Release of egg development neurosecretory hormone in Aedes aegypti and Aedes taeniorhynchus induced by an ovarian factor

Ovariectomized Aedes aegypti do not synthesize vitellogenin after a blood meal, unless an ovary from a blood-fed donor is implanted. Decapitation, however, prior to implantation inhibits vitellogenin synthesis. A female ovariectomized and decapitated 6 hr after a blood meal, synthesizes vitellogenin if an ovary from a blood-fed donor is implanted. On the other hand, females that are fed on blood and immediately decapitated can not be stimulated to synthesize vitellogenin with implanted ovaries removed from blood-fed donors. These experiments led to the hypothesis that the blood meal stimulates the ovary to secrete a corpus cardiacum stimulating factor, that in turn promotes release of egg development neurosecretory hormone stored in the corpus cardiacum.Injection of 20-hydroxy-ecdysone or ovarian extract prepared from ovaries removed from unfed females does not release egg development neurosecretory hormone. Thus corpus cardiacum stimulating factor is not 20-hydroxy-ecdysone, and ovaries removed from unfed females do not store it.The rate of inactivation of egg development neurosecretory hormone released from the corpus cardiacum after a blood meal was investigated by implanting an ovary into females that were blood fed for various intervals than decapitated and ovariectomized. Seventy per cent of implants grow when the operation is done 18 hr after feeding, and 30% when the operation is done between 18 and 24 hr after feeding, indicating that egg development neurosecretory hormone is stable for the first 18 hr after a blood meal.Aedes taeniorhynchus females ovariectomized 24 hr after adult emergence do not synthesize vitellogenin. When such a female is implanted with an ovary removed from a sugar-fed or blood-fed Aedes aegypti donor vitellogenin synthesis is initiated, and the implant grows. Decapitation prior to implantation inhibit vitellogenin synthesis and implants do not grow. These results indicate that corpus cardiacum stimulating factor is not species specific.     

The influence of mating on autogenous egg development in the mosquito, Aedes taeniorhynchus

In several strains of Aedes taeniorhynchus, the presence of males increased the levels of autogeny. To stimulate autogenous egg production, the males had to mate with the females. Ageing further enhanced the rates of autogeny in mated females but not in virgins. Males did not influence the size of the autogenous egg batch. Even after the sixth day following emergence some females still possessed the capacity to respond to the male stimulus. With regard to ovarian maturation in A. taeniorhynchus, there appeared to be 3 types of females: (1) those that did not require a mating stimulus to be autogenous, (2) those that needed this stimulus and (3) those that remained anautogenous whether mated or not.     

Effects of sucrose on blood avidity in mosquitoes.

Within 10 min after engorging on 10% sucrose, most females of Aedes aegypti do not seek a human blood meal, but remain quiescent and unresponsive to a human hand in a 1 ft³ cage. The duration of this inhibition in blood avidity varies greatly among individuals, but may last for 2 to 5 hr after drinking sucrose. There was no specific correlation between abdominal distension and blood avidity. When females engorged on varying concentrations of sucrose, it was found that as the concentration increased, fewer mosquitoes would take blood when it was offered after 1 hr. Only 25% of the females which engorged on 0·5 to 1 M sucrose took human blood at this time. As the concentration of sucrose increases, there is a marked decrease in spontaneous flight activity during the first hour after feeding. When unfed females are injected with 10% sucrose or trehalose, none of them took blood for 3 hr, whereas 50% of the saline-injected controls fed on blood.     

Susceptibility of adult mosquitoes to insecticides in aqueous sucrose baits

Mosquitoes characteristically feed on plant‐derived carbohydrates and honeydew just after emergence and intermittently during their lives. Development of toxic baits focusing on this carbohydrate‐seeking behavior may potentially contribute to localized control. In the present study, ten insecticides were fed to female Culex quinquefasciatus, Anopheles quadrimaculatus, and Aedes taeniorhynchus in a 10% sucrose solution. Active ingredients representative of five classes of insecticides (pyrethroids, phenylpyroles, pyrroles, neonicotinoids, and macrocyclic lactones) were selected for comparison with commercial formulations used to facilitate incorporation of active ingredients into aqueous sucrose solutions. Sucrose as a phagostimulant significantly enhanced mortality to toxicants. In general, the most effective active ingredients were fipronil, deltamethrin and imidacloprid, followed by spinosad, thiamethoxam, bifenthrin, permethrin, and cyfluthrin. The least effective ingredients were chlorfenapyr and ivermectin. For some of the ingredients tested, Cx. quinquefasciatus was the least susceptible species. One‐day‐old male Cx. quinquefasciatus were more susceptible than females; however, no differences existed between one‐ and seven‐day‐old mosquitoes. There were no differences in susceptibility between unfed and gravid ten‐day‐old female Cx. quinquefasciatus to bifenthrin. In conclusion, several pesticides from different classes of compounds have potential for use in development of toxic baits for mosquitoes.     

Dietary carbohydrates: role in feeding behavior and growth of the southwestern corn borer, Diatraea grandiosella

The effect of carbohydrates on feeding behaviour and growth and development of the southwestern corn borer, Diatraea grandiosella, was examined. A feeding behavioural biossay based on establishment of first stage larvae on test or control stations within 24 hr was employed. A nutritional bioassay evaluated larval growth rates and metamorphic success of larvae reared on test or control diets. The principal results showed that glucose, fructose, sucrose, and dextrins were feeding stimulants and permitted optimum growth and development. A dietary supplement of amylopectin allowed reasonably good growth while amylose was not a utilizable carbohydrate. The pentoses, arabinose, ribose, and xylose, as well as galactose, mannose, and sorbose, were found to inhibit larval growth. Since of all these sugars only xylose acted as a feeding deterrent it was proposed that at high concentrations they or metabolic derivatives were toxic. The results are discussed in relation to those obtained with several other insect species.     

Incrimination of the mosquito,Aedes taeniorhynchus,as the primary vector of heartworm,Dirofilaria immitis,in coastal Yucatan,Mexico

Mosquito collections were carried out on microfilaraemic dogs, positive for Dirofilaria sp., for 18 consecutive nights in the coastal town of Celestún, Yucatan, southeast Mexico, during the rainy season (August) of 2007. A total of 292 female mosquitoes representing 12 species of dipteran Culicidae were collected: Anopheles albimanus (Wiedemann); Anopheles crucians (Wiedemann); Anopheles pseudopunctipennis (Theobald); Culex coronator (Dyar & Knab); Culex interrogator (Dyar & Knab); Culex nigripalpus (Theobald); Culex quinquefasciatus (Say); Culex salinarius (Coquillett); Aedes aegypti (Linnaeus); Aedes scapularis (Rondani); Aedes sollicitans (Walker), and Aedes taeniorhynchus (Wiedemann). Aedes taeniorhynchus and Cx. quinquefasciatus were the species found most commonly feeding on the dogs. Filarial nematodes were observed by microscopy in nine of the mosquito species collected; however, third‐instar larvae were only observed in Ae. taeniorhynchus and An. crucians. Of 76 Ae. taeniorhynchus specimens found positive for Dirofilaria sp. by dissection, 14 were confirmed to be positive for Dirofilaria immitis (Leidy) by polymerase chain reaction (PCR). The resulting infection rate for D. immitis confirmed by PCR (6.2%) is higher than any infection rate for Ae. taeniorhynchus previously reported from the Americas.     

Cell replication in the follicular epithelium of the adult mosquito

Females of the mosquitoes Culex pipiens molestus, Aedes togoi, Mansonia uniformis, and Aedes aegypti show active mitosis and an increase in cell number in the follicular epithelium of the ovary immediately after emergence from the pupa. Development up to stage III in the autogenous species, when mitosis in the follicular epithelium ceases, depends upon the continuity of cell proliferation over the first 48 hr after emergence (C. p. molestus, A. togoi) and on the number of cells originally in the follicle at emergence (A. togoi). The follicular epithelium in the anautogenous species ceases to divide in Mansonia, or the rate of division is considerably reduced in A. aegypti, 24–48 hr after emergence. Mitosis in the follicular epithelium of A. aegypti is renewed after the blood meal. A number of cells are released from phase G2 of the mitotic cycle into mitosis and other cells are initiated into DNA synthesis within 4 hr of the mosquito feeding on blood.     

A comparative study of flight performance and fuel utilization as a function of age in females of Florida mosquitoes

Sugar-fed females of 7 species of Florida mosquitoes were flown for 4·5 hr on a flight-mill system twice a week during their life span and analysed for flight performance (speed of flight during the first hour, the distance flown at the end of 4·5 hr flight period, and per cent reduction in flight speed of the fourth hour as compared to the first hour) and for utilization of haemolymph sugars, glycogen, and triglycerides reserves.Species-specific differences occurred in 50 per cent survival age and flight performance. Aedes taeniorhynchus, Mansonia titillans, Culex nigripalpus, Psorophora confinnis, and A. sollicitans exhibited maximum flight potential during 2 to 8 weeks after emergence, as compared with only 1 to 2 weeks in A. aegypti and Anopheles quadrimaculatus. This suggested that the former group of mosquitoes possessed a greater potential for dispersal by searching flights during their life span when compared with the latter group. Glycogen was the only energy reserve utilized during sustained tethered flight in all species. The energy requirements as calculated from depletion of glycogen during sustained flight for 4·5 hr in different species varied from 0·06 to 0·09 cal/1000 m or 16 to 32 cal/hr per g. The considerably lower values of energy expended, on the average of 16 to 22 cal/hr per g in C. nigripalpus, P. confinnis, A. sollicitans, and A. aegypti, compared with 30 to 32 cal/hr per g in A. taeniorhynchus and M. titillans, is most probably due to the substantially lower speed of the former group of mosquitoes, 1000 to 1500 m/hr, than in the latter group of mosquitoes, 1500 to 2000 m/hr. A. sollicitans and M. titillans started to show wing abrasion and distinct signs of senescence during the last 2 to 3 weeks of their life span.Non-flown females of different species maintained on sugar ab lib. achieved maximum levels of glycogen and triglycerides reserves during the second week and they maintained these levels for the major portion of their life span, after which the levels of these reserves showed a distinct decline. It is suggested that this stabilization and decline of the energy reserves control longevity and flight potential in each mosquito species.     

Long-term regulation of sucrose intake by the female mosquito, Aedes taeniorhynchius

Newly emerged female Aedes taeniorhynchus were maintained in cups provided with potometers containing 5, 10, and 25% sucrose solutions. Mortality and the ab lib. intake of sucrose were recorded daily and groups were sampled at regular intervals for analysis of energy reserves.After a week of relatively substantial intake of sucrose at all three concentrations, a constancy in daily intake at much lower levels was observed during the next 4 weeks. The caloric intake was highest in the 25% sucrose solution group. There were no differences in mortality rates at these concentrations. Glycogen (0·7–1·0 cal/female) and triglycerides (3·5dash4 cal/female) reserves reached maximum levels after the first week and stabilized thereafter on all three concentrations. In this species the stabilization in intake of sucrose solution after the first week is correlated with the maximum accumulation of stored energy reserves as opposed to decreased activity or subtle changes associated with senescence.     

Development and ageing of the salivary glands of adult male Aedes aegypti (L.) and Aedes togoi (theobald) mosquitoes (Dipteria : Culcidae)

The salivary glands of adult male Aedes aegypti and Aedes togoi (Diptera : Culicidae), varying in age from less than 1 day after emergence to 42 days or 33 days respectively, were examined by light microscopy. Following emergence, the trilobed glands rapidly accumulate secretory product and attain their full size within about 48 hr. The amount of secretion in fully developed glands shows marked individual variation, but it is predominantly located in the posterior parts of the glands. Ageing changes begin to appear after about 8 days (A. aegypti) or 10–11 days (A. togoi), and although there is wide individual variation in their extent, in general, they become progressively more severe until at the age of 4–5 weeks all mosquitoes are substantially affected. Since other tissues, including ganglia, also regress with age, it is unlikely that salivary gland changes are the prime cause of death.     

The role of the male accessory gland fluid in stimulating vitellogenesis in Aedes taeniorhynchus

Injection of 20-hydroxyecdysone (20-OH-ecdysone) at high concentrations (5.0 μg) into intact or decapitated female Aedes taeniorhynchus induced vitellogenin synthesis, whereas low concentrations (5.0 ng) were ineffective. Injections of male accessory gland fluid (MAGF), however, at a concentration that was equivalent to 0.25 of the content of a pair of accessory glands, into intact or decapitated A. taeniorhynchus induced viteliogenin synthesis only in intact females. Ovariectomized mosquitoes did not synthesize vitellogenin after MAGF injection or blood feeding. Females that were first injected with MAGF and decapitated 12 h later synthesized viteliogenin at a rate that was 80% of intact controls. Egg development neurosecretory hormone (EDNH) activity in the heads of ovariectomized or intact females injected with MAGF was 9.0 pmol/min/head and 2.5 pmol/min/head, respectively, indicating that MAGF does not stimulate the corpus cardiacum (CC) to release EDNH. Incubation of MAGF and EDNH with fat bodies failed to induce vitellogenin synthesis. These results indicate that in A. taeniorhynchus the MAGF induces the ovary to release corpus cardiacum stimulating factor, which then signals CC to release stored EDNH.     

Internal regulation of rate of digestion of blood meals in the mosquito, Aedes aegypti.

Rate of digestion of blood meals proceeded more rapidly in females of Aedes aegypti that were inseminated or injected with matrone (extract of male accessory glands) than in virgin females. Digestion rate was determined by interfacial precipitin tests and immunodiffusion tests for undigested blood-meal proteins. Application of a cervical ligature within 1 hr of blood feeding retarded the digestion rate. Ligated females that received brain transplants from blood-fed donors digested their blood meals at a rate similar to that of unligated controls. When ligatures were not applied until 12 hr after feeding no delay in digestion was observed.     

A novel multiple membrane blood‐feeding system for investigating and maintaining Aedes aegypti and Aedes albopictus mosquitoes

A novel multiple membrane blood‐feeding system for mosquitoes has been developed for the study and routine maintenance of Aedes aegypti L. and Aedes albopictus Skuse that require a meal of vertebrate blood to produce eggs. This blood‐feeding system uses cattle collagen sausage‐casing membrane to facilitate feeding. The efficiency of this blood‐feeding system was compared to a live mice blood source. We observed that Ae. aegypti that fed on pig whole blood had 89.7% (w/o ATP) and 90.7% (w/ ATP) blood‐feeding rates, which were not significantly different from the mice‐fed ones (98.0%). Ae. albopictus fed on pig whole blood (w/ ATP) had a success rate of 84.4%, which was significantly different from the mice‐fed mosquitoes (51.1%). The feeding rates did not differ between sausage‐casing membrane and Parafilm‐M®. The survival rate, fecundity, pupation, and pupal emergence rates of Aedes females fed on pig whole blood were not significantly different from the mice‐fed ones. The artificial blood feeder can be applied to replace live animals as blood sources. Considering that this simple, inexpensive, convenient, and efficient feeding device can be built with common laboratory materials for research on Aedes mosquitoes.     

Bioassay of three strains of Bacillus sphaericus on field-collected mosquito larvae.

Bacillus sphaericus strains 1593, 1404, and SSII-1 were assayed for infectivity against field-collected larvae of Psorophora columbiae, Culex nigripalpus, and Aedes taeniorhynchus in southwest Florida. Results indicate that all three strains are highly active against the Psorophora and Culex species. A. taeniorhynchus is also susceptible but requires higher dosages to achieve lethal responses. Tests were also conducted on the rate of infection and the differences in susceptibility of different instars to B. sphaericus. These tests indicate that nearly 75% of the mortality that occurs in the course of exposure to B. sphaericus occurs within 48 hr post-incubation with the bacteria. Furthermore, our tests indicate P. columbiae larvae decrease in susceptibility to the Bacillus with increase in larval age (instar). This investigation shows B. sphaericus to be a feasible biological control agent that warrants further study.     

Host species diversity and post-blood feeding carbohydrate availability enhance survival of females and fecundity in Aedes albopictus (Diptera: Culicidae)

Aedes albopictus mosquito is an opportunistic blood feeder and has a broad host range. The feeding behavior and habits of this mosquito are liable to increase the transmission potential of arboviruses. The survival and fecundity in A. albopictus fed on different hosts and post-blood meal provision of sugar were investigated in a laboratory-reared colony. Adult survival of caged female A. albopictus that were fed on blood of two different hosts (double meal) was higher than the females fed only on one host (single meal) (mean survival: 70.2 ± 9.6 vs. 55.5 ± 5.5%, respectively) when held in the laboratory for 72 h after blood feeding. Mean survival of females provided 10% sucrose solution (in water) after a single or double blood meal was higher (90.5 ± 6.4% and 89.3 ± 6.5%, respectively) than in the respective groups receiving water only following blood feeding (double meal: 49.0 ± 9.6%; single meal: 45.3 ± 10.9%). Females receiving a double meal were more fecund on average (89.0 ± 6.6 eggs) than females provided a single meal (82.3 ± 8.2 eggs).     

An isotonic saline for the adult blowfly, Phormia regina, and its application to perfusion experiments

Measurements have been made of Na (119 mM), K (5·6 mM), and Ca (2·4 mM) concentrations and total osmotic pressure (487 mOs/kg) of blood of adult Phormia regina. From these data an isotonic saline has been constructed which can be coupled successfully with a newly described total perfusion technique. Using this method it has been shown that adult male Phormia 5 days after emergence recover 50 per cent of their blood trehalose within 12 hr after total perfusion, and are back to normal with reference to this carbohydrate between 24 and 48 hr.     

Effects of blood meal sources on the biological characteristics of Aedes aegypti and Culex pipiens (Diptera: Culicidae)

Mosquitoes transmit many diseases to humans and animals e.g., malaria, yellow fever, dengue, filariasis and encephalitis. The fundamental target of this search was to study the effect of three different blood meal sources (human; rabbit and pigeon) on some biological and behavioral properties of Aedes aegypti and Culex pipiens. The results have assured that the females of the mosquito Ae. aegypti that were fed on human blood meal has registered the highest feeding activity from feeding on the blood meal whereas the females of the other mosquito Cx. pipiens have shown the highest feeding activity after being fed on pigeons when compared with its feeding on other factors. The results have shown non-significant variation in the average time necessary to digest the blood meal on both mosquito species Ae. aegypti and Cx. pipiens that were fed on vertebrate hosts under laboratory conditions. Furthermore, results assured that the difference in blood meal sources has yielded distinct variation in the reproductive capacity and efficiency of both female mosquitoes under investigation where both species Ae. aegypti and Cx. pipiens already fed on human blood meal have yielded a pronounced distinctive increase in egg production (oviposition) when compared with females that were fed on pigeon or rabbit blood meal respectively. Moreover, feeding of the female mosquitoes under lab conditions on different blood meal sources did not affect the level of the hatching eggs that were laid by both mosquito females.     

A survival and reproduction trade-off is resolved in accordance with resource availability by virgin female mosquitoes

The first 2-4 days after an Anopheles gambiae female mosquito emerges are critical to her survival and reproductive success. Yet, the order of behavioural events (mating, sugar feeding, blood feeding) during this time has received little attention. We discovered that among female cohorts sampled from emergence, sugar feeding had a higher probability than blood feeding of occurring first, and mating rarely occurred before a meal was taken. The night after emergence, 48% of females fed on sugar in mesocosms, and 25% fed on human blood; in the absence of sugar, 49% of females fed on human blood. After 5 days, 39% of the sugar-supplied females had blood fed and mated, and were fructose negative, whereas only 8% of the sugar-denied females had both blood fed and mated by this time. The model that best explained the transitions suggests that females made use of two distinct behavioural pathways, the most common one being to sugar-feed, then mate, and then seek blood. Other females sought blood first, then mated, and forwent a sugar meal. Lipid levels were higher in females with access to sugar than in females without access to sugar, particularly for those in later gonotrophic stages, while glycogen levels in the sugar-supplied group were higher throughout. In single-night experiments with females having had access to sucrose since emergence, those given a blood meal 1 day before spending a night with males had higher insemination rates than those not receiving the blood meal. These results indicate that the trade-off between survival and immediate reproduction is resolved by young adult females in accordance with availability of resources and gonotrophic state.     

Variable expressions of autogeny in three mosquito species

Patterns of autogeny were compared in 3 mosquito species from a coastal site in Indian River County, Florida. Both autogenous and anautogenous females were found in Aedes taeniorhynchus (Wiedemann) and Wyeomyia vanduzeei Dyar and Knab populations. Mating was a prerequisite for autogeny in certain females of both species (see Tables I and II). All of the Deinocerites cancer Theobald females were autogenous, whether mated or not.

The expression of autogeny in A. taeniorhynchus depended upon environmental conditions during the larval stages and the geographical origin of the population. For some A. taeniorhynchus females, mating was needed for autogenous ovarian maturation under all experimental conditions, whereas for others mating became a requirement for autogeny only when the mosquitoes encountered the less favorable larval conditions. In nature, the dominant form of autogeny in A. taeniorhynchus appeared to be the male-induced type.

Among W. vanduzeei and A. taeniorhynchus populations, the male-induced form of autogeny was associated with relatively low levels of autogenous fecundity. However, females that possess the capacity for male-induced autogeny have a greater potential for enhancing the size of their initial egg batch by blood-feeding than do females that can express autogeny independent of mating.     

Expression and regulation of vitellogenin messenger RNA in the mosquito,Aedes aegypti

Vitellogenin (yolk protein) gene expression in the mosquito was investigated at the level of mRNA using a subcloned fragment (403-1c) of the vitellogenin DNA derived from an Aedes aegypti genomic library. Message appeared 1–3 hr after a blood meal, peaked at 36 hr and was rapidly degraded thereafter. Fluctuations in levels of 20-hydroxyecdysone after a blood meal coincided with accumulation of vitellogenin message. Blood-fed, decapitated females injected with 5 μg of 20-hydroxyecdysone accumulated up to 75% of the message found in blood-fed controls. Fat bodies from non-blood-fed females incubated with physiological levels of 20-hydroxyecdysone and the juvenile hormone analog methoprene contained twice as much vitellogenin message as those incubated with 20-hydroxyecdysone alone. Methoprene alone had no effect.