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.     

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.     

Reproductive aspects of the mosquito Culex quinquefasciatus (Diptera:Culicidae) infected with Wuchereria bancrofti (Spirurida: Onchocercidae)

This study reports on the relationship between Wuchereria bancrofti infection and female body size, intake of blood and fecundity in the mosquito Culex quinquefasciatus, vector of this filarial parasite in Recife (Brazil). Adults from field collected larvae were infected via a membrane feeding procedure, using blood with parasitaemia ranging from 724-6,000 mf/ml. A positive correlation was observed between mosquito size (measured by wing length) and egg production in uninfected females. However, this relationship did not exist in W. bancrofti infected mosquitoes. This change is unlikely to be the result of changes in blood ingestion as no significant difference was found when infected and uninfected females were compared. Variation in egg production observed between trials could not be associated with parasite density in the blood. These results suggest infection with W. bancrofti may disrupt the relationship between mosquito size and egg production during the first gonotrophic cycle of C. quinquefasciatus such that fecundity is sometimes reduced. However, this overall affect is variable and many groups of mosquitoes do not respond in this way.     

Laboratory experiments on infection rates of Amblyospora dyxenoides (Microsporida: Amblyosporidae) in the mosquito Culex annulirostris

Laboratory observations were made of the microsporidian parasite Amblyospora dyxenoides in its natural mosquito host, Culex annulirostris. There were no differences in the numbers of eggs laid and in the proportions which hatched between infected and uninfected females, indicating that the parasite did not affect fecundity. Unlike other species of Amblyospora which have been studied the development of binucleate spores in adult mosquitoes increase with age of the host in both sexes and in females it proceeds independently of egg development and blood feeding. The same trend is apparent for adult mosquitoes which acquired the infection in the larval stage by horizontal transmission from the intermediate copepod host as well as for mosquitoes which acquired oenocytic infections by transovarial transmission. There was considerable variation in the proportion of mosquitoes which became infected after exposure to A. dyxenoides infected copepods. Infections in larval progeny of female mosquitoes infected via spores produced in copepods ranged from 0 to 100% in individual batches and averaged 45.6% with meiospore infections, 19.3% with oenocytic infections, with the remaining 35.7% being uninfected. Similar variability was observed in the progeny of infected female mosquitoes in the second generation after exposure to infected copepods. During experiments in which the microsporidium was maintained in C. annulirostris through 9 successive transovarially transmitted cycles (by selectively rearing the progeny of females infected with binucleate spores after an initial exposure to infected copepods) the proportion of infected progeny with oenocytic infections increased from 25 to around 50% whereas the incidence of meiospore infections declined from 50 to 10%.(ABSTRACT TRUNCATED AT 250 WORDS)     

Seasonal abundance, biting cycle and parity of the mosquito Haemagogus leucocelaenus in Trinidad, West Indies

Adult female populations of Haemagogus leucocelaenus (Dyar and Shannon), the sylvan vector of yellow fever, were monitored weekly during 1981–82 by human collectors on the ground at Point Gourde in Chaguaramas Forest, 16 km west of Port of Spain, Trinidad.
Hg.leucocelaenus showed only diurnal landing activity, from 06.00 to 18.00 hours (sunrise to sunset, universal time), with a single peak of activity between 10.00 and 14.00 hours.
Densities of Hg.leucocelaenus during the wet season (May–November) were about double the level recorded during the dry season (December–April).
Monthly parous rates averaged 53.9% (range 25–90%) and some females were up to five-pars. Retained eggs (range 2–6, mean 4/female) were found in the ovaries of 0.34% of landing females, all of which had stage 1 ovarian follicles for the next gonotrophic cycle. Therefore blood-feeding is not inhibited by egg retention. Hg. leucocelaenus vector potential is reappraised in the light of these findings.     

Age determination in the blackfly Simulium woodi, a vector of onchocerciasis in Tanzania

Abstract. Age-dependent changes in the ovarioles of Simulium woodi (Diptera: Simuliidae) and the age structure of a wild population of this species in the Amani hills of north-eastern Tanzania were studied using the ovarian oil injection technique. Contrary to previous theories, egg sacs degenerate completely and do not form dilatations. The physiological age of the females could be determined only by gonotrophic dilatations formed from degenerating follicles during gonotrophic cycles. In individual females, the proportions of ovarioles with degenerating follicles were 3–54% (mean 22%) in the first cycle and 8–61% (mean 36%) in the second gonotrophic cycle. Agonotrophic degenerating follicles occurred in 2% of ovarioles in 12% of females. Additional information with regard to the degree of parity is given by the level of granulation in the basal body of each ovariole, a group of six to eight cells in the calyx wall enclosed by the end of the ovariolar sheath. Their granulation progressively increased in intensity following each subsequent ovulation.     

Infection of the malaria mosquito Anopheles gambiae with the entomopathogenic fungus Metarhizium anisopliae reduces blood feeding and fecundity

The entomopathogenic fungus Metarhizium anisopliae is being considered as a biocontrol agent against adult African malaria vectors. In addition to causing significant mortality, this pathogen is known to cause reductions in feeding and fecundity in a range of insects. In the present study we investigated whether infection with M. anisopliae affected blood feeding and fecundity of adult female malaria vectors Anopheles gambiae Giles sensu stricto. Mosquitoes were contaminated with either a low or a moderately high dose of oil-formulated conidia of M. anisopliae, and offered a single human blood meal 48, 72, or 96 h later to assess feeding propensity and individual blood meal size. In a second experiment, individual fungus-infected females were offered a blood meal every third day (to a total of 8 gonotrophic cycles), and allowed to oviposit after each cycle in order to quantify feeding propensity and fecundity. Infected females took smaller blood meals and displayed reduced feeding propensity. It was found that mosquitoes, inoculated with a moderately high dose of fungal conidia, exhibited reduced appetite related to increasing fungal growth. Of the fungus-infected females, the proportion of mosquitoes taking the second blood meal was reduced with 51%. This was further reduced to 35.3% by the 4th blood meal. During 8 feeding opportunities, the average number of blood meals taken by uninfected females was 4.39, against 3.40 (low dose), and 2.07 (high dose) blood meals for the fungus-infected females. Moreover, infected females produced fewer eggs per gonotrophic cycle and had a lower life-time fecundity. Epidemiological models show that both blood feeding and fecundity are among the most important factors affecting the likelihood of a mosquito transmitting malaria, which suggests that this fungus may have potential as biocontrol agent for vector-borne disease control.     

The malaria parasite,Plasmodium falciparum,increases the frequency of multiple feeding of its mosquito vector,Anopheles gambiae.

It has often been suggested that vector-borne parasites alter their vector''s feeding behaviour to increase their transmission, but these claims are often based on laboratory studies and lack rigorous testing in a natural situation. We show in this field study that the malaria parasite, Plasmodium falciparum, alters the blood-feeding behaviour of its mosquito vector, Anopheles gambiae s.l., in two ways. First, mosquitoes infected with sporozoited, the parasite stage that is transmitted from the mosquito to a human, took up larger blood meals than uninfected mosquitoes. Whereas 72% of the uninfected mosquitoes had obtained a full blood meal, 82% of the infected ones had engorged fully. Second, mosquitoes harbouring sporozoites were more likely to bite several people per night. Twenty-two per cent of the infected mosquitoes, but only 10% of the uninfected mosquitoes, contained blood from at least two people. We conclude that the observed changes in blood-feeding behaviour allow the parasite to spread more rapidly among human hosts, and thus confirm that the parasite manipulates the mosquito to increase its own transmission.     

Christophers' stage durations and effect of interrupted blood meal in the mosquito Aedes caspius (Diptera: Culicidae)

Christophers' stages durations and effect of interrupted blood meal were investigated in laboratory to study the gonotrophic cycle of Aedes caspius (Pallas, 1771). A first experiment was done with replete females (full blood meal) and females with an interrupted blood meal. Females were then regularly dissected, the durations of Christophers' stages I, II, III, IV, V were up to 8, 8, 32, 8, 48 h, respectively. A second experiment was done with replete females, females with an interrupted blood meal and females with an interrupted blood meal completed 24 h later. Interrupted females matured 21 +/- 5 follicles, interrupted-completed females 92 +/- 11, and replete females 120 +/- 8 follicles.     

Nectar feeding by mosquitoes in Sweden, with special reference to Culex pipiens and Cx torrentium

1. Nectar feeding by mosquitoes collected from tansy (Tanacetum vulgare) flowers was studied in July and August 1983-85 at two sites in central and south-western Sweden. Prior to fructose analysis, gonotrophic state and parity was determined. 2. A total of 1010 mosquitoes (70% males) of eighteen species was collected. Fructose was detected in 75% of the males and 78% of the females. Most (86%) mosquitoes collected belonged to Culex pipiens and Cx torrentium. 3. Among 219 Cx pipiens females, for most of which the abdomen appeared gravid (52%) or empty (42%), 81% were fructose-positive. Females of other species were also proved to have fed on plant sugars in both early and later stages of the gonotrophic cycle. 4. In Cx pipiens and males of Cx torrentium peak nectar feeding occurred between 22.00 and 04.00 hours. Data for males of both species suggested a V-shaped pattern of nectar feeding activity during the night. 5. At about 16 degrees C nearly all mosquitoes became fructose-negative in the anthrone test within 20 h after collection from tansy flowers. 6. At least 44% of Cx pipiens females that were attracted to a dove-baited trap had fed on plant sugars shortly before.     

Multiple host feeding in field populations of Anopheles culicifacies and An. subpictus in Sri Lanka

A histological technique was used to detect the multiple blood-feeding of female mosquitoes, within the same gonotrophic cycle, in field populations of the malaria vectors Anopheles culicifacies and An. subpictus (Diptera: Culicidae) at a village in the low country of Sri Lanka, during 1994-96. Among 3306 An. culicifacies and 871 An. subpictus engorged females examined, respectively, 34.4% and 30.4% were multiple-fed. In these two species, double meals accounted for 92.7% and 89.5%, and triple meals for 7.3% and 10.5% of multiple meals, respectively. More females of An. culicifacies (53.7%) than An. subpictus (44.5%) multiple-fed on different nights. Multiple feeding rates in the two species were independent of sample size and field abundance. In An. culicifacies, but not An. subpictus, these rates were proportional to ambient temperature but not to humidity. Bloodmeal ELISA showed that 8.3% of 242 An. culicifacies were human-fed and 80% of these (i.e. 6.6%) were concurrently bovid-fed. Combining the histological and ELISA data, it was estimated that multiple feeding involving a human host had occurred in 7.2% of the blood-feeding An. culicifacies population at this study site. Only 1.2% of 406 An. subpictus were human-fed and all of these were concurrently bovid-fed. Multiple bloodfeeding within the same gonotrophic cycle was attributed to a local 'frequent feeding strategy' in these primarily zoophagic and endophilic malaria vectors. Unfortunately this strategy enhances their human-biting rate and hence their vectorial capacity.     

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.     

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.     

Seasonality, biting cycle and parity of the yellow fever vector mosquito Haemagogus janthinomys in Trinidad

1. Age composition, seasonal abundance and diel patterns of landing activity of the sylvan vector of yellow fever Haemagogus janthinomys Dyar were monitored weekly during 1981-82 by human collectors on the ground at Point Gourde in Chaguaramas Forest, 16 km west of Port of Spain, Trinidad. 2. Landing collections of Hg. janthinomys showed only diurnal activity, from 06.00 to 18.00 (sunrise to sunset, universal time), with a single peak of activity between 10.00 and 16.00 hours. 3. Densities of Hg. janthinomys were about 6 times greater during the wet season (May-November) than during the dry season (December-April); the annual Williams' mean landing rate on two collectors was 9.3 per day. 4. Monthly parous rates averaged 59% (range 0-86%) and some females were up to seven-pars. Retained eggs (range 1-21, mean 7.7/female) were found in the ovaries of 1.3% of landing females, all of which had stage I ovarian follicles for the next gonotrophic cycle. Hence blood-feeding is not inhibited by egg retention, which might promote transovarial transmission of virus. Implications of these findings are discussed in relation to yellow fever epidemiology.     

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.     

Utilization of pre-existing energy stores of female Aedes aegypti mosquitoes during the first gonotrophic cycle

Pre-existing energy reserves may play an important role in regulating the utilization of blood meal proteins in female anautogenous mosquitoes. Determining the fate of reserves derived from the sugar meal and larval food during the first gonotrophic cycle would help to elucidate the relative contributions of larval and adult nutrition to survival and reproduction. We measured the allocation of pre-blood-meal reserves to egg production or energy production during the first gonotrophic cycle by using [14C]-labeled female Aedes aegypti mosquitoes. Feeding adults [3,4-14C]-glucose labeled the glycogen and sugar stores (approximately 50%), lipid stores (approximately 25%), and protein and amino acid stores (approximately 25%). During the first gonotrophic cycle, about 60% of the glycogen and sugar stores were metabolized and all were used for energy production. About 33% of the labeled protein and 72% of the labeled amino acid stores were metabolized, with about 9% being transferred to the eggs and the rest oxidized. About 30% of the lipid was metabolized, with about 65% being transferred to the eggs and the rest oxidized. Feeding [1-14C]-oleic acid to larvae effectively labeled adult lipid stores with about 75% of the label in lipid stores and 16% in proteins and 6% in glycogen. During the first gonotrophic cycle, about 35% of the labeled lipid stores were metabolized, with equal amounts being oxidized and transferred to the eggs. None of the other maternal stores labeled by fatty acid were metabolized during the first gonotrophic cycle. These results show that carbohydrate reserves are a critical source of energy during the first gonotrophic cycle, while lipid reserves are used equally for energy production and provisioning the eggs.     

Significance of transovarial infections of Amblyospora sp. (Microspora:Thelohaniidae) in relation to parasite maintenance in the mosquito Culex salinarius

Adult females of Culex salinarius, transovarially infected with the microsporidium Amblyospora sp., showed no significant differences in overall fecundity, physiological longevity, and preoviposition periods when compared to healthy adults under laboratory conditions. Development times and survival rates for congenitally infected young to reproductive age were also indistinguishable from those of healthy controls. A significant reduction of 52% in egg hatch was observed for infected eggs when compared to healthy eggs. Prevalence rates of infection for progeny produced by infected females declined with each successive gonotrophic cycle and averaged 90%. Transovarial transmission is not sufficient for the maintenance of the microsporidium in a population of mosquitoes. An alternate host is suggested as a mechanism whereby the microsporidium can reenter a healthy mosquito population.     

Vectorial Capacity of Aedes aegypti for Dengue Virus Type 2 Is Reduced with Co-infection of Metarhizium anisopliae

Background

Aedes aegypti, is the major dengue vector and a worldwide public health threat combated basically by chemical insecticides. In this study, the vectorial competence of Ae. aegypti co-infected with a mildly virulent Metarhizium anisopliae and fed with blood infected with the DENV-2 virus, was examined.

Methodology/Principal Findings

The study encompassed three bioassays (B). In B1 the median lethal time (LT₅₀) of Ae. aegypti exposed to M. anisopliae was determined in four treatments: co-infected (CI), single-fungus infection (SF), single-virus infection (SV) and control (C). In B2, the mortality and viral infection rate in midgut and in head were registered in fifty females of CI and in SV. In B3, the same treatments as in B1 but with females separated individually were tested to evaluate the effect on fecundity and gonotrophic cycle length. Survival in CI and SF females was 70% shorter than the one of those in SV and control. Overall viral infection rate in CI and SV were 76 and 84% but the mortality at day six post-infection was 78% (54% infected) and 6% respectively. Survivors with virus in head at day seven post-infection were 12 and 64% in both CI and SV mosquitoes. Fecundity and gonotrophic cycle length were reduced in 52 and 40% in CI compared to the ones in control.

Conclusion/Significance

Fungus-induced mortality for the CI group was 78%. Of the survivors, 12% (6/50) could potentially transmit DENV-2, as opposed to 64% (32/50) of the SV group, meaning a 5-fold reduction in the number of infective mosquitoes. This is the first report on a fungus that reduces the vectorial capacity of Ae. aegypti infected with the DENV-2 virus.     

Age-Dependent Effects of Oral Infection with Dengue Virus on Aedes aegypti (Diptera: Culicidae) Feeding Behavior,Survival, Oviposition Success and Fecundity

Background

Aedes aegypti is the main vector of dengue, a disease that is increasing its geographical range as well as incidence rates. Despite its public health importance, the effect of dengue virus (DENV) on some mosquito traits remains unknown. Here, we investigated the impact of DENV-2 infection on the feeding behavior, survival, oviposition success and fecundity of Ae. aegypti females.

Methods/Principal Findings

After orally-challenging Ae. aegypti females with a DENV-2 strain using a membrane feeder, we monitored the feeding behavior, survival, oviposition success and fecundity throughout the mosquito lifespan. We observed an age-dependent cost of DENV infection on mosquito feeding behavior and fecundity. Infected individuals took more time to ingest blood from anesthetized mice in the 2^nd and 3^rd weeks post-infection, and also longer overall blood-feeding times in the 3^rd week post-infection, when females were around 20 days old. Often, infected Ae. aegypti females did not lay eggs and when they were laid, smaller number of eggs were laid compared to uninfected controls. A reduction in the number of eggs laid per female was evident starting on the 3^rd week post-infection. DENV-2 negatively affected mosquito lifespan, since overall the longevity of infected females was halved compared to that of the uninfected control group.

Conclusions

The DENV-2 strain tested significantly affected Ae. aegypti traits directly correlated with vectorial capacity or mosquito population density, such as feeding behavior, survival, fecundity and oviposition success. Infected mosquitoes spent more time ingesting blood, had reduced lifespan, laid eggs less frequently, and when they did lay eggs, the clutches were smaller than uninfected mosquitoes.     

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.