Oviposition and flight orientation response of Aedes aegypti to certain aromatic aryl hydrazono esters

Aedes aegypti is a day-biting, highly anthropophilic mosquito and a potential vector of dengue and chikungunya in India. A. aegypti is a container breeder, generally oviposit in the stored and fresh water bodies, and discarded containers near residential areas that provide suitable habitats for oviposition by gravid females. The diurnal activity and endophilic nature of these mosquitoes have increased the frequency of contact with human being. Assured blood meal from human host in an infested area leads to increased disease occurrence. Gravid mosquitoes can potentially be lured to attractant-treated traps and could subsequently be killed with insecticides or growth regulators. In this direction, oviposition by A. aegypti females to aryl hydrazono esters (AHE)-treated bowls at 10?ppm concentration was tested in dual choice experiment, and their orientation response to these ester compounds was studied in Y-tube olfactometer. Among the esters tested, AHE-2, AHE-11 and AHE-12 elicited increased egg deposition with oviposition activity indices (OAI) of +0.39, +0.24 and +0.48, respectively, compared to control; in contrast, AHE-8, AHE-9 and AHE-10 showed negative oviposition response with OAI of -0.46, -0.35 and -0.29, respectively, at 10?mg/L. In the Y-tube olfactometer bioassay, AHE-2 attracted 60?% females compared to control, while to the odour of AHE-11 and AHE-12, about 70?% of the females were trapped in treated chambers. In contrast, only 27-30?% of gravid females entered the chamber releasing AHE-8, AHE-9 and AHE-10 odour plumes, while 70?% entered control chamber, evincing a possible non-preference of treatment odours as well as interference with olfactory receptors. These compounds have the potential for application as oviposition stimulants or deterrents for surveillance and control of mosquito population using ovitraps.     

Insecticide susceptibility of Aedes aegypti and Aedes albopictus across Thailand

Aedes aegypti (L.) and Aedes albopictus (Skuse), two important vectors of dengue fever and dengue hemorrhagic fever, were collected from Mae Sot, Nakhon Sawan, Nakhon Ratchasima, Surat Thani, and Phatthalung, Thailand, from July 2003 to April 2004. The patterns of insecticide susceptibility to temephos, malathion, and permethrin of both Ae. aegypti and Ae. albopictus larvae were determined. Ae. aegypti from all study sites were resistant to permethrin, they but were susceptible to malathion. Resistance to temephos was detected in all strains of Ae. aegypti, except those from Nakhon Ratchasima. Ae. albopictus larvae had low levels of resistance to all three insecticides, except Mae Sot and Phatthalung strains, which were resistant to permethrin.     

Blood feeding patterns of Aedes aegypti and Aedes albopictus in Thailand

Aedes aegypti (L.) and Aedes albopictus (Skuse) were collected with aspirators from Mae Sot, Nakhon Sawan, Nakhon Ratchasima, Surat Thani, and Phatthalung study sites in Thailand from July 2003 though April 2004. The sandwich-B enzyme-linked immunosorbent assay was used to analyze 1,021 blood-fed specimens. Ae. aegypti almost exclusively fed on humans (99%, 658/664) in single host species, and 97% (86/88) of multiple-host bloodmeals included at least one human host. A low frequency of other hosts, including bovine, swine, cat, rat, and chicken were detected, but they represented <1% of bloodmeals. An even higher percentage of human feeding was detected in Ae. albopictus. Hosts of Ae. albopictus collected from sites in southern Thailand were entirely human (100%, n = 105) from both single and mixed meals. In the small number of double-host meals from Ae. albopictus, we detected 3.8% as swine-human and <1% from dog-human and cat-human. Forage ratios for Ae. aegypti indicated that human, dog, and swine were preferred hosts in order of preference. In contrast, bovine and chicken were avoided hosts for this species in Thailand.     

Comparative study on nocturnal behavior of Aedes aegypti and Aedes albopictus

Nocturnal behavior of nonblood-fed females of Aedes aegypti (L.) and Aedes albopictus (Skuse) was studied using an automatic recording device equipped with a photoelectric sensor. Carbon dioxide, heating, and the contrast of the black and white colors were used as attractive cues for mosquitoes. The nocturnal host-seeking activity positively correlated with the increasing light intensity in both species. Ae. aegypti was found to be more sensitive to light than Ae. albopictus. The threshold of light intensity for the activation of the nocturnal host-seeking activity was <0.1 lx (approximately 0.01 foot candle) in Ae. aegypti and >10 lx (approximately 1 foot candle) in Ae. albopictus. Complete darkness during the daytime deactivated the host-seeking activity of both species, irrespective of their increasing flight activity controlled by their intrinsic circadian rhythms. This finding suggested that visual cues are indispensable for host-seeking behavior. The eye parameter value, the product of the ommatidial diameter, and the interommatidial angle were significantly larger in Ae. aegypti than those in Ae. albopictus, indicating that the eye of Ae. aegypti is more adapted to a darker environment.     

Behavioral and electrophysiological responses of Aedes albopictus to certain acids and alcohols present in human skin emanations

Human skin emanations attract hungry female mosquitoes toward their host for blood feeding. In this study, we report the flight orientation and electroantennogram response of Aedes albopictus females to certain unsaturated acids and alcohols found in human skin. In the Y-tube olfactometer, odors of lactic acid and 2-methyl-3-pentanol attracted 54–65 % of Ae. albopictus females at all doses in a dose-dependent manner. However, at the highest dose (10^?2 g), the acids repelled 40–45 % females. Attractancy (ca. 62–68 %) at lower doses and repellency (ca. 30–45 %) at higher doses were recorded for 3-methyl-3-pentanol and 1-octen-3-ol, while 5-hexen-1-ol, cis-2-hexen-1-ol, and trans 2-hexen-1-ol odor repelled ca. 55–65 % of Ae. albopictus females at all doses. Antenna of female Ae. albopictus exhibited a dose-dependent EAG response up to 10^?3 g of l-lactic acid, trans-2-methyl-2-pentenoic acid, 2-octenoic acid, trans-2-hexen-1-ol and 1-octen-3-ol stimulations; however, the highest dose (10^?2 g) caused a little decline in the EAG response. EAG response of 9–10-fold was elicited by lactic acid, 2-octenoic acid, trans-2-hexenoic acid, and 3-methyl-3-pentanol, while cis-2-hexen-1-ol and trans-2-methyl pentenoic acid elicited 1–5-fold responses compared to solvent control. A blend of attractive compounds could be utilized in odor-baited trap for surveillance and repellent molecules with suitable formulation could be used to reduce the biting menace of mosquitoes.     

Molecular and morphological characterization of Aedes albopictus in northwestern Greece and differentiation from Aedes cretinus and Aedes aegypti

The presence of Aedes albopictus (Skuse) was recently confirmed for the first time in northwestern Greece. This location is within the distribution range of a morphologically similar species, Aedes cretinus Edwards, and is a potentially favorable region for the reintroduction of Aedes aegypti (L.). It was thus compelling to use methods in addition to morphology-based keys to correctly identify specimens badly damaged, rubbed, or otherwise altered in their external characteristics. It was decided to use molecular techniques as a novel and reliable method for differentiating the three Stegomyia species. The nuclear internal transcribed spacer 2 (ITS2) fragments from morphologically identified Ae. albopictus and Ae. cretinus specimens were amplified, and their sequences were compared with those in GenBank for Ae. albopictus, Ae. cretinus, and Ae. aegypti. Also, mitochondrial cytochrome oxidase I (COI) fragments were amplified for Ae. albopictus and Ae. cretinus (so far not available in GenBank) and compared with Ae. aegypti fragments. ITS2 and COI sequences generated in our study were deposited in GenBank and could be useful in future studies of mosquitoes by other research workers.     

Laboratory evaluation of the response of Aedes aegypti and Aedes albopictus uninfected and infected with dengue virus to deet

Laboratory studies were conducted to compare the response of Aedes aegypti (L.) and Aedes albopictus (Skuse) adults, uninfected and infected with four serotypes of dengue virus to a repellent containing 5% N, N-diethyl-3-methylbenzamide (deet). The results showed that mosquitoes infected with the four serotypes of dengue responded similarly to uninfected mosquitoes.     

Susceptibility of selected strains of Aedes aegypti and Aedes albopictus (Diptera: Culicidae) to chikungunya virus.

The relative susceptibility of selected strains of Aedes aegypti (L.) and Aedes albopictus (Skuse) fed on a viremic monkey to infection with chikungunya virus was determined. Infection rates were consistently higher in 10 strains of Ae. albopictus tested than in 7 strains of Ae. aegypti tested, regardless of the geographic location from which the strains originated or the dose of virus ingested. Similarly, virus dissemination rates were higher in the Ae. albopictus strains compared with the Ae. aegypti strains. For nearly all (11 of 12) strains tested of both species, groups of mosquitoes with one or more females with a disseminated infection transmitted virus by bite to weanling mice. Based on these studies, Ae. albopictus appears to be a more competent laboratory vector of chikungunya virus than does Ae. aegypti.     

Differential survival of Aedes aegypti and Aedes albopictus (Diptera: Culicidae) larvae exposed to low temperatures in Taiwan

Aedes aegypti (L.) and Aedes albopictus (Skuse) differ in their distribution in Taiwan. The former species is distributed in the south of Taiwan, whereas the latter is found throughout the island. One possible explanation proposes that low temperatures in the winter prevent the expansion of Ae. aegypti. Hence, the impact of low temperatures on immatures of both species was studied in the laboratory and in the field. Our study showed that, under most conditions, Ae. aegypti were more sensitive to low temperatures than Ae. albopictus both in the laboratory and in the field. The survival rates at 10 degrees C for the first and fourth instars of Ae. albopictus were significantly better than those of Ae. aegypti. At 2.5 and 5.0 degrees C, the first instars of Ae. albopictus survived better than the same stadium of Ae. aegypti, but the fourth instars of Ae. aegypti survived better. Short exposures to low temperatures did not affect the acclimatization of Ae. aegypti immatures but longer exposures did increase the physiological adaptation to low temperatures. For Ae. albopictus, exposure to low temperatures increases the acclimatization of this species. In field experiments, Ae. aegypti larvae had a significantly higher mortality than Ae. albopictus during exposures to cold fronts in the 2004 winter. We conclude that low temperatures in northern and central Taiwan have a negative impact on the distribution of Ae. aegypti, but this factor alone is not sufficient to prevent this species from occupying the rest of Taiwan.     

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.     

Comparative laboratory study on the reaction of Aedes aegypti and Aedes albopictus to different attractive cues in a mosquito trap

The behavioral responses of Aedes aegypti (L.) and Aedes albopictus (Skuse) adults to several attractive cues, as reactions to mosquito traps, are compared in the laboratory, and differences in the primary attractive factors for both species are discussed. Target-attacking frequency of unfed Ae. aegypti females was >30 times that of unfed Ae. albopictus females under simulated conditions. Changes in the percentage of trapped mosquitoes under several attractive conditions using commercial mosquito traps showed that Ae. aegypti mosquitoes were trapped 2-3 times faster than Ae. albopictus. For Ae. aegypti, the combination of a visual cue + CO, alone enhanced attractiveness, whereas both a visual cue + CO, as well as a visual cue + octenol enhanced Ae. albopictus. The combination of at least three factors, such as a visual cue, CO2, and a chemical cue is thought to be valuable for trapping and estimating the relative adult population sizes of Ae. aegypti and Ae. albopictus     

A simple parafilm M-based method for blood-feeding Aedes aegypti and Aedes albopictus (Diptera: Culicidae)

A simple device for blood-feeding Aedes (Stegomyia) mosquitoes is described. Parafilm M is stretched and pressed into fiberglass window screen to form a packet for holding warmed blood. The method has been used successfully to maintain Aedes albopictus colonies for >2 yr. In typical blood-feeding trials, 53 +/- 0.8% (+/-SE) of Aedes aegypti (Linnaeus) and 31 +/- 6% of Ae. albopictus (Skuse) fed to repletion.     

Invertebrate carcasses as a resource for competing Aedes albopictus and Aedes aegypti (Diptera: Culicidae)

Terrestrial invertebrate carcasses are an important resource for insects developing in pitcher plants. However, little is known of the role of these carcasses in other containers, which also receive leaf fall and stemflow inputs. This experiment investigated effects of accumulated invertebrate carcasses as a resource for two competing mosquitoes, Aedes albopictus (Skuse) and Aedes aegypti (L.), whether either species differentially benefited from accumulated carcasses, and if such a benefit affected interspecific competition. First, we measured accumulation of invertebrate carcasses in standard containers at a field site. We then used a replacement series with five different species ratios at the same total density, and varied the input of invertebrate carcasses [dead Drosophila melanogaster (Meigen) ] in three levels: none, the average input from our field site, or the maximum input recorded at our field site. Survivorship, development time, and mass were measured for each mosquito species as correlates of population growth, and were used to calculate a population performance index, lambda'. There were strong positive effects of invertebrate carcass additions on all growth correlates and lambda'. Differences in performance between species were pronounced in small or no carcass additions and absent in large inputs of invertebrate carcasses, but there was little evidence that inputs of invertebrate carcasses altered the competitive advantage in this system. These results suggest that terrestrial invertebrate carcasses may be an important resource for many types of container communities, and large accumulations of dead invertebrates may reduce resource competition between these mosquitoes, thus favoring coexistence. We propose that the total amount of resource, including accumulated invertebrate carcasses, may explain observed patterns of replacement involving these mosquitoes.     

Convergent habitat segregation of Aedes aegypti and Aedes albopictus (Diptera: Culicidae) in southeastern Brazil and Florida

During the rainy season of 2001, the incidence of the dengue vectors Aedes aegypti and Ae. albopictus was examined in different habitats of two cities (Rio de Janeiro and Nova Igua?u) in Rio de Janeiro State, Brazil, and in two cities (Palm Beach and Boca Raton) in Florida. Oviposition trap collections were performed in urban, suburban, and rural habitats in both areas. Our hypothesis that the abundances and frequencies of occurrence of Ae. aegypti and Ae albopictus are affected in opposite ways by increasing urbanization was only partially supported. City, habitat, and their interaction significantly affected the abundance of both species. Cities with high abundance of Ae. aegypti also had a high abundance of Ae. albopictus. The two species were most abundant in the cities of Rio de Janeiro state and the lowest in Boca Raton. Habitat had a significant but opposite effect on the abundances of Ae. aegypti and Ae. albopictus. In general, Ae. aegypti was most prevalent in highly urbanized areas and Ae. albopictus in rural, suburban, and vegetated urban areas in Rio de Janeiro state and Florida. However, abundances of the two species were similar in most suburban areas. Analyses of frequencies of occurrence showed an unexpected high level of co-occurrence of both species in the same oviposition trap. Despite the different geographical origins of Ae. albopictus in Brazil and the United States, the habitats used by this recent invader are remarkably similar in the two countries.     

Laboratory study of competition between United States strains of Aedes albopictus and Aedes aegypti (Diptera: Culicidae)

Mosquito abatement workers in Houston, Tex., and New Orleans, La., have observed that the recent introduction of Aedes albopictus (Skuse) has been accompanied by a decline and virtual disappearance of Ae. aegypti (L.). This suggests competitive displacement but contradicts the direction of displacement observed in native habitats of Ae. albopictus. The paper reports a series of laboratory studies on competition between U.S. strains of the two species. Larval survivorship, size, and development time were monitored in increasing densities of pure and mixed cultures of the two species under limited and optimal diets. Oviposition preferences were examined by offering gravid females cups containing first or fourth instars of either species. Ethological isolation was studied by simultaneously offering virgin females of one species to males of both species and monitoring courtship behavior as well as rates of oviposition, percentage of hatch, and embryonation. The results of the larval competition studies suggest that interspecific competition increased development time only slightly and had no effect on survival of Ae. albopictus. Competition increased survival in Ae. aegypti. Size of both species was influenced by interspecific competition, but the magnitude and direction of the effect was inconsistent between strains and diets such that neither species emerged consistently larger. The results of the oviposition study indicated a higher fecundity in Ae. aegypti but otherwise demonstrated that both species oviposit without regard to the presence, age, or species of larvae in the oviposition container. The ethological isolation tests demonstrated that Ae. aegypti males were more sexually aggressive than males or Ae. albopictus. However, Ae. albopitus females placed with increasing densities of Ae. aegypti males demonstrated no decrease in rates of oviposition, and eggs laid showed equal rates of hatch and embryonation. In general, the results do not suggest that the U.S Ae. albopictus population is inherently more competitive in the laboratory than Ae. aegypti. Other reasons for the observed decline in Ae. aegypti in the United States are discussed.     

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.     

Wing shape as an indicator of larval rearing conditions for Aedes albopictus and Aedes aegypti (Diptera: Culicidae)

Estimating a mosquito's vector competence, or likelihood of transmitting disease, if it takes an infectious bloodmeal, is an important aspect of predicting when and where outbreaks of infectious diseases will occur. Vector competence can be affected by rearing temperature and inter- and intraspecific competition experienced by the individual mosquito during its larval development. This research investigates whether a new morphological indicator of larval rearing conditions, wing shape, can be used to distinguish reliably temperature and competitive conditions experienced during larval stages. Aedes albopictus (Skuse) and Aedes aegypti (L.) (Diptera: Culicidae) larvae were reared in low intraspecific, high intraspecific, or high interspecific competition treatments at either 22 or 32 degrees C. The right wing of each dried female was removed and photographed. Nineteen landmarks and 20 semilandmarks were digitized on each wing. Shape variables were calculated using geometric morphometric software. Canonical variate analysis, randomization multivariate analysis of variance, and visualization of landmark movement using deformation grids provided evidence that although semilandmark position was significantly affected by larval competition and temperature for both species, the differences in position did not translate into differences in wing shape, as shown in deformation grids. Two classification procedures yielded success rates of 26 - 49%. Accounting for wing size produced no increase in classification success. There seemed to be a significant relationship between shape and size. These results, particularly the low success rate of classification based on wing shape, show that shape is unlikely to be a reliable indicator of larval rearing competition and temperature conditions for Ae. albopictus and Ae. aegypti.