Current resistance status of Aedes aegypti and Aedes albopictus populations in Penang Island,Malaysia

Objective:To determine the current insecticide resistance status of Aedes(Ae.)aegypti and Ae.albopictus to four insecticides,namely 0.05%deltamethrin,0.75%permethrin,5%malathion and 0.25%pirimiphos-methyl using the World Health Organisation(WHO)susceptibility test kit.Methods:Adult bioassays were carried out using the standard protocol of the World Health Organisation.All F1 generation urban and suburban field strains of Ae.aegypti and Ae.albopictus were tested against pyrethroid and organophosphate insecticides,including the presence of piperonyl butoxide(PBO)in four replicates of 25 non-blood-fed female mosquitoes ranging from 3 to 5 days old.The Vector Control Research Unit(VCRU)laboratory strain served as a reference strain.Results:In this study,0.05%deltamethrin demonstrated a lower value of knockdown time when 50%of the mosquito population died(KT50)and knockdown time when 95%of the mosquito population died(KT95),which is significantly more effective compared to 0.75%permethrin against adult female Ae.aegypti(urban and suburban)and Ae.albopictus(urban and suburban)(ANOVA,P<0.01).Meanwhile,5%malathion was a more effective insecticide,amounting to the shorter KT50 and KT95 compared to 0.25%pirimiphos-methyl against Ae.aegypti(urban and suburban)and Ae.albopictus(urban and suburban).Ae.aegypti urban and Ae.aegypti suburban performed a higher resistance ratio(RR)towards both 0.05%deltamethrin and 0.75%permethrin due to the wide use of permethrin in dengue vector control programs in Malaysia.However,Ae.albopictus urban and suburban have lower resistance than Ae.aegypti urban and suburban towards 0.05%deltamethrin and 0.75%permethrin at 24 hours post-treatment.The addition of PBO with these insecticides successfully reduced knockdown time(KT50 and KT95)values of most of the Ae.aegypti and Ae.albopictus field strains except PBO+0.75%permethrin against Ae.aegypti suburban.Conclusions:The addition of PBO to insecticides has significantly reduced the knockdown time(KT50 and KT95)values on most of Ae.aegypti and Ae.albopictus urban strain except PBO+5%malathion against Ae.albopictus urban strain and PBO+0.75%permethrin against Ae.albopictus suburban strain in comparison to exposure to insecticides without PBO.Ae.aegypti showed a higher resistance ratio of 50(RR50)when compared with the VCRU laboratory reference strain(susceptible strain)at the exposure to the deltamethrin,including with pre-exposure to PBO.This study found that the addition of PBO with organophosphates(5%malathion and 0.25%pirimiphos-methyl)was significantly more effective than pyrethroids against Ae.aegypti and Ae.albopictus(urban and suburban)due to their high mortality rate at 24 hours.It can be concluded that the usage of PBO can help reduce resistance alteration in Aedes mosquitoes.

The biology and demographic parameters of Aedes albopictus in northern peninsular Malaysia

Objective:To generate life table characteristics for the dengue vector Aedes albopictus(A. albopictus) under uncontrolled conditions,incorporating both the aquatic and the adult stages. Methods:Ten females derived from wild pupae were allowed to fully blood-feed on restrained mice.774 eggs were hatched in seasoned water.F1 larvae were followed for development until their F2 counterparts emerged as adults.Some population parameters were monitored(Fl) or estimated(F2).Results:A.albopictus exhibited increased fecundity and egg hatch success. Immature development was quick.Immature survival was high,with lowest rate in the pupal stage.Adult emergence was about 81%and sex ratio was close to 1:1.Generational mortality(K) was about 28%.A high proportion of females completed a reproductive cycle and the obtained parity rate was predicted to lead to higher fecundity in the next generation.Conclusios:It can be concluded that natural A.albopictus populations in Penang seem largely determined by quick development in combination with low immature loss and increased oviposition.

Household survey of container-breeding mosquitoes and climatic factors influencing the prevalence of Aedes aegypti(Diptera:Culicidae)in Makkah City,Saudi Arabia

Objective:To investigate the prevalence of container breeding mosquitoes with emphasis on the seasonality and larval habitats of Aedes aegypti(Ae.aegypti) in Makkah City,adjoining an environmental monitoring and dengue incidence.Methods:Monthly visits were performed between April 2008 and March 2009 to randomly selected houses.During each visit,mosquito larvae were collected from indoors and outdoors containers by either dipping or pipetting. Mosquitoes were morphologically identified.Data on temperature,relative humidity,rain/ precipitations during the survey period was retrieved from governmental sources and analyzed. Results:The city was warmer in dry season(DS) than wet season(WS).No rain occurred at all during DS and even precipitations did fall,wetting events were much greaterduring WS.Larval survey revealed the co-breeding of Aedes,Culex and Anopheles in a variety of artificial containers in and around homes.32109 larvae representing 1st,2nd,3rd,and 4th stages were collected from 22618 container habitats.Culicines was far the commonest and Aedes genus was as numerous as the Culex population.Ae.aegypti larval abundance exhibited marked temporal variations,overall, being usually more abundant during WS.Ten types of artificial containers were found with developing larvae.70%of these habitats were located indoors.71.42%of indoor containers were permanent and 28.58* was semi-permanent during WS.Cement tanks was the only container type permanent during DS.Ae.aegypti larval indices(CI,HI,Bl) recorded were greater during WS. Conclusions:Taken together,these results indicate a high risk of dengue transmission in the holy city.

Aquatic Phoretic Mites (Acari: Hydrachnidia) Associated with Ectoparasitism of Mosquitoes (Diptera: Culicidae) in the Midwest Region of Brazil

Water mites (Hydrachnidia) are common external parasites of the medically important mosquitoes (Culicidae). Between April 2014 and April 2015, 64 mites from three genus, Arrenurus 71.9%, Limnochares 3.1%, and Hydrachna 25.0%, were collected from female mosquitoes in two rural locations near Cuiabá, Mato Grosso, Brazil. Dipterous species parasitized by water mites belonging to seven species: Anopheles (Nys.) darling, An. evansae, Aedes (Och.) scapularis, Ae. serratus, Mansonia (Man.) wilsoni, Psorophora (Jan.) ferox, Ps. varipes. The most common specimens to accommodate the water mites were Anopheles (Nys.) darlingi and Psorophora (Jan.) varipes. The prevalence of parasitism of mosquitoes by water mites found in this study was less than 5. However, few studies have addressed the ecological role of mites and their biotopes, as well as host-parasite interactions in Brazil.

Aquatic Phoretic Mites (Acari: Hydrachnidia) Associated with Ectoparasitism of Mosquitoes (Diptera: Culicidae) in the Midwest Region of Brazil

Water mites (Hydrachnidia) are common external parasites of the medically important mosquitoes (Culicidae). Between April 2014 and April 2015, 64 mites from three genus, Arrenurus 71.9%, Limnochares 3.1%, and Hydrachna 25.0%, were collected from female mosquitoes in two rural locations near Cuiabá, Mato Grosso, Brazil. Dipterous species parasitized by water mites belonging to seven species: Anopheles (Nys.) darling, An. evansae, Aedes (Och.) scapularis, Ae. serratus, Mansonia (Man.) wilsoni, Psorophora (Jan.) ferox, Ps. varipes. The most common specimens to accommodate the water mites were Anopheles (Nys.) darlingi and Psorophora (Jan.) varipes. The prevalence of parasitism of mosquitoes by water mites found in this study was less than 5. However, few studies have addressed the ecological role of mites and their biotopes, as well as host-parasite interactions in Brazil.

Addressing Chagas disease from a One Health perspective:risk factors,lessons learned and prevention of oral transmission outbreaks in Colombia

Background:Chagas disease(CD)is transmitted by vectors but can also be transmitted orally through contaminated food,drinks,or meat.The One Health perspective aims to understand the complex interaction between human,animal,and environmental health in controlling disease.This study analyzed risk factors and drew lessons from past outbreaks of orally transmitted CD to develop effective preventive strategies.Methods:A simultaneous mixed methods study was conducted.The study consisted of two phases:an ecological epidemiological analysis at the municipal level using secondary data spanning from 1992 to 2023,and semistructured interviews with health providers and policymakers at the national level in Colombia.The results from both phases were triangulated to gain a comprehensive understanding of the topic.Results:A total of 64 outbreaks,infecting 302 individuals,were reported.Most of these outbreaks(89.2%)were classified as family-related,and they occurred most frequently during the months of April to June(46.6%).It is worth noting that a significant number of these outbreaks took place in municipalities that lacked vector control plans.Risk factors for oral transmission included the location of food preparation,poor housing quality,food preparation water source,the presence of vectors/marsupials,forest type,and climatic variables.Interviews conducted emphasized the importance of implementing outbreak plans and providing staff training to effectively address the issue.Conclusion:A One Health approach strengthening prevention,surveillance,case management and cross-sectoral collaboration is needed to control outbreaks and reduce transmission in Colombia.Preparedness plans and education of health professionals are also important.This study identified modifiable risk factors to guide public health interventions.

Satyrization and satyrization-resistance in competitive displacements of invasive mosquito species

Competitive displacements or reductions of resident populations of insects, often effected by a related species, may be caused by a variety of mechanisms. Satyrization is a form of mating interference in which males of one species mate with females of another species, significantly decreasing their fitness and not generating hybrids. Satyriza- tion has been established to be the probable cause of competitive displacements of resident mosquitoes by invasive species, especially of Aedes aegypti by Aedes albopictus, two important vectors of dengue and chikungunya viruses. Mathematical models predict that even low levels of asymmetric mating interference are capable of producing competitive displacements or reductions. Couplings of virgin Ae. aegypti females with Ae. albopictus males effectively sterilize these females through the monogamizing actions of male ac- cessory gland products, but the converse interspecific mating does not impact the future reproduction ofAe. albopictus females. Populations ofAe. aegypti exposed to satyrization quickly evolve resistance to interspecific mating, which is believed to ameliorate repro- ductive interference from, and promote co-existence with, Ae. albopictus. The evolution of satyrization resistance among Ae. aegypti in laboratory cages is accompanied by fitness costs, such as reduced fecundity and slower receptivity to conspecific males. Cage exper- iments and field observations indicate that Ae. albopictus males are capable of satyrizing females of other species of the Stegomvia subgenus, potentially leading to competitive displacements, and possible extinctions, especially of endemic species on islands. Exam- ination of other examples of reproductive interference in insects reveals few parallels to the mechanism and outcomes of satyrization by Ae. albopictus. We conclude by posing the hypothesis that satyrization may favor the ecological success of Ae. albopictus, and suggest many lines for future research on this phenomenon.