Tires as habitats for mosquitoes: a review of studies within the eastern United States

Discarded vehicle tires are a common habitat for a variety of container mosquito species. I reviewed the literature from the last 50 yr on mosquitoes collected within tires in the eastern United States with four objectives: to examine the historical and contemporary issues of tires as a habitat for mosquitoes, to identify tire-inhabiting species, to summarize findings from studies that focused on biotic and abiotic characteristics of tires, and to offer future directions to aid our understanding of tire-inhabiting mosquitoes. Thirty-two species have been documented, including seven invasives, with the most frequently encountered being Aedes triseriatus, Ae. albopictus, Ae. atropalpus, Culex restuans, Cx. pipiens, Cx. territans, Anopheles punctipennis, and Toxorhynchites rutilus. The proclivity of these species to occupy small containers is one possible explanation for their occurrence in tires. The native species Ae. triseriatus was abundant and the most often collected, particularly in central and northern regions, whereas the invasive Ae. albopictus was most abundant in the south. One half of the studies investigating aspects of the tire environment compared mosquito populations between sunlit and shaded tires, with the general finding that this factor alone led to dramatic differences in larval species composition and abundance patterns. Less frequently investigated factors, e.g., tire orientation, detritus, and proximity to humans, also were found to affect patterns of occupancy by mosquitoes. For the future, I suggest more surveys are needed in understudied areas, as well as quantitative experiments to determine habitat associations and community dynamics in tires, which are especially necessary to assist in understanding invasions. Discarded tires are important for studies of vector dynamics, because of their abundance near human populations and because they expand the habitat range of mosquitoes that vector pathogens.     

Constitutive differences between natural and artificial container mosquito habitats: vector communities, resources, microorganisms, and habitat parameters

Aquatic containers, including tree holes and vehicle tires, harbor a diverse assemblage of mosquitoes capable of vectoring important diseases. Many studies have examined containers as a mosquito breeding site, although no data exist that have simultaneously compared mosquito communities between tree holes and tires, and few have quantified differences in environmental factors or food resources that may be important for explaining population or community differences. At two times (early and late summer 2009) we sampled two tire and two tree hole sites in south-central Mississippi, and for each container we enumerated mosquito larvae and measured several environmental parameters (canopy cover, water volume, and detritus), and biomass and productivity of fungi and bacteria, and species richness and abundance of protozoans. Tree holes held less water but were more shaded compared with tires; however, after correcting for volume differences, tree holes contained more detritus and were higher in some microorganism measures (protozoan richness, bacterial productivity in the water column). Based on community dissimilarity analysis of mosquitoes, strong differences existed between container types and sampling period; Aedes albopictus (Skuse) and Culex quinquefasciatus (Say) were dominant in tires, whereas Ae. triseriatus (Say) and Orthopodomyia signifera (Coquillett) were dominant in tree holes. This study also reports the use of tires by the invasive mosquito Cx. coronator (Dyar and Knab). Tree holes supported a higher density of larvae but fewer species than tires, though there was variation across time. Our work illustrates that detrital inputs and some microorganisms differ in fundamental ways between tires and tree holes, and because of compositional differences in mosquito communities, these small aquatic habitats cannot be considered to be homogeneous mosquito habitats.     

Habitat preferences and phenology of Ochlerotatus triseriatus and Aedes albopictus (Diptera: Culicidae) in southwestern Virginia

Recently, the number of reported human cases of La Crosse encephalitis, an illness caused by mosquito-borne La Crosse virus (LAC), has increased in southwestern Virginia, resulting in a need for better understanding of the virus cycle and the biology of its vectors in the region. This study examined the spatial and temporal distributions of the primary vector of LAC, Ochlerotatus triseriatus (Say), and a potential secondary vector, Aedes albopictus (Skuse). Ovitrapping surveys were conducted in 1998 and 1999 to determine distributions and oviposition habitat preferences of the two species in southwestern Virginia. Mosquitoes also were collected for virus assay from a tire dump and a human La Crosse encephalitis case site between 1998 and 2000. Oc. triseriatus and Ae. albopictus were collected from all ovitrap sites surveyed, and numbers of Oc. triseriatus eggs generally were higher than those of Ae. albopictus. Numbers of Oc. triseriatus remained high during most of the summer, while Ae. albopictus numbers increased gradually, reaching a peak in late August and declining thereafter. In Wise County, relative Ae. albopictus abundance was highest in sites with traps placed in open residential areas. Lowest numbers of both species were found in densely forested areas. Ovitrapping during consecutive years revealed that Ae. albopictus was well established and overwintering in the area. An oviposition comparison between the yard and adjacent forest at a human La Crosse encephalitis case site in 1999 showed that Ae. albopictus preferentially oviposited in the yard surrounding the home, but Oc. triseriatus showed no preference. LAC isolations from larval and adult collections of Oc. triseriatus females from the same case site indicated the occurrence of transovarial transmission.     

Interspecific competition among Aedes aegypti, Ae. albopictus, and Ae. triseriatus (Diptera: Culicidae): larval development in mixed cultures

Interactions among the larvae of Aedes aegypti (L.), Ae. albopictus (Skuse), and Ae. triseriatus (Say) were studied in trispecific and bispecific mixed populations under laboratory and field conditions. Competitive stress (as evidenced by the average time to first, 50, and 75% pupation and the total pupation periods for mixed populations of each species in comparison with their single species controls) was more pronounced in mixed cultures reared in glass jars in the laboratory than in tires under field conditions. In the laboratory, the larval development of Ae. aegypti reared together with Ae. albopictus or Ae. triseriatus, or both, larvae was accelerated significantly. Conversely, the time to pupation for Ae. albopictus and Ae. triseriatus was delayed when reared with Ae. aegypti. However, the average wing length of female Ae. albopictus and Ae. triseriatus was greater in the mixed cultures than in single species cultures. These data indicated that the effect of intraspecific competition was greater than interspecific competition. Adequate food and higher temperature appeared to promote rapid development and higher survival of the immature stages of the three Aedes species in tires placed in the field. In general, Ae. triseriatus larvae required a longer period for larval development and had greater larval mortality than either Ae. aegypti or Ae. albopictus. In mixed populations of Ae, albopictus and Ae. aegypti in the jars and food-rich tires, the periods needed to attain first, 50, and 75% cumulative pupation were not significantly different than in single species controls. We conclude that no clear-cut displacement occurred in mixed experimental populations of Ae. aegypti and Ae. albopictus.     

Intraguild predation among larval treehole mosquitoes, Aedes albopictus, Ae. aegypti, and Ae. triseriatus (Diptera: Culicidae), in laboratory microcosms.

We compared the tendency for 4th-instar larvae to prey on newly hatched larvae, and the vulnerability of those 1st instars to such predation for Aedes triseriatus (Say), Ae. aegypti (L.), and Ae. albopictus (Skuse), all container-breeding mosquitoes. The latter 2 species were introduced to North America and are now sympatric with Ae. triseriatus, a native species in eastern North America. The experiment also enabled the assessment of species-specific influences of food supplements and spatial heterogeneity on predatory behavior. Ae. triseriatus was substantially more predatory and less susceptible to attack than the other 2 species. These differences were amplified in food-deprived and spatially simple conditions, indicating that Ae. triseriatus predatory behavior may have important retarding effects on the colonization of occupied treehole habitats by Ae. albopictus. Ae. aegypti and Ae. albopictus were similar in imposing little (Ae. aegypti) or almost no (Ae. albopictus) predation on 1st instars and in being susceptible to predation by Ae. triseriatus. The general lack of species-specific differences between Ae. aegypti and Ae. albopictus indicates that interspecific predation is not a likely explanation for the rapid displacement of Ae. aegypti by Ae. albopictus in domestic containers in the southeastern United States.     

Development and survival of immature Aedes albopictus and Aedes triseriatus (Diptera: Culicidae) in the laboratory: effects of density, food, and competition on response to temperature

Effects of food, density, and heterospecific interactions on temperature-dependent development of Aedes albopictus (Skuse) and Aedes triseriatus (Say) larvae and pupae were described using a degree-day model. Under all conditions, the predicted number of degree-days (DD(T0)) to complete larval development was less, and the threshold temperature (T0) for initiation of larval development was higher for Ae. albopictus than for Ae. triseriatus. The DD(T0) for both species was food and density dependent. However, the per capita food ration appeared to exert a greater influence on the developmental times of Ae. triseriatus immatures, whereas for Ae. albopictus effects of density were not completely eliminated by an increase in the per capita food ration. The presence of heterospecific larvae did not prolong the DD(T0) of either species. At the low food ration, DD(T0) for both species were significantly greater under conspecific conditions. The DD(T0) for Ae. triseriatus increased directly as the proportion of conspecific larvae increased. However, when a higher per capita food ration was provided, conspecific effects on DD(T0) were mitigated. For Ae. albopictus, estimated DD(T0) values for larvae reared in pure culture were significantly higher than when heterospecific larvae were present, regardless of the per capita amount of food provided. Survivorship of immatures was density and food-dependent for both species. Ae. albopictus exhibited higher immature survivorship under all conditions relative to Ae. triseriatus. For both species, survival probabilities were lowest under conditions of high density and low food. Addition of food improved survival for both species. The presence of heterospecific larvae exerted a differential effect on the survivorship response of Ae. albopictus immatures to temperature. Lowest probability of survival for Ae. albopictus was occurred at low temperature when the proportion of heterospecific larvae in containers was the highest. In contrast, at high temperatures, survivorship of immatures improved, but was lowest for pure species cultures. For Ae. triseriatus, survivorship of immatures was consistently lower for pure species cultures regardless of the temperature. Standing crop production of adults of both species was primarily food rather that density-dependent. Under field conditions, Ae. triseriatus were predicted to initiate development sooner and exhibit faster population growth early in the season than Ae. albopictus. However, because of the shorter DD(T0), Ae. albopictus population growth was predicted to surpass that of Ae. triseriatus populations later in the season. Based on optimal DD(T0) values from laboratory experiments, spring emergence dates of Ae. triseriatus females in western North Carolina for 1989 and 1990 were predicted from accumulated degree-days calculated from local air temperature records. Predicted emergence dates were congruent with results of a previous survey for the same locality, indicating that accumulated degree-days can be used to accurately predict the seasonal occurrence of Ae. triseriatus. The utility of the degree-day approach in predicting the phenology of Ae. albopictus remains to be established.     

Comparative potential of Aedes triseriatus, Aedes albopictus, and Aedes aegypti (Diptera: Culicidae) to transovarially transmit La Crosse virus

Aedes triseriatus (Say) (Diptera: Culicidae), the major vector of La Crosse (LAC) virus, efficiently transmits LAC virus both horizontally and transovarially. We compared the vector competence and transovarial transmission ability of Ae. triseriatus, Aedes albopictus Skuse, and Aedes aegypti (L.) for LAC virus. Ae. triseriatus and Ae. albopictus were significantly more susceptible to oral infection with LAC virus than Ae. aegypti. The three species also differed in oral and disseminated infection rates (DIRs). Transovarial transmission (TOT) rates and filial infection rates (FIRs) were greater for Ae. triseriatus than either Ae. albopictus or Ae. aegypti. These measures were integrated into a single numerical score, the transmission amplification potential (TAP) for each species. Differences in TAP scores were due mainly to the differences in DIRs and FIRs among these mosquitoes. Although the TAP score for Ae. albopictus was lower than that of Ae. triseriatus, it was 10-fold greater than that for Ae. aegypti.     

Spatial and temporal variation in the mosquitoes (Diptera: Culicidae) inhabiting waste tires in Nicholas County,West Virginia

Larvae of 12 mosquito species were collected from abandoned tire piles at peridomestic and forested sites in Nicholas County, WV, from March through November of 2001. No larvae were found in March, but the numbers of species increased to 10 by July and remained relatively constant, at 9-11 in any given month, throughout November. Larvae of Ochlerotatus triseriatus (Say), the most commonly encountered species in every month of collection, were significantly more likely to be found in forested tire pile sites. Conversely, Culex restuans Theobald, Anopheles punctipennis (Say), Cx. territans Walker, and Aedes albopictus (Skuse) larvae were significantly more likely to be found in peridomestic tire piles. Larvae of the remaining seven species were either found in equal proportions at peridomestic and woodland sites, or there were too few collections to make statistical inferences. Opportunities for competitive interactions between Ae. albopictus and Oc. triseriatus in Nicholas County would be minimized because the peak occurrence of the two species differ temporally and spatially.     

Behavioral differences of invasive container-dwelling mosquitoes to a native predator

Aquatic prey show behavioral modifications in the presence of predation-risk cues that alleviate their risk from predation. Aedes albopictus (Skuse), Aedes japonicus (Theobald), and Culex pipiens L. are invasive mosquitoes in North America, and their larvae are prey for the native mosquito predator, Toxorhynchites rutilus (Coquillett). Ae. albopictus and Ae. japonicus are recent invaders, whereas Cx. pipiens has been in the United States for >100 yr. In the presence of predation-risk cues from Tx. rutilus larvae, Cx. pipiens larvae increased the time spent resting at the surface (least risky behavior) more than the other prey species. Ae. japonicus larvae increased resting at the surface of the containers more than Ae. albopictus larvae in the presence of predation-risk cues. Cx. pipiens larvae spent more time motionless at the surface even in the absence of predation-risk cues when compared with the other species, indicating that Cx. pipiens larvae are the least vulnerable prey. As compared with the other prey species, Ae. albopictus larvae exhibited more high-risk behaviors both in the presence and absence of predation-risk cues, indicating that they are the most vulnerable prey. Ae. albopictus is the superior competitor; however, predation by Tx. rutilus larvae may prevent competitive exclusion by Ae. albopictus and promote coexistence among the three prey species.     

Host-feeding patterns of Aedes albopictus (Diptera: Culicidae) in relation to availability of human and domestic animals in suburban landscapes of central North Carolina

Aedes albopictus (Skuse) (Diptera: Culicidae) is a major nuisance mosquito and a potential arbovirus vector. The host-feeding patterns of Ae. albopictus were investigated during the 2002 and 2003 mosquito seasons in suburban neighborhoods in Wake County, Raleigh, NC. Hosts of blood-fed Ae. albopictus (n = 1,094) were identified with an indirect enzyme-linked immunosorbent assay, by using antisera made in New Zealand White rabbits to the sera of animals that would commonly occur in peridomestic habitats. Ae. albopictus fed predominantly on mammalian hosts (83%). Common mammalian hosts included humans (24%), cats (21%), and dogs (14%). However, a notable proportion (7%) of bloodmeals also was taken from avian hosts. Some bloodmeals taken from birds were identified to species by a polymerase chain reaction-heteroduplex assay (PCR-HDA). Ae. albopictus fed predominantly on chickens and a northern cardinal. PCR-HDA failed to produce detectable products for 29 (58%) of 50 bloodmeals for which DNA had been amplified, indicating that these mosquitoes took mixed bloodmeals from avian and nonavian hosts. Ae. albopictus preference for humans, dogs, and cats was determined by calculating host-feeding indices for the three host pairs based on the proportion of host specific blood-fed mosquitoes collected in relation to the number of specific hosts per residence as established by a door-to-door survey conducted in 2003. Estimates of the average amount of time that residents and their pets (cats and dogs) spent out of doors were obtained. Host-feeding indices based only on host abundance indicated that Ae. albopictus was more likely to feed on domestic animals. However, when feeding indices were time-weighted, Ae. albopictus fed preferentially upon humans. Ae. albopictus blood feeding on humans was investigated using a STR/PCR-DNA profiling technique that involved amplification of three short tandem repeats loci. Of 40 human bloodmeals, 32 (80%) were from a single human, whereas eight (20%) were multiple bloodmeals taken from more than one human host. We conclude that the blood-feeding preference of Ae. albopictus for mammals will limit acquisition of arboviruses by this species from infected avian amplification hosts. This feeding preference likely limits the vector potential of Ae. albopictus for North American arboviruses.     

Overwintering and establishment of Aedes albopictus (Diptera: Culicidae) in an urban La Crosse virus enzootic site in Illinois

In 1997, Aedes albopictus (Skuse) was discovered in Peoria, IL, a known focus of La Crosse (LAC) virus transmission. This accidental introduction provided an opportunity to determine whether Ae. albopictus would reemerge in the spring or summer and, if successful overwintering occurred, to follow changes in the geographic range of Ae. albopictus, and to compare its distribution to that of the local treehole mosquito and LAC vector Aedes triseriatus (Say). In 1998, 25 oviposition traps were placed in and around the area of the initial finding of Ae. albopictus, with adult collections by aspirators and larval collections from water-holding containers used to identify areas of additional activity. Ae. albopictus successfully survived the mild 1997-1998 El Ni?o winter, and expanded its range during 1998. By September 1998, Ae. albopictus oviposited in all 25 traps, including traps near and in wooded sites. Intensity of oviposition activity (number of eggs per positive trap) ranged from 20-40, lower than the range for Ae. triseriatus, which was as high as 175 eggs per infested trap in mid-August. Prevalence of Ae. albopictus increased through September, where as the prevalence of Ae. triseriatus declined starting in mid-July. Although direct competition between the two mosquito species cannot be inferred based on this surveillance effort, a gradual range expansion was observed, and Ae. albopictus eggs were collected in traps where initially only Ae. triseriatus oviposition activity was detected.     

Brugia malayi microfilariae (Nematoda: Filaridae) enhance the infectivity of Venezuelan equine encephalitis virus to Aedes mosquitoes (Diptera: Culicidae)

We examined the potentially conflicting effects that microfilarial (MF) enhancement of viral infectivity and MF-induced mortality in mosquitoes have on the vectorial capacity of Aedes aegypti (L.), Aedes triseriatus (Say), and Aedes taeniorhynchus (Wiedemann) for Venezuelan equine encephalitis virus (VEE) when mosquitoes feed on gerbils co-infected with Brugia malayi (Buckley). Groups of mosquitoes were fed on gerbils that were either dually infected (VEE plus B. malayi MF) or singly infected (VEE only). Mosquito mortality was recorded daily, and 5-8 d later, surviving mosquitoes were assayed for disseminated viral infection. The contrasting effects of MF enhancement and MF-induced mortality differed among mosquito species and were determined by the nature and consequences of MF penetration through the mosquito midgut, but not to differences in mosquito susceptibilities to parenterally introduced virus. In Ae. aegypti, MF-induced mortality was high and tended to eliminate any significant effect of MF enhancement. In Ae. triseriatus, MF-induced mortality was low, and feeding on dually infected hosts resulted in 9 times as many mosquitoes with disseminated viral infections as did feeding on singly-infected hosts. In Ae. taeniorhynchus, MF-induced mortality was extremely high, yet under our experimental conditions, feeding on a dually infected hosts resulted in nearly 30 times as many disseminated infections as did feeding on singly infected hosts. The final outcome on vectorial capacity depended on the specific combination of MF, virus, and mosquito species involved. Therefore, future efforts toward understanding MF enhancement should be directed toward mosquito-virus-parasite species combinations that occur together in nature.     

Vector competence of rural and urban strains of Aedes (Stegomyia) albopictus (Diptera: Culicidae) from São Paulo State, Brazil for IC, ID, and IF subtypes of Venezuelan equine encephalitis virus

Aedes albopictus (Skuse) is an Asiatic mosquito species that has spread and colonized all continents except Antarctica. It has major public health importance because it is a potential vector of several pathogens. The objectives of our study were to analyze the vector competence of urban and rural strains of Ae. albopictus from S?o Paulo State (Brazil) for Venezuelan equine encephalitis virus (VEE) subtypes IC, ID, and IF, and to evaluate the effect of infection with subtype IC of VEE on mosquito longevity. Both mosquito strains were susceptible to subtypes IC and ID, but the infection rate for subtype IF was low. Infection and transmission rates of Ae. albopictus for subtype IC were similar to those reported for Ochlerotatus taeniorhynchus (Wiedemann). The high infection, dissemination, and transmission rates for subtype ID reported for Oc. fulvus (Wiedemann) and Culex (Melanoconion) spp. are comparable with those found in this study. We found significant differences in the susceptibility to subtype IC between rural and urban populations of S?o Paulo. Significant survival rate differences were observed between uninfected and infected mosquitoes, but there were no differences in survival between rural and urban mosquito strains.     

Vector competence of Aedes aegypti and Aedes albopictus (Diptera: Culicidae) for dengue virus in the Florida Keys

In 2009-2011, Monroe County in southern Florida experienced locally acquired and traveler-imported focal dengue outbreaks. Aedes aegypti (L.) is the primary vector of dengue virus (DENV) worldwide, is prevalent in Monroe County, and is the suspected vector in Florida. Ae. albopictus (Skuse) is also known to be an important vector of DENV and this species is ubiquitous in Florida; however, it is not yet established in Monroe County. Florida Ae. aegypti (Key West and Stock Island geographic colonies) and Ae. albopictus (Vero Beach geographic colony) were fed blood containing 3.7 Log10 plaque-forming unit equivalents of DENV serotype 1 isolated from a patient involved in the Key West, FL, outbreak in 2010. Mosquitoes were maintained at extrinsic incubation temperatures of 28 or 30 degrees C for an incubation period of 14 d. Vector competence was assessed using rates of infection (percent with virus-positive bodies), dissemination (percent infected with virus-positive legs), and transmission (percent infected with virus-positive saliva). No significant differences were observed in rates of infection or dissemination between Ae. aegypti or Ae. albopictus at either extrinsic incubation temperature. Transmission was observed only at 28 degrees C in both Ae. aegypti (Key West) and Ae. albopictus. The assessment of local mosquito populations for their DENV vector competence is essential and will aid mosquito control operators interested in pinpointing specific vector populations for control. The extent to which vector competence is affected by seasonal changes in temperature is discussed and provides baseline risk assessment data to mosquito control agencies.     

Experimental transmission of eastern equine encephalitis virus by Ochlerotatus j. japonicus (Diptera: Culicidae)

We evaluated the potential for Ochlerotatus j. japonicus (Theobald), a newly recognized invasive mosquito species in the United States, to transmit eastern equine encephalitis (EEE) virus. Aedes albopictus (Skuse) and Culex pipiens (L.) were similarly tested for comparison. Ochlerotatus j. japonicus and Ae. albopictus became infected and transmitted EEE virus by bite after feeding on young chickens 1 d after they had been inoculated with EEE virus (viremias ranging from 10(7.0-8.7) plaque-forming units [PFU]/ml of blood). No Cx. pipiens (n = 20) had detectable levels of virus 14 d after feeding on an EEE-virus infected chicken with a viremia of 10(8.1) PFU per ml of blood. Depending on the viral titer in the donor chicken, infection rates ranged from 55-100% for Oc. j. japonicus and 93-100% for Ae. albopictus. In these two species, dissemination rates were identical to or nearly identical to infection rates. Depending on the viral titer in the blood meal, estimated transmission rates ranged from 15 to 25% for Oc. j. japonicus and 59-63% for Ae. albopictus. Studies of replication of EEE virus in Oc. j. japonicus showed that there was an "eclipse phase" in the first 4 d after an infectious blood meal, that viral titers peak by day 7 at around 10(5.7) per mosquito, and that virus escaped the mid-gut as soon as 3 d after the infectious blood meal. These data, combined with the opportunistic feeding behavior of Oc. j. japonicus in Asia and the reported expansion of its range in the eastern United States, indicate that it could function as a bridge vector for EEE virus between the enzootic Culiseta melanura (Coquillett)-avian cycle and susceptible mammalian hosts.     

Laboratory evaluation of mosquito repellents against Aedes albopictus, Culex nigripalpus, and Ochierotatus triseriatus (Diptera: Culicidae)

Four synthetic mosquito repellents (Autan [10% KBR3023], IR3535 [7.5%], Off! [15% deet], Skinsations [7% deet]) and eight natural (primarily plant extracts and/or essential oils) product-based repellents (Bite Blocker [2% soybean oil], ByGone, GonE!, Natrapel [10% citronella], Neem Aura, Sunswat, MosquitoSafe [25% geraniol], and Repel [26% p-menthane-3,8-diol]) were tested in the laboratory against Aedes albopictus Skuse, Culex nigripalpus Theobald, and Ochlerotatus triseriatus (Say). When estimated mean protection time (eMPT) responses for each repellent were averaged for all three mosquito species, Autan, Bite Blocker, Off!, and Repel prevented biting for > or =7.2 h; IR3535, MosquitoSafe, and Skinsations for 3.2-4.8 h; and ByGone, Natrapel, GonE, NeemAura, and SunSwat for 0.9-2.3 h. Against Ae. albopictus, the eMPT for Off! and Repel exceeded 7.0 h and ranged from 5.0 to 5.7 h for Autan, Bite Blocker, and Skinsations. Bygone, GonE, NeemAura, and SunSwat provided 0.2 h protection against Ae. albopictus and Oc. triseriatus, whereas Autan, Bite Blocker, Off., and Repel prevented bites by Oc. triseriatus for > or =7.3 h. All 12 repellents provided an eMPT > or =2.8 h against Cx. nigripalpus (maximum: 8.5 h for Bite Blocker). When the average eMPT for each repellent (for all species) was divided by the eMPT for 7% deet (Skinsations), the order of repellent effectiveness and the corresponding repellency index (R,) was Repel (1.7) > Bite Blocker (1.5) = Autan (1.5) = Off! (1.5) > Skinsations (1.0) > IR3535 (0.8) > MosquitoSafe (0.6) > Natrapel (0.5) > Neem Aura (0.3) = SunSwat (0.3) = Bygone (0.3) > GonE (0.2).     

Field evaluation of the Off! Clip-on Mosquito Repellent (metofluthrin) against Aedes albopictus and Aedes taeniorhynchus (Diptera: Culicidae) in northeastern Florida

Repellent efficacy of the Off! Clip-on Mosquito Repellent device (S. C. Johnson and Son, Inc., Racine, WI) containing Metofluthrin was evaluated on six human volunteers against the container-breeding mosquito Aedes albopictus (Skuse) and the salt marsh mosquito Aedes taeniorhynchus (Wiedemann) at two field locations in northeastern Florida. The device repelled mosquitoes by releasing a vaporized form of the pyrethroid insecticide metofluthrin ([AI] 31.2%) and provided 70% protection from Ae. albopictus bites for > 3 h. For the second field trial, a repellent device that was used in the first trial was tested after being open for >1 wk. This device provided 79% protection from Ae. taeniorhynchus bites for 3 h. Our field results showed that the repellent device was 70 and 79% effective at repelling Ae. albopictus and Ae. taeniorhynchus from human test subjects in both field locations in northeastern Florida.     

Direct and indirect effects of animal detritus on growth, survival, and mass of invasive container mosquito Aedes albopictus (Diptera: Culicidae)

Compared with plant detritus, animal detritus yields higher growth rates, survival, adult mass, and population growth of container-dwelling mosquitoes. It is unclear whether the benefit from animal detritus to larvae results from greater microorganism growth, direct ingestion of animal detritus by larvae, or some other mechanism. We tested alternative mechanisms by which animal detritus may benefit the invasive container-dwelling mosquito Aedes albopictus (Skuse) (Diptera: Culicidae). In the laboratory, larvae were reared under three conditions with access to 1) detritus, but where microorganisms in the water column were reduced through periodic flushing; 2) water column microorganisms, but larvae had no direct access to detritus; or 3) both water column microorganisms and detritus. Access treatments were conducted for three masses of animal detritus: 0.005, 0.010, and 0.020 g. Water column bacterial productivity (measured via incorporation of [3H] leucine) decreased significantly with flushing and with larval presence. Removing microorganisms through flushing significantly reduced mass of adult mosquitoes (both sexes), and it significantly prolonged developmental times of females compared with treatments where water column microorganisms or microorganisms and detritus were available. Survival to adulthood was greatest when larvae had access to both water column microorganisms and 0.020 g of detritus, but it declined when only water column microorganisms were available or when 0.005 g of detritus was used. These findings indicate both direct (as a food source) and indirect (assisting with decomposition of detritus) roles of microorganisms in producing the benefit of animal detritus to container mosquito larvae.     

Detritus type alters the outcome of interspecific competition between Aedes aegypti and Aedes albopictus (Diptera: Culicidae)

Many studies of interspecific competition between Aedes albopictus (Skuse) and Aedes aegypti (L.) (Diptera: Culicidae) larvae show that Ae. albopictus are superior resource competitors to Ae. aegypti. Single-species studies indicate that growth and survival of Ae. albopictus and Ae. aegypti larvae are affected by the type of detritus present in containers, which presumably affects the amount and quality of microorganisms that the mosquito larvae consume. We tested whether different detritus types alter the intensity of larval competition by raising 10 different density/species combinations of Ae. albopictus and Ae. aegypti larvae under standard laboratory conditions, with one of four detritus types (oak, pine, grass, or insect) provided as a nutrient base. Intraspecific competitive effects on survival were present with all detritus types. Ae. albopictus survivorship was unaffected by interspecific competition in all treatments. Negative interspecific effects on Ae. aegypti survivorship were present with three of four detritus types, but absent with grass. Estimated finite rate of increase (lambda') was lower with pine detritus than with any other detritus type for both species. Furthermore, Ae. aegypti lambda' was negatively affected by high interspecific density in all detritus types except grass. Thus, our experiment confirms competitive asymmetry in favor of Ae. albopictus with oak, pine, or insect detritus, but also demonstrates that certain detritus types may eliminate interspecific competition among the larvae of these species, which may allow for stable coexistence. Such variation in competitive outcome with detritus type may help to account for observed patterns of coexistence/exclusion of Ae. albopictus and Ae. aegypti in the field.     

Comparison of larval foraging behavior of Aedes albopictus and Aedes japonicus (Diptera: Culicidae)

Aedes albopictus (Skuse) (Diptera: Culicidae) invaded the United States in 1985 and spread rapidly across eastern North America, whereas Aedes japonicus (Theobald) invaded and became established in the United States more recently (1998). The two species may co-occur in container habitats, and they are of potential public health concern as arbovirus vectors. To evaluate ecological differences between Ae. albopictus and Ae.japonicus, we compared larval foraging behavior of these two species. Based on results from a previous competition experiment, we predicted that Ae. albopictus would be a more active forager than Ae. japonicus. However, Ae. japonicus exhibited greater foraging activity than Ae. albopictus in four of six food environments, including a "no food" control treatment. Our results, therefore, suggest that more active foraging does not connote superior competitive ability, and competitive interactions between these species may be mediated by factors other than feeding behavior.