Aegypti Strains Research Articles

Genetic Stability and Fitness of Aedes aegypti Red-Eye Genetic Sexing Strains With Pakistani Genomic Background for Sterile Insect Technique Applications.

The mosquito species Aedes aegypti is the primary transmitter of viruses that cause endemic diseases like dengue in Pakistan. It is also a cause of other vector-borne diseases like yellow fever, Zika fever, and chikungunya, which significantly impact human health worldwide. In the absence of efficient vaccines (except for yellow fever) or drugs, vector control methods, such as the sterile insect technique (SIT), have been proposed as additional tools for the management of these diseases. Mosquito SIT programs are based on the release of sterile males and it is important female releases to be ideally zero or to be kept at a minimum, since females are the ones that bite, blood-feed and transmit pathogens. Recently, an Ae. aegypti genetic sexing strain (GSS), with and without a recombination-suppressing inversion (Inv35), was developed using the eye color as a selectable marker, with males having black eyes and females red eyes. In the present study, we introgressed the sexing features and the Inv35 of the Ae. aegypti red-eye GSS into the Pakistani genomic background aiming to their future use for SIT applications in the country. Both introgressed strains, the Red-eye GSS-PAK and the Red-eye GSS/Inv35-PAK, were evaluated in respect to their genetic stability and biological quality by assessing parameters like recombination rate, fecundity, fertility, pupal and adult recovery, time of development, pupal weight, survival, and flight ability in comparison with a wild Pakistani population (PAK). The results suggest that the sexing features and the recombination suppression properties of Inv35 were not affected after their introgression into the local genomic background; however, some biological traits of the two newly constructed strains were affected, positively or negatively, suggesting that a thorough quality control analysis should be performed after the introgression of a GSS into a new genomic background prior to its use in SIT field trials or applications. The importance of using GSS with local genomic background for SIT applications against Aedes aegypti is also discussed.

IMPACTS OF BARRIER INSECTICIDE MIXTURES ON MOSQUITO, AEDES AEGYPTI AND NON-TARGET HONEY BEE, APIS MELLIFERA

Four novel commercial insecticide mixtures, composed of pyrethroid and nicotinoid active ingredients, were evaluated in a series of experiments in the laboratory, semi-field and field to determine acute toxicity (LC50) against pyrethroid-susceptible (ORL1952) and resistant (Puerto Rico) strains of Aedes aegypti L., and non-target adult European honey bees, Apis mellifera L. The four products were Tandem, Temprid FX, Transport Mikron, and Crossfire. The acute toxicity data showed that pyrethroid-resistant Ae. aegypti PR exhibited decreased sensitivity to all 4 insecticide mixtures, compared to pyrethroid-susceptible Ae. aegypti ORL1952. Tandem, Temprid FX, and Transport Mikron were more toxic to Ae. aegypti ORL1952 than to A. mellifera, but Crossfire was the least toxic. Transport Mikron was also more toxic to Ae. aegypti PR than to A. mellifera. The Honey bee Tolerance Indexes, determined with LC50 data of pyrethroid-susceptible mosquitoes, demonstrated that while Transport Mikron, Tandem, and Temprid FX were more toxic to Ae. aegypti ORL1952 than to A. mellifera, Crossfire was less toxic. The honey bee Tolerance Indexes decreased substantially when calculated with LC50 data from pyrethroid- resistant mosquitoes, but honey bees remained tolerant of Transport Mikron. Notably, while the insecticide mixtures did not control the PR resistant Ae. aegypti strain when applied as residual sprays to perimeter vegetation at label rates, susceptible Ae. aegypti ORL1951 were controlled, but applications affected honeybees (A. mellifera) for up to 28 days after treatment. Temprid FX resulted in 74% and 99% mortality, in adult Ae. aegypti ORL1952 and A. mellifera, respectively, for 28 days post-treatment. Transport Mikron and Tandem residues killed Ae. aegypti ORL1952 for up to 21 days post-treatment, while the effect of Crossfire lasted only 14 days. All three insecticides killed A. mellifera for up to 28 days post-treatment but at decreased mortality rates. For operational mosquito control, these data indicate that Transport Mikron has a reasonable safety margin (~25%) when targeting susceptible mosquitoes, compared to Tandem, Temprid FX, and Crossfire. The tested insecticide formulations need to be applied in higher doses to control resistant strains of mosquitoes that may be detrimental to honey bees. The ULV data indicated that pyrethroid resistance can be overcome with the insecticide mixtures.

Reversion of CYP450 monooxygenase-mediated acetamiprid larval resistance in dengue fever mosquito, Aedes aegypti L.

Aedes-borne diseases are on the rampant rise despite continued application of chemical insecticide-based interventions. The appearance of high degree of insecticide resistance in Aedes species and noxious effects on environment and non-targets have raised further concerns. Among new chemical interventions, neonicotinoids are considered a safe and effective approach. The present study investigated the control potency of acetamiprid and development of resistance in Aedes aegypti larvae; and the involvement of CYP450 monooxygenases in inducing resistance. The early fourth instars of Ae. aegypti parent susceptible strain (PS) were selected with acetamiprid for 15 generations (ACSF strain) increasing the resistance to 19.74-fold in ACSF-10 and 36.71-fold in ACSF-15. The ACSF-10 larvae were assayed with acetamiprid combined with piperonyl butoxide (PBO) in three different ratios (1:1, 1:5 and 1:10) and selected for next five generations with 1:10 combination. Selection with synergized acetamiprid (APSF strains) reversed as well as reduced the rate of resistance development resulting in only 1.35-fold resistance in APSF-15. The APSF strains showed %monooxygenase dependency ranging from 86.71 to 96.72%. The estimation of the monooxygenases levels in parent and selected larvae showed increased monooxygenase level in the ACSF strains by 2.42-2.87-fold. The APSF-15 strains exhibited 57.95% lower enzyme production than ACSF-15 strain. The reduction and reversion of resistance by using PBO and the elevated levels of monooxygenases in ACSF and reduction in APSF strains recommend the involvement of CYP450-mediated mechanism in the development of acetamiprid resistance in Ae. aegypti. These studies could help in devising resistance management strategies in order to preserve the efficiency of pre-existing insecticides.

Introgression of the Aedes aegypti Red-Eye Genetic Sexing Strains Into Different Genomic Backgrounds for Sterile Insect Technique Applications.

Aedes aegypti is an invasive mosquito species and major vector of human arboviruses. A wide variety of control methods have been employed to combat mosquito populations. One of them is the sterile insect technique (SIT) that has recently attracted considerable research efforts due to its proven record of success and the absence of harmful environmental footprints. The efficiency and cost-effectiveness of SIT is significantly enhanced by male-only releases. For mosquito SIT, male-only releases are ideally needed since females bite, blood-feed and transmit the pathogens. Ae. aegypti genetic sexing strains (GSS) have recently become available and are based on eye colour mutations that were chosen as selectable markers. These genetic sexing strains were developed through classical genetics and it was shown to be subjected to genetic recombination, a phenomenon that is not suppressed in males as is the case in many Diptera. The genetic stability of these GSS was strengthened by the induction and isolation of radiation-induced inversions. In this study, we used the red eye mutation and the inversion Inv35 line of the Ae. aegypti red-eye GSS s and introgressed them in six different genomic backgrounds to develop GSS with the respective local genomic backgrounds. Our goal was to assess whether the recombination frequencies in the strains with and without the inversion are affected by the different genomic backgrounds. In all cases the recombination events were suppressed in all Inv35 GSS strains, thus indicating that the genomic background does not negatively affect the inversion result. Absence of any effect that could be ascribed to genetic differences, enables the introgression of the key elements of the GSS into the local genomic background prior to release to the target areas. Maintaining the local background increases the chances for successful matings between released males and wild females and addresses potential regulatory concerns regarding biosafety and biosecurity.

Uji Efek Larvasida Ekstrak Daun Gamal (Gliricida sepium) terhadap Larva Nyamuk Aedes aegypti

Gamal leaves (Gliricidia sepium) well known as liquid organic fertilizer, are also known to have potential as vegetable larvicides because there are flavonoids, triterpenoids, coumarin, coumaric acid, mitotic acid, and stigmastanol glucoside which can be identified and isolated from various parts from Gamal. The aim of this study was to examine the larvicidal effect of Gamal (G. sepium) leaf extract against larvae of Aedes aegypti mosquitoes. The study was conducted using an experimental design with a posttest-only control group design and a completely randomized design consisting of 6 treatment groups. Two groups as control (positive and negative control), while 4 other groups received treatment of Gamal leaf extract (G. sepium) at doses of 50 ppm (P1), 150 ppm (P2), 250 ppm (P3), and 350 ppm (P4). There was no mortality of larvae Aedes aegypti from pure lines after giving Gamal leaf extract, but mortality only occurred in Aedes aegypti larvae positive control group originating from the field. Unknown LC50 and LC90. A total of 13 (52%) Ae. aegypti strain classified as tolerant, while as many as 19 (76%) larvae of Aedes aegypti originating from the field are classified as resistant.

Molecular identification and phylogeny of Steinernema and Heterorhabditis nematodes and their efficacy in controlling the larvae of Aedes aegypti, a major vector of the dengue virus

Aedes aegypti is the mosquito vector of several arboviruses, especially the dengue virus. Aedes aegypti strain resistant to chemical insecticides have been reported worldwide. To tackle this, an entomopathogenic nematode (EPN) may be an alternative bio-control agent. To this end, this study aims to isolate, identify, and analyze the phylogeny of EPNs in Thailand and evaluate their efficacy for controlling the Ae. aegypti larvae. From 12 provinces in Thailand, soil samples were randomly collected, with 118 out of 1,100 them being positive for EPNs (10.73% prevalence) in genera Steinernema (4.46%) and Heterorhabditis (6.27%). Then, molecular discrimination of these two genus was performed based on the sequencing and phylogenetic analysis of the 28S rDNA and internal transcribed spacer regions. The most abundant species of EPN were Heterorhabditis indica, with minor species of Heterorhabditis sp. SGmg3, H. baujardi, S. surkhetense, S. kushidai, S. siamkayai, Steinernema sp. YNd80, Steinernema sp. YNc215, S. guangdongense, and S. huense. The larvicidal activity of five selected EPN isolates were tested against Ae. aegypti. Ten larvae of Ae. aegypti were incubated with different concentration (80, 160, 320, and 640 IJs/larva) of the infective juveniles of EPN in a 24-well and 6-well plates for 4 days. The mortality rates of the larvae were observed daily. Steinernema surkhetense (ePYO8.5_TH) showed the potential to kill mosquito larvae, with the highest mortality rate of 92 ± 9.37% and 89 ± 9.91% after it was treated with 640 IJs/larva in a 24-well plate and 1600 IJs/larva in a 6-well plate, respectively. There is an abundant distribution of EPNs across the country, and S. surkhetense ePYO8.5_TH may be used as a biocontrol agent against Ae. aegypti larvae.

Lab-scale characterization and semi-field trials of Wolbachia Strain wAlbB in a Taiwan Wolbachia introgressed Ae. aegypti strain.

Dengue fever is one of the most severe viral diseases transmitted by Aedes mosquitoes, with traditional approaches of disease control proving insufficient to prevent significant disease burden. Release of Wolbachia-transinfected mosquitoes offers a promising alternative control methodologies; Wolbachia-transinfected female Aedes aegypti demonstrate reduced dengue virus transmission, whilst Wolbachia-transinfected males cause zygotic lethality when crossed with uninfected females, providing a method for suppressing mosquito populations. Although highly promising, the delicate nature of population control strategies and differences between local species populations means that controlled releases of Wolbachia-transinfected mosquitoes cannot be performed without extensive testing on specific local Ae. aegypti populations. In order to investigate the potential for using Wolbachia to suppress local Ae. aegypti populations in Taiwan, we performed lab-based and semi-field fitness trials. We first transinfected the Wolbachia strain wAlbB into a local Ae. aegypti population (wAlbB-Tw) and found no significant changes in lifespan, fecundity and fertility when compared to controls. In the laboratory, we found that as the proportion of released male mosquitoes carrying Wolbachia was increased, population suppression could reach up to 100%. Equivalent experiments in semi-field experiments found suppression rates of up to 70%. The release of different ratios of wAlbB-Tw males in the semi-field system provided an estimate of the optimal size of male releases. Our results indicate that wAlbB-Tw has significant potential for use in vector control strategies aimed at Ae. aegypti population suppression in Taiwan. Open field release trials are now necessary to confirm that wAlbB-Tw mediated suppression is feasible in natural environments.

Assessing transfluthrin mortality against Aedes aegypti and Culex quinquefasciatus inside and outside US military tents in a northern Florida environment

Mortality caused by passive resin transfluthrin diffusers (∼5 mg AI per 24 h release rate) suspended in small 2-person tents was measured for colony-reared sentinel pyrethroid susceptible Aedes aegypti and Culex quinquefasciatus female mosquitoes, as well as a pyrethroid-resistant strain of Aedes aegypti, in a USA military field camp scenario. Mortality effects were investigated for impact by factors such as sentinel cage location (inside tent, tent doorway and outside tent), exposure time (15, 30, 45 and 60 min), and environmental temperature (°C), all of which were examined over an 8-week period. Analyses determined there was a significant interaction between mosquito strain and transfluthrin susceptibility, with the two susceptible strains experiencing significantly greater mean mortality than the resistant Ae. aegypti strain. Significant differences were likewise observed between the mosquito strains over the 8-week study period, where study week and temperature were both positively correlated with an increase in observed mean mosquito mortality. Mosquito proximity to the transfluthrin diffusers was also influenced by week and showed that sentinel cage placement in the environment demonstrates different mortality measurements, depending on the environmental conditions. The length of exposure to transfluthrin, however, was determined to not significantly impact transfluthrin efficacy on the examined mosquito strains, although increased exposure did result in increased susceptible strain mortality. These results suggest that transfluthrin is highly effective in causing mortality against susceptible Ae. aegypti and Cx. quinquefasciatus mosquitoes under field conditions but is minimally effective against pyrethroid-resistant Ae. aegypti mosquitoes. Transfluthrin-infused devices are influenced by environmental factors that can combine to impact mosquito mortality in the field.

Expansive and Diverse Phenotypic Landscape of Field Aedes aegypti (Diptera: Culicidae) Larvae with Differential Susceptibility to Temephos: Beyond Metabolic Detoxification.

Arboviruses including dengue, Zika, and chikungunya are amongst the most significant public health concerns worldwide. Arbovirus control relies on the use of insecticides to control the vector mosquito Aedes aegypti (Linnaeus), the success of which is threatened by widespread insecticide resistance. The work presented here profiled the gene expression of Ae. aegypti larvae from field populations of Ae. aegypti with differential susceptibility to temephos originating from two Colombian urban locations, Bello and Cúcuta, previously reported to have distinctive disease incidence, socioeconomics, and climate. We demonstrated that an exclusive field-to-lab (Ae. aegypti strain New Orleans) comparison generates an over estimation of differential gene expression (DGE) and that the inclusion of a geographically relevant field control yields a more discrete, and likely, more specific set of genes. The composition of the obtained DGE profiles is varied, with commonly reported resistance associated genes including detoxifying enzymes having only a small representation. We identify cuticle biosynthesis, ion exchange homeostasis, an extensive number of long noncoding RNAs, and chromatin modelling among the differentially expressed genes in field resistant Ae. aegypti larvae. It was also shown that temephos resistant larvae undertake further gene expression responses when temporarily exposed to temephos. The results from the sampling triangulation approach here contribute a discrete DGE profiling with reduced noise that permitted the observation of a greater gene diversity, increasing the number of potential targets for the control of insecticide resistant mosquitoes and widening our knowledge base on the complex phenotypic network of the Ae. aegypti response to insecticides.

A comparative study and characterization of Azadirachta indica mediated nano‐insecticide and ethanolic extract against mosquito vectors – Arabian and Indian strains

AbstractVector borne disease are found all over the world, this becomes a major economic and social problem in developing and developed countries. Chemical insecticides have quieted their action by developed resistance, environment contaminations, non‐target effects on beneficial insects etc. Ethanolic extracted Azadirachta indica has shown virtuous mortality against Indian strains Aedes aegypti, Anopheles stephensi, Culex quinquefasciatus and Arabian strains Cx. pipiens, Ae. aegypti. The green synthesized AgNPs insecticide developed from Az. indica which was characterized through UV, TEM, EDX, XRD showed notable larvicidal and adulticidal activity at lower concentrations when compared with ethanolic extract. The lethal concentration LC50 and LC90 of larvae by nano‐insecticide was 30.8, 63.01 μg/mL, (An. stephensi), 33.5, 71.5 μg/mL (Ae. aegypti), 39, 81.4 μg/mL (Cx. quinquefasciatus) against Indian strains and 62.5, 100.8 μg/mL (Ae. aegypti), 61.2, 92.04 μg/mL (Cx. pipiens). The adulticidal activity of AgNPs for LC50 and LC90 against Arabian strain was 20.1, 92.0 μg/mL against Ae. aegypti, 367.8, 1521.7 μg/mL against Cx. pipiens. The larvicidal and aduticidal activity of AgNPs developed from Az. indica was superior to crude ethanolic leaf extract. Thus AgNPs are a promising potential larvicidal, adulticidal insecticide against Cx. quinquefasciatus, Cx. pipiens, Ae. aegypti and An. stephensi.

The determination of effective concentration of acethonilic Ipomoea cairica leaves extract against laboratory and field strains of Aedes albopictus and Aedes aegypti mosquito larvae.

Inundated with escalating dengue outbreaks, there is an urgent call to find alternate potential vector control methods as the currently employed method fails to curb the expanding of dengue virus transmission in Malaysia. Supported by this aim, we are interested in exploiting the potential of Ipomoea cairica leaves extract towards primary and secondary vectors of dengue fever, Aedes aegypti and Aedes albopictus. To assess the effectiveness of this plant extracts towards Aedes larvae, we carried out two complementary analyses. First, we observed the comparative effectiveness of larvicidal activity I. cairica extract against the laboratory and field strains of Ae. aegypti and Ae. albopictus. Then, we determined the effective lethal dose of this plant extract against Aedes larvae using log-probit regression analysis of the SPSS 20.0 programme. Results from bioassay demonstrated that I. cairica leaves extract was highly effective to induce larvicidal mortality of Ae. albopictus and Ae. aegypti within 24 and 48 hours post-treatment. Results from the factorial analysis of variance (ANOVA) also indicated that there were significant differences in larvicidal activity between species and strains used (P<0.05). It is interesting to notify that the sequence of effectiveness for the larvicidal activities of I. cairica acethonilic leaves extract is in the manner; Ae. albopictus field strain > Ae. aegypti laboratory strain > Ae. aegypti field strain > Ae. albopictus laboratory strain. The I. cairica leaves extract displayed high larvicidal activity against Ae. albopictus as compared to Ae. aegypti. This is the first evaluation involving the comparison of I. cairica leaves extract effects for the laboratory strain and field strain of Ae. albopictus and Ae. Aegypti.

Vector competence of Aedes aegypti and screening for differentially expressed microRNAs exposed to Zika virus

BackgroundZika virus (ZIKV) is transmitted to humans primarily by Aedes aegypti. Previous studies on Ae. aegypti from Jiegao (JG) and Mengding (MD) in Yunnan province, China have shown that these mosquitoes are able to transmit ZIKV to their offspring through vertical transmission, indicating that these two Ae. aegypti strains pose a potential risk for ZIKV transmission. However, the vector competence of these two Ae. aegypti strains to ZIKV has not been evaluated and the molecular mechanisms influencing vector competence are still unclear.MethodsAedes aegypti mosquitoes from JG and MD were orally infected with ZIKV, and the infection rate (IR), dissemination rate (DR), transmission rate (TR) and transmission efficiency (TE) of these two mosquito strains were explored to evaluate their vector competence to ZIKV. On 2, 4 and 6 days post-infection (dpi), the small RNA profiles between ZIKV-infected and non-infected Ae. aegypti midgut and salivary gland tissues were compared to gain insights into the molecular interactions between ZIKV and Ae. aegypti.ResultsThere were no significant differences in the IR, DR, TR and TE between the two Ae. aegypti strains (P > 0.05). However, ZIKV RNA appeared 2 days earlier in saliva of the JG strain, which indicated a higher competence of the JG strain to transmit ZIKV. Significant differences in the microRNA (miRNA) expression profiles between ZIKV-infected and non-infected Ae. aegypti were found in the 2-dpi libraries of both the midgut and salivary gland tissues from the two strains. In addition, 27 and 74 miRNAs (|log2 fold change| > 2) were selected from the miRNA expression profiles of ZIKV-infected and non-infected midgut and salivary gland tissues from the JG and MD strains, respectively.ConclusionsOur results provide novel insights into the ZIKV–mosquito interactions and build a foundation for future research on how miRNAs regulate the vector competence of mosquitoes to this arbovirus.Graphical abstract

Assessment of fitness and vector competence of a New Caledonia wMel Aedes aegypti strain before field-release.

BackgroundBiological control programs involving Wolbachia-infected Aedes aegypti are currently deployed in different epidemiological settings. New Caledonia (NC) is an ideal location for the implementation and evaluation of such a strategy as the only proven vector for dengue virus (DENV) is Ae. aegypti and dengue outbreaks frequency and severity are increasing. We report the generation of a NC Wolbachia-infected Ae. aegypti strain and the results of experiments to assess the vector competence and fitness of this strain for future implementation as a disease control strategy in Noumea, NC.Methods/principal findingsThe NC Wolbachia strain (NC-wMel) was obtained by backcrossing Australian AUS-wMel females with New Caledonian Wild-Type (NC-WT) males. Blocking of DENV, chikungunya (CHIKV), and Zika (ZIKV) viruses were evaluated via mosquito oral feeding experiments and intrathoracic DENV challenge. Significant reduction in infection rates were observed for NC-wMel Ae. aegypti compared to WT Ae. aegypti. No transmission was observed for NC-wMel Ae. aegypti. Maternal transmission, cytoplasmic incompatibility, fertility, fecundity, wing length, and insecticide resistance were also assessed in laboratory experiments. Ae. aegypti NC-wMel showed complete cytoplasmic incompatibility and a strong maternal transmission. Ae. aegypti NC-wMel fitness seemed to be reduced compared to NC-WT Ae. aegypti and AUS-wMel Ae. aegypti regarding fertility and fecundity. However further experiments are required to assess it accurately.Conclusions/significanceOur results demonstrated that the NC-wMel Ae. aegypti strain is a strong inhibitor of DENV, CHIKV, and ZIKV infection and prevents transmission of infectious viral particles in mosquito saliva. Furthermore, our NC-wMel Ae. aegypti strain induces reproductive cytoplasmic incompatibility with minimal apparent fitness costs and high maternal transmission, supporting field-releases in Noumea, NC.

Aedes aegypti continuously exposed to Bacillus thuringiensis svar. israelensis does not exhibit changes in life traits but displays increased susceptibility for Zika virus

BackgroundAedes aegypti can transmit arboviruses worldwide, and Bacillus thuringiensis svar. israelensis (Bti)-based larvicides represent an effective tool for controlling this species. The safety of Bti and lack of resistance have been widely reported; however, little is known regarding the impact of the extensive use of these larvicides on the life traits of mosquitoes. Therefore, this study investigated biological parameters, including susceptibility to arbovirus, of an Ae. aegypti strain (RecBti) subjected to 29 generations of exposure to Bti compared with the RecL reference strain.MethodsThe biological parameters of individuals reared under controlled conditions were compared. Also, the viral susceptibility of females not exposed to Bti during their larval stage was analysed by oral infection and followed until 14 or 21 days post-infection (dpi).ResultsRecBti individuals did not display alterations in the traits that were assessed (fecundity, fertility, pupal weight, developmental time, emergence rate, sex ratio and haematophagic capacity) compared to RecL individuals. Females from both strains were susceptible to dengue serotype 2 (DENV-2) and Zika virus (ZIKV). However, RecBti females showed significantly higher rates of ZIKV infection compared with RecL females at 7 (90% versus 68%, Chi-square: χ2 = 7.27, df = 1, P = 0.006) and 14 dpi (100% versus 87%, Chi-square: χ2 = 7.69, df = 1, P = 0.005) and for dissemination at 7 dpi (83.3% versus 36%, Fisher’s exact test: P < 0.0001, OR = 0.11, 95% CI 0.03–0.32). Quantification of DENV-2 and ZIKV viral particles produced statistically similar results for females from both strains.ConclusionsProlonged exposure of Ae. aegypti larvae to Bti did not alter most of the evaluated biological parameters, except that RecBti females exhibited a higher vector susceptibility for ZIKV. This finding is related to a background of Bti exposure for several generations but not to a previous exposure of the tested females during the larval stage. This study highlights mosquito responses that could be associated with the chronic exposure to Bti in addition to the primary larvicidal effect elicited by this control agent.Graphical abstract

INSECTICIDE EFFICACY OF SPATIAL REPELLENT COMPOUND-METOFLUTHRIN AGAINST SUSCEPTIBLE AND RESISTANT STRAINS OF AEDES AEGYPTI

Spatial repellents (SR), include pyrethroid insecticides that are highly volatile at low temperatures and with high lethal activities against mosquitoes, mainly Aedes vectors of arboviral diseases. Of these SR, metofluthrin is widely used in various devices for repellent consumer products. This article reports the susceptibility status of Ae. aegypti Puerto Rico permethrin-resistant laboratory strain (PR) and Orlando susceptible laboratory strain (ORL) to metofluthrin and permethrin using the CDC glass bottle bioassay. The time-mortality relationships showed that the permethrin-resistant PR strain is highly resistant to both permethrin and metofluthrin compared to the susceptible ORL strain. The resistant ratio (RR) based on the killing time (KT) (KT50 -PR/KT50 -ORL) was 30- and 5- folds for permethrin and metofluthrin, respectively. The results also showed that the PR strain is less resistance to metofluthrin than to permethrin, with a three-fold RR (KT50 -PR-per/KT50 -PR-met). These results indicate the potential risk of developing cross-resistance of metofluthrin in permethrin-resistant mosquitoes. Integrated vector management in mosquito control should be considerate of how consumer products and field operations interact to accelerate cross resistance to pyrethroids.

High larvicidal efficacy of yeast-encapsulated orange oil against Aedes aegypti strains from Brazil

BackgroundBotanical substances such as essential oils (EOs) have demonstrated insecticidal properties and are a valid option for vector control. However, free EOs are unreliable as mosquito larvicides due their easy degradation by environmental exposure to ultraviolet light and higher temperatures. Here, we assessed the efficacy of a mosquito larvicide based on orange oil in a yeast-based delivery system against Aedes aegypti strains with different resistance status towards chemical neurotoxic insecticides. This larvicide preparation was physicochemically characterized in a previous report.MethodsLarvae of four Ae. aegypti strains from different regions of Brazil and different resistance profiles for deltamethrin (pyrethroid) and temephos (organophosphate) were tested against yeast-encapsulated orange oil (YEOO) in laboratory conditions for measurement of LC50 and LC90 values. The same assays were performed with the Belo Horizonte strain under environmental conditions (natural light and temperature). The resistance profiles of these strains were compared to the Rockefeller reference strain in all conditions.ResultsYEOO was found to be a highly active larvicide (LC50 < 50 mg/L) against all Ae. aegypti strains tested in both laboratory conditions (LC50 = 8.1–24.7 mg/L) and environmental conditions with natural light and temperature fluctuation (LC50 = 20.0–49.9 mg/L). Moreover, all strains were considered susceptible (RR < 5) to YEOO, considering resistance ratios calculated based on the Rockefeller strain. The resistance ratios were only higher than 2.5 for LC90–95 of Belo Horizonte in the laboratory, probably due the higher heterogeneity associated with older egg papers (> 5 months).ConclusionYEOO demonstrates high larvicidal activity against Ae. aegypti strains with resistant phenotypes for deltamethrin (PY) and temephos (OP). This larvicidal activity suggests the potential for the development of YEOO as an alternative intervention to synthetic insecticides in integrated vector management programs, for populations with resistance to commonly used insecticides.Graphical

Determining vector competence of Aedes aegypti from Ghana in transmitting dengue virus serotypes 1 and 2

BackgroundDengue virus (DENV) is a mosquito-borne arbovirus transmitted by Aedes mosquitoes, but is not endemic in all areas where this vector is found. For example, the relatively sparse distribution of cases in West Africa is generally attributed to the refractory nature of West African Aedes aegypti (Ae. aegypti) to DENV infection, and particularly the forest-dwelling Ae. aegypti formosus. However, recent studies have shown these mosquitoes to be competent vectors within some West African countries that have suffered outbreaks in the past, such as Senegal. There is however little information on the vector competence of the Ae. aegypti in West African countries such as Ghana with no reported outbreaks.MethodsThis study examined the vector competence of 4 Ae. aegypti colonies from urban, semi-urban, and two rural locations in Ghana in transmitting DENV serotypes 1 and 2, using a single colony from Vietnam as control. Midgut infection and virus dissemination were determined by quantitative reverse transcription polymerase chain reaction (qRT-PCR), while the presence and concentration of DENV in the saliva of infectious mosquitoes was determined by the focus forming assay.ResultsThere were significant differences in the colonies’ susceptibility to virus infection, dissemination, and transmission. All examined Ghanaian mosquitoes were refractory to infection by DENV serotype 2, while some colonies exhibited potential to transmit DENV serotype 1. None of the tested colonies were as competent as the control group colony.ConclusionsThese findings give insight into the possible risk of outbreaks, particularly in the urban areas in the south of Ghana, and highlight the need for continuous surveillance to determine the transmission status and outbreak risk. This study also highlights the need to prevent importation of different DENV strains and potential invasion of new highly vector-competent Ae. aegypti strains, particularly around the ports of entry.Graphical

Fitness costs of individual and combined pyrethroid resistance mechanisms, kdr and CYP-mediated detoxification, in Aedes aegypti.

BackgroundAedes aegypti is an important vector of many human diseases and a serious threat to human health due to its wide geographic distribution and preference for human hosts. A. aegypti also has evolved widespread resistance to pyrethroids due to the extensive use of this insecticide class over the past decades. Mutations that cause insecticide resistance result in fitness costs in the absence of insecticides. The fitness costs of pyrethroid resistance mutations in A. aegypti are still poorly understood despite their implications for arbovirus transmission.Methodology/Principle findingsWe evaluated fitness based both on allele-competition and by measuring specific fitness components (i.e. life table and mating competition) to determine the costs of the different resistance mechanisms individually and in combination. We used four congenic A. aegypti strains: Rockefeller (ROCK) is susceptible to insecticides; KDR:ROCK (KR) contains only voltage-sensitive sodium channel (Vssc) mutations S989P+V1016G (kdr); CYP:ROCK (CR) contains only CYP-mediated resistance; and CYP+KDR:ROCK (CKR) contains both CYP-mediated resistance and kdr. The kdr allele frequency decreased over nine generations in the allele-competition study regardless of the presence of CYP-mediated resistance. Specific fitness costs were variable by strain and component measured. CR and CKR had a lower net reproductive rate (R0) than ROCK or KR, and KR was not different than ROCK. There was no correlation between the level of permethrin resistance conferred by the different mechanisms and their fitness cost ratio. We also found that CKR males had a reduced mating success relative to ROCK males when attempting to mate with ROCK females.Conclusions/SignificanceBoth kdr and CYP-mediated resistance have a fitness cost affecting different physiological aspects of the mosquito. CYP-mediated resistance negatively affected adult longevity and mating competition, whereas the specific fitness costs of kdr remains elusive. Understanding fitness costs helps us determine whether and how quickly resistance will be lost after pesticide application has ceased.

Colonization and Various Parameters Affecting Egg Hatch and Development of the Old Balara Strain (Philippines), Aedes aegypti

Aedes aegypti strain obtained from field collections in Old Balara, Quezon City, Philippines was colonized at the Department of Science and Technology–Philippine Nuclear Research Institute (DOST-PNRI) laboratory. The number of eggs and their weight followed a significant linear relationship for the Ae. aegypti colony. Storing the hatching solution composed of nutrient broth (NB) and brewer’s yeast (BY) longer for at least 16 h hatched the mosquito fastest within 4h. Among the different ages tested, 2-wk-old eggs had the highest hatch rate. After collecting eggs from rearing cages, eggs for 6 wk still produced a high hatch rate and pupal recovery. Mosquito eggs can be effectively stored in cup and ziplock with a hatch rate of at least 77% on the third week, and at least 71% on the fourth week. Eggs stored in plastic cups can be best stored at 17–20 °C in the incubator 4 wk without a decrease in hatch rate. Eggs at these temperatures still produced about 50% egg hatch even until 3 mo.

Rhamnolipids on Aedes aegypti larvae: a potential weapon against resistance selection.

The resistance of Aedes aegypti to chemical insecticides has been reported and our work proposes the use of biosurfactants as an alternative larvicide. We evaluated the effect of rhamnolipids against larvae of pyrethroid-resistant and susceptible A. aegypti strains. Time-mortality and sublethal effects were evaluated via survival analysis and swimming behavior, respectively. Rhamnolipids showed larvicidal effect at all tested concentrations. Rhamnolipids at 300mg L-1 killed 100% of both susceptible and resistant larvae within 24h of exposure and 99% after 30-days stored (pyrethroid-susceptible larvae). Regarding the sublethal effects, the swimming rate was reduced in 50 and 100mg L-1 of rhamnolipids in grouped (pyrethroid-susceptible) larvae. Rhamnolipids at 50mg L-1 reduced the distance and speed and increased the number of stops and resting time of individualized pyrethroid-susceptible larvae. The larvicidal effect of the rhamnolipids evaluated demonstrates that these compounds represent an alternative to control A. aegypti.