Insecticide susceptible/resistance status in Aedes (Stegomyia) aegypti and Aedes (Stegomyia) albopictus (Diptera: Culicidae) in Thailand during 2003-2005

Susceptibility baselines and diagnostic doses of the technical grade insecticides deltamethrin, permethrin, fenitrothion, and propoxur were established based on Aedes aegypti (L.), Bora (French Polynesia), a reference susceptible strain. Field-collected Aedes mosquitoes from each part of Thailand were subjected to bioassay for their susceptibility to the diagnostic doses of each insecticide. Almost all Ae. aegypti collected were incipient resistant or resistant to deltamethrin and permethrin, except those from some areas of Songkhla (southern) and Phan district of Chiang Rai (northern) province. Susceptibility to fenitrothion was found in mosquitoes from Bangkok (central), Chonburi (eastern), Chiang Rai, Kanchanaburi (western), and Songkhla, whereas they were resistant in almost all areas of Nakhon Sawan (north central) and Nakhon Ratchasima (northeastern) provinces. Most of Ae. aegypti were susceptible to propoxur except those from Mae Wong, Nakhon Sawan province. Various levels of insecticide resistance and susceptibility in adjacent areas revealed a focal susceptible/resistance profile in the country. It could be noted that almost all of Ae. albopictus were susceptible to the insecticides tested at the same diagnostic doses. In conclusion, resistance to pyrethroids (permethrin and deltamethrin) has developed in Ae. aegypti in most of the collected areas, suggesting that an alternative choice of insecticide or other control measures should be applied.     

Trend of temephos resistance in Aedes (Stegomyia) mosquitoes in Thailand during 2003-2005

The diagnostic dose for temephos susceptibility test was established based on Aedes aegypti, the susceptible Bora (French Polynesia) strain, for practical and routine use. The diagnostic dose was subsequently used to evaluate the susceptibility/resistance status in F1 progenies of field-collected samples from Bangkok and various parts of Thailand. It appeared that Ae. aegypti mosquitoes of one collection site each in Bangkok, Nakhon Sawan (northcentral), and Nakhon Ratchasrima (northeast) were resistant to temephos, with mortality ranging from 50.5 to 71.4%. Moreover, there was a trend of resistance to temephos among Ae. aegypti populations of all studied districts of Nakorn Ratchasima and most areas of Nakhon Sawan, of which those in one area were susceptible. However, various levels of temephos susceptibility were found in Bangkok populations, including resistance and incipient resistance. In Chonburi Province (eastern), all mosquitoes were susceptible to temephos with an indication of tolerance in one sample. Additionally, mosquitoes from Songkhla (south), Chiang Rai (north), Kanchanaburi (west), and Chanthaburi (east) remained susceptible to temephos during the sample collecting period. Bioassay tests on Aedes albopictus populations collected in this study from Nakhon Sawan, Nakorn Ratchasima, Songkhla, and Kanchanaburi revealed high susceptibility to temephos. Although the use of temephos seems to be potentially effective in many areas of the country, a noticeable trend of resistance indicated that alternative vector control methods should be periodically applied.     

Susceptibility of Aedes aegypti and Aedes albopictus larvae to Ascogregarina culicis and Ascogregarina taiwanensis (Apicomplexa: Lecudinidae) from Florida

The susceptibility of Aedes aegypti to Ascogregarina culicis and Aedes albopictus to Ascogregarina taiwanensis was examined with mosquito and parasite strains from Tampa, FL. When each host was bioassayed with its natural gregarine, the infection intensity indicated that Ae. aegypti was 59% more susceptible to A. culicis (87 gamonts/larva) than Ae. albopictus to A. taiwanensis (47 gamonts/larva). Infections in single and mixed host populations exposed to 100 oocysts/larva of one and both parasites demonstrated that Ae. aegypti harbors higher A. culicis gamont loads than Ae. albopictus of A. taiwanensis. In dual gregarine exposures of single host populations, the A. culicis infection intensity in Ae. aegypti was reduced by approximately 50%. A. taiwanensis exhibited the same capability of infecting Ae. albopictus in single and dual exposures. In mixed host populations there were no cross infections, but A. taiwanensis in Ae. albopictus produced an infection intensity of approximately 70% lower than that of A. culicis in Ae. aegypti.     

Resistance of Aedes aegypti from the state of São Paulo,Brazil, to organophosphates insecticides

Since the reintroduction of Aedes aegypti in the state of S o Paulo, in the middle of the 1980-decade, organophosphate insecticides are being used to control the dengue vector. In 1996, an annual program for monitoring the susceptibility of Ae. aegypti to the insecticides was implemented. Some of the results of this monitoring program are presented. Ae. aegypti populations from ten localities have been submitted to bioassays with the diagnostic dose of temephos and fenitrothion. Only two (Mar lia and Presidente Prudente) remain susceptible to both insecticides and one (Santos) exhibits true resistance. Ae. aegypti from the remaining localities showed an incipient altered susceptibility. Resistance ratios varied from 1.2 to 2.9 for temephos and from 1.5 to 3.2 to fenitrothion, indicating moderate levels of resistance. Biochemical assays did not detect alterations in the enzyme acetilcholinesterase, but indicated that resistance is associated with esterases.     

The naturally derived insecticide spinosad is highly toxic to Aedes and Anopheles mosquito larvae

Spinosad is a naturally derived biorational insecticide with an environmentally favourable toxicity profile, so we investigated its potency against mosquito larvae (Diptera: Culicidae). By laboratory bioassays of a suspension concentrate formulation of spinosad (Tracer), the 24 h lethal concentration (LC50) against Aedes aegypti (L.) third and fourth instars was estimated at 0.025 p.p.m. following logit regression. The concentration-mortality response of third- and fourth-instar Anopheles albimanus Weidemann did not conform to a logit model. The LC50 value of spinosad in Anopheles albimanus was 0.024 p.p.m. by quadratic linear regression. A field trial in southern Mexico demonstrated that spinosad 1 p.p.m. compared with the standard temephos (Abate) 1% granules 100 g/m3 water prevented Ae. aegypti breeding in plastic containers of water for 8 weeks; at 10 p.p.m. spinosad prevented breeding for > 22 weeks. In another field trial, spinosad at 5 p.p.m. and temephos both completely eliminated reproduction of Ae. aegypti for 13 weeks. In contrast, the bacterial insecticide Bacillus thuringiensis var. israelensis (Bti, Vectobac) AS) performed poorly with just 2 weeks of complete inhibition of Ae. aegypti breeding. Spinosad also effectively prevented breeding of Culex mosquitoes and chironomids in both trials to a degree similar to that of temephos. We conclude that spinosad merits evaluation as a replacement for organophosphate or Bti treatment of domestic water tanks in Mesoamerica. We also predict that spinosad is likely to be an effective larvicide for treatment of mosquito breeding sites.     

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。     

The efficacy of a chitin synthesis inhibitor against field populations of organophosphate-resistant Aedes aegypti in Brazil

The mosquito Aedes aegypti is the main focus of dengue control campaigns. Because of widespread resistance against conventional chemical insecticides, chitin synthesis inhibitors (CSIs) are considered control alternatives. We evaluated the resistance status of four Brazilian Ae. aegypti populations to both the organophosphate temephos and the pyrethroid deltamethrin, which are used in Brazil to control larvae and adults, respectively. All vector populations exhibited high levels of temephos resistance and varying rates of alterations in their susceptibility to pyrethroids. The effect of the CSI novaluron on these populations was also investigated. Novaluron was effective against all populations under laboratory conditions. Field-simulated assays with partial water replacement were conducted to evaluate novaluron persistence. Bioassays were continued until an adult emergence inhibition of at least 70% was attained. We found a residual effect of eight weeks under indoor conditions and novaluron persisted for five-six weeks in assays conducted in an external area. Our data show that novaluron is effective against the Ae. aegypti populations tested, regardless of their resistance to conventional chemical insecticides.     

Sodium channel gene expression in mosquitoes, Aeries albopictus （S.）

A mosquito strain of Aedes albopictus, HAmAal^G0, from Huntsville, Alabama, USA, showed a normal susceptibility and low tolerance to permethrin and resmethrin （pyrethroid insecticides） compared to a susceptible Ikaken strain, even though these pyrethroid insecticides have been used in the field for a long period of time in Alabama. Recently, we treated HAmAal^G0 in the laboratory with permethrin for five generations and detected no significant change in the level of resistance to permethrin in the selected mosquitoes, HAmAal^G0, compared with the parental strain HAmAal^G0. We then examined the allelic expression at the L-to-F kdr site of the sodium channel gene in the Aedes mosquitoes to address our hypothesis that the L-to-F kdr mutation was not present in HAmAal^G0 and HAmAal^G5 mosquitoes. We found that every tested individual in Ikaken, HAmAal^G5, and HAmAal^G5 populations expressed a codon of CTA at the L-to-F kdr site encoding Leu, strongly corresponding to their susceptibility to insecticides.     

qPCR Identification of the kdr Allele F1534C in Voltage-Gated Sodium Channel Gene (vgsc) of the Major Mosquito Vectors Aedes aegypti and Aedes albopictus in Northern and Central Vietnam

Russian Journal of Genetics - Pyrethroid insecticides are currently the main tool for controlling major mosquito vectors of hemorrhagic fevers—Aedes aegypti and Ae. albopictus. The widespread...     

Insecticide susceptibility status of Aedes aegypti (Diptera: Culicidae) from Townsville

Insecticide susceptibility of a 1995 Townsville Aedes aegypti (L.) population was investigated in the laboratory according to World Health Organization guidelines. Using baseline data from two Townsville populations (1955 and 1989), larval bioassays detected significant increases in susceptibility to synthetic pyrethroids and malathion, and significant reductions in susceptibility to most organophosphates and propoxur. Adult bioassays detected significant resistance to bendiocarb and DDT. Comparison of larval data with the international reference ROCK strain showed substantial resistance to have developed to malathion and fenthion. Further analysis revealed the presence of distinct substrains in the baseline 1989 population, which displayed varying levels of temephos susceptibility. We concluded that susceptibility investigations should assess mosquito populations collected from many sites within an area rather than taking a single population from one site, and that the 1989 Ae. aegypti colony would be unsuitable for use as a susceptible reference population.     

Preliminary data on the performance of Aedes aegypti and Aedes albopictus immatures developing in water-filled tires in Rio de Janeiro

A monthly survey of Aedes aegypti and Aedes albopictus immatures in discarded tires at a site in metropolitan Rio de Janeiro showed that Ae. albopictus was much more abundant in the rainy season, but Ae. aegypti abundance showed a less clear seasonal pattern. Pupal masses for Ae. albopictus showed a seasonal trend. In contrast, Ae. aegypti pupae did not show any clear trend in weight. Large Ae. albopictus pupae were found in the warmer months, when water volume was higher, pH lower and larval abundance lower. Further studies should be carried out to assess how seasonal variations in body size may impact vector competence of these species in Brazil.     

Parasitism of Ascogregarina taiwanensis and Ascogregarina culicis (Apicomplexa: Lecudinidae) in larvae of Aedes albopictus and Aedes aegypti (Diptera: Culicidae) from Manaus, Amazon region, Brazil

The aim of the study was to determine the existence of Ascogregarina spp. in larvae of Aedes albopictus and Aedes aegypti collected in urban and suburban areas of Manaus, Amazon region, Brazil. Between May 2004 and July 2005, the mid-gut of 3rd and 4th instar larvae, collected in tire traps in six neighborhoods of Manaus, was examined for the presence of trophozoites of Ascogregarina. Coexistence of Ae. albopictus larvae infected by A. taiwanensis, and Ae. aegypti larvae by A. culicis, was detected in traps in the field. The percentage of Ae. albopictus larvae infected by A. taiwanensis ranged from 21% to 93.5% and of Ae. aegypti larvae infected by A. culicis from 22% to 95%. The mean infection intensity was similar in both species of Aedes. In traps located in Mauazinho, the replacement of Ae. aegypti by Ae. albopictus larvae was observed. In Manaus, Ae. albopictus larvae were parasitized by A. taiwanensis, and Ae. aegypti larvae by A. culicis. Infection rates were high when the species of Aedes were found separately.     

The first report of Aedes (Stegomyia) albopictus in Haiti

Aedes albopictus was found in six of the 10 departments of Haiti and in 14 of the 35 communes surveyed. The survey found the larvae of Ae. albopictus in 13 different types of containers. Used tires and tins were by far the most common breeding sites used by this mosquito species. At the breeding sites, Ae. albopictus was associated with other mosquito species, such as Aedes aegypti, Culex nigripalpus and Aedes mediovittatus. The highest proportion of association was with Ae. aegypti. This study represents the first report of Ae. albopictus in Haiti.     

Elevated activity of an Epsilon class glutathione transferase confers DDT resistance in the dengue vector, Aedes aegypti

Glutathione transferases (GSTs) play a central role in the detoxification of xenobiotics such as insecticides and elevated GST expression is an important mechanism of insecticide resistance. In the mosquito, Anopheles gambiae, increased expression of an Epsilon class GST, GSTE2, confers resistance to DDT. We have identified eight GST genes in the dengue vector, Aedes aegypti. Four of these belong to the insect specific GST classes Delta and Epsilon and three are from the more ubiquitously distributed Theta and Sigma classes. The expression levels of the two Epsilon genes, a Theta GST and a previously identified Ae. aegypti GST [Grant and Hammock, 1992. Molecular and General Genetics 234, 169-176] were established for an insecticide susceptible and a resistant strain. We show that the putative ortholog of GSTe2 in Ae. aegypti (AaGSTe2) is over expressed in mosquitoes that are resistant to the insecticides DDT and permethrin. Characterisation of recombinant AaGSTE2-2 confirmed the role of this enzyme in DDT metabolism. In addition, unlike its Anopheles ortholog, AaGSTE2-2 also exhibited glutathione peroxidase activity.     

Larval development of Aedes aegypti and Aedes albopictus in peri-urban brackish water and its implications for transmission of arboviral diseases

Aedes aegypti (Linnaeus) and Aedes albopictus Skuse mosquitoes transmit serious human arboviral diseases including yellow fever, dengue and chikungunya in many tropical and sub-tropical countries. Females of the two species have adapted to undergo preimaginal development in natural or artificial collections of freshwater near human habitations and feed on human blood. While there is an effective vaccine against yellow fever, the control of dengue and chikungunya is mainly dependent on reducing freshwater preimaginal development habitats of the two vectors. We show here that Ae. aegypti and Ae. albopictus lay eggs and their larvae survive to emerge as adults in brackish water (water with <0.5 ppt or parts per thousand, 0.5-30 ppt and >30 ppt salt are termed fresh, brackish and saline respectively). Brackish water with salinity of 2 to 15 ppt in discarded plastic and glass containers, abandoned fishing boats and unused wells in coastal peri-urban environment were found to contain Ae. aegypti and Ae. albopictus larvae. Relatively high incidence of dengue in Jaffna city, Sri Lanka was observed in the vicinity of brackish water habitats containing Ae. aegypti larvae. These observations raise the possibility that brackish water-adapted Ae. aegypti and Ae. albopictus may play a hitherto unrecognized role in transmitting dengue, chikungunya and yellow fever in coastal urban areas. National and international health authorities therefore need to take the findings into consideration and extend their vector control efforts, which are presently focused on urban freshwater habitats, to include brackish water larval development habitats.     

Aedes albopictus (Diptera: Culicidae) in Rome: experimental study of relevant control strategy parameters

Since 1997, Aedes albopictus has colonised and then rapidly invaded the city of Rome (Italy) and its peripheral areas. Presently, the control of this mosquito in Italy relies mainly on larvicidal treatment of street storm sewer catch basins with the organophosphate temephos. We have therefore obtained baseline data on the susceptibility to temephos of the Roman Ae. albopictus population by laboratory bioassays on F1 fourth-instar larvae following standard WHO protocols. Estimated lethal concentrations were 0.014 mg/l (LC50) and 0.022 mg/l (LC90) indicating a lack of resistance to this compound. The persistence of temephos in sewer catch basins was evaluated by follow-up of catch basins treated with a dose of 1.5 mg of active ingredient. Mosquito larvae were recovered in 10% and 50% of the treated basins at 9 and 18 days posttreatment, respectively. In order to understand the relative contribution of this larval habitat to adult populations, we conducted a survey in the Zoo of Rome to estimate the larval density of mosquitoes breeding in sewer catch basins. A complete census of a 16.5 ha area mapped 243 catch basins, but only 25 (10.3%) contained water; of the latter 8 (32.0%) hosted mosquito larvae. All positive catch basins contained larvae of Culex pipiens, which were associated with Culiseta longiareolata and/or Ae. albopictus in 6 and 3 cases, respectively. A longitudinal survey of one catch basin over 4 months showed that the mean larval density of Ae. albopictus was markedly lower than that of Cx pipiens and Cs. Iongiareolata, ranging between 0 and 1.3 larvae/dip as compared to 0-33.2 and 0-22.7 larvae/dip, respectively. However, adult densities of Ae. albopictus in this area estimated during the same period with 20 ovitraps showed consistently high values (proportion of positive ovitraps around 100%). These preliminary observations suggest that whenever alternative larval biotopes other than sewer catch basins are widely available, they might be more productive and/or preferred substrates to catch basins for Ae. albopictus breeding.     

Susceptibility and fitness cost of Aedes albopictus on their survivability after the exposure to the insecticide

The present study was undertaken to investigate the lethal and sub-lethal effects of insecticides on the life history of Aedes albopictus mosquitoes from urban and sub-urban areas in Penang, Malaysia. The female mosquitoes aged two to five days old were exposed to; (1) diagnostic dose (lethal dose) at 5% malathion and 0.75% permethrin; and (2) sub-lethal concentration of 1.5% malathion, and 0.2% permethrin, respectively and adult female survivors from sub-lethal concentrations were evaluated for fitness parameters. Fecundity, fertility, adult longevity, development time and survival of mosquitoes were the crucial point in their life history had studied. Aedes albopictus species from urban Sg. Dua strain has developed high resistance towards 0.75% permethrin and was confirmed on resistance after 24 h of reading. While sub-urban Batu Maung strain is still susceptible to both 5% malathion and 0.75% permethrin. At the sub-lethal dose, we discovered 0.2% permethrin insecticide have significantly more effects on the fitness cost of Ae. albopictus as compared to 1.5% malathion; with decreasing on fecundity, lesser time was needed to reach each development stages, and more male adult was emerged compared to female mosquitoes for both urban and sub-urban strains. Whereas, malathion insecticide only affected the number of eggs laid by the parent mosquitoes and the development time to reach adult stages. Even though, Ae. albopictus mosquitoes had developed resistance towards permethrin resulted in decreasing mortality, but subsequent effects on their fitness cost still continued on the first generation. Thus, it will benefit in reducing the transmission of mosquito-borne diseases.     

Functional and immunohistochemical characterization of CCEae3a,a carboxylesterase associated with temephos resistance in the major arbovirus vectors Aedes aegypti and Ae. albopictus

Temephos is a major organophosphate (OP) larvicide that has been used extensively for the control of Aedes albopictus and Aedes aegypti, the major vectors for viral diseases, such as dengue fever, zika and chikungunya. Resistance to temephos has been recently detected and associated with the upregulation of carboxylesterases (CCEs) through gene amplification, in both species. Here, we expressed the CCEae3a genes which showed the most striking up-regulation in resistant Aedes strains, using the baculovirus system. All CCEae3a variants encoded functional enzymes, with high activity and preference for p-nitrophenyl butyrate, a substrate that was shown capable to differentiate temephos resistant from susceptible Aedes larvae. Enzyme kinetic studies showed that CCEae3as from both Ae. aegypti and Ae. albopictus (CCEae3a_aeg and CCEae3a_alb, respectively) strongly interact with temephos oxon and slowly released the OP molecule, indicating a sequestration resistance mechanism. No difference was detected between resistant and susceptible CCEae3a_aeg variants (CCEae3a_aegR and CCEae3a_aegS, respectively), indicating that previously reported polymorphism is unlikely to play a role in temephos resistance. HPLC/MS showed that CCEae3as were able to metabolize temephos oxon to the temephos monoester [(4-hydroxyphenyl) sulfanyl] phenyl O,O-dimethylphosphorothioate. Western blot and immunolocalization studies, based on a specific antibody raised against the CCEae3a_alb showed that the enzyme is expressed at higher levels in resistant insects, primarily in malpighian tubules (MT) and nerve tissues.