Chikungunya Virus Transmission Potential by Local Aedes Mosquitoes in the Americas and Europe

Background

Chikungunya virus (CHIKV), mainly transmitted in urban areas by the mosquitoes Aedes aegypti and Aedes albopictus, constitutes a major public health problem. In late 2013, CHIKV emerged on Saint-Martin Island in the Caribbean and spread throughout the region reaching more than 40 countries. Thus far, Ae. aegypti mosquitoes have been implicated as the sole vector in the outbreaks, leading to the hypothesis that CHIKV spread could be limited only to regions where this mosquito species is dominant.

Methodology/Principal Findings

We determined the ability of local populations of Ae. aegypti and Ae. albopictus from the Americas and Europe to transmit the CHIKV strain of the Asian genotype isolated from Saint-Martin Island (CHIKV_SM) during the recent epidemic, and an East-Central-South African (ECSA) genotype CHIKV strain isolated from La Réunion Island (CHIKV_LR) as a well-characterized control virus. We also evaluated the effect of temperature on transmission of CHIKV_SM by European Ae. albopictus. We found that (i) Aedes aegypti from Saint-Martin Island transmit CHIKV_SM and CHIKV_LR with similar efficiency, (ii) Ae. aegypti from the Americas display similar transmission efficiency for CHIKV_SM, (iii) American and European populations of the alternative vector species Ae. albopictus were as competent as Ae. aegypti populations with respect to transmission of CHIKV_SM and (iv) exposure of European Ae. albopictus to low temperatures (20°C) significantly reduced the transmission potential for CHIKV_SM.

Conclusions/Significance

CHIKV strains belonging to the ECSA genotype could also have initiated local transmission in the new world. Additionally, the ongoing CHIKV outbreak in the Americas could potentially spread throughout Ae. aegypti- and Ae. albopictus-infested regions of the Americas with possible imported cases of CHIKV to Ae. albopictus-infested regions in Europe. Colder temperatures may decrease the local transmission of CHIKV_SM by European Ae. albopictus, potentially explaining the lack of autochthonous transmission of CHIKV_SM in Europe despite the hundreds of imported CHIKV cases returning from the Caribbean.     

Molecular Differentiation of the African Yellow Fever Vector Aedes bromeliae (Diptera: Culicidae) from Its Sympatric Non-vector Sister Species,Aedes lilii

Introduction

Yellow fever continues to be a problem in sub-Saharan Africa with repeated epidemics occurring. The mosquito Aedes bromeliae is a major vector of yellow fever, but it cannot be readily differentiated from its non-vector zoophilic sister species Ae. lilii using morphological characters. Genetic differences have been reported between anthropophilic Ae. bromeliae and zoophilic Ae. lilii and between forest and domestic populations. However, due to the application of different molecular markers and non-overlapping populations employed in previous studies, interpretation of species delimitation is unclear.

Methodology/Principle Findings

DNA sequences were generated from specimens of Ae. simpsoni s.l. from the Republic of Benin, Tanzania and Uganda for two nuclear genes apolipophorin 2 (apoLp2) and cytochrome p450 (CYPJ92), the ribosomal internal transcribed spacer region (ITS) and the mitochondrial cytochrome c oxidase (COI) barcoding region. Nuclear genes apoLp2 and CYPJ92 were unable to differentiate between species Ae. bromeliae and Ae. lilii due to ancestral lineage sorting, while ITS sequence data provided clear topological separation on a phylogeny. The standard COI barcoding region was shown to be subject to species introgression and unable to clearly distinguish the two taxa. Here we present a reliable direct PCR-based method for differentiation of the vector species Ae. bromeliae from its isomorphic, sympatric and non-biomedically important sister taxon, Ae. lilii, based on the ITS region. Using molecular species verification, we describe novel immature habitats for Ae. lilii and report both sympatric and allopatric populations. Whereas only Ae. lilii is found in the Republic of Benin and only Ae. bromeliae in Tanzania, both species are sympatric in Uganda.

Conclusions/Significance

Our accurate identification method will allow informed distribution and detailed ecological studies that will facilitate assessment of arboviral disease risk and development of future targeted vector control.     

Copulation Activity,Sperm Production and Conidia Transfer in Aedes aegypti Males Contaminated by Metarhizium anisopliae: A Biological Control Prospect

Background

Dengue is the most prevalent arboviral disease transmitted by Aedes aegypti worldwide, whose chemical control is difficult, expensive, and of inconsistent efficacy. Releases of Metarhizium anisopliae—exposed Ae. aegypti males to disseminate conidia among female mosquitoes by mating represents a promising biological control approach against this important vector. A better understanding of fungus virulence and impact on reproductive parameters of Ae. aegypti, is need before testing auto-dissemination strategies.

Methodology/Principal Findings

Mortality, mating competitiveness, sperm production, and the capacity to auto-disseminate the fungus to females up to the 5^thcopulation, were compared between Aedes aegypti males exposed to 5.96 x 10⁷ conidia per cm² of M. anisopliae and uninfected males. Half (50%) of fungus-exposed males (FEMs) died within the first 4 days post-exposure (PE). FEMs required 34% more time to successively copulate with 5 females (165 ± 3 minutes) than uninfected males (109 ± 3 minutes). Additionally, fungus infection reduced the sperm production by 87% at 5 days PE. Some beneficial impacts were observed, FEMs were able to successfully compete with uninfected males in cages, inseminating an equivalent number of females (about 25%). Under semi-field conditions, the ability of FEMs to search for and inseminate females was also equivalent to uninfected males (both inseminating about 40% females); but for the remaining females that were not inseminated, evidence of tarsal contact (transfer of fluorescent dust) was significantly greater in FEMs compared to controls. The estimated conidia load of a female exposed on the 5^th copulation was 5,200 mL^-1 which was sufficient to cause mortality.

Conclusion/Significance

Our study is the first to demonstrate auto-dissemination of M. anisopliae through transfer of fungus from males to female Ae. aegypti during mating under semi-field conditions. Our results suggest that auto-dissemination studies using releases of FEMs inside households could successfully infect wild Ae. aegypti females, providing another viable biological control tool for this important the dengue vector.     

Diapause induction in the oblique-banded leafroller Choristoneura rosaceana (Lepidoptera: Tortricidae): Role of photoperiod and temperature

Induction of diapause in the larval stage of the oblique-banded leafroller, Choristoneura rosaceana (Harris), was found to be dependent on both photoperiod and temperature. At constant temperatures of 24, 20 and 16°C, short photoperiods induced diapause. The critical photoperiod was between 14–15 h of light per day at 20 and 16°C. At 14 h light: 10 h dark, all larvae expressed diapause. Temperature had a modifying effect, and slightly shifted the larval response to diapause-inducing photoperiods. High constant temperatures of 28°C and above induced diapause in some individuals (< 20%), while fluctuating temperatures of 32 and 16°C in a 12-h cycle resulted in 67% diapause induction, suggesting that diapause could also be induced by fluctuating temperatures, particularly if the higher temperature exceeds 25°C.The first- and the second-instar larvae were the only two stages sensitive to diapause induction. Exposure of adult, egg and third, fourth, and fifth-larval instars to diapause-inducing conditions did not produce diapause. Although diapause was induced in the first or the second instars, it was always expressed in the third or fourth instar.     

Photoperiodic induction of the pupal diapause in the tobacco hornworm, Manduca sexta

A study was made of photoperiodic induction of the facultative pupal diapause in the tobacco hornworm, Manduca sexta, reared on artificial diet in the laboratory. The species entered a prolonged diapause when the egg and larval feeding stages were reared in daily photoperiods of 13·5 hr or less. Diapause was induced in all insects at photoperiods ranging from 1 to 13 hr, and part of the population entered diapause at only 15 to 30 min of light per day. Photoperiods of 14 hr or more and continous darkness prevented diapause. Duration of diapause varied with the inductive photoperiod in which the hornworms were reared during the sensitive period. Insects reared in longer diapause-inducing photoperiods within a range of 12 to 13·25 hr remained in diapause longer than those reared in shorter photoperiods. There was no difference in the rate of larval development of hornworms reared in diapause-inducing vs diapause-preventing photoperiods. Temperatures of 26 to 30°C were most favourable for the photoperiodic induction of diapause; at 21°C, the critical photoperiod and incidence of diapause were decreased. Diapause induction was suppressed by low (18°C) and higher (33°C) temperatures. The number of inductive 12L:12D (light = 12 hr; dark = 12 hr) cycles required to induce diapause ranged from as few as 5 for some insects to as many as 12 for others when the post-inductive régimen was continuous light, but with insects previously held in continuous dark, as few as 2 12L:12D cycles during the last 2 days of larval feeding induced diapause in 38 per cent of the population. Only 3 to 4 cycles of 15L:9D during the final larval instar reversed inductive effects of 14 to 15 12L:12D cycles. Photoperiodic sensitivity extended from the late embryo to the end of larval feeding but showed considerable fluctuation during development with maximum sensitivity occurring just before egg hatch and during larval growth.Light breaks applied at different times during the dark period of 12L:12D cycles generated different response curves, depending on the number of cycles in which light breaks were repeated. When repeated for 6 cycles, a unimodal response curve was obtained; 10 cycles produced a bimodal curve and light breaks given for 18 cycles throughout the sensitive period averted diapause regardless of time of night applied. It is suggested that diapause is regulated by a photo- and thermolabile substance that accumulates during long nights (11 hr or more) and acts during the early pupal stage to inhibit the translocation and release of development-promoting neurosecretion from the brain.     

Parity and Longevity of Aedes aegypti According to Temperatures in Controlled Conditions and Consequences on Dengue Transmission Risks

Background

In Guadeloupe, Aedes aegypti mosquitoes are the only vectors of dengue and chikungunya viruses. For both diseases, vector control is the only tool for preventing epidemics since no vaccine or specific treatment is available. However, to efficiently implement control of mosquitoes vectors, a reliable estimation of the transmission risks is necessary. To become infective an Ae. aegypti female must ingest the virus during a blood meal and will not be able to transmit the virus during another blood-meal until the extrinsic incubation period is completed. Consequently the aged females will carry more infectious risks. The objectives of the present study were to estimate under controlled conditions the expectation of infective life for females and thus the transmission risks in relation with their reproductive cycle and parity status.

Methodology/Principal Findings

Larvae of Ae. aegypti were collected in central Guadeloupe and breed under laboratory conditions until adult emergence. The experiments were performed at constant temperatures (± 1.5°C) of 24°C, 27°C and 30°C on adults females from first generation (F1). Females were kept and fed individually and records of blood-feeding, egg-laying and survival were done daily. Some females were dissected at different physiological stages to observe the ovaries development. The data were analyzed to follow the evolution of parity rates, the number of gonotrophic cycles, the fecundity and to study the mean expectation of life and the mean expectation of infective life for Ae. aegypti females according to temperatures. The expectation of life varies with the parity rates and according to the temperatures, with durations from about 10 days at low parity rates at the higher temperature to an optimal duration of about 35 days when 70% of females are parous at 27°C. Infective life expectancy was found highly variable in the lower parous rates and again the optimal durations were found when more than 50% of females are parous for the mean temperatures of 27°C and 30°C.

Conclusion

Parity rates can be determined for field collected females and could be a good proxy of the expectation of infective life according to temperatures. However, for the same parity rates, the estimation of infective life expectation is very different between Ae. aegypti and Anopheles gambiae mosquitoes. Correlation of field parity rates with transmission risks requires absolutely to be based on Ae. aegypti models, since available Anopheles sp. models underestimate greatly the females longevity.     

Indoor-Breeding of Aedes albopictus in Northern Peninsular Malaysia and Its Potential Epidemiological Implications

Background

The mosquito Ae. albopictus is usually adapted to the peri-domestic environment and typically breeds outdoors. However, we observed its larvae in most containers within homes in northern peninsular Malaysia. To anticipate the epidemiological implications of this indoor-breeding, we assessed some fitness traits affecting vectorial capacity during colonization process. Specifically, we examined whether Ae. albopictus exhibits increased survival, gonotrophic activity and fecundity due to the potential increase in blood feeding opportunities.

Methodology/Principal Findings

In a series of experiments involving outdoors and indoors breeding populations, we found that Ae. albopictus lives longer in the indoor environment. We also observed increased nighttime biting activity and lifetime fecundity in indoor/domestic adapted females, although they were similar to recently colonized females in body size.

Conclusion/Significance

Taken together these data suggest that accommodation of Ae. albopictus to indoor/domestic environment may increase its lifespan, blood feeding success, nuisance and thus vectorial capacity (both in terms of increased vector-host contacts and vector population density). These changes in the breeding behavior of Ae. albopictus, a potential vector of several human pathogens including dengue viruses, require special attention.     

River Boats Contribute to the Regional Spread of the Dengue Vector Aedes aegypti in the Peruvian Amazon

Background and Objectives

The dramatic range expansion of the dengue vector Aedes aegypti is associated with various anthropogenic transport activities, but little is known about the underlying mechanisms driving this geographic expansion. We longitudinally characterized infestation of different vehicle types (cars, boats, etc.) to estimate the frequency and intensity of mosquito introductions into novel locations (propagule pressure).

Methods

Exhaustive adult and immature Ae. aegypti collections were performed on six different vehicle types at five ports and two bus/ taxi departure points in the Amazonian city of Iquitos, Peru during 2013. Aquatic vehicles included 32 large and 33 medium-sized barges, 53 water taxis, and 41 speed boats. Terrestrial vehicles sampled included 40 buses and 30 taxis traveling on the only highway in the region. Ae. aegypti adult infestation rates and immature indices were analyzed by vehicle type, location within vehicles, and sampling date.

Results

Large barges (71.9% infested) and medium barges (39.4% infested) accounted for most of the infestations. Notably, buses had an overall infestation rate of 12.5%. On large barges, the greatest number of Ae. aegypti adults were found in October, whereas most immatures were found in February followed by October. The vast majority of larvae (85.9%) and pupae (76.7%) collected in large barges were produced in puddles formed in cargo holds.

Conclusions

Because larges barges provide suitable mosquito habitats (due to dark, damp cargo storage spaces and ample oviposition sites), we conclude that they likely serve as significant contributors to mosquitoes’ propagule pressure across long distances throughout the Peruvian Amazon. This information can help anticipate vector population mixing and future range expansions of dengue and other viruses transmitted by Ae. aegypti.     

Assessment of the Impact of Potential Tetracycline Exposure on the Phenotype of Aedes aegypti OX513A: Implications for Field Use

Background

Aedes aegypti is the primary vector of dengue fever, a viral disease which has an estimated incidence of 390 million infections annually. Conventional vector control methods have been unable to curb the transmission of the disease. We have previously reported a novel method of vector control using a tetracycline repressible self-limiting strain of Ae. aegypti OX513A which has achieved >90% suppression of wild populations.

Methodology/Principal Findings

We investigated the impact of tetracycline and its analogues on the phenotype of OX513A from the perspective of possible routes and levels of environmental exposure. We determined the minimum concentration of tetracycline and its analogues that will allow an increased survivorship and found these to be greater than the maximum concentration of tetracyclines found in known Ae. aegypti breeding sites and their surrounding areas. Furthermore, we determined that OX513A parents fed tetracycline are unable to pre-load their progeny with sufficient antidote to increase their survivorship. Finally, we studied the changes in concentration of tetracycline in the mass production rearing water of OX513A and the developing insect.

Conclusion/Significance

Together, these studies demonstrate that potential routes of exposure of OX513A individuals to tetracycline and its analogues in the environment are not expected to increase the survivorship of OX513A.     

Genetic Diversity and Phylogeny of Aedes aegypti,the Main Arbovirus Vector in the Pacific

Background

The Pacific region is an area unique in the world, composed of thousands of islands with differing climates and environments. The spreading and establishment of the mosquito Aedes aegypti in these islands might be linked to human migration. Ae. aegypti is the major vector of arboviruses (dengue, chikungunya and Zika viruses) in the region. The intense circulation of these viruses in the Pacific during the last decade led to an increase of vector control measures by local health authorities. The aim of this study is to analyze the genetic relationships among Ae. aegypti populations in this region.

Methodology/Principal Finding

We studied the genetic variability and population genetics of 270 Ae. aegypti, sampled from 9 locations in New Caledonia, Fiji, Tonga and French Polynesia by analyzing nine microsatellites and two mitochondrial DNA regions (CO1 and ND4). Microsatellite markers revealed heterogeneity in the genetic structure between the western, central and eastern Pacific island countries. The microsatellite markers indicate a statistically moderate differentiation (F_ST = 0.136; P < = 0.001) in relation to island isolation. A high degree of mixed ancestry can be observed in the most important towns (e.g. Noumea, Suva and Papeete) compared with the most isolated islands (e.g. Ouvea and Vaitahu). Phylogenetic analysis indicated that most of samples are related to Asian and American specimens.

Conclusions/Significance

Our results suggest a link between human migrations in the Pacific region and the origin of Ae. aegypti populations. The genetic pattern observed might be linked to the island isolation and to the different environmental conditions or ecosystems.     

Genome wide gene-expression analysis of facultative reproductive diapause in the two-spotted spider mite Tetranychus urticae

Background

Diapause or developmental arrest, is one of the major adaptations that allows mites and insects to survive unfavorable conditions. Diapause evokes a number of physiological, morphological and molecular modifications. In general, diapause is characterized by a suppression of the metabolism, change in behavior, increased stress tolerance and often by the synthesis of cryoprotectants. At the molecular level, diapause is less studied but characterized by a complex and regulated change in gene-expression. The spider mite Tetranychus urticae is a serious polyphagous pest that exhibits a reproductive facultative diapause, which allows it to survive winter conditions. Diapausing mites turn deeply orange in color, stop feeding and do not lay eggs.

Results

We investigated essential physiological processes in diapausing mites by studying genome-wide expression changes, using a custom built microarray. Analysis of this dataset showed that a remarkable number, 11% of the total number of predicted T. urticae genes, were differentially expressed. Gene Ontology analysis revealed that many metabolic pathways were affected in diapausing females. Genes related to digestion and detoxification, cryoprotection, carotenoid synthesis and the organization of the cytoskeleton were profoundly influenced by the state of diapause. Furthermore, we identified and analyzed an unique class of putative antifreeze proteins that were highly upregulated in diapausing females. We also further confirmed the involvement of horizontally transferred carotenoid synthesis genes in diapause and different color morphs of T. urticae.

Conclusions

This study offers the first in-depth analysis of genome-wide gene-expression patterns related to diapause in a member of the Chelicerata, and further adds to our understanding of the overall strategies of diapause in arthropods.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2164-14-815) contains supplementary material, which is available to authorized users.     

Two Chikungunya isolates from the outbreak of La Reunion (Indian Ocean) exhibit different patterns of infection in the mosquito, Aedes albopictus

Background

A Chikungunya (CHIK) outbreak hit La Réunion Island in 2005–2006. The implicated vector was Aedes albopictus. Here, we present the first study on the susceptibility of Ae. albopictus populations to sympatric CHIKV isolates from La Réunion Island and compare it to other virus/vector combinations.

Methodology and Findings

We orally infected 8 Ae. albopictus collections from La Réunion and 3 from Mayotte collected in March 2006 with two Chikungunya virus (CHIKV) from La Réunion: (i) strain 05.115 collected in June 2005 with an Alanine at the position 226 of the glycoprotein E1 and (ii) strain 06.21 collected in November 2005 with a substitution A226V. Two other CHIKV isolates and four additional mosquito strains/species were also tested. The viral titer of the infectious blood-meal was 10⁷ plaque forming units (pfu)/mL. Dissemination rates were assessed by immunofluorescent staining on head squashes of surviving females 14 days after infection. Rates were at least two times higher with CHIKV 06.21 compared to CHIKV 05.115. In addition, 10 individuals were analyzed every day by quantitative RT-PCR. Viral RNA was quantified on (i) whole females and (ii) midguts and salivary glands of infected females. When comparing profiles, CHIKV 06.21 produced nearly 2 log more viral RNA copies than CHIKV 05.115. Furthermore, females infected with CHIKV 05.115 could be divided in two categories: weakly susceptible or strongly susceptible, comparable to those infected by CHIKV 06.21. Histological analysis detected the presence of CHIKV in salivary glands two days after infection. In addition, Ae. albopictus from La Réunion was as efficient vector as Ae. aegypti and Ae. albopictus from Vietnam when infected with the CHIKV 06.21.

Conclusions

Our findings support the hypothesis that the CHIK outbreak in La Réunion Island was due to a highly competent vector Ae. albopictus which allowed an efficient replication and dissemination of CHIKV 06.21.     

Female-specific flightless (fsRIDL) phenotype for control of Aedes albopictus

Background

Aedes albopictus, the Asian tiger mosquito, is a vector of several arboviruses including dengue and chikungunya, and is also a significant nuisance mosquito. It is one of the most invasive of mosquitoes with a relentlessly increasing geographic distribution. Conventional control methods have so far failed to control Ae. albopictus adequately. Novel genetics-based strategies offer a promising alternative or aid towards efficient control of this mosquito.

Methodology/Principal Findings

We describe here the isolation, characterisation and use of the Ae. albopictus Actin-4 gene to drive a dominant lethal gene in the indirect flight muscles of Ae. albopictus, thus inducing a conditional female-specific late-acting flightless phenotype. We also show that in this context, the Actin-4 regulatory regions from both Ae. albopictus and Ae. aegypti can be used to provide conditional female-specific flightlessness in either species.

Conclusion/Significance

With the disease-transmitting females incapacitated, the female flightless phenotype encompasses a genetic sexing mechanism and would be suitable for controlling Ae. albopictus using a male-only release approach as part of an integrated pest management strategy.     

Understanding Water Storage Practices of Urban Residents of an Endemic Dengue Area in Colombia: Perceptions,Rationale and Socio-Demographic Characteristics

Introduction

The main preventive measure against dengue virus transmission is often based on actions to control Ae. Aegypti reproduction by targeting water containers of clean and stagnant water. Household water storage has received special attention in prevention strategies but the evidence about the rationale of this human practice is limited. The objective was to identify and describe water storage practices among residents of an urban area in Colombia (Girardot) and its association with reported perceptions, rationales and socio-demographic characteristics with a mixed methods approach.

Methods

Knowledge, attitudes and practices and entomological surveys from 1,721 households and 26 semi-structured interviews were conducted among residents of Girardot and technicians of the local vector borne disease program. A multivariate analysis was performed to identify associations between a water storage practice and socio-demographic characteristics, and knowledge, attitudes and practices about dengue and immature forms of the vector, which were then triangulated with qualitative information.

Results

Water storage is a cultural practice in Girardot. There are two main reasons for storage: The scarcity concern based on a long history of shortages of water in the region and the perception of high prices in water rates, contrary to what was reported by the local water company. The practice of water storage was associated with being a housewife (Inverse OR: 2.6, 95% CI 1.5 -4.3). The use of stored water depends on the type of container used, while water stored in alberca (Intra household cement basins) is mainly used for domestic cleaning chores, water in plastic containers is used for cooking.

Conclusions

It is essential to understand social practices that can increase or reduce the number of breeding sites of Ae. Aegypti. Identification of individuals who store water and the rationale of such storage allow a better understanding of the social dynamics that lead to water accumulation.     

Surveillance and Control of Aedes albopictus in the Swiss-Italian Border Region: Differences in Egg Densities between Intervention and Non-intervention Areas

Background

Aedes albopictus, the Asian tiger mosquito, originates from the tropical and subtropical regions of Southeast Asia. Over the recent decades it has been passively spread across the globe, primarily through the used tyre trade and passive transportation along major traffic routes. A. albopictus is a proven vector for many arboviruses, most notably chikungunya and dengue, with recent outbreaks also in continental Europe. In southern Switzerland, in the Canton of Ticino A. albopictus was spotted for the first time in 2003. Since then the local authorities have implemented a control programme based on larval source reduction. Despite these efforts, mosquito densities have increased over the last decade, casting doubts on the effectiveness of such larval control programmes.

Methodology/Principal Findings

The Italian communities just across the Swiss-Italian border lack a control programme. This motivated us to compare the intervention and the non-intervention areas side by side in an attempt to find evidence for, or against, the effectiveness of larval A. albopictus control. Using ovitraps and a randomised sampling scheme, we examined the seasonal and spatial abundance of A. albopictus in sylvatic and urban environments across the Swiss-Italian border in 2012 and 2013. In the urban environments of the non-intervention area, egg densities were 2.26 times higher as compared to the intervention area. In the sylvatic environments, as compared to the urban environments, egg densities were 36% in the intervention area and 18% in the non-intervention area.

Conclusions/Significance

Though alternative explanations are also valid, the results support the hypothesis that the Ticino intervention programme does have an impact. At the same time the data also suggest that current larval interventions fall short in gaining full control over the mosquito, calling for the evaluation of additional, or alternative, approaches. Ideally, these should also consider inclusion of the neighbouring Italian communities in the surveillance and control efforts.     

Effects of extending the light phase on diapause induction in a Japanese population of the two-spotted spider mite, <Emphasis Type="Italic">Tetranychus urticae</Emphasis>

Artificial lighting is a merit of a ‘plant factory’, which might be utilized to suppress an increase in pest population. We investigated the effects of extending the light phase on diapause induction in the two-spotted spider mite (TSSM), Tetranychus urticae. TSSM were reared at 18°C under light phases ranging from 2 to 64 h combined with a constant dark phase of 16 h in aluminum bottles, with white light emitting diodes attached inside to minimize fluctuations in air temperature between the light and dark phases. Diapause was induced in adult TSSM females when the light phase was 24 h or shorter, and diapause induction was inhibited when the light phase extended over 32 h. The development of deutonymphs was delayed under a diapause-inducing photoperiod. Diapause inducing photoperiods may suppress an increase in the TSSM population, by slowing down development and reproduction.     

Genetic structure of the tiger mosquito, Aedes albopictus, in Cameroon (Central Africa)

Background

Aedes albopictus (Skuse, 1884) (Diptera: Culicidae), a mosquito native to Asia, has recently invaded all five continents. In Central Africa it was first reported in the early 2000s, and has since been implicated in the emergence of arboviruses such as dengue and chikungunya in this region. Recent genetic studies of invasive species have shown that multiple introductions are a key factor for successful expansion in new areas. As a result, phenotypic characters such as vector competence and insecticide susceptibility may vary within invasive pest species, potentially affecting vector efficiency and pest management. Here we assessed the genetic variability and population genetics of Ae. albopictus isolates in Cameroon (Central Africa), thereby deducing their likely geographic origin.

Methods and Results

Mosquitoes were sampled in 2007 in 12 localities in southern Cameroon and analyzed for polymorphism at six microsatellite loci and in two mitochondrial DNA regions (ND5 and COI). All the microsatellite markers were successfully amplified and were polymorphic, showing moderate genetic structureamong geographic populations (F_ST = 0.068, P<0.0001). Analysis of mtDNA sequences revealed four haplotypes each for the COI and ND5 genes, with a dominant haplotype shared by all Cameroonian samples. The weak genetic variation estimated from the mtDNA genes is consistent with the recent arrival of Ae. albopictus in Cameroon. Phylogeographic analysis based on COI polymorphism indicated that Ae. albopictus populations from Cameroon are related to tropical rather than temperate or subtropical outgroups.

Conclusion

The moderate genetic diversity observed among Cameroonian Ae. albopictus isolates is in keeping with recent introduction and spread in this country. The genetic structure of natural populations points to multiple introductions from tropical regions.     

Permethrin-Treated Clothing as Protection against the Dengue Vector,Aedes aegypti: Extent and Duration of Protection

Introduction

Dengue transmission by the mosquito vector, Aedes aegypti, occurs indoors and outdoors during the day. Personal protection of individuals, particularly when outside, is challenging. Here we assess the efficacy and durability of different types of insecticide-treated clothing on laboratory-reared Ae. aegypti.

Methods

Standardised World Health Organisation Pesticide Evaluation Scheme (WHOPES) cone tests and arm-in-cage assays were used to assess knockdown (KD) and mortality of Ae. aegypti tested against factory-treated fabric, home-dipped fabric and microencapsulated fabric. Based on the testing of these three different treatment types, the most protective was selected for further analysis using arm-in cage assays with the effect of washing, ultra-violet light, and ironing investigated using high pressure liquid chromatography.

Results

Efficacy varied between the microencapsulated and factory dipped fabrics in cone testing. Factory-dipped clothing showed the greatest effect on KD (3 min 38.1%; 1 hour 96.5%) and mortality (97.1%) with no significant difference between this and the factory dipped school uniforms. Factory-dipped clothing was therefore selected for further testing. Factory dipped clothing provided 59% (95% CI = 49.2%– 66.9%) reduction in landing and a 100% reduction in biting in arm-in-cage tests. Washing duration and technique had a significant effect, with insecticidal longevity shown to be greater with machine washing (LW₅₀ = 33.4) compared to simulated hand washing (LW₅₀ = 17.6). Ironing significantly reduced permethrin content after 1 week of simulated use, with a 96.7% decrease after 3 months although UV exposure did not reduce permethrin content within clothing significantly after 3 months simulated use.

Conclusion

Permethrin-treated clothing may be a promising intervention in reducing dengue transmission. However, our findings also suggest that clothing may provide only short-term protection due to the effect of washing and ironing, highlighting the need for improved fabric treatment techniques.