Satyrization without evidence of successful insemination from interspecific mating between invasive mosquitoes

Previous research has documented low frequencies of interspecific mating in nature between the invasive vectors Aedes aegypti and Aedes albopictus. It is also known that heterospecific male accessory gland substances transferred during mating sterilize A. aegypti but not A. albopictus females, leading to satyrization, a form of reproductive interference. This paper demonstrates that satyrization of A. aegypti by A. albopictus may occur without evidence of successful insemination. Our results show that A. aegypti females, previously exposed to A. albopictus males, are rendered refractory to subsequent conspecific mating even though their spermathecae contain no heterospecific sperm. Additional experiments demonstrating transfer of labelled semen from A. albopictus males to A. aegypti females and low production of viable eggs of females housed with conspecific males, following exposure to A. albopictus males, confirm higher incidences of satyrization than expected, based on heterospecific insemination rates. We conclude that frequencies of satyrization based on detection of interspecific sperm in spermathecae may underestimate the impact of this form of reproductive interference.     

登革热媒介昆虫抗药性的研究进展

近年来,登革热在全球的流行迅速增长,埃及伊蚊Aedes aegypti(L.)和白纹伊蚊Aedes albopictus(Skuse)是登革热传播的主要媒介。目前,化学防治仍然是防治蚊虫的主要手段,每年化学杀虫剂的大量使用直接或间接地导致其产生了抗药性。关于埃及伊蚊和白纹伊蚊的抗药性研究,主要集中于DDT、有机磷和拟除虫菊酯类杀虫剂导致的抗药性,并已深入到抗药性分子机理的研究。文章就埃及伊蚊和白纹伊蚊对杀虫剂诱导的抗药性现状及抗性机理的研究进展进行综述。     

Pathogenicity of entomopathogenic fungus,Metarhizium anisopliae MET-GRA4 isolate on dengue vectors,Aedes albopictus and Aedes aegypti mosquito larvae (Diptera: Culicidae)

Considering the rapid transmission of the dengue virus, substantial efforts need to be conducted to ward-off the epidemics of dengue viruses. The control effort is depending on chemical insecticides and had aroused undesirable conflicts of insecticide resistance. Here, we study the entomopathogenic fungus, Metarhizium anisopliae as a promising new biological control agent for vector control. The pathogenicity effects of Metarhizium anisopliae against field and laboratory strains of Aedes albopictus and Aedes aegypti larvae were tested using the larvicidal bioassay technique. The results demonstrate that the treatments using M. anisopliae isolate MET-GRA4 were highly effective and able to kill 100% of both Ae. albopictus and Ae. aegypti mosquito larvae at a conidia concentration of 1 × 10?/ml within 7 days of the treatment period. The fungus displayed high larvicidal activity against laboratory and field strain of Ae. aegypti larvae with LC₅₀ values (9.6 × 10³/ml, 1.3 × 10³/ml) and LC₉₅ values (1.2 × 10?/ml, 5.5 × 10⁵/ml) respectively. For Ae. albopictus, LC₅₀ values for laboratory and field strains were (1.7 × 10⁴/ml, 2.7 × 10⁴/ml) and the LC₉₅ values were (2.1 × 10?/ml, 7.0 × 10⁵/ml) respectively. Interestingly, the susceptibility of field strain towards M. anisopliae was higher as compared to the laboratory strain Aedes larvae. In which, the causative agents of all the dead larvae were verified by the virulence of M. anisopliae and caused morphological deformities on larval body. The findings from this study identify this isolate could be an effective potential biocontrol agent for vector mosquitoes in Malaysia.     

Electronic mosquito repellers induce increased biting rates in Aedes aegypti mosquitoes (Diptera: Culicidae)

Studies have demonstrated that electronic mosquito repellers are useless and that some of them could even increase the attraction of mosquitoes. While testing some electronic repellers, we noted that they also promoted an increase in biting rates. The present work has evaluated three commercial devices and a computer program working on five different sound frequencies. In a test chamber, the number of Aedes aegypti L. bite attempts was computed during four cycles of 3 min each by alternately turning the devices off and on. The mosquito biting rates for five sound frequencies (ranging from 9.6 kHz to 18.2 kHz) initially demonstrated a significant increase (ranging from around 20% to 50%), which decreased from 8.3% to 25.1% when the repellers were turned off. The biting rate significantly increased at 11.8 kHz (33.7%) when the device was turned on again. The danger of using electronic repellers and the role of sound frequencies stimulating mosquito biting are discussed.     

The community ecology of Aedes egg hatching: implications for a mosquito invasion

Abstract. 1. A recently introduced treehole mosquito from Asia, Aedes albopictus , is spreading throughout eastern North America, especially in tyre-refuse piles. Previous studies have identified inhibitory effects of larvae on egg hatch as a potential population regulatory mechanism within Aedes. Larva-egg interactions may also occur between species. This experiment assesses the ability of larvae of A. albopictus and two possible competitors in North America, A.triseriatus and A.aegypti , to suppress hatching of conspecific and congeneric eggs.
2. We exposed eggs of each species to varying combinations of larval species and density for 24h and assessed subsequent hatch rates. Aedes albopictus eggs exhibited the lowest level of inhibition when exposed to high larval densities; moreover, at the lowest larval density they imposed the most intense interspecific hatch inhibition.
3. Discretionary hatching in response to larval density may influence community composition by promoting the spread of A.albopictus , perhaps even leading to its dominance within North American Aedes communities.     

Competition and resistance to starvation in larvae of container-inhabiting Aedes mosquitoes

Abstract. 1. Hypotheses about declining populations of container-inhabiting Aedes mosquitoes following the invasion by additional species were tested.
2. The larval competition hypothesis was studied experimentally in pure and mixed cultures of Aedes aegypti (L.), A.albopictus (Skuse) and A.triseriatus (Say). The experiments used decomposing leaf litter in the laboratory, as opposed to most previous research which used non-natural food.
3. Resistance to starvation is introduced as a new measure of larval performance and competitiveness. The hypothesis is that more successful larvae store larger energy reserves and resist the lack of food longer.
4. Contrary to previous research showing better performance of A.aegypti in mixed cultures, A.albopictus developed faster and had greater survival when natural food was used.
5. Resistance to starvation was greater in the better performing species (i.e. A.aegypti with non-natural food and A.albopictus with leaf litter). Oxygen consumption by starved larvae was similar in the three container species, and in the ground-water mosquito, A.taeniorhynchus (Wied.), whose resistance to starvation was comparatively very low.     

Herpetomonas,with Bacterium-like Inclusions,in Malaysian Aedes aegypti and Aedes albopictus*

SYNOPSIS Herpetomonas sp. was found repeatedly in the Malpighian tubules of laboratory-reared male and female Aedes aegypti and Aedes albopictus in Malaysia. The flagellates occurred irregularly, in batches, and were absent during long periods. The data suggest an exogenous source of infection for the mosquitoes, presumably from another insect, probably of another genus. Thirty to 40% of the flagellates of Aedes contained intracytoplasmic rod-shaped structures strongly resembling bacteria. These were found often in groups suggesting intracellular multiplication. They were passed to the Herpetomonas daughter cells during division. Parasitism of Aedes by Herpetomonas is extremely unusual, only one previous record, an inconclusive one, having been found. Parasitism by Herpetomonas containing bacterium-like rods has apparently never been reported.     

The importance of an invasive tree fruit as a resource for mosquito larvae

Invasive plants are common and may provide resources through litter for container mosquito larvae. Invasive plant reproductive parts can make up a substantial part of litter but have mostly been ignored as a resource for mosquito larvae. We hypothesized that the reproductive fruits of the invasive eastern red cedar, Juniperus virginiana, provide high quality resources for the invasive, container mosquito Aedes albopictus at the western margin of its invasive range in North America. To test this hypothesis, we performed two laboratory experiments. The first examined the response of individual larvae of Ae. albopictus to different amounts of J. virginiana leaf (fresh and senesced) and J. virginiana fruit (ripe and unripe), as well as to a control leaf (Quercus virginiana, live oak). The second experiment examined the response of different densities of Ae. albopictus larvae to each litter type. We found significant differences in response by individual larvae to different amounts of litter and litter types. We also found J. virginiana litter components could support positive population growth rates as a function of initial larval density where the control leaf could not. We conclude that invasive plants may provide high quality resources, and that the reproductive parts (fruits, flowers, cones) may be an important and overlooked component in provisioning larval habitats. Therefore, the expansion of J. virginiana into grassland areas may contribute to the expansion of Ae. albopictus westward in North America.     

Genetic changes in methotrexate-resistant mosquito cells.

A stepwise selection procedure was used to obtain from Mtx-5011 Aedes albopictus cells, variants with increased resistance to methotrexate (mtx). On the basis of growth, the Mtx-5011 derivatives were 270- to 3,000-fold more resistant to mtx than wild-type mosquito cells. Properties associated with mtx resistance in these cells were consistent with amplification of the dihydrofolate reductase (DHFR) gene. The cells overproduced DHFR protein, were enriched with DHFR mRNA, and DNA from resistant cells was enriched for a band that likely contained the DHFR coding sequence. Karyotype analysis indicated that high levels of resistance were accompanied by a conversion to tetraploidy, chromosome rearrangements, and an apparent duplication of one of the mosquito chromosomes.     

Increased ribonucleotide reductase activity in hydroxyurea-resistant mosquito cells

Hydroxyurea-resistant Aedes albopictus mosquito cells were selected by incremental exposure of unmutagenized cells to hydroxyurea concentrations ranging from 0.1 to 8 mM. Clonal populations that had become 40-fold more resistant to hydroxyurea than wild-type cells varied in morphology, and their growth rate decreased to a ∼45 h doubling time, relative to an 18 h doubling time in unselected cells. At this level of resistance, the cells remained diploid, with a modal chromosome number of 6. When labelled with ³⁵S[methionine/cysteine], clone HU1062, which grew in the presence of 8 mM hydroxyurea, overproduced a labeled protein with the approximate size of the 45,000 dalton M2 subunit of ribonucleotide reductase. Consistent with this observation, ribonucleotide reductase activity in HU-1062 cells was approximately 10-fold higher than in wild-type control cells. This is the first example of an hydroxyurea-resistant insect cell line. © 1997 Wiley-Liss, Inc.     

Cloning and characterization of a chitin synthase cDNA from the mosquito Aedes aegypti

Characterization of the enzymes involved in the chitin biosynthetic pathway in mosquitoes is critical due to the importance of chitin in the formation of the peritrophic matrix [PM] and its potential impact on vector competence. Chitin is the homopolymer of the amino sugar N-acetyl-D glucosamine [GlcNAc]. The final step of incorporation of GlcNAc into the chitin polymer is catalyzed by the enzyme chitin synthase [CS]. CS is a membrane bound enzyme, but the mechanism of its action in the biosynthesis of the PM is not understood. We have isolated and sequenced a CS-encoding cDNA clone from the mosquito Aedes aegypti, compared its sequence with CS from other organisms and studied its RNA expression. The cDNA is 3.5 kb in length with an open reading frame of 2.6 kb that encodes a protein of 865 amino acids with a predicted molecular mass of 99.5 kDa. The putative translation product shares 90% similarity to two CS proteins from Caenorhabditis elegans and 50% similarity to Saccharomyces cerevisiae in the catalytic domain of CS enzymes. Data suggest that CS is a single copy gene. RT-PCR analysis shows CS message in whole non-blood-fed females, whole blood-fed females, non-blood-fed midguts and in midguts dissected at different time points post-blood-feeding. In situ hybridization studies of midgut samples revealed that CS mRNA increases following a bloodmeal and is localized to the periphery of the epithelial cells facing the midgut lumen.     

Distribution and habitats of mosquito larvae in the Kingdom of Tonga

Abstract  Mosquitoes are a significant pest and human health issue in the Kingdom of Tonga. The occurrence of species and habitats used by mosquito larvae were investigated to determine the potential for control through larval habitat management. Forty-two sites, including 22 villages and 20 farm plantations on the six islands of Tongatapu, Pangaimotu, Vava'u, Pangaimotu (Vava'u group), 'Utungake and Nuku, were surveyed in April 2006. A total of eight mosquito species were collected: Aedes aegypti (Linnaeus), Ae. horrescens (Edwards), Ae. nocturnus (Theobold), Ae. tongae (Edwards), Culex albinervis (Edwards), Cx. annulirostris (Skuse), Cx. quinquefasciatus (Say) and Cx. sitiens (Wiedemann). Several species were widespread, particularly Ae. aegypti and Ae. nocturnus on the main island of Tongatapu, whereas Ae. aegypti dominated sites on islands of the Vava'u group. Comparative sampling of 17 village and 17 rural sites showed that larval habitat was more abundant in towns than in rural areas. Larvae were found in a wide range of habitats but were particularly abundant in artificial water bodies (e.g. disused concrete water tanks, 44-gallon drums and used car tyres). In rural sites, habitats were generally sparse except in rain-filled branch stems of giant taro plants. Mosquito populations in artificial habitats could be markedly reduced by seeding disused water tanks with aquatic predators already present in Tonga, using mesh-net covers over 44-gallon drums, and drilling holes in used car tyres.     

The cost of immunity in the yellow fever mosquito, Aedes aegypti depends on immune activation

Although host immunity offers the obvious benefit of reducing parasite infection, it is often traded-off with other fitness components. We investigated whether the cost of an immune response in the yellow fever mosquito, Aedes aegypti, is modulated by the antigen that activates the melanization immune response. Thus, one of three different novel antigens were injected into the mosquito's thorax--either a glass bead, a negatively charged (C-25) Sephadex bead, or a neutral (G-25) Sephadex bead--and fecundity and bead melanization were observed. Glass beads are immunologically inert and were therefore used as an inoculation control. The fecundity of mosquitoes inoculated with these beads did not differ from the fecundity of mosquitoes that did not melanize negatively charged or neutral beads. The ability of A. aegypti to melanize negatively charged Sephadex beads was associated with reduced fecundity, showing a clear cost of immunity. In contrast, melanization of the neutral beads was quite strong but had no effect on fecundity. Thus, the cost of what appeared to be the same immune response--melanization of a bead--depended on the type of bead that stimulated the immune system. Such differences might help to explain variation of immune efficacy against different parasites in natural populations.     

Detection and localization of antibody ingested with a mosquito bloodmeal

Mouse immunoglobulins were found to persist in Aedes aegypti (L.) mosquito bloodmeals for 2-3 days after ingestion. Immunoenzyme labelling revealed mouse antibody specifically bound to the mosquito midgut epithelium after ingestion; immunogold labelling of thin sections revealed mouse antibody within the cytoplasm of the microvilli on the midgut epithelium. Ingested mouse antibody was not conclusively demonstrated bound to tissues outside the gut, though antibody was detected in mosquito haemolymph using a sensitive ELISA test. Possible mechanisms by which antibody may cross mosquito gut barriers and actions that in vivo antibody:antigen reactions may have on these bloodfed insects are discussed.     

白纹伊蚊和埃及伊蚊对基孔肯雅病毒的易感性和传播性的研究

用４株基孔肯雅病毒经口感染白纹伊蚊和埃及伊蚊,进行了易感性和传播性的研究。结果表明,这两种蚊虫对基孔肯雅病毒易感。无论白纹伊蚊或埃及伊蚊,感染后第５－６天即可通过吸血将病毒传播给乳鼠,至第８－１３天,传播率可高达５５．５５％－１００％。感染蚊亦可经叮咬将病毒传播给小鸡。埃及伊蚊的易感性和传播率高于白纹伊蚊。实验还发现,不同来源毒株之间存在一定差异,如分离自云南白纹伊蚊的Ｍ８１株的感染率和传播率均高于其它毒株。这些结果表明,白纹伊蚊和埃及伊蚊在基孔肯雅病毒的保存和传播中起重要作用。     

Selective and frequency dependent predation of aquatic mosquito predator Diplonychus indicus Venkatesan & Rao (Hemiptera: Belostomatidae) on immature stages of three mosquito species

Frequency dependent mosquito larval size (II and IV instars) and species selection by the water bug Diplonychus indicus against three mosquito species Culex quinquefasciatus, Aedes aegypti and Anopheles stephensi was studied in the laboratory. The different frequencies used for each species selection were 20:30:50, 30:50:20, 50:20:30, 25:35:40, 35:40:25 and 40:25:35 of fourth instars of the respective three prey species. All nymphal water bugs (I–V instars) selected IV instar mosquito larvae and the mean proportion of late (larger) larvae eaten by the predator instars was significantly higher than the mean proportion of early (smaller) larvae eaten (F= 2.28; P < 0.001). In all six ratios used to determine the frequency dependent mosquito species selection, all the stages of the water bug selected Ae. aegypti over the other two species (F= 452.43; P < 0.001). The mean number of mosquito larvae eaten increased as its density increased based on various ratios of larvae offered. The study indicated that the predatory efficiency of D. indicus was high when Ae. aegypti was offered as prey, suggesting the utility of this mosquito predator in the control of dengue vectors.     

Heteropteran insects as mosquito predators in water jars in southern Vietnam

Residents of Vietnam living in areas with water shortages and/or poor tap water maintain water storage containers, such as jars, in and around their domiciles in order to store water used in daily life. Although these water jars are known to be important breeding sources of the Aedes mosquito, use of chemical larvicides in such containers is legally prohibited in Vietnam. In this study, we identified the dominant mosquito insect predators in water jars in and around residences located in Tan Chanh, Long An, southern Vietnam. Of 3,646 Heteroptera collected from such jars, Corixidae (Micronecta spp.) and Veliidae (Microvelia spp.) were revealed to be the dominant predators. Polymerase chain reaction (PCR) analysis revealed that 40% of Micronecta and 12% of Veliidae had Aedes aegypti‐positive reactions, indicating that these two dominant Heteroptera are important predators of Ae. aegypti. Our results suggest that aquatic Heteroptera may be an important mosquito control agent in addition to the currently used copepods.