Epidemic risk of arboviral diseases: Determining the habitats,spatial-temporal distribution,and abundance of immature Aedes aegypti in the Urban and Rural areas of Zanzibar,Tanzania

BackgroundIn Zanzibar, little is known about the arboviral disease vector Aedes aegypti in terms of abundance, spatio-temporal distribution of its larval habitats or factors associated with its proliferation. Effective control of the vector requires knowledge on ecology and habitat characteristics and is currently the only available option for reducing the risk of arboviral epidemics in the island nation of Zanzibar.MethodologyWe conducted entomological surveys in households and surrounding compounds from February to May 2018 in the urban (Mwembemakumbi and Chumbuni) and rural (Chuini and Kama) Shehias (lowest government administrative unit) situated in the Urban-West region of Unguja island, Zanzibar. Larvae and pupae were collected, transported to the insectary, reared to adult, and identified to species level. Characteristics and types of water containers were also recorded on site. Generalized linear mixed models with binomial and negative binomial distributions were applied to determine factors associated with presence of Ae. aegypti immatures (i.e. both larvae and pupae) or pupae, alone and significant predictors of the abundance of immature Ae. aegypti or pupae, respectively.ResultsThe survey provided evidence of widespread presence and abundance of Ae. aegypti mosquitoes in both urban and rural settings of Unguja Island. Interestingly, rural setting had higher numbers of infested containers, all immatures, and pupae than urban setting. Likewise, higher House and Breteau indices were recorded in rural compared to the urban setting. There was no statistically significant difference in Stegomyia indices between seasons across settings. Plastics, metal containers and car tires were identified as the most productive habitats which collectively produced over 90% of all Ae. aegypti pupae. Water storage, sun exposure, vegetation, and organic matter were significant predictors of the abundance of immature Ae. aegypti.ConclusionsWidespread presence and abundance of Ae. aegypti were found in rural and urban areas of Unguja, the main island of Zanzibar. Information on productive habitats and predictors of colonization of water containers are important for the development of a routine Aedes surveillance system and targeted control interventions in Zanzibar and similar settings.     

Effects of NeemAzal on marker enzymes and hemocyte phagocytic activity of larvae and pupae of the vector mosquito Aedes aegypti

Many of the neem based botanical biocides are currently studied to a greater extent because of the possibility of their use in eco-friendly control of pests and vectors. However, no report was available to assess the impact of neem based formulation, NeemAzal on marker enzymes and hemocyte mediated cellular immune responses of important vector mosquito A. aegypti. The NeemAzal found to exert larvicidal and pupicidal activities against A. aegypti developmental stages. The pupae appear to be more susceptible to the treatment. Further, a significant increase in the level of total protein (31%), α-carboxylesterase (121%), β-carboxylesterase (46%), acid phosphatase (62%) and alkaline phosphatase (37%) was observed in larvae upon exposure to NeemAzal. Moreover, treated pupae showed increased level of acetylcholinesterase (116%) and acid phosphatase (43%) while α-carboxylesterase (34%), β-carboxylesterase (12%) levels were simultaneously decreased, and no significant changes in alkaline phosphatase were noticed. Qualitative analysis also revealed that the exposure considerably modulated the larval β-carboxylesterase isoenzyme profile whereas little changes were noticed on phosphatases. On the other hand hemocyte viability of larvae (18%) and pupae (16%) as well as phagocytic ability of larval (48%) and pupal hemocytes (44%) against yeast target was significantly reduced upon NeemAzal exposure. We demonstrated for the first time that the NeemAzal differentially affected the marker enzymes and created immuno-suppressive state by reducing the phagocytic ability of hemocytes of larvae and pupae of A. aegypti.     

Shifting Patterns of Aedes aegypti Fine Scale Spatial Clustering in Iquitos,Peru

Background

Empiric evidence shows that Aedes aegypti abundance is spatially heterogeneous and that some areas and larval habitats produce more mosquitoes than others. There is a knowledge gap, however, with regards to the temporal persistence of such Ae. aegypti abundance hotspots. In this study, we used a longitudinal entomologic dataset from the city of Iquitos, Peru, to (1) quantify the spatial clustering patterns of adult Ae. aegypti and pupae counts per house, (2) determine overlap between clusters, (3) quantify the temporal stability of clusters over nine entomologic surveys spaced four months apart, and (4) quantify the extent of clustering at the household and neighborhood levels.

Methodologies/Principal Findings

Data from 13,662 household entomological visits performed in two Iquitos neighborhoods differing in Ae. aegypti abundance and dengue virus transmission was analyzed using global and local spatial statistics. The location and extent of Ae. aegypti pupae and adult hotspots (i.e., small groups of houses with significantly [p<0.05] high mosquito abundance) were calculated for each of the 9 entomologic surveys. The extent of clustering was used to quantify the probability of finding spatially correlated populations. Our analyses indicate that Ae. aegypti distribution was highly focal (most clusters do not extend beyond 30 meters) and that hotspots of high vector abundance were common on every survey date, but they were temporally unstable over the period of study.

Conclusions/Significance

Our findings have implications for understanding Ae. aegypti distribution and for the design of surveillance and control activities relying on household-level data. In settings like Iquitos, where there is a relatively low percentage of Ae. aegypti in permanent water-holding containers, identifying and targeting key premises will be significantly challenged by shifting hotspots of Ae. aegypti infestation. Focusing efforts in large geographic areas with historically high levels of transmission may be more effective than targeting Ae. aegypti hotspots.     

Field efficacy of triflumuron against Aedes and Culex mosquitoes in temperate Argentina

Aedes aegypti and Culex pipiens s.l. (Linnaeus, 1762 and 1758, respectively) (Diptera: Culicidae) are important vectors of diseases to humans and a growing public health concern. In order to contribute to the control of mosquito vectors by low environmental impact approaches we assessed the susceptibility of natural populations of container-breeding mosquitoes to triflumuron, an insect growth regulator, in temperate Argentina. A field trial was conducted to evaluate the efficacy of two doses (0.5 ppm and 1 ppm) of triflumuron (SC 48%) against natural populations of Ae. aegypti and Culex spp. immatures in flower vases of four cemeteries. The results demonstrated the susceptibility of both target mosquitoes to triflumuron in field conditions. For Ae. aegypti, dose-dependent reductions were achieved in the presence of pupae and the percentage of water-holding containers harbouring L3–4 and/or pupae, whereas the larvae abundance was equally reduced for both doses. For Culex spp., similar levels of reduction of larvae abundance and pupae presence were achieved with both doses. Significant effects on the response variables measured were recorded up to six to eight weeks post-intervention. Bimonthly applying 1 ppm triflumuron in the context of an integrated mosquito management should achieve a lasting control of Ae. aegypti and Culex spp. in small artificial containers with minimal environmental impacts.     

Microbial synthesis of spherical nanosilver and nanogold for mosquito control

Biosynthesis of metal nanoparticles using microorganisms is an important area of research in nanobiotechnology, which is an emerging eco-friendly science of well-defined sizes, shapes and controlled monodispersity. The present study proposed a green process for the extracellular production of silver (Ag) and gold (Au) nanoparticles (NPs) using the soil fungi Chrysosporium keratinophilum and Verticillium lecanii. The synthesized NPs were formed fairly uniform with spherical shape determined by Transmission Electron Microscope (TEM) and confirmed by Scanning Electron Microscope (SEM). Elemental analysis on single particle was carried by EDX analysis. The results were further supported by UV-vis spectrophotometry. In addition, we have also investigated the effect of synthesized AgNPs and AuNPs against the larvae and pupae of Anopheles stephensi, Culex quinquefasciatus and Aedes aegypti. The efficacy test was performed at different concentrations for periods of different lengths by the probit analysis. The larvae and pupae of Cx. quinquefasciatus, An. stephensi and Ae. aegypti were found highly susceptible to the synthesized AgNPs than the AuNPs. The larvae of Cx. quinquefasciatus and Ae. aegypti were found to be more susceptible to the AgNPs and AuNPs synthesized using the C. keratinophilum and V. lecanii compared with the larvae of An. stephensi. The pupae of Ae. aegypti have shown higher mortality against the synthesized AgNPs than the pupa of Cx. quinquefasciatus, while no adverse effects could be observed in the pupa of An. stephensi. By this approach, it is suggested that this rapid synthesis of nanoparticles would be useful for developing a biological process for mosquito control.     

Immunocompetence of the red turpentine beetle, Dendroctonus valens LeConte (Coleoptera: Curculionidae, Scolytinae): Variation between developmental stages and sexes in populations in China

Immune defense imposes fitness costs as well as benefits, so organisms should optimize, not maximize, their immune function through their life cycle. We investigated this issue in the red turpentine beetle, Dendroctonus valens LeConte (Coleoptera: Curculionidae, Scolytinae), which is a pine-killing invasive beetle in China, though it is usually considered as a secondary pest in its native range of North America. We hypothesized that pathogen pressure may affect these beetles differently throughout their life history. We measured the insect's immunocompetence throughout life, determining encapsulation ability and phenoloxidase activity in larval stages, pupae and adults. Pupae had the highest encapsulation ability, but encapsulation was not different between final instar larvae and adults. Phenoloxidase (PO) activity was highest in final instar larvae and pupae, followed by the second instar larvae and adults. Total phenoloxidase activity increased significantly from the second instar larval stage to pupae, and then decreased in adults. Although the second instar larvae had the lowest phenoloxidase activity, more than 90% of total PO existed in the hemolymph in the form of the active enzyme, as compared with pupae, in which over 60% of PO occurred as a proenzyme. Both active PO and total PO were much higher in females than in males, though no significant differences were detected between the encapsulation ability of male and female adults. This result suggests the existence of a sexual dimorphism of immunocompetence in D. valens adults. Variations in immunocompetence across developmental stages suggest that D. valens adopts diverse investment strategies in immunocompetence during different stages. Potential reasons for variation in immunocompetence among developmental stages and between the sexes of D. valens are discussed.     

Use of Dactylopius coccus Costa (Hemiptera: Coccoidea) Pigments in the Detection of Larvae and Pupae of Plutella xylostella (L.) (Lepidoptera: Yponomeutidae)

Carmines obtained from the dye of Dactylopius coccus Costa (Hemiptera: Coccoidea) were used for the detection of larvae and pupae of Plutella xylostella (L.) (Lepidoptera: Yponomeutidae) in broccoli inflorescences. Larvae were dyed with carmine II and red cochineal, while the majority of the dyes, with the exception of carmine III and the aqueous extract, were suitable to dye pupae. In the broccoli lumps exposed to the dyes, only the verge of the stems were actually dyed, right in the position where the incision took place, an appropriate characteristic for implementing this technique for commercial use.     

Susceptibility of the Carrot Weevil (Coleoptera: Curculionidae) to Steinernema feltiae,S. bibionis,and Heterorhabditis heliothidis

Larvae, pupae, and adults of the carrot weevil (Listronotus oregonensis) were infected and killed by the three entomophagous nematodes (Steinernema feltiae, S. bibionis, and Heterorhabditis heliothidis) under controlled conditions. Third-stage larvae were more susceptible than pupae or adults. S. feltiae and S. bibionis were the most aggressive nematode species, causing larval mortality after 24-48 hours in both continuous and 2-hour contact with nematode suspension. The nematodes multiplied sufficiently in all insects at all stages of development; however, production of infective-stage larvae per host cadaver was variable.     

Biological Differences between Brackish and Fresh Water-Derived Aedes aegypti from Two Locations in the Jaffna Peninsula of Sri Lanka and the Implications for Arboviral Disease Transmission

The mainly fresh water arboviral vector Aedes aegypti L. (Diptera: Culicidae) can also undergo pre-imaginal development in brackish water of up to 15 ppt (parts per thousand) salt in coastal areas. We investigated differences in salinity tolerance, egg laying preference, egg hatching and larval development times and resistance to common insecticides in Ae. aegypti collected from brackish and fresh water habitats in Jaffna, Sri Lanka. Brackish water-derived Ae. aegypti were more tolerant of salinity than fresh water-derived Ae. aegypti and this difference was only partly reduced after their transfer to fresh water for up to five generations. Brackish water-derived Ae. aegypti did not significantly discriminate between 10 ppt salt brackish water and fresh water for oviposition, while fresh water-derived Ae. aegypti preferred fresh water. The hatching of eggs from both brackish and fresh water-derived Ae. aegypti was less efficient and the time taken for larvae to develop into pupae was prolonged in 10 ppt salt brackish water. Ae. aegypti isolated from coastal brackish water were less resistant to the organophosphate insecticide malathion than inland fresh water Ae. aegypti. Brackish and fresh water-derived Ae. aegypti however were able to mate and produce viable offspring in the laboratory. The results suggest that development in brackish water is characterised by pertinent biological changes, and that there is restricted genetic exchange between coastal brackish and inland fresh water Ae. aegypti isolates from sites 5 km apart. The findings highlight the need for monitoring Ae. aegypti developing in coastal brackish waters and extending vector control measures to their habitats.     

First comprehensive analysis of Aedes aegypti bionomics during an arbovirus outbreak in west Africa: Dengue in Ouagadougou,Burkina Faso, 2016–2017

BackgroundDengue’s emergence in West Africa was typified by the Burkina Faso outbreaks in 2016 and 2017, the nation’s largest to date. In both years, we undertook three-month surveys of Aedes populations in or near the capital city Ouagadougou, where the outbreaks were centered.MethodologyIn 1200LG (urban), Tabtenga (peri-urban) and Goundry (rural) localities, we collected indoor and outdoor resting mosquito adults, characterized larval habitats and containers producing pupae and reared immature stages to adulthood in the laboratory for identification. All mosquito adults were identified morphologically. Host species (from which bloodmeals were taken) were identified by PCR. Generalized mixed models were used to investigate relationships between adult or larval densities and multiple explanatory variables.ResultsFrom samples in 1,780 houses, adult Ae. aegypti were significantly more abundant in the two urban localities (Tabtenga and 1200 LG) in both years than in the rural site (Goundry), where Anopheles spp. were far more common. Results from adult collections indicated a highly exophilic and anthropophilic (>90% bloodmeals of human origin) vector population, but with a relatively high proportion of bloodfed females caught inside houses. Habitats producing most pupae were waste tires (37% of total pupae), animal troughs (44%) and large water barrels (30%).While Stegomyia indices were not reliable indicators of adult mosquito abundance, shared influences on adult and immature stage densities included rainfall and container water level, collection month and container type/purpose. Spatial analysis showed autocorrelation of densities, with a partial overlap in adult and immature stage hotspots.ConclusionResults provide an evidence base for the selection of appropriate vector control methods to minimize the risk, frequency and magnitude of future outbreaks in Ouagadougou. An integrated strategy combining community-driven practices, waste disposal and insecticide-based interventions is proposed. The prospects for developing a regional approach to arbovirus control in West Africa or across Africa are discussed.     

Multi‐scale analysis of the associations among egg,larval and pupal surveys and the presence and abundance of adult female Aedes aegypti (Stegomyia aegypti) in the city of Merida,Mexico

Despite decades of research, there is still no agreement on which indices of Aedes aegypti (Stegomyia aegypti) (Diptera: Culicidae) presence and abundance better quantify entomological risk for dengue. This study reports the results of a multi‐scale, cross‐sectional entomological survey carried out in 1160 households in the city of Merida, Mexico to establish: (a) the correlation between levels of Ae. aegypti presence and abundance detected with aspirators and ovitraps; (b) which immature and egg indices correlate with the presence and abundance of Ae. aegypti females, and (c) the correlations amongst traditional Aedes indices and their modifications for pupae at the household level and within medium‐sized geographic areas used for vector surveillance. Our analyses show that ovitrap positivity was significantly associated with indoor adult Ae. aegypti presence [odds ratio (OR) = 1.50; P = 0.03], that the presence of pupae is associated with adult presence at the household level (OR = 2.27; P = 0.001), that classic Aedes indices are informative only when they account for pupae, and that window screens provide a significant level of protection against peridomestic Ae. aegypti (OR = 0.59; P = 0.02). Results reinforce the potential of using both positive collections in outdoor ovitraps and the presence of pupae as sensitive indicators of indoor adult female presence.     

Biological studies ofDiadegma semiclausum (Hym., Ichneumonidae), a parasite of diamondback moth

Laboratory studies were conducted on certain aspects of biology ofDiadegma semiclausum Hellén, a larval parasite of a crucifer pest,Plutella xylostella (L.). Within the range of 15°C to 35°C, the higher temperature, the shorter was the duration of larval and adult stages. Egg hatching and adult emergence were high at 15°C to 30°C but were significantly reduced at 35°C. The higher the temperature, the higher was the proportion of males produced. Temperature threshold was 5.74°C for eggs, 3.80°C for larvae, 5.91°C for pupae and 6.60°C for adults.D. semiclausum oviposition in the first threeP. xylostella larval instars produced more parasite males than females but oviposition in the fourth instar produced significantly more females than males. Parasite adults tended to emerge from their pupae from 06∶00 to 09∶00 hours although some emerged at other hours during the photophase. Adult longevity and production of eggs increased when adults were provided with a food source (honey) compared with no food or provision of water alone. Parasite adults survived and laid eggs for 28 days when provided with food but for only three days when deprived of food.     

Effect of Aedes aegypti (Diptera:Culicidae) Age on Sex Ratios in Romanomermis culicivorax (Nematoda:Mermithidae)

First, second, third, early and late fourth-instar larvae, and pupae of Aedes aegypti were infected with Romanomerrais culicivorax and reared at 20, 25, and 30 C. An increase in the ratio of male to female nematodes was observed with increase in host age at the time of infection at each temperature. The number of pupal and late fourth-instar infections was low, but R. culicivorax continued to develop in adult A. aegypti. Since male nematodes were recovered from both male and female hosts infected as late fourth instars or pupae, the sex of the host did not influence the sex of the nematode.     

Ontogenetic patterns of cold-hardiness and glycerol production in Sarcophaga crassipalpis

Developmental patterns of low-temperature tolerance and glycerol production were determined for larval, pupal and adult stages of the flesh fly Sarcophaga crassipalpis Macquart (Diptera: Sarcophagidae). Both diapause and non-diapause-destined flies were reared at relatively high temperatures, 20° or 25°C, prior to testing. Cold tolerance was greatest for diapause pupae aged 12–35 days after pupariation. Among non-diapause-destined flies, pupae exhibited a greater level of low temperature tolerance than larvae or adults. Although diapause pupae were more tolerant than non-diapause pupae maximal cold tolerance was not attained in either group until 10 days after pupariation. Non-diapause-destined feeding and wandering larvae had higher glycerol levels than larvae destined for diapause. During the first 6 weeks after pupariation glycerol titres increased steadily in diapause pupae. Rapid loss of glycerol is associated with the termination of pupal diapause.     

Insecticidal and Repellent Activity of Siparuna guianensis Aubl. (Negramina) against Aedes aegypti and Culex quinquefasciatus

This study investigated the toxic effects of essential oils isolated from Siparuna guianensis against Aedes aegypti, Culex quinquefasciatus (eggs, larvae, pupae, and adult) and Aedes albopictus (C6/36) cells. The oviposition-deterring activity, egg viability, and repellence activity in the presence of different essential oils concentrations were determined. The essential oils showed high toxicity to all developmental stages of A. aegypti and C. quinquefasciatus. Furthermore, the oils also showed high repellent activity towards the adult stage of mosquitoes (0.025 to 0.550 μg/cm2 skin conferred 100% repellence up to 120 min) and in contact with cultured insect cells (C6/36) induced death possibly by necrosis. The results presented in this work show the potential of S. guianensis essential oils for the development of an alternative and effective method for the natural control of mosquitoes in homes and urban areas.     

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.     

Inhibition of Dirofilaria immitis in gregarine-infected Aedes aegypti: preliminary observations.

This study examined some of the effects of Ascocystis culicis infections in Aedes aegypti mosquitoes and on the development of dog heartworm, Dirofilaria immitis, in A. culicis-infected A. aegypti. Infections of 100 or more gregarines had an adverse effect on mosquito larvae and the resulting pupae weighed 1 to 2 mg less than the gregarine-free stock mosquitoes. Intensity of gregarine-induced pathology of adult mosquitoes was best estimated by counting the cells of the Malpighian tubules. Larvae infected with approximately 100 gregarines per larva had at least half the number of cells in their tubules destroyed, and development of D. immitis was greatly reduced. Thus, gregarine infections may be useful in reducing populations of aedine mosquitoes and, in areas endemic for heartworm, may interrupt transmission of D. immitis.     

Aedes aegypti midgut remodeling during metamorphosis

The Aedes aegypti midgut is restructured during metamorphosis; its epithelium is renewed by replacing the digestive and endocrine cells through stem or regenerative cell differentiation. Shortly after pupation (white pupae) begins, the larval digestive cells are histolized and show signs of degeneration, such as autophagic vacuoles and disintegrating microvilli. Simultaneously, differentiating cells derived from larval stem cells form an electron-dense layer that is visible 24 h after pupation begins. Forty-eight hours after pupation onset, the differentiating cells yield an electron-lucent cytoplasm rich in microvilli and organelles. Dividing stem cells were observed in the fourth instar larvae and during the first 24 h of pupation, which suggests that stem cells proliferate at the end of the larval period and during pupation. This study discusses various aspects of the changes during midgut remodeling for pupating A. aegypti.     

Prediction of survival ratios of Cadra cautella (Lepidoptera: Pyralidae) different life stages after treated with ultraviolet radiation in dates

Date palm, is a tree of economic importance which is grown around the world, including Saudi Arabia. Its fruit is nutritious and possesses medicinal benefits. Almond moth, is a serious date fruits pest in the field as well as in the storage and causes severe economic losses. In the given research, ultraviolet radiation type B (UV-B, 315 nm) harmful effects were evaluated against all developmental stages of C. cautella. One and 3-d-old eggs, 12 and 18-d-old larvae, 1-d and 6-d-old pupae, and 1-d-old adults, were exposed to UV-B for different intervals. Eggs were exposed for 0–30 min and 0% hatchability was achieved both for 1-d and 3-d-old eggs after 30 min. The larvae were exposed for 6–24 h, and after 24 h, mortality was 100 and 97% for 12 and 18-d-old larvae, respectively. Similarly, the pupae were exposed for 0–30 h, and 100% mortality was achieved after 30 h for 1-d-old pupae. Furthermore, none of the 6-d-old pupae emerged as an adult after 12 h of exposure. When adults were exposed for 1–4 d, no mortality was observed; however, UV-B reduced fecundity and hatchability in the treated adults. The susceptibility order was as follows: eggs > larvae > pupae > adults. Several uncharacteristic behaviors of C. cautella were noted, such as females depositing eggs openly on food items and containers, mature larvae exiting from food, larvae starting to wander for pupation, and pupation occurring typically outside the food. The application of UV-B could be an effective management strategy because all developmental stages of C. cautella were susceptible to UV-B that might be helpful to protect the dates from C. cautella infestation.