Incrimination of the mosquito,Aedes taeniorhynchus,as the primary vector of heartworm,Dirofilaria immitis,in coastal Yucatan,Mexico

Mosquito collections were carried out on microfilaraemic dogs, positive for Dirofilaria sp., for 18 consecutive nights in the coastal town of Celestún, Yucatan, southeast Mexico, during the rainy season (August) of 2007. A total of 292 female mosquitoes representing 12 species of dipteran Culicidae were collected: Anopheles albimanus (Wiedemann); Anopheles crucians (Wiedemann); Anopheles pseudopunctipennis (Theobald); Culex coronator (Dyar & Knab); Culex interrogator (Dyar & Knab); Culex nigripalpus (Theobald); Culex quinquefasciatus (Say); Culex salinarius (Coquillett); Aedes aegypti (Linnaeus); Aedes scapularis (Rondani); Aedes sollicitans (Walker), and Aedes taeniorhynchus (Wiedemann). Aedes taeniorhynchus and Cx. quinquefasciatus were the species found most commonly feeding on the dogs. Filarial nematodes were observed by microscopy in nine of the mosquito species collected; however, third‐instar larvae were only observed in Ae. taeniorhynchus and An. crucians. Of 76 Ae. taeniorhynchus specimens found positive for Dirofilaria sp. by dissection, 14 were confirmed to be positive for Dirofilaria immitis (Leidy) by polymerase chain reaction (PCR). The resulting infection rate for D. immitis confirmed by PCR (6.2%) is higher than any infection rate for Ae. taeniorhynchus previously reported from the Americas.     

Effect of CO2 concentration on mosquito collection rate using odor‐baited suction traps

Carbon dioxide (CO₂) has been used for decades to enhance capture of host‐seeking mosquitoes when released in association with traps commonly used by mosquito and vector control agencies. However, there is little published work evaluating the effect of altering CO₂ release rates relative to the number of mosquitoes captured in these traps. This study investigated how varying CO₂ concentration altered the mosquito collection rate at a freshwater wetlands in southern California. Host‐seeking mosquitoes were captured in CDC‐style traps baited with one of six CO₂ release rates ranging from 0–1,495 ml/min from gas cylinders. Species captured were Aedes vexans, Anopheles franciscanus, An. hermsi, Culex erythrothorax, and Cx. tarsalis. A biting midge, Culicoides sonorensis, was also captured. For all species, increasing CO₂ release rates resulted in increasing numbers of individual females captured, with the relative magnitude of this increase associated to some extent with known feeding preferences of these species. We found that variation in CO₂ release rate can significantly alter mosquito capture rates, potentially leading to imprecise estimates of vector activity if the relationship of CO₂ release rate to mosquito capture rate is not considered.     

Patterns of spatio‐temporal distribution,abundance, and diversity in a mosquito community from the eastern Smoky Hills of Kansas

Nearly 30% of emerging infectious disease events are caused by vector‐borne pathogens with wildlife origins. Their transmission involves a complex interplay among pathogens, arthropod vectors, the environment and host species, and they pose a risk for public health, livestock and wildlife species. Examining habitat associations of vector species known to transmit infectious diseases, and quantifying spatio‐temporal dynamics of mosquito vector communities is one aspect of the holistic One Health approach that is necessary to develop effective control measures. A survey was conducted from May to August, 2010 of the abundance and diversity of mosquito species occurring in the mixed‐grass prairie habitat of the Smoky Hills of Kansas. This region is an important breeding ground for North America's grassland nesting birds and, as such, it could represent an important habitat for the enzootic amplification cycle of avian malaria and infectious encephalitides, as well as spill‐over events to humans and livestock. A total of 11 species, belonging to the three genera Aedes, Anopheles, and Culex, was collected during this study. Aedes nigromaculis, Ae. sollicitans, Ae. taeniorhynchus, Culex salinarius, and Cx. tarsalis accounted for 98% of the collected species. Multiple linear regression models suggested that mosquito abundances in the grasslands of the central Great Plains were explained by meteorological and environmental variables. Temporal dynamics in mosquito abundances were well supported by models that included maximum and minimum temperature indices (adjusted R²= 0.73). Spatial dynamics of mosquito abundances were best explained by a model containing the following environmental variables (adjusted R²=0.37): ground curvature, topographic wetness index, distance to woodland, and distance to road. The mosquito species we detected are known vectors for infectious encephalitides, including West Nile virus. Understanding the microhabitat characteristics of these mosquito species in a grassland ecosystem will aid in the control and management of these disease vectors.     

Host range of the parasite Strelkovimermis spiculatus (Nematoda: Mermithidae) in Argentina mosquitoes

Strelkovimermis spiculatus ( Poinar and Camino 1986 ) is a nematode parasite of mosquitoes isolated from the Neotropical region. We investigated the host range of this parasite in mosquito populations for a better understanding of the dynamics of temporary breeding sites. Five grassy‐pool habitats filled by rainwater were sampled from the summer 2007 through the fall 2008. Eight mosquito species were collected: Anopheles albitarsis, Culex chidesteri, Culex dolosus, Culex maxi, Aedes albifasciatus, Psorophora ciliata, Psorophora cyanescens, and Psorophora albigenu. Six of these species were parasitized: Cx. chidesteri, Cx. dolosus, Cx. maxi, Ae. albifasciatus, Ps. ciliata, and Ps. cyanescens. The occurrence of this mermithid in natural mosquito populations was increased from the end of winter to the end of the spring. Prevalence ranged from 11% to 100%. High levels of infections were registered only in Ae. albifasciatus larvae, the most abundant mosquito species (95%), followed by Cx. dolosus (2.7%). Strelkovimermis spiculatus completed its development in all infected mosquito larvae. The presence of S. spiculatus in six natural mosquito populations increases the number of susceptible species to 24.     

Seasonal dynamics of mosquitoes (Diptera: Culicidae) in Osijek (Croatia) for the period 1995–2004

The ten year research (1995–2004) of adult mosquitoes in the area of Osijek by dry ice baited CDC traps has provided significant information on mosquito species, species prevalence, their dynamics and seasonal activity. A total of 207,136 adult mosquitoes comprising twenty species belonging to the following genera: Anopheles, Ochlerotatus, Aedes, Culex, Coquillettidia, Culiseta and Uranotaenia were collected. The seven most common species collected during this study were: Aedes vexans (75.6%), Ochlerotatus sticticus (13.3%), Culex pipiens complex (5.9%), Anopheles maculipennis complex (1.9%), Oc. cantans (0.9%), Oc. caspius (0.6%) and Oc. excrucians (0.6%). The temporal changes in the relative abundance of the twenty mosquito species in the Osijek area were reflected in three peaks: in May, July and September. Seasonal population dynamics differed between years and between mosquito species in relation to wetland, urban and forest habitats and was influenced by water level of the Drava and the Danube rivers.     

The distribution of mosquitoes across an altitudinal gradient in the Galapagos Islands

An avian malaria parasite (genus Plasmodium) has been detected consistently in the Galapagos Penguin (Spheniscus mendiculus) and less frequently in some passerines. We sampled three resident mosquito species (Aedes taeniorhynchus, Culex quinquefasciatus, and Aedes aegypti) using CDC light and gravid traps on three islands in 2012, 2013, and 2014. We sampled along altitudinal gradients to ask whether there are mosquito‐free refugia at higher elevations as there are in Hawaii. We captured both Ae. taeniorhynchus and Cx. quinquefasciatus at all sites. However, abundances differed across islands and years and declined significantly with elevation. Aedes aegypti were scarce and limited to areas of human inhabitation. These results were corroborated by two negative binomial regression models which found altitude, year, trap type, and island as categorized by human inhabitation to be significant factors influencing the distributions of both Ae. taeniorhynchus and Cx. quinquefasciatus. Annual differences at the highest altitudes in Isabela and Santa Cruz indicate the lack of a stable highland refuge if either species is found to be a major vector of a parasite, such as avian malaria in Galapagos. Further work is needed to confirm the vector potential of both species to understand the disease dynamics of avian malaria in Galapagos.     

Evidence of vertical transmission of West Nile virus in field‐collected mosquitoes

Male and nulliparous female mosquitoes were surveyed for evidence of vertical WNV infection in East Baton Rouge Parish, Louisiana. Adult male mosquitoes collected by trapping and aspiration, and adult male and nulliparous female mosquitoes reared from field‐collected larvae were tested. Adult male Culex spp., female Aedes albopictus (Skuse), and female Culex quinquifasciatus Say mosquitoes that were collected as larvae were test‐positive for WNV RNA. Infectious WNV was detected using virus isolation in field‐collected male Aedes triseriatus Say and Culex salinarius Coquillett; these data represent the first field evidence of vertical transmission of WNV in Ae. triseriatus and Cx. salinarius.     

Laboratory Evaluation of Controlled-release Repellent Treated Pulp Fabric on Human Volunteers Against Mosquito Vectors

Three controlled‐release personal‐use pulp fabric impregnated insect repellent formulations of 5% N, N‐diethyl‐3‐methylbenzamide (DEET), and 10% and 15% neem oils were evaluated in an environmental chamber on volunteers for their repellent efficacy against three mosquito species, Culex pipiens pallens, Aedes aegypti and Ochlerotatus togoi. The 5% DEET formulation showed significant repellency in pulp fabric (5 mm in width) against Culex pipiens pallens and Aedes aegypti (P < 0.05), providing an average repellency of 88.0%, 66.3%, and 46.8% of Cx. pipiens pallens, Ae. Aegypti and O. togoi bites, respectively, during the 6 hours of exposure period. Against night‐biting mosquitoes Cx. pipiens pallens, the DEET formulation provided mostly complete protection for at least 4 hours after the application. In pulp fabric of 10 mm in width, the 5% deet formulation showed significantly the highest repellency among the repellents against O. togoi (P<0.05), providing an average repellency of 52.3% during the 6 hours of exposure period. However, the pulp fabrics treated with 10% and 15% neem oil were less effective than 5% DEET against three mosquito species. This study demonstrated the potential of 5% DEET as pulp fabric repellent against both day‐ and night‐biting mosquitoes.     

Plasmodium berghei: mechanisms and sites of resistance to sporogonic development in different mosquitoes

An experimental study of the mechanisms and patterns of resistance to Plasmodium berghei in different mosquito species revealed a diversity of factors which prevent or inhibit sporogonic development in its different phases and in different sites in the mosquito vector. The experiments showed that Culex salinarius was a totally resistant species in which exflagellation and ookinete formation are prevented. In Aedes aegypti, ookinetes in small or moderate numbers are formed but penetration of the mosquito midgut wall is blocked and oocysts are not formed. In the three experimental vectors, Anopheles quadrimaculatus, Anopheles aztecus, and Anopheles stephensi grades of enhanced susceptibility are recognized. They are expressed in lesser numbers of abnormal and degenerative oocysts, in higher numbers of sporozoites in the salivary gland, and greater viability and invasiveness of these sporozoites. In Anopheles dureni, the natural vector of rodent malaria, one observes both in nature and under experimental conditions the highest adaptation and most pronounced grade of susceptibility to P. berghei.     

Experimental infection of Aedes (Stegomyia) albopictus and Culex pipiens mosquitoes with Bluetongue virus

Bluetongue disease (BT), caused by Bluetongue virus (BTV), infects wild and domestic ruminants, causing severe economic damage in the cattle and sheep industry. Proven vectors of BTV are biting midges belonging to the Culicoides genus, but other arthropods are considered potential vectors, such as ticks, mosquitoes, wingless flies, and sand flies. The present study represents the first attempt to evaluate the vectorial capacity of Culex pipiens and Aedes albopictus for BTV. Mosquitoes were artificially fed with blood containing BTV serotype 1. Infection, dissemination and transmission rates were evaluated at 0, 3, 7, 14 and 21 days after an infected blood meal. Viral RNA was only detected up to 3 days post infection in the bodies of both species. This study indicates that the two Italian populations of Cx. pipiens and Ae. albopictus are not susceptible to BTV infection.     

The Effect of West Nile Virus Perceptions and Knowledge on Protective Behavior and Mosquito Breeding in Residential Yards in Upstate New York

A knowledge, attitudes, and practices (KAP) questionnaire combined with entomological surveys of residential mosquito-breeding sites were conducted in two Upstate New York neighborhoods. We tested the hypothesis that “correct” West Nile virus (WNV) knowledge and perceptions correspond with the use of practices that prevent mosquitoes from breeding and biting. Our results demonstrate that perceptions of WNV relate to the number of positive containers in yards and the use of mosquito preventive measures. In contrast, WNV knowledge was not related. Culex pipiens and Cx. restuans were common species found breeding in containers. Aedes japonicus was the most abundant species in 77% of positive containers (buckets, flower pots, and birdbaths). This new, invasive mosquito together with the Culex species identified in this study represent significant potential as vectors of WNV and other arboviruses affecting human and animal health. We conclude that more training and education programs should focus on WNV control strategies and recognizing mosquito breeding in residential yards. This is the first study to directly investigate the relationship between KAP and breeding of WNV vectors in residential yards.     

Seasonal Prevalence of Mosquitoes Collected from Light Traps in Gyeongsangnam Province,Republic of Korea (2013–2014)

Adult mosquito surveillance was conducted from 2013 through 2014 at four cattle sheds, a wild bird refuge, and two residential areas located in Gyeongnam Province in the Republic of Korea. Adult mosquitoes were collected in black light traps from April 1, through November 30. Mosquito surveillance was conducted to figure out population densities of vector mosquitoes, possibly invaded mosquitoes and identify various virus infections at the selected sites. A total of 107,466 females comprising 14 species and 7 genera were collected from 2013 to 2014. The most common species collected were Culex tritaeniorhynchus Giles (63.8%), Anopheles sinensis s.l. (18.9%), Aedes vexans nipponii (Theobald) (7.7%), and Culex pipiens Coquillett (5.1%). Trap indices (TIs) varied widely for species over their range, due to geographical distribution and degree of association with rural and urban communities . The most collected An. sinensis s.l. and Cx. tritaeniorhynchus appeared at a cow shed in Hapcheon (TI 347.5) and a pigsty in Daejeo‐1‐dong, Busan (TI 1,040.8), respectively, due in part to their situation near breeding sites such as rice paddies. The bi‐weekly population densities for mosquito species were variable for each of the years, apparently as a result of variable annual weather conditions. None of the mosquito species collected tested for the flavivirus including Japanese Encephalitis Virus, West Nile Virus, Dengue Virus, and Zika Virus infections by polymerase chain reaction (PCR) assay were positive.     

Shift in the spatial and temporal distribution of Aedes taeniorhynchus following environmental and local developments in St. Johns County,Florida

The Anastasia Mosquito Control District (AMCD) of St. Johns County (SJC), St. Augustine, Florida, USA, was formed in 1948 to cover the 27 km² of Anastasia Island and control the black salt marsh mosquito, Aedes taeniorhynchus (Wiedemann). Today AMCD covers the entirety of SJC (1588 km²) and Ae. taeniorhynchus is still the most abundant mosquito species in the county. Here we present the findings from 16 years’ worth of surveillance records of AMCD mosquito populations in conjunction with annual land-use land-cover (LULC) change and climate data to better understand how environmental factors have impacted SJC Ae. taeniorhynchus populations in recent history. The statistical regression and geospatial analyses demonstrated the presence of spatial and temporal clusters of Ae. taeniorhynchus populations in terms of abundance and distribution. Additionally, Ae. taeniorhynchus abundance and distribution were significantly influenced by the annual changes of LULC and climate variables. The linear regression analysis using standard least square and corrected Akaike Information Criterion revealed a migration of mangrove swamps and saltwater marshes that corresponded to a southern shift in the spatial–temporal distribution of Ae. taeniorhynchus communities. This was confirmed by the significant change in LULC characteristics between three representative years (2004, 2009, 2014) and the redistribution of Ae. taeniorhynchus abundances represented by Moran’s I index values. The annual values of four climate variables (average and minimum temperature, mean dew point, and maximum vapor pressure deficit) and three LULC types (mangrove swamps, saltwater pools within saltmarshes, and upland nonforested) significantly predicted annual abundance and redistribution of Ae. taeniorhynchus.

     

Diversity,distribution, abundance,and feeding pattern of tropical ornithophilic mosquitoes

Bird–biting mosquitoes act as bridge vectors of diverse pathogens of emerging infectious diseases. In this study, we report for the first time the abundance, diversity, distribution, and feeding pattern of bird‐biting mosquitoes on an island where avifaunal diversity is rich. Monthly mosquito collections were done at six different habitats in three different climatic zones using bird‐baited traps over a year. Collected mosquitoes were identified using morphological and molecular tools. A total of 2,655 bird‐biting mosquitoes of eight genera and 25 species were identified. Of these, 52% were Culex species, which represents 35% of the Culex species in the country. The most abundant species were Culex sitiens, Cx. pseudovishnui, Cx. nigropunctatus and Cx. quinquefasciatus, whereas the latter two were common to all habitats. The highest abundance was reported in lowland forests (49.6%), while it was lowest in highland forests (22.3%). Highest species similarity was reported from highland forests. Seasonal variations of the most abundant species were significantly different in selected habitats (p< 0.05). Two distinct biting peaks were identified, from 06:00 to 21:00 and 22:00 to 02:00. The biting nature of identified ornithophilic mosquitoes suggests the potential vector status of these mosquitoes.     

Estimating Culicoides sonorensis biting midge abundance using digital image analysis

ImageJ is an open‐source software tool used for a variety of scientific objectives including cell counting, shape analysis and image correction. This technology has previously been used to estimate mosquito abundance in surveillance efforts. However, the utility of this application for estimating abundance or parity in the surveillance of Culicoides spp. (Diptera: Ceratopogonidae) has not yet been tested. Culicoides sonorensis (Wirth and Jones), a biting midge often measuring 2.0–2.5 mm in length, is an economically important vector of ruminant arboviruses in California. Current surveillance methods use visual sorting for the characteristics of midges and are very time‐intensive for large studies. This project tested the utility of ImageJ as a tool to assist in gross trap enumeration as well as in parity analysis of C. sonorensis in comparison with traditional visual methods of enumeration using a dissecting microscope. Results confirmed that automated counting of midges is a reliable means of approximating midge numbers under certain conditions. Further evaluation confirmed accurate and time‐efficient parity analysis in comparison with hand sorting. The ImageJ software shows promise as a tool that can assist and expedite C. sonorensis surveillance. Further, these methods may be useful in other insect surveillance activities.     

Sensilla basiconica (grooved pegs) on the antennae of female mosquitoes: electrophysiology and morphology

The sensilla basiconica or grooved pegs of mosquitoes consist of two morphologically and functionally distinct classes. Short grooved pegs house sensory cells that are excited by lactic acid whereas lactic acid-excited cells are absent in long grooved pegs. This correlation was found in four species of mosquito examined:Aedes aegypti, Aedes atropalpus, Aedes epactius, andCulex pipiens. InAedes epactius, both short and long grooved pegs house receptors that are sensitive to butyric acid.     

Mosquito and biting fly surveillance on Camp Zama Army Base,Kanagawa Prefecture,Japan

Camp Zama, Japan, and the associated military housing and depot storage areas have been occupied by the US military for over 50 years. The military base has experienced less urbanization and development during those 50 years when compared to the surrounding cities of Zama and Sagamihara. We present an annotated comparative checklist of historical records of biting flies (mosquitoes, black flies, biting midges, stable flies, and horse flies) with recent collections. Overall 24 species of biting flies have been reported from Camp Zama, with 17 of these species collected during the last 5 years. Vectors of human and veterinary pathogens were collected including Anopheles sinensis, Aedes albopictus, Culex tritaeniorhynchus, and Simulium bidentatum.     

Electronic mosquito repellers induce increased biting rates in Aedes aegypti mosquitoes (Diptera: Culicidae)

Studies have demonstrated that electronic mosquito repellers are useless and that some of them could even increase the attraction of mosquitoes. While testing some electronic repellers, we noted that they also promoted an increase in biting rates. The present work has evaluated three commercial devices and a computer program working on five different sound frequencies. In a test chamber, the number of Aedes aegypti L. bite attempts was computed during four cycles of 3 min each by alternately turning the devices off and on. The mosquito biting rates for five sound frequencies (ranging from 9.6 kHz to 18.2 kHz) initially demonstrated a significant increase (ranging from around 20% to 50%), which decreased from 8.3% to 25.1% when the repellers were turned off. The biting rate significantly increased at 11.8 kHz (33.7%) when the device was turned on again. The danger of using electronic repellers and the role of sound frequencies stimulating mosquito biting are discussed.