Spontaneous flight activity of Aedes trivittatus infected with Dirofilaria immitis

Spontaneous flight activity of Dirofilaria immitis-infected Aedes trivittatus was evaluated by using an acoustic activity system. The activity of mosquitoes infected with low numbers of filarial larvae (1-4) was similar to that of uninfected mosquitoes. However, mosquitoes infected with more than 4 larvae became more active than uninfected mosquitoes 8 days after infection. Peak flight activity (circadian) occurred at the same time in both infected and uninfected mosquitoes, but infected mosquitoes were much more active during normal periods of quiescence. Flight activity of mosquitoes infected with more than 4 larvae was suppressed on days 10 and 14 postinfection, corresponding to times of greatest disruption of the Malpighian tubules by the developing larvae.     

The ability of Aedes aegypti mosquitoes to survive and transmit infective larvae of Brugia pahangi over successive blood meals

The mortality of Aedes aegypti mosquitoes increased; immediately following a blood meal containing microfilariae of Brugia pahangi, when infective larvae began to migrate out of the flight muscles and when infective larvae were lost from the mosquitoes during a blood meal. When infective mosquitoes took a second blood meal 86.2% of the infective larvae escaped from their bodies. However, only 50.3% escaped when mosquitoes fed through a thin layer of cotton. Infective larvae in the abdomen of the mosquitoes stood the least chance of escaping from the insects. When infective mosquitoes were offered a third blood meal four days later, the proportion of infective larvae in the head and labium had risen from 56.6% in the control group to 66.0% and 69.4% in the two test groups. At this third feed 54.7% and 75.7% of the infective larvae were lost from mosquitoes with a low and medium pre-feeding worm burden respectively. This suggests that the escape of infective larvae from mosquitoes with only a few worms is less efficient than from mosquitoes with a medium worm burden.     

The impact of maturation delay of mosquitoes on the transmission of West Nile virus

We formulate and analyze a delay differential equation model for the transmission of West Nile virus between vector mosquitoes and avian hosts that incorporates maturation delay for mosquitoes. The maturation time from eggs to adult mosquitoes is sensitive to weather conditions, in particular the temperature, and the model allows us to investigate the impact of this maturation time on transmission dynamics of the virus among mosquitoes and birds. Numerical results of the model show that a combination of the maturation time and the vertical transmission of the virus in mosquitoes has substantial influence on the abundance and number of infection peaks of the infectious mosquitoes.     

Mosquito phytophagy – sources exploited,ecological function,and evolutionary transition to haematophagy

For a very long time, mosquitoes have been known or suspected to consume plant liquids. Recently eclosed mosquitoes cannot survive long without consuming sugary plant liquids that provide fuel for flight and enable blood-feeding and mating. Populations of even highly synanthropic mosquitoes may not be able to persist without phytophagy, even when vertebrate blood is readily available. Phytophagy is a key element of mosquito ecology, and understanding it is critical to combat mosquito-borne diseases. In this review, we summarize the current knowledge about mosquito phytophagy and outline future research needs. Specifically, we review the many plant-derived food sources mosquitoes exploit, study the pollination function of mosquitoes, highlight the predation risks of plant-foraging mosquitoes, investigate the role of microbes in the sugar-foraging ecology of mosquitoes, and shed light on the evolution of haematophagy.     

Malaria-induced reduction of fecundity during the first gonotrophic cycle of Anopheles Stephensi mosquitoes

Abstract. Anopheles stephensi mosquitoes which had fed upon mice infected with Plasmodium yoelii nigeriensis malaria parasites produced significantly fewer eggs than mosquitoes fed on an uninfected mouse. Fecundity reduction was more pronounced when the bloodmeal contained malaria gametocytes and the mosquitoes developed oocysts. Egg production and haematin excretion were correlated for uninfected bloodfed mosquitoes; the presence of P.y. nigeriensis in the blood affected this relationship. Reduced fecundity was associated with a significant reduction of bloodmeal size (measured by haematin excretion) in mosquitoes which ingested gametocytaemic blood. The bloodmeal size in mosquitoes fed on parasitaemic blood without gametocytes was not significantly reduced. The use of haematin assays for determination of bloodmeal size in mosquitoes is discussed.     

Herbicide treatment alters the effects of water hyacinth on larval mosquito abundance

Invasive aquatic weeds are managed with herbicides to reduce their negative impacts on waterways in many areas, including the California Delta Region. Herbicides create a dynamic environment of living and decomposing plant matter that could affect larval mosquitoes and other invertebrates, such as their predators and competitors. Our objective was to compare the number of larval mosquitoes in water or water hyacinth, before and after an herbicide treatment. We created replicated pond mesocosms with water hyacinth, water hyacinth treated with glyphosate and an oil adjuvant, open water, and water with glyphosate plus adjuvant. We sampled for larval mosquitoes and other aquatic invertebrates. Before herbicide addition, there was a trend for more larval mosquitoes in open water tanks than in tanks with water hyacinth. Herbicide application resulted in an immediate decrease of larval mosquitoes. As decay progressed, larval mosquitoes became most abundant in mesocosms with herbicide‐treated hyacinth and very few larval mosquitoes were found in other habitat treatments. Although the numbers of predatory and competitor insects had some variation between treatments, no clear pattern emerged. This information on how invasive weed management with herbicides affects larval mosquitoes will allow control practices for larval mosquitoes and invasive weeds to be better integrated.     

Identification of super-infected Aedes triseriatus mosquitoes collected as eggs from the field and partial characterization of the infecting La Crosse viruses

Background

La Crosse virus (LACV) is a pathogenic arbovirus that is transovarially transmitted by Aedes triseriatus mosquitoes and overwinters in diapausing eggs. However, previous models predicted transovarial transmission (TOT) to be insufficient to maintain LACV in nature.

Results

To investigate this issue, we reared mosquitoes from field-collected eggs and assayed adults individually for LACV antigen, viral RNA by RT-PCR, and infectious virus. The mosquitoes had three distinct infection phenotypes: 1) super infected (SI+) mosquitoes contained infectious virus, large accumulations of viral antigen and RNA and comprised 17 of 17,825 (0.09%) of assayed mosquitoes, 2) infected mosquitoes (I+) contained no detectable infectious virus, lesser amounts of viral antigen and RNA, and comprised 3.7% of mosquitoes, and 3) non-infected mosquitoes (I-) contained no detectable viral antigen, RNA, or infectious virus and comprised 96.21% of mosquitoes. SI+ mosquitoes were recovered in consecutive years at one field site, suggesting that lineages of TOT stably-infected and geographically isolated Ae. triseriatus exist in nature. Analyses of LACV genomes showed that SI+ isolates are not monophyletic nor phylogenetically distinct and that synonymous substitution rates exceed replacement rates in all genes and isolates. Analysis of singleton versus shared mutations (Fu and Li's F*) revealed that the SI+ LACV M segment, with a large and significant excess of intermediate-frequency alleles, evolves through disruptive selection that maintains SI+ alleles at higher frequencies than the average mutation rate. A QTN in the LACV NSm gene was detected in SI+ mosquitoes, but not in I+ mosquitoes. Four amino acid changes were detected in the LACV NSm gene from SI+ but not I+ mosquitoes from one site, and may condition vector super infection. In contrast to NSm, the NSs sequences of LACV from SI+ and I+ mosquitoes were identical.

Conclusions

SI+ mosquitoes may represent stabilized infections of Ae. triseriatus mosquitoes, which could maintain LACV in nature. A gene-for-gene interaction involving the viral NSm gene and a vector innate immune response gene may condition stabilized infection.     

雌蚊翅振音及其在蚊虫防治中的应用

蚊虫飞翔时 ,翅上下拍打会形成连续的翅振音。雌蚊翅振音频率会随蚊种、蚊体长和日龄及环境温度而变化 ,一般在 3 0 0～ 5 0 0Hz之间。同种个体间翅振音频率变化较小 ,常在平均频率± 5 0Hz范围内。雄蚊只对基本频率的雌蚊翅振音起反应 ,雌蚊翅振音的偶然变化不会降低其对雄蚊的引诱力。雄蚊对雌蚊翅振音具有敏感反应的主要原因是其听觉器官对雌蚊翅振音形成了良好的适应性。因此 ,许多蚊虫研究者希望利用雌蚊翅振音来防治蚊虫。因该方法对环境安全 ,在今后蚊虫防治中其重要性将会日益显现。     

Dirofilaria immitis: effect on hemolymph polypeptide synthesis in Aedes aegypti during melanotic encapsulation reactions against microfilariae

[35S]Methionine-labeled hemolymph polypeptides from adult, female Aedes aegypti Liverpool strain mosquitoes inoculated with the microfilariae of the filarial nematode Dirofilaria immitis were compared with those from saline-inoculated and uninoculated controls by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) followed by fluorography. SDS-PAGE analysis of cell-free hemolymph collected via perfusion at 6, 12, 24, 48, 72, and 96 hr postinoculation (PI) detected the enhanced expression of an 84-kDa polypeptide. This polypeptide, expressed constitutively in the hemolymph of all three groups of mosquitoes, increased considerably in inoculated mosquitoes as time progressed as compared with uninoculated controls. Moreover, the 84-kDa polypeptide was expressed at higher levels in D. immitis-inoculated mosquitoes than in saline-inoculated controls. This stimulation of de novo biosynthesis of the 84-kDa polypeptide in inoculated mosquitoes may play a role in the immune response of mosquitoes. Since it is likely that the wound healing response in insects involves many of the same chemical processes as occur in melanotic encapsulation reactions of mosquitoes against filarial worms, the preferential expression of the 84-kDa polypeptide in saline-inoculated mosquitoes seen in this study may reflect a wound healing response. The greater increase in synthesis of this protein in D. immitis-inoculated mosquitoes may reflect production of melanotic material required for parasite destruction as well as for wound healing.     

Enhanced survival of Plasmodium-infected mosquitoes during starvation

Plasmodium spp. are pathogenic to their vertebrate hosts and also apparently, impose a fitness cost on their insect vectors. We show here, however, that Plasmodium-infected mosquitoes survive starvation significantly better than uninfected mosquitoes. This survival advantage during starvation is associated with higher energy resource storage that infected mosquitoes accumulate during period of Plasmodium oocyst development. Microarray analysis revealed that the metabolism of sated mosquitoes is altered in the presence of rapidly growing oocysts, including the down-regulation of several enzymes involved in carbohydrate catabolism. In addition, enhanced expression of several insulin-like peptides was observed in Plasmodium-infected mosquitoes. Blocking insulin-like signaling pathway resulted in impaired Plasmodium development. We conclude that Plasmodium infection alters metabolic pathways in mosquitoes, epitomized by enhanced insulin-like signaling - thereby conferring a survival advantage to the insects during periods of starvation. Manipulation of this pathway might provide new strategies to influence the ability of mosquitoes to survive and transmit the protozoa that cause malaria.     

The Identification of Plasmodium vivax Infected Anopheles sinensis by Enzyme-Linked Immunosorbent Assay, Republic of Korea, 1998

ABSTRACT To figure out how far spread the malaria parasite infected mosquitoes from Demilitarized Zone (DMZ). We investigated the sporozoite-infected mosquitoes in Chosan-ri and Hajiseok-ri of Paju-shi, Tonae-dong of Koyang-shi, Mudeung-ri of Yonchon-gun, Soyo-dong of Tongduchon-shi, and Tukjeong-ri of Yangju-gun, Kyonggi-do province in 1998. They were known as highly epidemic areas in the Republic of Korea. Anopheline mosquitoes were collected by human biting collection method from the 2nd week of June to the 5th week of August. A total of 3,256 anopheles mosquitoes were captured in these areas. A sandwich enzyme-linked immununosorbent assay (ELISA) for identifying Plasmodium vivax sporozoites in mosquitoes was used in this survey. Only one mosquito which was captured in Chosan-ri, on 2nd week of July showed positive reaction in this test. This mosquito was identified as Anopheles sinensis. This showed a 0.068% (1/1,465) positive rate in Chosan-ri on 2nd week of July. We could not detect positive mosquitoes the other areas. So we concluded the parasite infected mosquitoes may be highly limited near the DMZ.     

Optimal control strategy of malaria vector using genetically modified mosquitoes

The development of transgenic mosquitoes that are resistant to diseases may provide a new and effective weapon of diseases control. Such an approach relies on transgenic mosquitoes being able to survive and compete with wild-type populations. These transgenic mosquitoes carry a specific code that inhibits the plasmodium evolution in its organism. It is said that this characteristic is hereditary and consequently the disease fades away after some time. Once transgenic mosquitoes are released, interactions between the two populations and inter-specific mating between the two types of mosquitoes take place. We present a mathematical model that considers the generation overlapping and variable environment factors. Based on this continuous model, the malaria vector control is formulated and solved as an optimal control problem, indicating how genetically modified mosquitoes should be introduced in the environment. Numerical simulations show the effectiveness of the proposed control.     

Evaluation of the pathogenicity and infectivity of entomopathogenic hypocrealean fungi,isolated from wild mosquitoes in Japan and Burkina Faso,against female adult Anopheles stephensi mosquitoes

We investigated the potential of entomopathogenic hypocrealean fungi that naturally occur in or on adult mosquitoes for use as biocontrol agents of vector mosquitoes. The fungi were isolated from wild mosquitoes collected in Japan and Burkina Faso using two isolation methods (with and without surface sterilization). Detected fungal species included Beauveria bassiana sensu lato, Isaria spp., Paecilomyces spp., Lecanicillium spp., and Simplicillium spp. These isolates were used in bioassays against adult female Anopheles stephensi mosquitoes. The median survival time ranged from 5.8 to 14.9 d (control, 17.0 d). Reduced survival times were observed in the isolates from surface-sterilized mosquitoes from Japan, with the isolate B. bassiana s.l. 60-2 exhibiting the highest virulence. This study indicates that adult mosquitoes are naturally infected with various entomopathogenic hypocrealean fungi, and that some of these isolates have the potential for use as fungal pesticides to control vector mosquitoes.     

Dynamics of malaria transmission model with sterile mosquitoes

In this paper, a malaria transmission model with sterile mosquitoes is considered. We first formulate a simple SEIR malaria transmission model as our baseline model. Then sterile mosquitoes are introduced into the baseline model. We consider the case that the release rate of sterile mosquitoes is proportional to the wild mosquito population size. To investigate the impact of releasing sterile mosquitoes on the malaria transmission, the dynamics of the baseline model and the models with the sterile mosquitoes are discussed. We derive formulas of the reproductive numbers and explore the existence of endemic equilibrium as the reproductive number is more than unity for these models. It is shown that both the baseline model and the models with the sterile mosquitoes undergo backward bifurcations. Based on theoretical analysis and numerical simulation, we investigate the impact of releasing sterile mosquitoes on malaria transmission.     

Mosquitoes (Diptera: Culicidae) of anthropogenic territories in the North of Tomsk Region (by an example of the Strezhevoy town)

An ecological-faunistic analysis of mosquitoes has been carried out in the Strezhevoy town (Tomsk Region). Thirty-one species of mosquitoes have been recorded in the territory examined. The population peak of mosquitoes is recorded in the 1-2 ten-days of July. Characteristics of the biotopic distribution and daily activity of the dominant mosquito species are revealed. Limiting factors of daily activity of mosquitoes in the investigated territory are characterized.     

Probing behaviour and sporozoite delivery by Anopheles stephensi infected with Plasmodium berghei

We observed that Plasmodium berghei sporozoite-infected Anopheles stephensi was not impaired in its ability to locate blood on a host. When probing rats, infected mosquitoes took as long as non-infected mosquitoes to locate blood. Contrary to previous suggestions, infective mosquitoes delivered sporozoites into mineral oil even after extensively probing a vertebrate host. We observed that, in mosquitoes having probed a host, both the mean number of sporozoites ejected over 3 min into oil (35.9 v. 31.7 sporozoites) and the proportion of mosquitoes delivering sporozoites (60% v. 50%) were similar to mosquitoes not having probed. We then developed a model of sporozoite delivery, taking into account observations that sporozoites are clumped in the lumen of the glands as well as upon delivery, and that output is uneven and inconsistent. We conclude that clumping optimizes transmission, if a threshold of infection exists and the mean number of sporozoites per clump is greater than the threshold.     

A general theory for host seeking decisions in mosquitoes

We develop a theory for host seeking decisions in mosquitoes that explicitly considers the tradeoffs mosquitoes face in allocation to somatic and gametic function. Specifically, we consider conditions under which mosquitoes should seek out nectar and blood hosts upon encountering host odours. Results from development of a dynamic model that considers free and crop energy states suggest that mosquitoes should seek out blood hosts under a wide variety of conditions but that decisions to seek nectar depends upon crop volume, concentration and free energy. This pattern arises because mosquitoes carrying large crop loads are constrained in their ability to obtain large blood meals due to space limitations in the abdomen. The predicted patterns of behaviour are supported by published observations of mosquito behaviour.     

Evidence that sulfisoxazole, an antibacterial sulfonamide, can adversely affect the development of Brugia pahangi in Aedes aegypti mosquitoes

The average number of infective larvae recovered from Brugia pahangi-infected Aedes aegypti was approximately one-half that recovered from the controls after the former group of infected mosquitoes had ingested a 1.0% solution of sulfisoxazole diolamine (SXZ) in 10% sucrose-water for 4 consecutive days, beginning 4 days after infection. Most of the filarial larvae from the SXZ-treated mosquitoes were small and sluggish compared with those from the controls. There was no increased mortality of mosquitoes that ingested 1.0% SXZ in sugar-water for 4 days. Average filarial larval burdens were not decreased in mosquitoes that ingested a solution of 10(-6) M methotrexate (MTX), a potent dihydrofolate reductase inhibitor, in sugar-water for 4 days, beginning 4 days after infection. The distributional pattern of larval burdens in mosquitoes that ingested combined 1.0% SXZ and 10(-6) M MTX in sugar-water for 4 days closely resembled that seen in mosquitoes that had imbibed 1.0% SXZ only. Average filarial larval burdens were not decreased in mosquitoes with 4-day-old B. pahangi infections that fed upon jirds which received intraperitoneal injections of SXZ (2 g/kg) and MTX (1 mh/kh), alone and in combination, 1 hr previously. Survival of the mosquitoes that fed upon the drug-treated hosts was unaffected, as was the hatchability of their eggs and subsequent growth and development of the mosquito larvae.     

Borrelia burgdorferi sensu lato infection in mosquitoes from Szczecin area

The aim of the study was to determine the level of infection in mosquitoes with spirochetes Borrelia burgdorferi sensu lato in the woody areas of Szczecin. The mosquitoes were collected from May to September 2003. The spirochetes, Borrelia burgdorferi s. l., present in mosquitoes were detected in mosquitoes with indirect immunofluorescence assay (IFA) using rabbit anti-Borrelia burgdorferi antibodies and goat anti-rabbit IgG marked with fluorescein isocyanate (FITC). A total of 1557 females and 58 males were collected. They represented the genera Aedes (63%) and Culex (37%). The infection level of the mosquitoes from the area studied amounted to 1.7%. The results of the present study confirm the potential of these arthropods to spread Lyme borreliosis.