Efficacy of alpha-cypermethrin and lambda-cyhalothrin applications to prevent Aedes breeding in tires

Integrated Control of Aedes albopictus in a Residential Area Through a Community-Based Approach: NESCOTIGER, a Large-Scale Field Trial in Valencia, Spain

Aedes albopictus has established populations in several European countries with a sustained spreading pattern through the continent. This invasive mosquito is a public health threat due to its vector competence for multiple arboviruses. Notably, the peri-domestic habits of this hematophagous insect greatly diminish the efficacy of regular control activities, as individuals may harbor in private areas. The oviposition behavior can be exploited for targeting adults and immature stages through different types of traps. An experimental integrated control program, which included a community-based mass trapping intervention in private areas, control of public street-catch basins, and an educational campaign, was developed in an infested residential area in Valencia (Eastern Spain). Focusing on mass trapping, participating residents deployed traps belonging to three modes of action in their gardens during the mosquito season. A total of 1028 families participated in the project, and 2884 traps were deployed. The study sector where adult lethal ovitraps were used showed the lowest adult collections, and residents living in this sector reported the highest satisfaction rates in a perception survey. The mass deployment through a community-based approach of the adulticidal oviposition trap type appears to be a promising tool for controlling Ae. albopictus in residential areas.

Resting habitat, blood meal source and viral infection rate of Aedes aegypti (Diptera: Culicidae) in the Southern Afar Region of Ethiopia

BACKGROUND

Knowledge of Aedes species distribution, preference to feed on humans, and susceptibility to viruses is crucial in preventing transmission of Aedes-transmitted viruses. This study aimed to determine resting behavior, blood sources, and viral infection status of Aedes aegypti in Awash Sebat, Awash Arba, and Werer towns of Afar Region.

METHODS

Adult mosquitoes were collected using a Prokopack aspirator between 8:00-14:00 and 15:00-18:00 h both indoor and outdoor of the house. The mosquitoes were sorted by sex, date of collection, collection places, and abdominal status and identified by species/genus using standard keys. Blood meal sources and dengue virus and chikungunya virus infection status of Ae. aegypti were determined using ELISA and RT-qPCR respectively.

RESULT

A total of 2,745 adult mosquitoes comprising the genera Aedes (1433; 52.2%) Culex (1292; 47.1%) and Anopheles (20; 0.7%) were collected. The proportion of female Ae. aegypti in Awash Sebat (611; 36%) was highest as compared to females Ae. aegypti in Awash Arba (172; 33.8%), and in Werer (59; 11%). A higher proportion of outdoor resting of Ae. aegypti was caught from tyres rather than other indoor and outdoor locations (314; 37.29%) (X2 27.374, df = 12; p = 0.007). Seasonal and monthly variation was observed in Ae. aegypti collection, where the wet season and the months of August 2022, September 2022, and October 2022 had high Ae aegypti density. The overall human blood and bovine blood indices of Ae. aegypti were 53/145 (36.6%) and 18/145 (12.4%), respectively. Furthermore, dengue and chikungunya viruses were not detected from the Ae. aegypti examined.

CONCLUSION

The majority of Ae. aegypti collections were made during the wet season from outdoor resting sites, particularly from tyres. Thus, outdoor targeted management of Ae. aegypti is recommended as a strategy particularly tyre removal during the wet season, to reduce resting and proliferation of Ae. aegypti and hence prevent the risks of Aedes-borne disease transmission.

Detection and Establishment of Aedes notoscriptus (Diptera: Culicidae) Mosquitoes in Southern California, United States

Aedes notoscriptus (Skuse), the Australian backyard mosquito, is a pestiferous daytime-biting species native to Australia and the surrounding southwestern Pacific region. It is suspected to play a role in the transmission of several arboviruses and is considered a competent vector of dog heartworm, Dirofilaria immitis (Leidy). This highly adaptable mosquito thrives in natural and artificial water-holding containers in both forested and urbanized areas, from tropical to temperate climates, and has benefitted from a close association with humans, increasing in abundance within its native range. It invaded and successfully established in New Zealand as well as in previously unoccupied temperate and arid regions of Australia. Ae. notoscriptus was discovered in Los Angeles County, CA, in 2014, marking the first time this species had been found outside the southwestern Pacific region. By the end of 2019, immature and adult mosquitoes had been collected from 364 unique locations within 44 cities spanning three southern California counties. The discovery, establishment, and rapid spread of this species in urban areas may signal the global movement and advent of a new invasive container-inhabiting species. The biting nuisance, public health, and veterinary health implications associated with the invasion of southern California by this mosquito are discussed.

Resting behavior of Aedes aegypti in southeastern Senegal

BACKGROUND

Only the sylvatic and zoophilic population of Aedes aegypti was formerly identified in southeastern Senegal. A newly established anthropophilic population was detected in the urban area of the Kedougou city. Because of its new behavior, this species could play a primary role in the transmission of dengue and other arboviruses in this area. Because these arboviruses have no vaccine and specific treatments, vector control remains the only effective way to control their outbreaks. Effective vector control strategies require to understand some aspects of the bioecology of the vector, specially resting behavior. The aims of this study were to investigate the sites and resting behavior of Ae. aegypti in southeastern Senegal.

METHODS

Mosquitoes were collected in several potential resting places (rooms, tires, bricks and scrap metal) by two technicians using a CDC back-pack aspirator in the Kedougou bus station and other sites within the city and the nearby rural area. Collected mosquitoes were identified and classified.

RESULTS

A total of 1291 mosquitoes belonging to 6 genera and 20 species were collected. Aedes aegypti was the dominant species in all the resting places investigated. This species was found resting equally in rooms, bricks, tires and scrap metal. The average number of Ae. aegypti collected in resting places was higher in the bus station (center of the city) compared to the other areas. The rates of unfed and fed females varied significantly in the different resting places while the proportions of gravid females which varied between 7.8% in tires and 1.8% in rooms were comparable.

CONCLUSIONS

This study showed that Ae. aegypti could be found resting indoors and in several sites, including in used tires outdoors. These data will be helpful in setting better arboviruses surveillance and vector control strategies.

Efficacy of Residual Pesticide-Treated Plant Saucers Against Aedes albopictus Larvae Under Semi-Field and Field Conditions

Plant saucers are ubiquitous, outdoor water-holding receptacles and are one of the most productive domestic mosquito habitats in the urban environment. Two kinds of commonly used plant saucers, clay and plastic, were manually treated with 3 residual insecticides, bifenthrin (Talstar® Professional), lambda-cyhalothrin (Lambda 9.7 CS), and tau-fluvalinate (Mavrik® Perimeter), at their maximum rates to assess their residual efficacy against Aedes albopictus larvae under semi-field and field conditions. Both clay and plastic saucers treated with bifenthrin and lambda-cyhalothrin provided weeks of control of 3rd instars of Ae. albopictus, whereas tau-fluvalinate provided only 1 day of control. Results from this study show that bifenthrin and lambda-cyhalothrin can provide good control of Ae. albopictus larvae for a considerable period of time and have great potential with regard to container mosquito management in the future.

Efficacy of Spinosad Granules and Lambda-Cyhalothrin Contrasts with Reduced Performance of Temephos for Control of Aedes spp. in Vehicle Tires in Veracruz, Mexico

The present study examined the efficacy of λ-cyhalothrin, pyriproxyfen and granular formulations of spinosad and temephos for the control of mosquito larvae present in experimental tires in Veracruz State, Mexico in the period 2015-2016. Both λ-cyhalothrin and spinosad granules provided control of larvae and pupae of Aedes aegypti, Ae. albopictus and Culex spp. in used tires in Veracruz State, Mexico, over a 9-12 week period, although numbers of Culex were low. The numbers of Aedes larvae + pupae in pyriproxyfen and temephos-treated tires were slightly less than half of the untreated control tires, probably a result the pupicidal characteristics of pyriproxyfen and possible resistance in the case of temephos. Spinosad was less harmful to predatory Toxorhynchites spp. than λ-cyhalothrin or temephos. The reduced susceptibility to temephos in Aedes populations was confirmed at five other sites in Veracruz. Public health authorities should consider incorporating spinosad as a larvicide in coastal areas at a high risk of dengue, chikungunya and Zika outbreaks in this region.

Bromeliad targeted foliar treatments with Aqualuer® 20-20 for hot spot mitigation using three hand sprayers against Aedes albopictus (Diptera: Culicidae)

Bromeliads serve as a key environmental resource for Aedes albopictus (Skuse) in some peridomestic landscapes and are not addressed through conventional source reduction. As an alternative, three handheld sprayers were evaluated in point-source applications of permethrin to bromeliads in Saint Augustine, FL. Each machine was screened for its utility in point-source harborage treatments, while we simultaneously evaluated bromeliad-focused treatments for reducing Ae. albopictus egg abundance in bromeliad plants. Semi-field tests against caged Ae. albopictus produced 100% mortality at 24 h with each sprayer. Three field sites were assigned to each machine and a control, and bromeliad residual applications of Aqualuer 20-20^® were assessed through egg surveillance using ovitraps both within and beyond 30 m of the treated bromeliad harborage. The treatment decreased Ae. albopictus egg abundance across the field sites for three weeks post-treatment with no significant differences among the equipment. Functional differences among machines, such as automated pressure control or leak guards on the nozzle, depend on the accessories that offer the greatest logistical benefit to the user. The field results suggest bromeliads are a viable target for harborage treatments. Selective treatments to bromeliads could offer a possible solution to containers that homeowners refuse to eliminate.

Efficacy of larvicides for the control of dengue, Zika, and chikungunya vectors in an urban cemetery in southern Mexico

Many countries in Latin America have recently experienced outbreaks of Zika and chikungunya fever, in additional to the usual burden imposed by dengue, all of which are transmitted by Aedes aegypti in this region. To identify potential larvicides, we determined the toxicity of eight modern insecticides to A. aegypti larvae from a colony that originated from field-collected insects in southern Mexico. The most toxic compounds were pyriproxyfen (which prevented adult emergence) and λ-cyhalothrin, followed by spinetoram, imidacloprid, thiamethoxam, and acetamiprid, with chlorantraniliprole and spiromesifen the least toxic products. Field trails performed in an urban cemetery during a chikungunya epidemic revealed that insecticide-treated ovitraps were completely protected from the presence of Aedes larvae and pupae for 6 and 7 weeks in spinosad (Natular G30) and λ-cyhalothrin-treated traps in both seasons, respectively, compared to 5-6 weeks for temephos granule-treated ovitraps, but was variable for pyriproxyfen-treated ovitraps with and 1 and 5 weeks of absolute control in the dry and rainy seasons, respectively. Insecticide treatments influenced the mean numbers of Aedes larvae + pupae in each ovitrap, mean numbers of eggs laid, and percentage of egg hatch over time in both trials. The dominant species was A. aegypti in both seasons, although the invasive vector Aedes albopictus was more prevalent in the rainy season (26.7%) compared to the dry season (10.2%). We conclude that the granular formulation of spinosad (Natular G30) and a suspension concentrate formulation of λ-cyhalothrin proved highly effective against Aedes spp. in both the dry and rainy seasons in the cemetery habitat in this region.

Holding back the tiger: Successful control program protects Australia from Aedes albopictus expansion

Background

The Asian tiger mosquito, Aedes albopictus, is an important vector of dengue, chikungunya and Zika viruses and is a highly invasive and aggressive biter. Established populations of this species were first recognised in Australia in 2005 when they were discovered on islands in the Torres Strait, between mainland Australia and Papua New Guinea. A control program was implemented with the original goal of eliminating Ae. albopictus from the Torres Strait. We describe the evolution of management strategies that provide a template for Ae. albopictus control that can be adopted elsewhere.

Methodology / Principal findings

The control strategy implemented between 2005 and 2008 targeted larval habitats using source reduction, insect-growth regulator and pyrethroid insecticide to control larvae and adults in the containers. However, the infrequency of insecticide reapplication, the continual accumulation and replacement of containers, and imminent re-introduction of mosquitoes through people’s movement from elsewhere compromised the program. Consequently, in 2009 the objective of the program changed from elimination to quarantine, with the goal of preventing Ae albopictus from infesting Thursday and Horn islands, which are the transport hubs connecting the Torres Strait to mainland Australia. However, larval control strategies did not prevent the species establishing on these islands in 2010. Thereafter, an additional strategy adopted by the quarantine program in early 2011 was harborage spraying, whereby the vegetated, well shaded resting sites of adult Ae. albopictus were treated with a residual pyrethroid insecticide. Inclusion of this additional measure led to a 97% decline in Ae. albopictus numbers within two years. In addition, the frequency of container treatment was increased to five weeks between treatments, compared to an average of 8 weeks that occurred in the earlier iterations of the program. By 2015 and 2016, Ae. albopictus populations on the two islands were undetectable in 70–90% of surveys conducted. Importantly, a comprehensive surveillance network in selected strategic areas has not identified established populations of this species on the Australian mainland.

Conclusions / Significance

The program has successfully reduced Ae. albopictus populations on Thursday Island and Horn Island to levels where it is undetectable in up to 90% of surveys, and has largely removed the risk of mainland establishment via that route. The vector management strategies adopted in the later years of the program have been demonstrably successful and provide a practical management framework for dengue, chikungunya or Zika virus outbreaks vectored by Ae. albopictus. As of June 2016, Ae. albopictus had not established on the Australian mainland and this program has likely contributed significantly to this outcome.

Aedes albopictus is a disease vector and biting nuisance of major public health concern. Established populations of Ae. albopictus were first recognised in Australia in 2005 after they were discovered on islands in the Torres Strait. Consequently, a control program was established in the same year to eliminate Ae. albopictus populations in the Torres Strait in order to reduce the risk of disease, as well as to prevent the mosquito from spreading to the mainland of Australia. In 2009, the goal of the program changed from elimination to quarantine (cordon sanitaire) focusing mainly on the inner islands of Thursday Island and Horn Island, which are the major population, administrative and transport centres linking the Torres Strait region to the Australian mainland. The cordon sanitaire strategy involved an integrated approach composed of harborage spraying, source reduction, insecticide treatment of containers, lethal tire piles, mosquito population monitoring and public awareness campaigns. Strategic improvements in management techniques led to a 97% decline in Ae. albopictus numbers on the two islands between 2011 and 2012. By 2015, the program had successfully reduced Ae. albopictus populations on Thursday Island and Horn Island to levels where the species was frequently undetectable, and had largely removed the risk of mainland incursion via that route. In 2016 the improved management strategies were also adopted to successfully control a dengue outbreak in which Ae. albopictus was the implicated vector on two outer islands of the Torres Strait.

Heat Sensitivity of wMel Wolbachia during Aedes aegypti Development

The wMel strain of Wolbachia bacteria is known to prevent dengue and Zika virus transmission in the mosquito vector Aedes aegypti. Accordingly, the release of wMel-infected A. aegypti in endemic regions has been recommended by the World Health Organization as a potential strategy for controlling dengue and Zika outbreaks. However, the utility of this approach could be limited if high temperatures in the aquatic habitats where A. aegypti develop are detrimental to Wolbachia. We exposed wMel-infected A. aegypti eggs and larvae to fluctuating daily temperatures of 30-40°C for three, five, or seven days during their development. We found that Wolbachia levels in females emerging from heat treatments were significantly lower than in the controls that had developed at 20-30°C. Notably, seven days of high temperatures starting at the egg stage reduced Wolbachia levels in emerging females to less than 0.1% of the wMel control levels. However, after adult females returned to 20-30°C for 4-7 days, they experienced differing degrees of Wolbachia recovery. Our findings suggest that the spread of Wolbachia in wild A. aegypti populations and any consequent protection from dengue and Zika viruses might be limited in ecosystems that experience periods of extreme heat, but Wolbachia levels recover partially after temperatures return to normal.

A critical assessment of vector control for dengue prevention

Recently, the Vaccines to Vaccinate (v2V) initiative was reconfigured into the Partnership for Dengue Control (PDC), a multi-sponsored and independent initiative. This redirection is consistent with the growing consensus among the dengue-prevention community that no single intervention will be sufficient to control dengue disease. The PDC's expectation is that when an effective dengue virus (DENV) vaccine is commercially available, the public health community will continue to rely on vector control because the two strategies complement and enhance one another. Although the concept of integrated intervention for dengue prevention is gaining increasingly broader acceptance, to date, no consensus has been reached regarding the details of how and what combination of approaches can be most effectively implemented to manage disease. To fill that gap, the PDC proposed a three step process: (1) a critical assessment of current vector control tools and those under development, (2) outlining a research agenda for determining, in a definitive way, what existing tools work best, and (3) determining how to combine the best vector control options, which have systematically been defined in this process, with DENV vaccines. To address the first step, the PDC convened a meeting of international experts during November 2013 in Washington, DC, to critically assess existing vector control interventions and tools under development. This report summarizes those deliberations.

Ground ultra-low volume adulticiding field trials using pyrethroids against Aedes albopictus in the Baix Llobregat region, Spain

Ground ultra-low volume (ULV) application against Aedes albopictus is a challenging methodology as its efficacy is strongly related to environmental conditions, insect behavior, and the pesticide formulation. Such operations are very relevant in many control programs, although their real efficacy is often unknown. Trials were carried out as part of real-world applications in urban scenarios in the Baix Llobregat region to evaluate the efficacy of 2 active ingredients, delatamethrin and alpha-cypermethrin. Both pyrethroids were tested against caged mosquitoes placed at a range of distances and under varying environmental conditions. Additionally, persistence on plants placed at the same distances was evaluated after 5 h, as well as droplet distribution using water-sensitive papers. The deltamethrin formulation used yielded significantly higher 24-h mortality than alpha-cypermethrin (100% direct mortality up to 25 m versus 10 m; and 73.9% residual 5-h mortality at 20 m compared to <50% at 5 m). The influence of environmental factors, a comparison with other field tests, and the real effect on uncaged mosquitoes is discussed.

Linking sub-individual and population level toxicity effects in Daphnia schoedleri (Cladocera: Anomopoda) exposed to sublethal concentrations of the pesticide α-cypermethrin

Synthetic pyrethroids are classified as moderately toxic to mammals and birds; nevertheless, they are highly toxic to non-target aquatic organisms such as fish and zooplankters. Chemical pollutants produce different effects in exposed organisms, ranging from biochemical to population responses. Cladocerans can modify the energy content of their offspring according to the surrounding medium as a way to improve their odds in case they have to cope with stressful conditions at birth. In this study, the effect of a synthetic pesticide on two levels of response in a Daphnia species different from those traditionally used as test organisms was evaluated. With this aim, Daphnia schoedleri neonates (<24 h) were exposed for 21 days to three sublethal concentrations of α-cypermethrin, 0.54, 5.4, and 54 ng L(-1), which correspond to 48-h EC1/100, EC1/10, and EC1, respectively. Effects were measured through a life table analysis for fecundity and survivorship. For effects on progeny, protein, carbohydrates, and lipids were determined and then transformed to caloric content. Biomarkers (BM) were expected to be the most sensitive evaluated response; nevertheless, population parameters such as survivorship and net reproductive rate (R0) were more sensitive since they presented significant differences with respect to controls at the lowest tested concentration. Neonates' caloric content varied during the reproductive period assessed and was negatively correlated to fecundity: as more neonates were born, less energy was provided by the adult females. Macromolecules concentration and caloric content values in cypermethrin-exposed adults were not different from those recorded in the control at the end of exposure time. The results herein presented suggest that stressed daphnids allocate more energy reserves to their offspring, although this strategy can vary depending on the number of reproductive events during the lifecycle, and on the toxicant's concentration. Sub-individual approaches to assess toxicant effects should be accompanied by demographic studies, which support population effect predictions inferred from BMs assessment.