bims-mosdis Biomed News
on Mosquito distribution and disease
Issue of 2020‒04‒12
eighteen papers selected by
Richard Halfpenny
Staffordshire University


  1. J Chem Ecol. 2020 Apr 09.
    Meza FC, Roberts JM, Sobhy IS, Okumu FO, Tripet F, Bruce TJA.
      Attractive Toxic Sugar Baits (ATSB) are used in a "lure-and-kill" approach for management of the malaria vector Anopheles gambiae, but the active chemicals were previously unknown. Here we collected volatiles from a mango, Mangifera indica, juice bait which is used in ATSBs in Tanzania and tested mosquito responses. In a Y-tube olfactometer, female mosquitoes were attracted to the mango volatiles collected 24-48 h, 48-72 h and 72-96 h after preparing the bait but volatiles collected at 96-120 h were no longer attractive. Volatile analysis revealed emission of 23 compounds in different chemical classes including alcohols, aldehydes, alkanes, benzenoids, monoterpenes, sesquiterpenes and oxygenated terpenes. Coupled GC-electroantennogram (GC-EAG) recordings from the antennae of An. gambiae showed robust responses to 4 compounds: humulene, (E)-caryophyllene, terpinolene and myrcene. In olfactometer bioassays, mosquitoes were attracted to humulene and terpinolene. (E)-caryophyllene was marginally attractive while myrcene elicited an avoidance response with female mosquitoes. A blend of humulene, (E)-caryophyllene and terpinolene was highly attractive to females (P < 0.001) when tested against a solvent blank. Furthermore, there was no preference when this synthetic blend was offered as a choice against the natural sample. Our study has identified the key compounds from mango juice baits that attract An. gambiae and this information may help to improve the ATSBs currently used against malaria vectors.
    Keywords:  Attractant; Kairomone; Malaria vector; Mango; Terpenoids
    DOI:  https://doi.org/10.1007/s10886-020-01172-8
  2. Malar J. 2020 Apr 07. 19(1): 140
    Hughes A, Foster GM, Guy A, Matope A, Abe M, Towers D, McCall PJ.
      BACKGROUND: Insecticide-treated nets (ITNs) are losing efficacy against pyrethroid-resistant malaria vector populations throughout Africa. Safeguarding bed net efficacy, vital for effective malaria control, requires greater knowledge of mosquito-ITN interactions and how this impacts on the mosquito.METHODS: A purpose-built benchtop apparatus with a closed 10 cm cubic chamber (the 'Baited-box') was used to video record behaviour of individual free-flying female Anopheles gambiae during approach and blood-feeding on a human hand through untreated nets and ITNs at close range. Time and duration of defined behavioural events, and knockdown and mortality at 1- and 24-h post-exposure respectively, were recorded for pyrethroid susceptible and resistant mosquitoes.
    RESULTS: Using three human volunteers differing in relative attractiveness to mosquitoes, 328 mosquitoes were individually tested. There were no significant differences between response rates to ITNs and untreated nets (P > 0.1) or between resistant (Tiassalé) and susceptible (Kisumu) mosquito strains, at untreated nets (P = 0.39) or PermaNet 2.0 (P = 1). The sequence of behavioural events from host-seeking to completion of blood-feeding was consistent in all tests but duration and start time of events involving net contact were reduced or delayed respectively with ITNs. Blood-feeding durations at untreated nets (means from 4.25 to 8.47 min (95% confidence interval (CI) = 3.39-9.89) at 3 human volunteers) were reduced by 37-50% at PermaNet 2.0, in susceptible (mean 2.59-4.72 min, 95% CI = 1.54-5.5, P = < 0.05) and resistant (mean 4.20 min, 95% CI = 3.42-4.97, P = 0.01) strains. Total accumulated net contact was approximately 50% lower at PermaNet and Olyset ITNs (P < 0.0001) in susceptible (two of the three volunteers) and resistant mosquitoes. Times prior to first net contact were similar at untreated nets and ITNs (P > 0.2), and neither ITN type showed detectable spatial repellency. After initial contact, blood-feeding commenced later at Olyset (mean 2.76 min, 95% CI = 1.74-3.76, P = 0.0009) and PermaNet (mean 2.4 min, 95% CI = 1.52-3.33, P = 0.0058) than untreated netting (mean 0.68 min, 95% CI = 0.42-0.94).
    CONCLUSIONS: The baited box offers a simple method for detailed characterization of mosquito behavioural responses to insecticidal nets, for comparing entomological modes of action between nets and for defining the behavioural responses of particular mosquito strains or populations. The device has potential as a screening assay in the search for novel net treatments and for investigations into behavioural resistance mechanisms.
    Keywords:  Anopheles; Bednet; Behaviour; Bioassay; Control; ITN; Insecticide; Malaria; Mosquito; Pyrethroid; Vector
    DOI:  https://doi.org/10.1186/s12936-020-03213-9
  3. Malar J. 2020 Apr 08. 19(1): 148
    Sangoro OP, Gavana T, Finda M, Mponzi W, Hape E, Limwagu A, Govella NJ, Chaki P, Okumu FO.
      BACKGROUND: Outdoor and early evening mosquito biting needs to be addressed if malaria elimination is to be achieved. While indoor-targeted interventions, such as insecticide-treated nets and indoor residual spraying, remain essential, complementary approaches that tackle persisting outdoor transmission are urgently required to maximize the impact. Major malaria vectors principally bite human hosts around the feet and ankles. Consequently, this study investigated whether sandals treated with efficacious spatial repellents can protect against outdoor biting mosquitoes.METHODOLOGY: Sandals affixed with hessian bands measuring 48 cm2 treated with 0.06 g, 0.10 g and 0.15 g of transfluthrin were tested in large cage semi-field and full field experiments. Sandals affixed with hessian bands measuring 240 cm2 and treated with 0.10 g and 0.15 g of transfluthrin were also tested semi field experiments. Human landing catches (HLC) were used to assess reduction in biting exposure by comparing proportions of mosquitoes landing on volunteers wearing treated and untreated sandals. Sandals were tested against insectary reared Anopheles arabiensis mosquitoes in semi-field experiments and against wild mosquito species in rural Tanzania.
    RESULTS: In semi-field tests, sandals fitted with hessian bands measuring 48 cm2 and treated with 0.15 g, 0.10 g and 0.06 g transfluthrin reduced mosquito landings by 45.9%, (95% confidence interval (C.I.) 28-59%), 61.1% (48-71%), and 25.9% (9-40%), respectively compared to untreated sandals. Sandals fitted with hessian bands measuring 240 cm2 and treated with 0.15 g and 0.10 g transfluthrin reduced mosquito landings by 59% (43-71%) and 64% (48-74%), respectively. In field experiments, sandals fitted with hessian bands measuring 48 cm2 and treated with 0.15 g transfluthrin reduced mosquito landings by 70% (60-76%) against Anopheles gambiae sensu lato, and 66.0% (59-71%) against all mosquito species combined.
    CONCLUSION: Transfluthrin-treated sandals conferred significant protection against mosquito bites in semi-field and field settings. Further evaluation is recommended for this tool as a potential complementary intervention against malaria. This intervention could be particularly useful for protecting against outdoor exposure to mosquito bites. Additional studies are necessary to optimize treatment techniques and substrates, establish safety profiles and determine epidemiological impact in different settings.
    Keywords:  Ifakara; New tools; Residual malaria transmission; Transfluthrin; Transfluthrin-treated footwear; Vector borne diseases
    DOI:  https://doi.org/10.1186/s12936-020-03215-7
  4. J Med Entomol. 2020 Apr 08. pii: tjaa055. [Epub ahead of print]
    Jeffrey Gutiérrez EH, Walker KR, Ernst KC, Riehle MA, Davidowitz G.
      The Aedes aegypti mosquito is the primary vector of dengue, yellow fever, chikungunya, and Zika viruses. Infection with the dengue virus alone occurs in an estimated 400 million people each year. Likelihood of infection with a virus transmitted by Ae. aegypti is most commonly attributed to abundance of the mosquito. However, the Arizona-Sonora desert region has abundant Ae. aegypti in most urban areas, yet local transmission of these arboviruses has not been reported in many of these cities. Previous work examined the role of differential Ae. aegypti longevity as a potential explanation for these discrepancies in transmission. To determine factors that were associated with Ae. aegypti longevity in the region, we collected eggs from ovitraps in Tucson, AZ and reared them under multiple experimental conditions in the laboratory to examine the relative impact of temperature and crowding during development, body size, fecundity, and relative humidity during the adult stage. Of the variables studied, we found that the combination of temperature during development, relative humidity, and body size produced the best model to explain variation in age at death. El mosquito Aedes aegypti es el vector primario de los virus de dengue, fiebre amarilla, chikungunya y Zika. Solamente las infecciones con los virus de dengue ocurren en aproximadamente 400 millones de personas cada año. La probabilidad de infección con un virus transmitido por Ae. aegypti es frecuentemente atribuido a la abundancia del mosquito. No obstante, la región del desierto de Arizona-Sonora tiene una abundancia de Ae. aegypti en la mayoría de las áreas urbanas, pero la transmisión local de estos arbovirus no ha sido reportada en muchas de estas ciudades. Trabajos previos han examinado el rol de las diferencias de longevidad en Ae. aegypti como explicación potencial por estas discrepancias en la transmisión. Para determinar que factores fueron asociados con longevidad en Ae. aegypti en la región, colectamos huevos de ovitrampas en Tucson, Arizona y los criamos debajo de múltiples condiciones experimentales en el laboratorio para examinar el impacto relativo de temperatura y competencia para nutrición durante desarrollo, tamaño del cuerpo, capacidad reproductiva, y humedad relativa durante adultez. De las variables estudiados, encontramos que la combinación de temperatura durante desarrollo, humedad relativa, y tamaño del cuerpo produjo el mejor modelo para explicar variación en edad al tiempo de la muerte.
    Keywords:   Aedes aegypti ; body size; longevity
    DOI:  https://doi.org/10.1093/jme/tjaa055
  5. Am J Trop Med Hyg. 2020 Apr 06.
    Hustedt J, Doum D, Keo V, Ly S, Sam B, Chan V, Boyer S, Liverani M, Alexander N, Bradley J, Prasetyo DB, Rachmat A, Lopes S, Leang R, Hii J.
      Aedes-transmitted diseases, especially dengue, are increasing throughout the world and the main preventive methods include vector control and the avoidance of mosquito bites. A simple Premise Condition Index (PCI) categorizing shade, house, and yard conditions was previously developed to help prioritize households or geographical areas where resources are limited. However, evidence about the accuracy of the PCI is mixed. The current study aimed to contribute to a better understanding of the relevance by collecting data from 2,400 premises at four time points over 1 year in Kampong Cham, Cambodia. Regression models were then used to identify associations between PCI and Aedes adult female mosquitoes and pupae. In addition, receiver operating characteristic curves were used to measure the ability of PCI to identify premises in the top quartile of mosquito abundance. The density of adult Aedes females was positively associated with PCI at the household (ratio of means = 1.16 per point on the PCI scale) and cluster level (ratio of means = 1.54). However, the number of Aedes pupae was negatively associated with PCI at the household level (rate ratio = 0.74) and did not have a statistically significant association at the cluster level. Receiver operating characteristic curves suggest the PCI score had "rather low accuracy" (area under the ROC curve = 0.52 and 0.54) at identifying top-quartile premises in terms of adult female Aedes and pupae, respectively. These results suggest that caution is warranted in the programmatic use of PCI in areas of similar geography and mosquito abundance.
    DOI:  https://doi.org/10.4269/ajtmh.19-0453
  6. Parasit Vectors. 2020 Apr 10. 13(1): 188
    Chan KK, Auguste AJ, Brewster CC, Paulson SL.
      BACKGROUND: Vector-borne diseases are a major public health concern and cause significant morbidity and mortality. Zika virus (ZIKV) is the etiologic agent of a massive outbreak in the Americas that originated in Brazil in 2015 and shows a strong association with congenital ZIKV syndrome in newborns. Cache Valley virus (CVV) is a bunyavirus that causes mild to severe illness in humans and ruminants. In this study, we investigated the vector competence of Virginia mosquitoes for ZIKV and CVV to explore their abilities to contribute to potential outbreaks.METHODS: To determine vector competence, mosquitoes were fed a blood meal comprised of defibrinated sheep blood and virus. The presence of midgut or salivary gland barriers to ZIKV infection were determined by intrathoracic inoculation vs oral infection. After 14-days post-exposure, individual mosquitoes were separated into bodies, legs and wings, and saliva expectorant. Virus presence was detected by plaque assay to determine midgut infection, dissemination, and transmission rates.
    RESULTS: Transmission rates for Ae. albopictus orally infected (24%) and intrathoracically inoculated (63%) with ZIKV was similar to Ae. aegypti (48% and 71%, respectively). Transmission rates of ZIKV in Ae. japonicus were low, and showed evidence of a midgut infection barrier demonstrated by low midgut infection and dissemination rates from oral infection (3%), but increased transmission rates after intrathoracic inoculation (19%). Aedes triseriatus was unable to transmit ZIKV following oral infection or intrathoracic inoculation. CVV transmission was dose-dependent where mosquitoes fed high titer (ht) virus blood meals developed higher rates of midgut infection, dissemination, and transmission compared to low titer (lt) virus blood meals. CVV was detected in the saliva of Ae. albopictus (ht: 68%, lt: 24%), Ae. triseriatus (ht: 52%, lt: 7%), Ae. japonicus (ht: 22%, lt: 0%) and Ae. aegypti (ht: 10%; lt: 7%). Culex pipiens and Cx. restuans were not competent for ZIKV or CVV.
    CONCLUSIONS: This laboratory transmission study provided further understanding of potential ZIKV and CVV transmission cycles with Aedes mosquitoes from Virginia. The ability for these mosquitoes to transmit ZIKV and CVV make them a public health concern and suggest targeted control programs by mosquito and vector abatement districts.
    Keywords:  Aedes aegypti; Aedes albopictus; Aedes japonicus; Aedes triseriatus; Cache Valley virus; Culex pipiens; Culex restuans; Infection barriers; Vector competence; Zika virus
    DOI:  https://doi.org/10.1186/s13071-020-04042-0
  7. R Soc Open Sci. 2020 Mar;7(3): 192041
    Francis S, Crawford J, McKenzie S, Campbell T, Wright D, Hamilton T, Huntley-Jones S, Spence S, Belemvire A, Alavi K, Gutierrez CT.
      Insecticide resistance has become problematic in tropical and subtropical regions, where Aedes mosquitoes and Aedes-borne arboviral diseases thrive. With the recent occurrence of chikungunya and the Zika virus in Jamaica, the Ministry of Health and Wellness, Jamaica, partnered with the United States Agency for International Development to implement multiple intervention activities to reduce the Aedes aegypti populations in seven parishes across the island and to assess the susceptibility of collected samples to various concentrations of temephos, Bacillus thuringiensis subsp. israelensis, (Bti), diflubenzuron and methoprene. Of the insecticides tested, only temephos has been used in routine larviciding activities in the island. The results showed that only temephos at concentrations 0.625 ppm and Bti at concentrations 6-8 ppm were effective at causing 98-100% mortality of local Ae. aegypti at 24 h exposure. Surprisingly, the growth inhibitors diflubenzuron and methoprene had minimal effect at preventing adult emergence in Ae. aegypti larvae in the populations tested. The results demonstrate the need for insecticide resistance testing as a routine part of vector control monitoring activies in order to determine useful tools that may be incorporated to reduce the abundance of Ae. aegypti.
    Keywords:  Aedes aegypti; Bti; Jamaica; growth inhibitors; insecticide resistance; temephos
    DOI:  https://doi.org/10.1098/rsos.192041
  8. Pathogens. 2020 Apr 05. pii: E265. [Epub ahead of print]9(4):
    Fontenille D, Powell JR.
      The past few decades have seen the emergence of several worldwide arbovirus epidemics (chikungunya, Zika), the expansion or recrudescence of historical arboviruses (dengue, yellow fever), and the modification of the distribution area of major vector mosquitoes such as Aedes aegypti and Ae. albopictus, raising questions about the risk of appearance of new vectors and new epidemics. In this opinion piece, we review the factors that led to the emergence of yellow fever in the Americas, define the conditions for a mosquito to become a vector, analyse the recent example of the new status of Aedes albopictus from neglected mosquito to major vector, and propose some scenarios for the future.
    Keywords:  Aedes aegypti; Aedes albopictus; arbovirus; culicidae; emergence; mosquito
    DOI:  https://doi.org/10.3390/pathogens9040265
  9. PLoS Negl Trop Dis. 2020 Apr 10. 14(4): e0008097
    Lenhart A, Morrison AC, Paz-Soldan VA, Forshey BM, Cordova-Lopez JJ, Astete H, Elder JP, Sihuincha M, Gotlieb EE, Halsey ES, Kochel TJ, Scott TW, Alexander N, McCall PJ.
      Dengue is one of the most important vector-borne diseases, resulting in an estimated hundreds of millions of infections annually throughout the tropics. Control of dengue is heavily dependent upon control of its primary mosquito vector, Aedes aegypti. Innovative interventions that are effective at targeting the adult stage of the mosquito are needed to increase the options for effective control. The use of insecticide-treated curtains (ITCs) has previously been shown to significantly reduce the abundance of Ae. aegypti in and around homes, but the impact of ITCs on dengue virus (DENV) transmission has not been rigorously quantified. A parallel arm cluster-randomized controlled trial was conducted in Iquitos, Peru to quantify the impact of ITCs on DENV seroconversion as measured through plaque-reduction neutralization tests. Seroconversion data showed that individuals living in the clusters that received ITCs were at greater risk to seroconverting to DENV, with an average seroconversion rate of 50.6 per 100 person-years (PY) (CI: 29.9-71.9), while those in the control arm had an average seroconversion rate of 37.4 per 100 PY (CI: 15.2-51.7). ITCs lost their insecticidal efficacy within 6 months of deployment, necessitating re-treatment with insecticide. Entomological indicators did not show statistically significant differences between ITC and non-ITC clusters. It's unclear how the lack of protective efficacy reported here is attributable to simple failure of the intervention to protect against Ae. aegypti bites, or the presence of a faulty intervention during much of the follow-up period. The higher risk of dengue seroconversion that was detected in the ITC clusters may have arisen due to a false sense of security that inadvertently led to less routine protective behaviors on the part of households that received the ITCs. Our study provides important lessons learned for conducting Randomized Cluster Trials for vector control interventions against Aedes-transmitted virus infections.
    DOI:  https://doi.org/10.1371/journal.pntd.0008097
  10. Parasit Vectors. 2020 Apr 07. 13(1): 179
    Grossman MK, Oliver SV, Brooke BD, Thomas MB.
      BACKGROUND: There is substantial concern that the spread of insecticide resistance will render long-lasting insecticide-treated nets (LLINs) ineffective. However, there is limited evidence supporting a clear association between insecticide resistance and malaria incidence or prevalence in the field. We suggest that one reason for this disconnect is that the standard WHO assays used in surveillance to classify mosquito populations as resistant are not designed to determine how resistance might impact LLIN efficacy. The standard assays expose young, unfed female mosquitoes to a diagnostic insecticide dose in a single, forced exposure, whereas in the field, mosquitoes vary in their age, blood-feeding status, and the frequency or intensity of LLIN exposure. These more realistic conditions could ultimately impact the capacity of "resistant" mosquitoes to transmit malaria.METHODS: Here, we test this hypothesis using two different assays that allow female mosquitoes to contact a LLIN as they host-seek and blood-feed. We quantified mortality after both single and multiple exposures, using seven different strains of Anopheles ranging in pyrethroid resistance intensity.
    RESULTS: We found that strains classified as 1×-resistant to the pyrethroid insecticide deltamethrin in the standard WHO assay exhibited > 90% mortality over 24 h following more realistic LLIN contact. Mosquitoes that were able to blood-feed had increased survival compared to their unfed counterparts, but none of the 1×-resistant strains survived for 12 days post-exposure (the typical period for malaria parasite development within the mosquito). Mosquitoes that were 5×- and 10×-resistant (i.e. moderate or high intensity resistance based on the WHO assays) survived a single LLIN exposure well. However, only about 2-3% of these mosquitoes survived multiple exposures over the course of 12 days and successfully blood-fed during the last exposure.
    CONCLUSIONS: These results suggest that the standard assays provide limited insight into how resistance might impact LLIN efficacy. In our laboratory setting, there appears little functional consequence of 1×-resistance and even mosquitoes with moderate (5×) or high (10×) intensity resistance can suffer substantial reduction in transmission potential. Monitoring efforts should focus on better characterizing intensity of resistance to inform resistance management strategies and prioritize deployment of next generation vector control products.
    Keywords:  Anopheles; Insecticide resistance; Malaria; Pyrethroids
    DOI:  https://doi.org/10.1186/s13071-020-04055-9
  11. Front Microbiol. 2020 ;11 362
    Sun J, Du S, Zheng Z, Cheng G, Jin X.
      Dengue virus (DENV) and Zika virus (ZIKV) are two mosquito-borne flaviviruses afflicting nearly half of the world population. Human infection by these viruses can either be asymptomatic or manifest as clinical diseases from mild to severe. Despite more cases are presented as self-limiting febrile illness, severe dengue disease can be manifested as hemorrhagic fever and hemorrhagic shock syndrome, and ZIKV infection has been linked to increased incidence of peripheral neuropathy Guillain-Barre syndrome and central neural disease such as microcephaly. The current prevention and treatment of these infectious diseases are either non-satisfactory or entirely lacking. Because DENV and ZIKV have much similarities in genomic and structural features, almost identical mode of mosquito-mediated transmission, and probably the same pattern of host innate and adaptive immunity toward them, it is reasonable and often desirable to investigate these two viruses side-by-side, and thereby devise common countermeasures against both. Here, we review the existing knowledge on DENV and ZIKV regarding epidemiology, molecular virology, protective immunity and vaccine development, discuss recent new discoveries on the functions of flavivirus NS1 protein in viral pathogenesis and transmission, and propose a one-two punch strategy using vaccine and vector blockade to overcome antibody-dependent enhancement and defeat Dengue and Zika viruses.
    Keywords:  Zika virus; dengue virus; epidemiology; mosquitoes; protective immunity; vaccine; virology
    DOI:  https://doi.org/10.3389/fmicb.2020.00362
  12. Nat Biotechnol. 2020 Apr;38(4): 482-492
    Crawford JE, Clarke DW, Criswell V, Desnoyer M, Cornel D, Deegan B, Gong K, Hopkins KC, Howell P, Hyde JS, Livni J, Behling C, Benza R, Chen W, Dobson KL, Eldershaw C, Greeley D, Han Y, Hughes B, Kakani E, Karbowski J, Kitchell A, Lee E, Lin T, Liu J, Lozano M, MacDonald W, Mains JW, Metlitz M, Mitchell SN, Moore D, Ohm JR, Parkes K, Porshnikoff A, Robuck C, Sheridan M, Sobecki R, Smith P, Stevenson J, Sullivan J, Wasson B, Weakley AM, Wilhelm M, Won J, Yasunaga A, Chan WC, Holeman J, Snoad N, Upson L, Zha T, Dobson SL, Mulligan FS, Massaro P, White BJ.
      The range of the mosquito Aedes aegypti continues to expand, putting more than two billion people at risk of arboviral infection. The sterile insect technique (SIT) has been used to successfully combat agricultural pests at large scale, but not mosquitoes, mainly because of challenges with consistent production and distribution of high-quality male mosquitoes. We describe automated processes to rear and release millions of competitive, sterile male Wolbachia-infected mosquitoes, and use of these males in a large-scale suppression trial in Fresno County, California. In 2018, we released 14.4 million males across three replicate neighborhoods encompassing 293 hectares. At peak mosquito season, the number of female mosquitoes was 95.5% lower (95% CI, 93.6-96.9) in release areas compared to non-release areas, with the most geographically isolated neighborhood reaching a 99% reduction. This work demonstrates the high efficacy of mosquito SIT in an area ninefold larger than in previous similar trials, supporting the potential of this approach in public health and nuisance-mosquito eradication programs.
    DOI:  https://doi.org/10.1038/s41587-020-0471-x
  13. Insects. 2020 Apr 03. pii: E224. [Epub ahead of print]11(4):
    Pintong AR, Ampawong S, Komalamisra N, Sriwichai P, Popruk S, Ruangsittichai J.
      Crude extracts and essential oils of A. conyzoides were tested with larva and adult stages of Ae. aegypti mosquitoes to determine their insecticidal properties. The crude extracts and essential oils came from three varieties of A. conyzoides (with white flowers, purple flowers, or white-purple flowers) and from two places on each plant (leaves and flowers), giving six types overall: leaf-white (LW); leaf-purple (LP); leaf white-purple (LW-P); flower-white (FW); flower-purple (FP); and flower white-purple (FW-P). Chemical constituents and components of the essential oils were identified using gas chromatography-mass spectrometry (GC-MS). Electron microscopic and histopathological studies were performed to determine the toxicological effects on mosquitoes in terms of morphological alterations. The six types of crude extracts exhibited no activity against individuals in the larval stages. However, six types of essential oils were effective against adult Ae. aegypti females. The mortality of adult Ae. aegypti females was higher from leaf extracts, particularly LP (median lethal dose, LD50 = 0.84%). The number of chemical constituents identified by GC-MS was high in flowers, especially W-P. Precocene I was the most abundant chemical component among the five types of essential oils, except in LP, in which precocene II was the most abundant. Histopathological alterations in adult Ae. aegypti females included compound eye degeneration, muscular damage with cellular infiltration, gut epithelial degeneration and necrosis, pyknotic nuclei in the malpighian epithelium and ovarian cell degeneration. FW and FP plant types exhibited the highest severity of histopathological alterations in mosquitoes compared with other plants, probably owing to the presence of monoterpene compounds in their tissues. The present study demonstrated LP plant extracts from A. conyzoides could be effective adulticides against adult Ae. aegypti. As natural products are biodegradable and exhibit low toxicity to mammalian and non-target organisms, they are suitable candidates for use in vector control programmes.
    Keywords:  Aedes; Asteraceae; crude extracts; essential oils; insecticide; pesticide; vector control
    DOI:  https://doi.org/10.3390/insects11040224
  14. Insect Biochem Mol Biol. 2020 Apr 07. pii: S0965-1748(20)30061-8. [Epub ahead of print] 103372
    Brown F, Paton DG, Catteruccia F, Ranson H, Ingham VA.
      Insecticide based vector control tools such as insecticide treated bednets and indoor residual spraying represent the cornerstones of malaria control programs. Resistance to chemistries used in these programs is now widespread and represents a significant threat to the gains seen in reducing malaria-related morbidity and mortality. Recently, disruption of the 20-hydroxyecdysone steroid hormone pathway was shown to reduce Plasmodium development and significantly reduce both longevity and egg production in a laboratory susceptible Anopheles gambiae population. Here, we demonstrate that disruption of this pathway by application of the dibenzoylhydrazine, methoxyfenozide (DBH-M), to insecticide resistant An. coluzzii, An. gambiae sl and An. funestus populations significantly reduces egg production in both topical and tarsal application. Moreover, DBH-M reduces adult longevity when applied topically, and tarsally after blood feeding. As the cytochrome p450s elevated in pyrethroid resistant Anopheles only bind DBH-M very weakly, this compound is unlikely to be subject to cross-resistance in a field-based setting. Manipulation of this hormonal signalling pathway therefore represents a potential complementary approach to current malaria control strategies, particularly in areas where high levels of insecticide resistance are compromising existing tools.
    Keywords:  20-Hydroxyecdysone; Anopheles; Insecticide resistance; Malaria; Methoxyfenozide; Vector control
    DOI:  https://doi.org/10.1016/j.ibmb.2020.103372
  15. Parasit Vectors. 2020 Apr 07. 13(1): 178
    Kramer IM, Kreß A, Klingelhöfer D, Scherer C, Phuyal P, Kuch U, Ahrens B, Groneberg DA, Dhimal M, Müller R.
      BACKGROUND: Aedes aegypti is a potential vector for several arboviruses including dengue and Zika viruses. The species seems to be restricted to subtropical/tropical habitats and has difficulties in establishing permanent populations in southern Europe, probably due to constraints during the winter season. The aim of this study was to systematically analyze the cold tolerance (CT) of Ae. aegypti in its most cold-resistant life stage, the eggs.METHODS: The CT of Ae. aegypti eggs was compared with that of Ae. albopictus which is well established in large parts of Europe. By systematically studying the literature (meta-analysis), we recognized that CT has been rarely tested in Ae. aegypti eggs, but eggs can survive at zero and sub-zero temperatures for certain exposure periods. To overcome potential bias from experimental differences between studies, we then conducted species comparisons using a harmonized high-resolution CT measuring method. From subtropical populations of the same origin, the survival (hatching in %) and emergence of adults of both species were measured after zero and sub-zero temperature exposures for up to 9 days (3 °C, 0 °C and - 2 °C: ≤ 9 days; - 6 °C: ≤ 2 days).
    RESULTS: Our data show that Ae. aegypti eggs can survive low and sub-zero temperatures for a short time period similar to or even better than those of Ae. albopictus. Moreover, after short sub-zero exposures of eggs of both species, individuals still developed into viable adults (Ae. aegypti: 3 adults emerged after 6 days at - 2 °C, Ae. albopictus: 1 adult emerged after 1 day at - 6 °C).
    CONCLUSIONS: Thus, both the literature and the present experimental data indicate that a cold winter may not be the preventing factor for the re-establishment of the dengue vector Ae. aegypti in southern Europe.
    Keywords:  Cold hardiness; Cold tolerance; Distribution limits; Overwintering; Phenotypic plasticity; Sub-zero exposure; Winter survival
    DOI:  https://doi.org/10.1186/s13071-020-04054-w
  16. Aquat Toxicol. 2020 Mar 19. pii: S0166-445X(20)30072-2. [Epub ahead of print]222 105474
    Yogarajalakshmi P, Venugopal Poonguzhali T, Ganesan R, Karthi S, Senthil-Nathan S, Krutmuang P, Radhakrishnan N, Mohammad F, Kim TJ, Vasantha-Srinivasan P.
      Larval toxicity of ethanolic extract of C. parvula (Ex-Cp) was prominent in the second and the third instars at the maximum lethal dosage of 100 ppm with 98 and 97 % mortality rate respectively. The LC50 and LC90 was displayed at 43 ppm and 88 ppm dosage respectively. Correspondingly, the sub-lethal dosage (65 ppm) of Ex-Cp significantly alters the carboxylesterase (α and β), GST and CYP450 enzyme level in both III and IV instar larvae in dose-dependent manner. Similarly, the Ex-Cp displayed significant repellent activity (97 %) with a maximum level of protection time (210 min). Photomicrography assay of Ex-Cp (65 ppm) were toxic to dengue larvae as compared to control. The non-target toxicity of Ex-Cp against the beneficial mosquito predators displayed less toxicity at the maximum dosage of 600 ppm as compared to Temephos. Thus the present research delivers the target and non-target toxicity of red algae C. parvula against the dengue mosquito vector.
    Keywords:  Dengue; Enzyme; Larvicide; Predators; Red-algae; Repellency
    DOI:  https://doi.org/10.1016/j.aquatox.2020.105474
  17. J Insect Physiol. 2020 Apr 03. pii: S0022-1910(19)30466-4. [Epub ahead of print] 104053
    Dittmer J, Gabrieli P.
      Mosquitoes are important vectors of human pathogens, which are transmitted by female mosquitoes via blood-feeding. Larval nutrition can have an important impact on the number of blood meals taken by adult females shortly after emergence, as nutritional deficiencies during the larval stage may result in pre-vitellogenic blood meals, which are not invested into egg development but into the endogenous nutrient reserves of the female. Here, we investigated the impact of nutrient deprivation during the larval stage on adult nutrient metabolism, longevity and blood-seeking behaviour in females of the invasive Asian tiger mosquito Aedes albopictus. We demonstrate that Ae. albopictus females are able to compensate for nutrient deprivation during the larval stage by increasing their development time until sufficient nutrients are acquired. Nonetheless, nutrient-poor larval conditions had a long-lasting priming effect on adult female metabolism, since these females accumulated lower nutrient reserves from carbohydrates and survived longer compared to females reared in nutrient-rich larval conditions. Moreover, nutrient and ATP levels of females from nutrient-poor larval conditions remained stable over a longer timespan without access to additional carbohydrates. This suggests differences in adult female metabolism in response to larval nutrition, with potential impact on the vectorial capacity of female mosquitoes.
    Keywords:  Mosquito; larval development; longevity; metabolism; nutrition
    DOI:  https://doi.org/10.1016/j.jinsphys.2020.104053
  18. BMC Public Health. 2020 Apr 06. 20(1): 465
    Suuron VM, Mwanri L, Tsourtos G, Owusu-Addo E.
      BACKGROUND: Despite the implementation of the World Health Organisation's recommended indoor residual spraying (IRS) intervention in the upper west region of Ghana to reduce malaria morbidity and mortality, the uptake of this intervention remains low. This study explores the facilitators and barriers to the acceptability and community uptake of indoor residual spraying in a highly endemic region of Ghana.METHODS: The health belief model (HBM) and realist evaluation framework were used to inform the study. A qualitative enquiry was conducted between April to October 2016. Data were collected through focus group discussions and semi-structured interviews with program stakeholders including community members, AngloGold Ashanti malaria control (AGA Mal) spray operators, and AGA Mal officials.
    RESULTS: A total of 101 people participated in the study. Considerable barriers to community acceptance of indoor residual spraying (IRS) were found, including, dislike of spray insecticides, inadequate information, religious and cultural beliefs, perceived low efficacy of IRS, difficulties with packing, unprofessional conduct of IRS spray operators, and other operational barriers to spraying. Facilitators of IRS uptake included a perceived effectiveness of IRS in preventing malaria and reducing mosquito bites, incidental benefits, respect for authority, training and capacity building, and sensitization activities.
    CONCLUSION: The numerous barriers to indoor residual spraying acceptance and implications show that acceptance levels could be improved. However, measures are required to address householders' concerns and streamline operational barriers to increase community uptake of indoor residual spraying.
    Keywords:  Acceptability; Barriers; Community; Facilitators; Ghana; Householders; IRS; Indoor residual spraying; Malaria; Mosquitoes
    DOI:  https://doi.org/10.1186/s12889-020-08505-y