Albopictus Females Research Articles

Geographic Variation of Photoperiodic Diapause but Not Adult Survival or Reproduction of the Invasive MosquitoAedes albopictus(Diptera: Culicidae) in North America

Climate differences across latitude can result in seasonal constraints and selection on life-history characters. Because Aedes albopictus (Skuse) invaded North America in the mid-1980s, it has spread across a range of ≈14° latitude and populations in the north experience complete adult mortality because of cold winter temperatures that are absent in the south. Life-table experiments were conducted to test for differences in the adult survival and reproductive schedules of Ae. albopictus females from three populations from the northern (Salem, NJ; Springfield, IL; Eureka, MO; ≈39° N) and southern (Palm Beach, Palmetto, Tampa, FL; ≈27-28° N) extremes of the species distribution in North America. There were consistent differences between northern and southern populations in incidence of photoperiodically-induced egg diapause. Under short daylength, diapause eggs constituted twice the proportion of total viable eggs from northern females (81.9-92.1%) than southern females (35.9-42.7%). There were no consistent differences between northern and southern populations in resource allocation between reproduction and maintenance, reproduction over time, and reproductive investment among offspring, and no apparent trade-offs between diapause incidence with reproduction or longevity. Our results suggest that the main response of North American Ae. albopictus to unfavorable winter climates is via the life history strategy of producing diapausing eggs, rather than quantitative variation in reproduction, and that there are no detectable costs to adult survival. Inherent geographic variation in the expression of diapause, consistent with the latitudinal extremes of A. albopictus, indicates evolutionary loss of diapause response in southern populations because of the invasion of A. albopictus in North America.

Discarded Cigarette Butts Attract Females and Kill the Progeny of Aedes albopictus

Discarded cigarette butts (DCB) waste occurs worldwide, pollutes landscapes, is unsightly, and results in added debris removal costs. There is, therefore, a great deal of current interest in making use of DCBs in beneficial ways. Despite evidence that DCBs are harmful to water fleas (Daphnia magna), which breed in aquatic environments as do mosquito larvae, their impact on dengue vectors is unknown. We examined whether Aedes albopictus alters its ovipositional responses, larval eclosion, and development in response to presence of DCBs in its habitats. We found oviposition activity in DCB-treated water similar to that of control water and that ovipositional activity in DCB solutions steadily increased over time as those solutions aged to 10 days. Larval eclosion was initially suppressed on day 1 in DCB solution, but increased thereafter to levels similar to control larval eclosion rates. The DCB-water solutions produced significantly higher mortality in both 1st and 2nd instars over control larvae for several days after initial exposure. Mortality rates decreased sharply 3 to 5 days postexposure as DCBs continued to decompose. We found increased survival rates during late development, but daily input of fresh DCBs prevented most young larvae from completing development. Taken together, these observations suggest that decomposing did not deter gravid Ae. albopictus females from ovipositing in treated containers and that DCB solutions had larvicidal effects on early instars. Our results are discussed in the context of DCB use to control container-breeding Ae. albopictus, a competent dengue vector in Asia and other parts of the world.

An autodissemination station for the transfer of an insect growth regulator to mosquito oviposition sites

A prototype autodissemination station to topically contaminate oviposition-seeking container-dwelling mosquitoes with the insect growth regulator, pyriproxyfen, was developed and tested in the laboratory. Our test subject was the Asian tiger mosquito, Aedes albopictus (Skuse) (Diptera: Culicidae), an urban species that colonizes small-volume cryptic larval habitats and is a skip ovipositor that visits multiple containers. The station consists of a water reservoir to attract gravid females, which is joined to a transfer chamber designed to contaminate visiting mosquitoes. The unit is easily constructed by moulding wet shredded cardboard using corn starch as a binder. The essential criteria that must be met to prove the efficacy of an autodissemination station require it to demonstrate effectiveness in attracting the target insect, in transferring the toxicant to the insect that will disperse the agent, and in facilitating the subsequent transfer of the toxicant from the insect to target habitats at a lethal concentration. Cage experiments demonstrated that the unit was readily accepted by gravid females as an oviposition site. A powder formulation of pyriproxyfen-impregnated silica particles adhered to visiting Ae. albopictus females (mean: 66 particles/female), although particles were lost over time. In cage (2.2 m(3) ) trials, pyriproxyfen-charged stations resulted in 100% inhibition of adult emergence, whereas in small-room (31.1 m(3) ) trials, 81% emergence inhibition was recorded. The venereal transfer of pyriproxyfen from contaminated males to virgin females was also observed, and pyriproxyfen was subsequently transferred to water-holding containers at concentrations that inhibited emergence. Key autodissemination station features include lack of maintenance requirements, biodegradable construction, low cost and low risk.

Effect of Temperature and Insecticide Stress on Life-History Traits of Culex restuans and Aedes albopictus (Diptera: Culicidae)

The chronic effects of exposure of Culex restuans (Theobald) and Aedes albopictus (Skuse) (Diptera: Culicidae) to low concentrations of malathion were examined by exposing larvae of the two species to four malathion doses at 20, 25, and 30 degrees C and maintaining the resulting adults at 25 degrees C. For both species, a significant temperature by malathion interaction on survival was found. Greater temperatures at the highest malathion dosage had significantly lower survivorship than in other treatments, but this effect was not observed at 20 degrees C. These results suggest that low temperature may buffer against some of the negative effects of malathion. For both species, temperature but not malathion had significant effects on female developmental time to adulthood and adult longevity. Temperature also affected adult female size for Ae. albopictus but not Cx. restuans. Ae. albopictus females developed faster as temperature increased, lived longer when larvae were maintained at 30 degrees C than at 20 degrees C, and were larger when larvae were maintained at 25 degrees C than at 20 or 30 degrees C. Cx. restuans females developed faster at 25 and 30 degrees C than at 20 degrees C and lived longer at 25 degrees C than at 20 or 30 degrees C. The estimated finite rate of increase (lambda') for Cx. restuans was significantly lower at 20 degrees C than at 25 and 30 degrees C, whereas that of Ae. albopictus was significantly influenced by an interaction between temperature and malathion with significantly lower lambda' at 20 degrees C than at 25 and 30 degrees C for all malathion treatments except 0.014 mg liter(-1). Understanding how pesticides interact with abiotic environmental conditions will contribute to management decisions about vector control practices.

Chikungunya, a new threat propagated by the cosmopolite Aedes albopictus

The recent outbreaks of chikungunya (CHIK) were due to an East-Central-South African genotype harbouring a substitution from an Alanine (E1-226A) to a Valine (E1-226V) at the position 226 in the E1 gene. The new variant E1-226V is very efficiently transmitted by an unusual mosquito vector, Aedes albopictus. We found that (i) Ae. albopictus females ensure a high replication rate of E1-226V up to 109 viral particles per female, (ii) the midgut plays a key role in limiting viral dissemination of E1-226A in the mosquito, (iii) the virus is detectable in the saliva as soon as two days after the infectious blood-meal, and (iv) Ae. albopictus is able to deliver up to 3000 viral particles with its saliva. All these characteristics led to exacerbate CHIK transmission by Ae. albopictus. However, this species is affected by the viral infection. Indeed, CHIK infection reduces sharply the survival of Ae. albopictus, females laying their eggs just before dying. Females did not die from an excess of viral replication but more likely in attempting to mount an immune antiviral response. Moreover, by removing the intracellular bacteria Wolbachia from Ae. albopictus through successive antibiotic treatments, we aimed to determine if Wolbachia interferes with CHIK replication in the mosquito. We found that Ae. albopictus cleaned of Wolbachia was not affected by CHIK infection. Thus, Wolbachia may regulate viral replication in Ae. albopictus with consequences on its survival. So, the response of a vector to a particular pathogen is also closely linked to the presence of other microorganisms. Finally, we showed that Ae. albopictus was able to be orally co-infected with CHIK and dengue (DEN) viruses and to deliver concomitantly infectious particles of both viruses in saliva. This finding is of particular concern as Ae. albopictus is still expanding its geographical range and as both CHIK and DEN viruses can co-circulate in the same geographical regions. Indeed, reports of co-infections in patients with both viruses are increasing.

The Effects of Moisture on Ovipositional Responses and Larval Eclosion of Aedes albopictus

Moisture plays a major role in the dynamics of mosquito populations, especially those breeding in container habitats. Despite this importance, the role of moisture conditions as they affect oviposition and egg development in Aedes vectors remains largely unexplored. We investigated the effect of exposing gravid female Aedes albopictus mosquitoes and their eggs to different moisture levels (MLs) for various periods on oviposition and hatching. Overall, high-moisture substrates (HMSs; 66% and 72%) provided better environments for egg laying. The timing of initial egg laying was far longer at the lowest substrate moisture level (LSML, 25% and 41.2%) than at HMSs. The numbers of eggs laid were much lower in the drier environments. At LSMLs, gravid females retained increasing numbers of mature eggs until death, and egg retention decreased gradually with increasing ML. The HMSs also provided better environments for larval eclosion. The numbers of eggs hatched were lower at the LSML than the HSML environment. No egg hatching occurred after 1 h exposure to moisture. However, egg hatching occurred by installment, with spontaneous hatching (SH) increasing gradually with increasing ML. High-moisture conditions combined with long exposure (30 h and 48 h) favored SH. These results suggest that Ae. albopictus females can respond to better moisture conditions for increased success of embryonation and larval eclosion. This information may be useful in the colonization of floodwater Aedes species.

Strain-Specific Differences in Mating, Oviposition, and Host-Seeking Behavior Between Wolbachia-Infected And Uninfected Aedes albopictus

Wolbachia are maternally inherited bacteria that cause various reproductive alterations in their arthropod hosts, including cytoplasmic incompatibility. In this study, we compared mating, oviposition, and host-seeking behavior of Wolbachia-infected (Houston [HOU], Gainesville [GNV]) and Houston uninfected (HT1) Aedes albopictus. In mating assays with virgin mosquitoes, mating success of Wolbachia-infected males was significantly higher than uninfected strains. Mating success was highest with HOU males exposed to infected (95%) and uninfected females (100%), and lowest with HT1 males exposed to infected (20%) and uninfected (25%) females. Results suggested that Wolbachia infection may influence the reproductive behavior of this mosquito. There were no clear differences in oviposition responses between strains, with all strains ovipositing significantly more often on hay infusion and larval rearing water than on water controls and least frequently on 4-methylphenol. Strains of Ae. albopictus females were host-seeking a human when given a choice. Responses to a human arm, acetone, CO2, and dichloromethane were generally higher from the Houston strains than from the GNV strain. Responses of HOU and HT1 females differed from GNV with greater responses to the arm and CO2.

Costs and benefits of Wolbachia infection in immature Aedes albopictus depend upon sex and competition level

Bacterial endosymbionts induce various effects on hosts and can dramatically impact host fitness and development. An example is provided by obligate, maternally-inherited Wolbachia, which infect a broad range of invertebrates. Wolbachia are capable of altering host reproduction, thereby promoting infection spread. Wolbachia also pose direct physiological costs and benefits to hosts, complicating their categorization as parasites or mutualists. This study examines for an effect of Wolbachia infection in intra-specific larval competition by Aedes albopictus mosquitoes, with the goal of examining for an impact of Wolbachia infection in mixed populations. Similar to prior work examining for an influence of Wolbachia infection on the fitness of A. albopictus in adults, the results presented here support the hypothesized impact of Wolbachia across all life stages, including immatures. The differential competitiveness of infected larvae detected in our experiments indicates that Wolbachia infected A. albopictus females are less competitive relative to uninfected females when competing under highly competitive conditions. In contrast, under low competitive pressures, infected females experience higher survivorship. Thus, Wolbachia infection shifts from parasitism to mutualism as a function of developmental conditions. Results are discussed in relation to the invasion and persistence of Wolbachia in A. albopictus populations. The results are important to the evolution of stable Wolbachia symbioses, including Wolbachia invasion of an uninfected population. The resulting infection dynamics that occur in an infected population are discussed.

Study ofAedes albopictusdispersal in Rome, Italy, using sticky traps in mark-release-recapture experiments

We report the results of three mark-release-recapture experiments carried out in an urban area in Rome, Italy, to study the active dispersal of Aedes albopictus (Diptera: Culicidae). The 4.3% recapture rate obtained supports the use of sticky traps in MRR experiments to study the dispersal of Ae. albopictus females. Most fluorescent dust-marked females were recaptured at the gravid stage at 50-200 m from the release sites during the first 9 days after release. The average of daily-MDTs (Mean Distance Traveled) was 119 m and the maximum observed distance travelled ranged from 199 m to 290 m in the three replicates. These data provide the first information about the dispersal of Ae. albopictus in a temperate European area and appear to be consistent with the few data available on this subject from other urban areas, where dispersal was constrained by physical barriers. Although caution should be taken in generalizing these results, they should be considered when planning control activities in urban areas in Italy, as well as in other European countries. This is particularly relevant if control is intended to interrupt pathogen transmission in cases of possible arbovirus epidemics, such as the Chikungunya outbreak that occurred in Ravenna, Italy in 2007.

Comparative Studies on Aedes aegypti and Aedes albopictus Adult Females Trespassing Commercial Nets

ABSTRACT. The abilities of Aedes aegypti and Ae. albopictus females in trespassing 5 different commercial nets, 2 nets impregnated with deltamethrin or permethrin and 3 non-impregnated nets (Guarany, Perame, and Ricca), were compared. The evaluating parameters were their percent trespassing success, the median trespassing time (TT50), and the relation between mosquito wing sizes and their trespassing success. Some mosquito behavioral traits were also observed. The trespassing success, directly related to opening areas, was found to be lower with impregnated nets for both species. The differences between the mosquito species were significant among all the nets except Ricca. Aedes albopictus showed a very high success rate in trespassing the non-impregnated Perame net and a lower success rate in trespassing Guarany. Aedes albopictus also showed a very high success rate in trespassing pyrethroid-impregnated nets. The TT50 values for the Ricca and Guarany nets were not significantly different between the species, but a significantly lower TT50 value was found for the net with the largest opening (Ricca). The smaller wingspan of Ae. albopictus seems to explain the higher trespassing success of this species.

Effects of Temperature and Rainfall on the Activity and Dynamics of Host-SeekingAedes albopictusFemales in Northern Italy

The Asian tiger mosquito, Aedes albopictus, has colonized nearly all the regions of Italy as well as other areas of Europe. During the summer of 2007 the tiger mosquito was responsible for an outbreak of Chikungunya in Italy, when this virus was brought in by a tourist of Indian origin returning from an endemic area. To increase the knowledge of tiger mosquito population dynamics, a survey was carried out from April to November 2008 in the municipalities of Arco and Riva del Garda (northern Italy) through a Biogents Sentinel™ (BG)-trap sampling. In particular, the aim of the study was to evaluate the influence of temperature and rainfall on the activity and dynamics of A. albopictus host-seeking females. The seasonal emergence of host-seeking females was strongly influenced by the minimum temperature, and a lower threshold of 13°C was identified. In addition, the threshold for the end of adult activity was found at a minimum temperature of 9°C. Host-seeking female abundance was positively affected by the accumulated temperatures over the period 3 and 4 weeks before the sampling week, possibly as a consequence of the positive effect of accumulated temperatures on larval density. Instead, accumulated precipitation over 1-4 weeks before sampling was negatively correlated with host-seeking female abundance. Finally, the activity of host-seeking females, estimated by the weekly increment in female abundance, was positively affected by the total abundance of females and by mean weekly temperatures. Our study provides useful information for predicting the dynamics of host-seeking Ae. albopictus females in northern Italy and for designing control strategies for preventing arbovirus outbreaks in areas colonized by Ae. albopictus.

Larvicidal Activity and Influence of Bacillus thuringiensis Var. Israelensis on Aedes albopictus Oviposition in Ovitraps During A Two-Week Check Interval Protocol

Toxicity persistence of Bacillus thuringiensis var. israelensis (Bti) was evaluated in laboratory and field trials to develop a new protocol for Aedes albopictus monitoring. In the laboratory, the residual toxicity of 5 Bti formulations was compared using the percentage mortality at days 4, 8, 12, and 16 of Culex pipiens larvae exposed for 24 h to Bti treatments. The results showed a good performance of all tested formulations (>97% mortality at day 14, for all the formulations), but only Vectobac 12AS at the concentration of 1 ml/liter showed an efficacy of 100% for 2 wk. A field study was designed to test the effect of Bti on the ovitrap check interval or influence of ovipositional response of gravid Ae. albopictus females. Three different ovitrap treatments were used: ovitraps with tap water checked weekly; ovitraps with tap water checked every 2 wk; ovitraps with Bti (Vectobac 12AS, dose of 1 ml/liter) checked every 2 wk. Our study demonstrated that in the ovitrap, the toxic action of a 1% solution of Bti was maintained for at least 14 days with mortality of 100% and that rainfall did not seem to negatively influence the residual action of Bti. Therefore the probability that the larvae may complete the developmental cycle in ovitraps with Bti seems to be very low. The oviposition activity index showed that Bti enhances the oviposition rate of Ae. albopictus by 17.4%.

Comparison of Infusions of Commercially Available Garden Products for Collection of Container-Breeding Mosquitoes

In 2004, gravid-trap infusions made from commercially available garden products were compared in field assays to determine their attractiveness to ovipositing female mosquitoes. Experiments were conducted simultaneously at a residential site and at an auto salvage yard in Lee County, AL, each site having an abundance of container-breeding mosquitoes. Several infusion types were initially screened, from which the following 4 infusions were selected to be compared using gravid traps for their attractiveness to mosquitoes under field conditions: oak leaves, pine straw, red (dyed) hardwood mulch, and composted manure. Culex quinquefasciatus was the only species collected in greater numbers with gravid traps than with light traps, and the difference was more than 5-fold at both study sites. Gravid traps collected (mean +/- SD) 3.1 +/- 4.3 and 6.9 +/- 11.5 Cx. quinquefasciatus females at the residential and auto salvage sites, respectively. The response of Cx. quinquefasciatus females to infusions tested was variable, and no single infusion was consistently more attractive throughout the experiment. Gravid traps collected 1.7 +/- 1.9 and 4.7 +/- 4.4 Aedes albopictus females, 0.3 +/- 1.4 and 0.5 +/- 1.3 Cx. nigripalpus females, and 0.3 +/- 0.9 and 0.2 +/- 0.8 Cx. restuans females at the residential and auto salvage sites, respectively. Roughly 5-, 20- and 10-fold the numbers of females of Aedes albopictus, Cx. nigripalpus, and Cx. restuans were collected by light traps than by gravid traps at both sites. Aedes albopictus females did not demonstrate a preference for any of the infusions tested. Significant difference among infusions for Cx. restuans and Cx. nigripalpus were detected on just 1 trap-night. On this occasion, traps with red (dyed) hardwood mulch collected significantly more females of Cx. restuans and Cx. nigripalpus than did traps with other infusions. This work indicates that gravid traps are effective tools for collecting Cx. quinquefasciatus females, and a wide variety of organic materials may be used to produce infusions that can be used to attract ovipositing container-breeding mosquitoes.

Evaluation of a Sticky Trap for Collecting Aedes (Stegomyia) Adults in a Dengue-endemic Area in Thailand

Development of new operational techniques for collection and monitoring of adult Stegomyia mosquitoes is considered a pressing need for surveillance and prevention of arboviruses. Here we report the results from a trial carried out in 2 dengue-endemic villages in Thailand to compare the ability to collect Aedes adults of a sticky trap versus a CDC backpack aspirator, which has been used routinely at the study area for entomological/epidemiological surveys. Our comparison was based on a comparable sampling effort required to carry out collections with 2 approaches. Over 19,000 specimens were collected, approximately 90% of which were Culex spp. Sticky traps collected significantly more Aedes aegypti and Aedes albopictus females than did backpack aspirators when located outdoors. The percentage of positive sticky-trap catches was double for Ae. aegypti and almost 20 times higher for Ae. albopictus. Operational benefits of the sticky trap are discussed within the context of the results obtained.

Aedes albopictus, vecteur des virus du chikungunya et de la dengue à la Réunion : biologie et contrôle

Chikungunya virus (CHIKV) and dengue virus (DENV) are mosquito-borne viruses transmitted by the Aedes genus. Dengue is considered as the most important arbovirus disease throughout the World. Chikungunya, known from epidemics in continental Africa and Asia, has up to now been poorly studied. It has been recently responsible for the severe 2004-2007 epidemic reported in the Indian Ocean (IO), which has caused several serious health and economic problems. This unprecedented epidemic of the IO has shown severe health troubles with morbidity and death associated, which had never been observed before. The two major vectors of those arboviruses in the IO area are Aedes aegypti and Aedes albopictus. The latest is considered as the main vector in most of the islands of the area, especially in Reunion Island. Ae. albopictus showed strong ecological plasticity. Small disposable containers were the principal urban breeding sites, and preferred natural developmental sites were bamboo stumps and rock holes in peri-urban and gully areas. The virus has been isolated from field collected Ae. albopictus females, and in two out of 500 pools of larvae, demonstrating vertical transmission. Experimental works showed that both Ae. albopictus and Ae. aegypti from west IO islands are efficient vectors of dengue and chikungunya viruses. Since 2006 and all along the epidemic of CHIKV, measures for the control of larvae (temephos then Bacillus thuringiensis) and adults (fenitrothion, then deltamethrine) of Ae. albopictus where applied along with individual and collective actions (by the use of repellents, and removal of breeding sites around houses) in Reunion Island. In order to prevent such epidemics, a preventive plan for arboviruses upsurge is ongoing processed. This plan would allow a quicker response to the threat and adapt it according to the virus and its specific vector.

Geographic variation in adult survival and reproductive tactics of the mosquito Aedes albopictus.

Climate differences across latitude can result in seasonal constraints and selection on life history characters. Since Aedes albopictus (Skuse) invaded North America in the mid-1980s, it has spread across a range of approximately 14 degrees latitude and populations in the north experience complete adult mortality due to cold winter temperatures that are absent in the south. Life table experiments were conducted to test for differences in the adult survival and reproductive schedules of Ae. albopictus females from two populations from the northern (Bloomington, IN [BL] and Manassas, VA [VA]; approximately 39 degrees N) and southern (Tampa, FL and Fort Myers, FL; approximately 27-28 degrees N) extremes of the species distribution in North America Regardless of population origin, age-specific hazard rate increased with reproductive output and decreased with number of bloodmeals. Larger females took fewer bloodmeals, and they had greater hazard rates than did smaller females. There were no consistent differences between northern versus southern populations in resource allocation between reproduction and maintenance, reproduction over time, and reproductive investment among offspring, suggesting that latitudinal variation in climate is probably not a main selective factor impinging on adult mortality and reproductive schedules. One possible effect of climate on geographic differences in life history was detected. BL had lower survivorship, lower lifetime reproductive output, and lower adult reproductive rate than did all other populations. This result may be an indirect result of lower egg survivorship due to the severity of winter in BL compared with other populations, including VA at approximately the same latitude. Such a scenario may make the BL population more prone to extinction, irregularly recolonized from more favorable sites, and thus more susceptible to founder effects, genetic drift, and inbreeding, resulting in lower mean values of fitness-related traits.

Description And Use Of The Harris County Gravid trap For West Nile Virus Surveillance 2003–061

The Harris County Gravid Trap (HCGT) used for West Nile virus (WNV) surveillance from 2003-06 is described. The HCGT collected 1,918,483 Culex quinquefasciatus females (over 36,627 periods), with 466,296.37 (8,452.74) yearly. Only 48,094 Aedes albopictus females (over 15,139 periods) were collected, with 10,277.79 (3,260.33) yearly. The highest mosquito production occurred in July for Cx. quinquefasciatus (63,851.25 +/- 0.13), and for Ae. albopictus (2,981.80 +/- 0.09). Integrating gravid traps within our program has increased our ability to detect WNV efficiently in both species.

Development of a novel sticky trap for container‐breeding mosquitoes and evaluation of its sampling properties to monitor urban populations of Aedes albopictus

Collection methods currently used for large-scale sampling of adult Stegomyia mosquitoes (Diptera: Culicidae) present several operational limitations, which constitute major drawbacks to the epidemiological surveillance of arboviruses, the evaluation of the impact of control strategies, and the surveillance of the spreading of allochthonous species into non-endemic regions. Here, we describe a new sticky trap designed to capture adult container-breeding mosquitoes and to monitor their population dynamics. We tested the sampling properties of the sticky trap in Rome, Italy, where Aedes (Stegomyia) albopictus is common. The results of our observations, and the comparison between sticky trap catches and catches made with the standard oviposition trap, are presented. The sticky trap collected significantly larger numbers of Ae. albopictus females than any other Culicidae species representing >90% of the total catches. A maximum of 83 An. albopictus females was collected in a single week. A high correlation (Pearson correlation coefficient r= 0.96) was found between the number of females and the number of eggs collected by the traps. The functional relationship between the number of eggs and the number of adult females was assessed by major axis regression fitted to log(1 +x)-transformed trap counts as y= 0.065 + 1.695x. Trap samples significantly departed from a random distribution; Taylor's power law was fitted to the trap samples to quantify the degree of aggregation in the catches, returning the equations s(2)= 2.401 m(1.325) for the sticky trap and s(2)= 13.068 m(1.441) for the ovitrap, with s(2) and m denoting the weekly catch variance and mean, respectively, indicating that eggs were significantly more aggregated than mosquitoes (P < 0.0001). Taylor's power law parameters were used to estimate the minimum number of sample units necessary to obtain sample estimates with a fixed degree of precision and sensitivity. For the range of densities encountered in our study area during the Ae. albopictus breeding season, the sticky trap was more precise and sensitive than the ovitrap. At low population densities (c. < 0.1 mosquito/trap), however, the ovitrap was more sensitive at detecting the presence of this species. Overall, our results indicate that our new model of sticky trap can be used to sample Ae. albopictus females in urban environments, and, possibly, other container-breeding Stegomyia mosquitoes (e.g. Aedes aegypti). The technical properties of the new trap are discussed with respect to its possible application in monitoring the population dynamics of container-breeding mosquitoes, in studying their bionomics, and in vector surveillance and, possibly, control.

FIELD COMPARISON OF BERMUDA-HAY INFUSION TO INFUSIONS OF EMERGENT AQUATIC VEGETATION FOR COLLECTING FEMALE MOSQUITOES

Field experiments were conducted in east-central Alabama in 2003 and 2004 to compare the attractiveness of selected gravid-trap infusions to ovipositing female mosquitoes. Comparisons were made among infusions of the following plants: Bermuda hay, Cynodon dactylon, and 3 species of emergent aquatic plants typical of Culex larval habitats, i.e., soft rush, Juncus effusus; a common sedge, Rhynchospora corniculata; and broad-leaf cattail, Typha latifolia. Experiments were conducted at a site in Lee County, AL, with an abundance of common nuisance mosquitoes, including Culex quinquefasciatus and Aedes albopictus. Carbon dioxide-baited miniature light traps were operated concurrently with gravid traps to provide an activity index of mosquito species at the site. Gravid traps with hay infusion collected the greatest numbers of Cx. quinquefasciatus and Culex restuans females (2003). The results indicate that hay infusion is highly attractive to Cx. quinquefasciatus and is the infusion of choice for collecting females of this species in gravid traps. In the case of Ae. albopictus, infusions were not determined to be significantly different from one another in their attractiveness to gravid females. In general, females of Cx. quinquefasciatus and Cx. restuans demonstrated selectivity when choosing an oviposition site, whereas Ae. albopictus females did not. Factors associated with the oviposition biology of the latter species most likely account for their lack of preference for any single infusion type.

Parity and ovarian development of Aedes aegypti and Ae. albopictus (Diptera: Culicidae) in metropolitan Rio de Janeiro

Vector blood-feeding frequency, parity, and ovarian development are important factors that can influence pathogen transmission. Parity rates of the dengue vectors Aedes aegypti and Ae. albopictus were determined from females collected from August 2002 to July 2004 in metropolitan Rio de Janeiro. A high frequency of parous Ae. aegypti (92.9%, n = 550) and Ae. albopictus (99.1%, n = 320) females suggested high survivorship of both species. A total of 69% of wild-caught Ae. aegypti females had blood in the midgut compared to 19% of Ae. albopictus. For Ae. aegypti, red-colored midgut contents were associated with ovaries in early stages of development, and brown-colored midguts were associated with ovaries in late stages of maturation. Ovaries of Ae. aegypti females without blood in the midgut were most frequently in stages I and V of Christophers.