metabolic purposes other than egg protein synthesis.Most of the histidine and about one half of the arginine content of the blood were excreted as free amino acids, but the other amino acids were lost in trace amounts.Nineteen per cent of the total ingested amino acids was incorporated into soluble yolk proteins and this proportion was constant even for small blood meals that result in a reduction in the numbers of eggs produced.The comparative aspects of nitrogen partitioning and blood meal utilization by haematophagous insects, as well as the factors that affect blood meal utilization and fecundity in A. aegypti are discussed.     

Arrest, resorption, or maturation of oöcytes in Aedes aegypti: dependence on the quantity of blood and the interval between blood meals

ABSTRACT. After emergence, the follicles of A. aegypti double in length and the oöcytes may deposit a small amount of yolk, but within 2 days growth is arrested. Renewed growth and vitellogenesis, as well as the number of eggs finally produced, depends on the quantity of blood ingested. All females, given either a small (1 μl) or large (4 μl) meal of rat blood by enema, began yolk deposition in a nearly equal number of oöcytes, and each oöcyte had about the same amount of yolk 8 h later. Within 48 h, females fed 4 μl had each produced more than 100 eggs, whereas females fed 1 μl either had continued yolk deposition in some oöcytes, while most degenerated, or had all re-entered oögenic arrest. Consequently, 48 h after the 1 μl meal, a female had either c. 50 or 0 eggs. Even by 14 h after a 1-μl meal, females were either committed to re-enter oögenic arrest or to complete maturation of some oöcytes and resorb the yolk of others. This was shown by removing and examining one ovary 14 h after a blood meal and then giving a second blood meal. The second meal stimulated meal maturation in the remaining ovary, but only in those females whose oöcytes had been in oögenic arrest when the first ovary was examined; the second meal had no effect on females whose first ovary had contained both vitellogenic and degenerating oöcytes. Oösorption was not reversed by a second blood meal. Our results do not support the hypothesis that the female 'evaluates' the ingested meal and begins vitellogenesis in an 'appropriate' number of oöcytes. The results demonstrate that the ovary is an unreliable indicator of the frequency of blood-feeding, when females take a small meal.     

Relationship between protein and proteolytic activity in the midgut of mosquitoes.

In female mosquitoes anal injections (enemas) of nutrient solutions were administered in measured amounts to allow direct comparison of protease activities.The amount of protein ingested had a pronounced effect upon the rate of protein digestion, but had little influence upon the rate of protease secretion. Maximal protease activity increased only slightly with increasing meal size and always coincided with the digestion of about 80 per cent of the protein ingested.The use of the enema technique provided an experimental means to reject clearly a neural stimulus for protease secretion. Proof is given for a secretagogue stimulus: the presence of globular proteins with a minimal molecular weight is required for protease secretion.Despite antitryptic factors which are known to occur in different titres in vertebrate bloods, no inhibition was observed in vivo when proteases were recorded after enemas of blood or plasma from several hosts into Aedes aegypti, Anopheles quadrimaculatus, and Culex pipiens quinquefasciatus.Mosquito trypsin was shown to account for about 75 per cent of the proteolytic activity in midgut homogenates. Chymotrypsin was present although with very low activity. Calcium did not stimulate mosquito trypsin as it does mammalian trypsin. Between 22 and 32°C a Q₁₀ of 2·0 was observed for proteases as well as for protein digestion.     

Effects of blood meal source on food resource use and reproduction in Triatoma patagonica Del Ponte (Hemiptera,Reduviidae)

Triatoma patagonica (Del Ponte, 1929) (Hemiptera‐Reduviidae) is a peridomestic vector of Chagas disease that has been frequently found colonizing peridomestic structures in several localities in Argentina. Studying relationships between feeding and reproductive factors is important because these traits regulate population density and define vectorial capacity. Since T. patagonica can circulate among peridomestic structures taking blood from both bird and mammal hosts, we evaluated the extent to which different blood meal sources affect food resource use and reproductive parameters. We used 5^th instar nymphs and females that fed on either guinea pigs or pigeons to estimate food resource use. We estimated reproductive parameters in adults that fed on these sources. Nymphs and adults showed differences in blood consumption between feeding sources. Females fed on pigeons ingested more blood and needed a higher amount of blood to produce an egg than females fed on guinea pigs. There were no differences in the number of eggs laid and hatched between insects fed on different feeding sources. The higher amount of blood ingested and consumed by T. patagonica fed on pigeons did not translate into higher fecundity or fertility. The lower amount of guinea pig blood ingested was offset by its high nutritional quality.     

Metabolic response to feeding in the Chinese striped-necked turtle, Ocadia sinensis

We measured oxygen consumption in juvenile Chinese striped-necked turtles (Ocadia sinensis) after they ingested food, either as a single meal or as double meals, to examine the influence of meal type and feeding frequency on specific dynamic action (SDA). Temporal variation in oxygen consumption after feeding was evident in the ingesting turtles but not in the unfed control turtles. In the single-meal experiment, the peak metabolic rate and the integrated SDA response (the whole energetic cost for the processes of digestion) both did not differ between turtles ingesting mealworms and shrimps when the influence of variation in ingested energy was removed, and the time to reach peak metabolic rate was not affected by meal type and the amount of food ingested. Turtles in the double-meal experiment ingested more energy and hence had a prolonged duration of SDA response than did those in the single-meal experiment, but the integrated SDA response did not differ between both experimental treatments when the influence of variation in ingested energy was removed. Our results show that meal type and feeding frequency have important consequences on the SDA response of juvenile O. sinensis. As the integrated SDA response remained remarkably constant either between turtles ingesting different food or between turtles ingesting the same food but at different frequencies when the influence of variation in ingested energy was removed, we therefore conclude that the energetic cost associated with ingestion is primarily determined by energy content of food ingested in juvenile O. sinensis.     

Plant secondary metabolites alter the feeding patterns of a mammalian herbivore (<Emphasis Type="Italic">Neotoma lepida</Emphasis>)

Mammalian herbivores are predicted to regulate concentrations of ingested plant secondary metabolites (PSMs) in the blood by modifying the size and frequency of feeding bouts. It is theorized that meal size is limited by a maximum tolerable concentration of PSMs in the blood, such that meal size is predicted to decrease as PSM concentration increases. We investigated the relationship between PSM concentration in the diet and feeding patterns in the herbivorous desert woodrat (Neotoma lepida) fed diets containing phenolic resin extracted from creosote bush (Larrea tridentata). Total daily intake, meal size and feeding frequency were quantified by observing the foraging behavior of woodrats on diets containing increasing concentrations of creosote resin. Desert woodrats reduced meal size as resin concentration in the diet increased, resulting in an overall reduction in daily intake and regulation of resin intake. Moreover, desert woodrats were able to detect resin concentrations in the diet and regulate the intake of resin very rapidly. We suggest that the immediate and sustained ability to detect and regulate the intake of resin concentrations during each foraging bout provides a behavioral mechanism to regulate blood concentrations of resin and allows desert woodrats to make “wise” foraging decisions.     

Dynamics of vitellogenin uptake in Aedes aegypti as demonstrated by trypan blue

Trypan blue has been shown to be a reliable indicator of the micropinocytotic uptake of vitellogenin by developing oöcytes. Trypan blue was injected into the mosquito Aedes aegypti to determine at what times after the blood meal vitellogenin was taken up. Histological sections examined by light microscopy showed that trypan blue began to be sequestered from 2 to 5 hr after the blood meal. Any association between dye and ovariole ended from 39 to 42 hr after the blood meal, in which period no dye was incorporated into spheres of yolk protein. Of the times investigated in this experiment, the greatest amount of dye was seen in the oöcyte at 24 hr after the blood meal. The onset and conclusion of trypan blue uptake correspond with the related events in the synthesis of vitellogenin by the fat body. The presence of trypan blue in occasional interfollicular spaces suggests that the route of entry of vitellogenin in Aedes aegypti is indeed an interfollicular one.     

An iterative learning strategy for the auto-tuning of the feedforward and feedback controller in type-1 diabetes

This paper proposes a scheme for the control of the blood glucose in subjects with type-1 diabetes mellitus based on the subcutaneous (s.c.) glucose measurement and s.c. insulin administration. The tuning of the controller is based on an iterative learning strategy that exploits the repetitiveness of the daily feeding habit of a patient. The control consists of a mixed feedback and feedforward contribution whose parameters are tuned through an iterative learning process that is based on the day-by-day automated analysis of the glucose response to the infusion of exogenous insulin. The scheme does not require any a priori information on the patient insulin/glucose response, on the meal times and on the amount of ingested carbohydrates (CHOs). Thanks to the learning mechanism the scheme is able to improve its performance over time. A specific logic is also introduced for the detection and prevention of possible hypoglycaemia events. The effectiveness of the methodology has been validated using long-term simulation studies applied to a set of nine in silico patients considering realistic uncertainties on the meal times and on the quantities of ingested CHOs.     

Plasmodium gallinaceum: ookinete formation and proteolytic enzyme dynamics in highly refractory Aedes aegypti populations

Despite significant progress in the identification of the genetic basis of the refractory phenotype, little is known about the physiological mechanism of refractoriness. This study therefore examined the physiological basis of mosquito refractoriness in the Aedes aegypti/P. gallinaceum system, in which a selected refractory strain does not permit Plasmodium oocyst formation. We examined the kinetics of two major proteolytic enzymes involved in blood meal digestion and the dynamics of ookinete formation for two refractory populations (strains Moyo-R and Formosus) and one susceptible population (strain Red). Healthy ookinetes were observed in both the susceptible and the refractory populations, although the susceptible population generally exhibited higher enzymatic activity for trypsin and aminopeptidase than the refractory populations. Parasite numbers in the susceptible Red population showed a 4- to 7-fold decrease in abundance during the transition from the ookinete stage to the oocyst stage, far less than the refractory populations (30- to 92-fold reduction). Due to its smaller body size, Moyo-R individuals generally ingest a smaller blood meal and thus intake fewer gametocytes than Red individuals. Thus, the possibility that refractoriness in the Moyo-R population results from fewer gametocytes being ingested is examined. We found that the Red population remained highly susceptible and the Moyo-R population stayed refractory when those individuals with similar blood meal size were compared. We conclude that failure of oocyst development in the refractory mosquitoes is not due to ookinete damage by proteolytic enzymes or to fewer gametocytes being ingested, but rather is due to a midgut barrier or to some other mechanism.     

Metabolic response to feeding in the Chinese striped-necked turtle, Ocadia sinensis

We measured oxygen consumption in juvenile Chinese striped-necked turtles (Ocadia sinensis) after they ingested food, either as a single meal or as double meals, to examine the influence of meal type and feeding frequency on specific dynamic action (SDA). Temporal variation in oxygen consumption after feeding was evident in the ingesting turtles but not in the unfed control turtles. In the single-meal experiment, the peak metabolic rate and the integrated SDA response (the whole energetic cost for the processes of digestion) both did not differ between turtles ingesting mealworms and shrimps when the influence of variation in ingested energy was removed, and the time to reach peak metabolic rate was not affected by meal type and the amount of food ingested. Turtles in the double-meal experiment ingested more energy and hence had a prolonged duration of SDA response than did those in the single-meal experiment, but the integrated SDA response did not differ between both experimental treatments when the influence of variation in ingested energy was removed. Our results show that meal type and feeding frequency have important consequences on the SDA response of juvenile O. sinensis. As the integrated SDA response remained remarkably constant either between turtles ingesting different food or between turtles ingesting the same food but at different frequencies when the influence of variation in ingested energy was removed, we therefore conclude that the energetic cost associated with ingestion is primarily determined by energy content of food ingested in juvenile O. sinensis.     

Correlation between digestion rate and feeding frequency in the stomachless teleost, Blennius pholis L.

Foregut emptying in Blennius pholis at 16–18°C is exponential ( S_t = S_o e^-Rt; R=0.006 when t is in min and s in mg dry weight). In consequence, the time for the foregut to empty completely varies in proportion to ln (meal size) in a chosen size of fish or to ln (body weight) in different sized fish fed to the same relative amount (% body weight). Appetite returns rapidly in comparison with other species (4–15 h for fish of 0.5−30 g) and, because of the tidal constraints imposed on this littoral fish, voluntarily ingested meals are large (14–9% body weight depending on fish size). Studies on digestion in small, stomachless fish are not adequately made using X-radiography and must be supported by sequential gut samples after a meal.     

NMDA receptor participation in control of food intake by the stomach

We previously reported that MK-801 (dizocilpine), an antagonist of N-methyl-D-aspartate (NMDA)-type glutamate receptors, increased meal size and duration in rats. MK-801 did not increase sham feeding or attenuate reduction of sham feeding by intraintestinal nutrient infusions. These results suggested that the MK-801-induced increase in meal size did not depend on antagonism of postgastric satiety signals. Consequently, we hypothesized that the NMDA antagonist might increase food intake by directly antagonizing gastric mechanosensory signals or by accelerating gastric emptying, thereby reducing gastric mechanoreceptive feedback. To test this hypothesis, we recorded intake of 15% sucrose in rats implanted with pyloric cuffs that could be closed to prevent gastric emptying. Sucrose intake was increased when the pyloric cuffs were open, allowing the stomach to empty. However, intake was not increased when the pyloric cuffs were inflated, causing gastric retention of all ingested sucrose. Direct measurements of gastric emptying revealed that MK-801 accelerated the emptying of 5-ml loads of 0.9% NaCl and 15% sucrose. Furthermore, MK-801 also accelerated the rate of emptying of freely ingested sucrose regardless of the volume ingested. Taken together with our previous findings, these results indicate that blockade of NMDA receptors with MK-801 does not increase food intake by antagonizing gastric mechanosensation. Rather, it accelerates gastric emptying, and thereby may indirectly reduce gastric mechanoreceptive cues, resulting in prolongation of eating. Modulation of gastric emptying rate by NMDA receptors could play an important role in the control of meal sizes.     

Changes in the hemolymph of the stable fly,Stomoxys calcitrans,after a blood meal

The stable fly hemolymph was analyzed after a blood meal. The hemolymph volume increased to approximately three times the pre-feeding level 3–6 h after a blood meal and gradually returned to normal 18 h after the blood meal. The osmotic pressure decreased approximately 10% following a blood meal and gradually returned to normal with a pattern that was a mirror-image of that of the hemolymph volume. Concentrations of cations and anions are not directly affected by the ingested blood, indicating a possible selective excretory mechanism.     

Leucine aminopeptidase,HlLAP, from the ixodid tick Haemaphysalis longicornis,plays vital roles in the development of oocytes

Female ixodid ticks are amazing invertebrate animals which efficiently convert a large amount of nutrients derived from their ingested blood meals into eggs. Although oocyte development (vitellogenesis) in ticks is triggered by a blood meal and is assumed to be supported by nutrition derived from ovarian cells connecting oocytes, little is known about the ovarian molecules processing nutrient materials for the vitellogenesis. In this study, we have suggested a putative function of leucine aminopeptidase (HlLAP) in the ovary of parthenogenetic adult ixodid tick Haemaphysalis longicornis regarding a negative output of reproduction following disruption of HlLAP gene by RNA interference. Endogenous HlLAP was shown to be localized in the ovarian cells, including ovarian epithelial and pedicel cells which were assumed to provide nutrients for the developing oocytes. Histological studies demonstrated that a majority of immature oocytes in HlLAP gene knockdown ticks were transformed into abnormal morpho-histological oocytes with vacuolated cytoplasm and/or condensed nucleus. Taken together, a reduction of the numbers of laid eggs in the HlLAP gene knockdown ticks may be due to the degeneration of immature oocytes following deprivation of nutrients such as amino acids supplied not only by midgut HlLAP but also by the ovarian HlLAP. Regulation of the tick molecules involved in nutrient metabolism for the reproduction, including blood digestion and vitellogenesis, would help in controlling the tick population and tick-borne pathogens.     

Characteristics of boli formed by dairy cows upon ingestion of fresh ryegrass,lucerne or chicory

This study examined the comminution of fresh herbage, subsequent nutrient release, and the characteristics of swallowed boli from three physically and chemically contrasting forages during ingestive mastication by dairy cows. The extent and pattern of nutrient release will determine their availability to rumen microflora, and potentially influence their efficiency of use. The forages evaluated were perennial ryegrass (ryegrass, Lolium perenne L., cv Alto AR37), lucerne (Medicago sativa L., cv Torlesse) and chicory (Cichorium intybus L., cv Choice). Experimental design was a 3×3 cross-over with three forages and three consecutive 1-day measurement periods, conducted twice. Six non-lactating, pregnant, multiparous Holstein-Friesian×Jersey cows (Bos taurus) were used, with the first cross-over applied to three mature (10.1±0.61 years old; BW 631±64 kg) cows, and the second to three young (4.8±0.02 years; BW 505±19 kg) cows. Fresh cut forage was offered to the cows following partial rumen evacuation. Swallowed boli were collected directly at the cardia at the commencement, middle and end of the first feeding bout of the first meal of the day. Forage species did not affect the fresh weight of ingested boli (mean 169 g, P=0.605) but the proportion of saliva in boli varied between forage. Boli of chicory contained the greatest amount of herbage material and least amount of saliva, whereas ryegrass boli were the opposite. Boli fresh weight tended to increase as time in the meal progressed, but the age of the cow was not shown to affect any boli characteristics or nutrient release. Particle size reduction was affected by forage, with 31%, 38% and 35% of chicory, lucerne and ryegrass herbage reduced to <2 mm. There was little evidence of relationship between comminution and any physical or chemical characteristic of the forage, except in ryegrass where extent of comminution was moderately correlated with herbage strength. Proportional release of herbage soluble carbohydrate exceeded that of N during mastication. Differences in loss of N were moderately correlated with the amount of N in the herbage (R²=0.53) but herbage comminution was not strongly correlated with release of either N or carbohydrate. These findings illustrate the complex animal×forage interactions that occur during mastication, and that it is not possible to infer nutrient loss from herbage based on herbage characteristics as the driver for this differ between species.     

Effects of azadirachtin on oogenesis in Aedes aegypti

ABSTRACT. . Azadirachtin in blood fed to adult female Aedes aegypti through an artificial membrane does not cause feeding inhibition over a wide dose range (0–200 ng/female), and high doses of ingested azadirachtin fail to inhibit or delay oviposition. However, significant, transient retardation of oocyte growth is observed for up to 72 h after feeding. Immature oocytes are observed in 86% of azadirachtin-fed females decapitated 10 h after a blood meal, whereas 96% of decapitated control females contain maturing oocytes. This suggests that azadirachtin delays the release of one or more factors from the head that regulate oogenesis. We propose that adult females overcome the effect of azadirachtin by rapid metabolism rather than by excretion of the compound, since by 2 h after a blood meal, only 0.1% of ingested azadirachtin was recovered from excreta and 5% recovered from the body.     

Mechanical and biochemical components of apparent specific dynamic action in largemouth bass, Micropterm salmoides Lacéepède

Apparent SDA was defined as the energy expenditure associated with the ingestion of a meal. In the present study apparent SDA was equated to an increase in oxygen consumption above the postabsorptive level subsequent to the ingestion of a meal. The energy cost for physically processing a meal, mechanical SDA, was equated to the oxygen uptake associated with the ingestion of non-digestible cellulose. The energy utilized by anabolic and catabolic processes associated with the ingestion of a standard diet was identified as biochemical SDA. Apparent, mechanical and biochemical SDA were each positively related to the energy intake of the standard diet. Apparent SDA expressed relatively to energy ingested equalled 10·5% and was independent of the caloric content of the meal. Mechanical SDA increased asymptotically with ingested meal size and energy content. Relative to apparent SDA, mechanical SDA decreased with meal size, suggestive of an enhancement in efficiency. Biochemical SDA rose exponentially with increase in ingested energy, reflective of the cost for growth and catabolism.     

Meal size and frequency: effect on potentiation of the thermal effect of food by prior exercise

Prior exercise potentiates the thermic effect of a carbohydrate meal. The purpose of this study was to determine if meal size or feeding pattern influences this response. Two groups of healthy, normal-weight young women exercised for 45 min on a cycle ergometer at 70% of maximal aerobic capacity. Once aerobic capacity returned to pre-exercise baseline, the thermic effect of food (TEF) was determined by indirect calorimetry over a 2-h period. One group of subjects ingested a 2510-kJ meal and the other a 5020-kJ meal. As a control, subjects ingested the test meal without prior exercise. In addition, subjects ingesting the 5020–kJ meal were studied for an additional 2 h. In a separate trial, these subjects ingested a 5020-kJ meal in two equal portions after a bout of exercise, the second portion 120 min after the first. TEF was less for the 2510-kJ meal compared with the 5020-kJ meal for both the control [mean (SE), 76 (17) vs 158 (19) kJ · 2h^–1,P < 0.01), and prior exercise [124 (23) vs 197 (24) kJ · 2h^–1,P<0.01) trials. However, the same increment in TEF resulted from the prior bout of exercise [48 (9) vs 40 (8) kJ · 2h^– for 2510-and 5020-kJ meals, respectively). TEF was 31 % lower when the 5020-kJ meal was given in two portions compared with one [281 (30) vs 369 (41) kJ · 4h^–1, P < 0.05]. No difference in TEF was found between the first and second 2510-kJ portion. The results suggest that potentiation of TEF by prior exercise is not influenced by caloric density or energy content of the meal. Rather, meal volume and hence meal frequency is a greater determinant of postexercise TEF.     

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.