Observations on the seasonal prevalence and vertical distribution patterns of oviposition by Aedes aegypti (L.) (Diptera: Culicidae) in urban high-rise apartments in Trinidad, West Indies.

The seasonal prevalence and vertical distribution of oviposition of Aedes aegypti were studied for 53 wk in 1999--2000 using modified ovitraps located at several elevations. The ovitraps were positioned both indoors and outdoors in high-rise apartments in the urban township of John John, Port of Spain, Trinidad, West Indies. Of 988 ovitraps, 490 were collected during the months of the wet season, with 404 (84.4%) positive with 18,536 Ae. aegypti eggs. Of 498 ovitraps collected during the dry season, 335 (67.3%) were positive with 12,255 Ae. aegypti eggs. Data from different elevations showed that significantly more eggs were collected at 13-24 m elevations than any other elevation. The results suggest that the invasion of high rise ecosystems by Ae. aegypti can enhance transmission of dengue. This ecological shift in the Ae. aegypti population exploited new habitats associated with human activity, suggesting that strategies should be developed to educate householders as well as creating appropriate vector control measures to prevent future threats of dengue transmission.     

Effects of forced egg-retention in Aedes albopictus on adult survival and reproduction following application of DEET as an oviposition deterrent.

The insect repellent DEET (0.1% concentration), used as a mosquito oviposition deterrent in the laboratory, influenced the retention and maintenance of mature eggs by caged gravid female Aedes albopictus Skuse. This egg-retention mechanism could benefit survival because the gravid females were ultimately able to lay maintained eggs upon availability of water, but the length of forced egg-retention time reduced the number of eggs laid per female. Gravid females with retained eggs also laid a higher percentage of eggs that failed to tan, and this percentage increased with time duration of egg-retention. Percent egg hatch was not significantly affected by DEET when used as an oviposition deterrent; however, percent hatch was affected by time duration of egg-retention in both treated (exposed to DEET) and untreated (control) gravid females. The rate of egg hatch was considerably reduced after three weeks of retention; this reduction declined to zero for treated and control females at six and four weeks post-treatment, respectively. The fecundity and fertility of gravid female Ae. albopictus were affected by the time duration of forced egg-retention.     

Larvicide and oviposition deterrent effects of fruit and leaf extracts from Melia azedarach L. on Aedes aegypti (L.) (Diptera: Culicidae)

Aedes aegypti (L.) (Diptera: Culicidae), the main urban vector of dengue, has developed resistance to various insecticides, making its control increasingly difficult. We explored the effects of Argentine Melia azedarach L. (Meliaceae) fruit and senescent leaf extracts on Ae. aegypti larval development and survival, by rearing cohorts of first instar mosquitoes in water with different extract concentrations. We also analysed oviposition deterrent activity in choice tests with extract-treated ovitraps. The leaf extract showed a strong larvicide activity, with all larvae dying before pupation, and significantly delayed development time. It strongly inhibited oviposition by Ae. aegypti females. The fruit extract showed much weaker effects. This first report of highly effective larvicidal, growth regulating and oviposition deterrent activity of a senescent leaf extract of M. azedarach against Ae. aegypti, suggests that such extract could represent a promising tool in the management of this mosquito pest.     

Field evaluation of the response of Aedes albopictus (Stegomyia albopicta) to three oviposition attractants and different ovitrap placements using black and clear autocidal ovitraps in a rural area of Same,Timor‐Leste

Known oviposition attractants or stimulants were compared, singly and in combination, using inexpensive autocidal ovitraps designed to trap emerging adults, in a rural area of Timor‐Leste during the dry season. In this area, the dengue vector Aedes albopictus (Stegomyia albopicta) Skuse (Diptera: Culicidae) was abundant, but Aedes aegypti (Stegomyia aegypti) L. was not detected. The attractants were: (a) a compound found in Aedes eggs (dodecanoic acid); (b) components of nitrogen, phosphorous and potassium‐based (NPK) fertilizer, and (c) infusions of discarded cigarette butts. A solution of ammonium phosphate and potassium nitrate was significantly more attractive to gravid Ae. albopictus than water only. Dodecanoic acid and cigarette butt infusions were not significantly more attractive than the control; however, they attracted various other Diptera and many non‐culicid larvae developed in ovitraps in which these substances were used; thus, the presence of eggs or larvae of other species may have deterred Aedes oviposition. Significantly more Aedes eggs were found in ovitraps under vegetation than in ovitraps placed inside houses or against external walls. Clear‐sided ovitraps in which black mesh was placed over a black ring floating on the water surface collected significantly fewer eggs than black ovitraps with identically placed mesh and rings.     

Studies of Aedes aegypti (Diptera: Culicidae) ovipositional responses to newly identified semiochemicals from conspecific eggs

Abstract  The chemical factors influencing the selection of oviposition site by gravid females of various mosquito species have been the subject of numerous investigations. Recent studies have revealed this behaviour to be controlled by semiochemicals. Here we report studies on semiochemicals of egg origin and their effect on the ovipositional behaviour of Aedes aegypti. The compounds present in egg extracts of Ae. aegypti mosquitoes were isolated and identified by gas chromatography-mass spectrometry. They were then evaluated for their effect on ovipositional behaviour against gravid females of Ae. aegypti mosquitoes at different concentrations. Gravid female Ae. aegypti were found to be sensitive to all the identified compounds: 6-hexanolactone, methyl dodecanoate, dodecanoic acid, methyl tetradecanoate, tetradecanoic acid, methyl (Z)-9-hexadecenoate, methyl hexadecanoate (Z)-9-hexadecenoic acid, hexadecanoic acid, methyl (Z)-9-octadecenoate, methyl octadecanoate (Z)-9-octadecenoic acid and octadecanoic acid. Among them, dodecanoic and (Z)-9-hexadecenoic acids showed significant positive ovipositional response at different concentrations whereas all the esters showed deterrent/repellent ovipositional effect.     

Evaluation of attractants and egg-laying substrate preference for oviposition by Aedes albopictus (Diptera: Culicidae).

Evaluation of oviposition attractants and substrate preferences of Aedes albopictus was carried out under laboratory and field conditions. To obtain candidate oviposition substances we used a water rinse of 3 mollusk species: blood cockle (Anadara granosa), carpet shell (Paphia undulata), and sea mussel (Mytilus smaragdinus), and the giant tiger prawn (Penaeus monodon). The rinse water of carpet shell and giant tiger prawn showed higher attractiveness for ovipostion than the other candidate attractants. The filter paper substrate received fewer eggs than the other two substrates. There was no significant difference between the mean number of eggs laid on hardboard paddles and sponge sheets. The hatching rate of Ae. albopictus eggs laid on hardboard paddles was higher than those from the filter papers and sponge sheets. The sponge had lethal effects on Ae. albopictus eggs, and very few eggs laid on sponge hatched. In field experiments, evaluation of attractiveness of carpet shell rinse in ovitraps lined with sponge sheet as egg-laying substrate was carried out in various habitats and different areas of Thailand. The mean number of eggs in traps containing carpet shell rinse was significantly higher than those laid in rainwater traps. These studies reveal that the carpet shell and giant tiger prawn rinses are sources of oviposition attractant for Ae. albopictus under both laboratory and field conditions and could possibly be used as an attractant in surveillance and control.     

Mosquito traps designed to capture Aedes aegypti (Diptera: Culicidae) females: preliminary comparison of Adultrap, MosquiTRAP and backpack aspirator efficiency in a dengue-endemic area of Brazil

In this report, the efficiency of Adultrap under field conditions is compared to a CDC backpack aspirator and to MosquiTRAP. An urban dengue-endemic area of Rio de Janeiro was selected to evaluate the efficiency of mosquito traps in capturing Aedes aegypti females. Adultrap and aspirator captured similar numbers of Ae. aegypti females, with the former showing high specificity to gravid individuals (93.6%). A subsequent mark-release-recapture experiment was conducted to evaluate Adultrap and MosquiTRAP efficiency concomitantly. With a 6.34% recapture rate, MosquiTRAP captured a higher mean number of female Ae. aegypti per trap than Adultrap (chi2 = 14.26; df = 1; p < 0,05). However, some MosquiTRAPs (28.12%) contained immature Ae. aegypti after 18 days of exposure in the field and could be pointed as an oviposition site for female mosquitoes. Both trapping methods, designed to collect gravid Ae. aegypti females, seem to be efficient, reliable and may aid routine Ae. aegypti surveillance.     

Oviposition activity and seasonal pattern of a population of Aedes (Stegomyia) aegypti (L.) (Diptera: Culicidae) in subtropical Argentina

Monthly oviposition activity and the seasonal density pattern of Aedes aegypti were studied using larvitraps and ovitraps during a research carried out by the Public Health Ministry of Salta Province, in Tartagal, Aguaray and Salvador Mazza cities, in subtropical Argentina. The A. aegypti population was active in both dry and wet seasons with a peak in March, accordant with the heaviest rainfall. From May to November, the immature population level remained low, but increased in December. Ae. aegypti oviposition activity increased during the fall and summer, when the relative humidity was 60% or higher. Eggs were found in large numbers of ovitraps during all seasons but few eggs were observed in each one during winter. The occurrence and the number of eggs laid were variable when both seasons and cities were compared. The reduction of the population during the winter months was related to the low in the relative humidity of the atmosphere. Significant differences were detected between oviposition occurrences in Tartagal and Aguaray and Salvador Mazza cities, but no differences in the number of eggs were observed. Two factors characterize the seasonal distribution pattern of Ae. aegypti in subtropical Argentina, the absence of a break during winter and an oviposition activity concomitant of the high relative humidity of the atmosphere.     

Better eggs today than psocids tomorrow: Aedes aegypti (Diptera: Culicidae) eggs exposed to Liposcelis sp. (Psocodea: Liposcelididae) has reduced hatching rates

For different research purposes, there is a need to mass rear mosquitoes, such as Aedes aegypti, under laboratory conditions. The rearing process begins with egg production followed by egg storage in a dry environment, inside containers. Stored eggs are susceptible to environmental threats when storage conditions are suboptimal. Some terrestrial insects can invade this environment and attack stored eggs. In this brief report, we assessed whether Ae. aegypti eggs exposed to Liposcelis sp. individuals had reduced hatching and immature development rates. We exposed 100 eggs in different treatment conditions (fixed in porous paper and loosed) to 30 Liposcelis sp. individuals for ten days and then we induced hatching. We observed a hatching rate of 99% reduced for those eggs adhered to porous paper and loosed eggs showed a hatching rate of 45% decreased for those eggs exposed to Liposcelis sp. The remaining larvae took longer to develop into pupae as well, showing a four-day delay on average to the final metamorphosis of the aquatic stage. These results reinforce the need to frequently monitor egg storage conditions to maintain laboratory colonies stable and free from pests that can interfere with mosquito life-history traits.     

Larvicidal and smoke repellency effect of Toddalia asiatica and Aegle marmelos against the dengue vector, Aedes aegypti (Insecta: Diptera: Culicidae)

Investigations were made to evaluate the larvicidal activity and smoke repellent potential of Toddalia asiatica (L.) and Aegle marmelos at different concentrations (20, 40, 60, 80 and 100 p.p.m.) against first to fourth instar larvae and pupae of Aedes aegypti (L.). The LC₅₀ of A. marmelos and T. asiatica against first instars was 50.960 and 47.893 p.p.m., respectively; against second instars, 52.979 and 50.922; third instars, 56.653 and 54.461; and fourth instars, 60.778 and 61.278. The LC₅₀ and LC₉₀ for A. marmelos and T. asiatica against pupae were 56.634 and 112.992, and 53.64 and 116.22 p.p.m., respectively. The smoke toxicity of T. asiatica against Ae. aegypti was greater than that of A. marmelos . Smoke-exposed gravid females oviposited fewer eggs when compared to those that were not exposed to smoke. Smoke-exposed females hatched a lower percentage of eggs compared to unexposed females.     

Laboratory experiments on factors affecting oviposition site selection in Toxorhynchites amboinensis (Diptera: Culicidae), with a report on the occurrence of egg cannibalism

Laboratory experiments tested the effects of water quality and the presence of conspecific and heterospecific immatures on oviposition by Toxorhynchites amboinensis (Doleschall). The females showed a highly significant preference for oak leaf infusion water over distilled water. When twenty starved third and fourth instar Tx.amboinensis larvae were present in the water, substantially fewer eggs were counted from pots containing these conspecifics, than from controls in which no larvae were present. Numbers of eggs from pots containing starved second instar larvae did not differ significantly from controls. Observations of larval behaviour while oviposition was occurring suggested that egg numbers were reduced in containers because of egg cannibalism with third and fourth instar larvae, and not because the larvae caused a deterrent effect. Subsequent experiments confirming the occurrence of substantial egg cannibalism by third and especially fourth instar larvae are described. As with larvae, the presence of Tx.amboinensis pupae in the water had little effect on oviposition. If placed in the water 24 h prior to test, pupae very slightly enhanced its attractiveness, but if introduced immediately before test there appeared to be a slight deterrent effect. With heterospecific larvae, twenty fourth instar Ae.aegypti larvae introduced into infusion water 24 h before test rendered the water slightly attractive, while water in which Ae.aegypti larvae had been reared for 48 h proved highly repellent.     

Dispersal of Aedes aegypti and Aedes albopictus (Diptera: Culicidae) in an urban endemic dengue area in the State of Rio de Janeiro,Brazil

Experimental releases of female Aedes (Stegomyia) aegypti and Aedes (Stegomyia) albopictus were performed in August and September 1999, in an urban area of Nova Igua u, State of Rio de Janeiro, Brazil, to estimate their flight range in a circular area of 1,600 m where 1,472 ovitraps were set. Releases of 3,055 Ae. aegypti and 2,225 Ae. albopictus females, fed with rubidium (Rb)-marked blood and surgically prevented from subsequent blood-feeding, were separated by 11 days. Rb was detected in ovitrap-collected eggs by atomic emission spectrophotometry. Rb-marked eggs of both species were detected up to 800 m from the release point. Eggs of Ae. albopictus were more numerous and more heterogeneously distributed in the area than those of Ae. aegypti. Eggs positively marked for Rb were found at all borders of the study area, suggesting that egg laying also occurred beyond these limits. Results from this study suggest that females can fly at least 800 m in 6 days and, if infected, potentially spread virus rapidly.     

Horizontal and vertical dispersal of dengue vector mosquitoes, Aedes aegypti and Aedes albopictus, in Singapore

To study the dispersal of dengue vector mosquitoes in Singapore, females of Aedes aegypti (L.) and Aedes albopictus (Skuse) (Diptera: Culicidae) were fed blood containing rubidium (Rb), which was detectable in their eggs by means of Graphite Furnace Atomic Absorption Spectrophotometry (GFAAS). Laboratory calibration of the Rb reading, for a range of egg numbers from Rb-fed females, indicated a reasonably linear relationship and an unequivocal distinction between results with zero and one marked egg. Rb-marked female Aedes mosquitoes aged 3-5 days were released in semi-rural and urbanized parts of Singapore, with an array of ovitraps extending to a radius of 320 m from the release point. Subsequently, Rb-marked Aedes eggs were detected throughout the array, with similar distributions on each of the 4 days after release. More Rb was detected nearer the release point. However, when correction was made for the greater areas of zones further from the release point (and therefore presumably existence of more alternative oviposition sites), there were no significant differences in the numbers of marked eggs per ovitrap in the zones nearer or further from the release points. It is concluded that females of both these Aedes (Stegomyia) species could disperse easily and quickly throughout areas of radius 320 m in search of oviposition sites. This contrasts with the general belief that Ae. aegypti seldom flies more than 50 m and that control operations can safely be based on such an assumption. Releases on level 12 of a 21-storey apartment block, with ovitraps on each storey, showed similar easy and rapid dispersal to the top and bottom of the block.     

The potential attractant or repellent effects of different water types on oviposition in Aedes aegypti L. (Dipt., Culicidae)

Abstract:  The selection of oviposition sites by the yellow-fever mosquito, Aedes aegypti , was studied in the laboratory. The repellent or attractant effects of salinity and the presence of bacteria in water collected from a local community on the Brazilian coast were investigated. Water contaminated with bacteria (waste water and lagoon water) elicited significantly more oviposition than distilled water. Oviposition decreased with an increase in salinity, with almost no oviposition above 12%. The salinity tolerance of A. aegypti larvae was investigated by measuring their mortality in response to salt concentrations ranging from 10 to 15%. The LD₅₀ of salt for A. aegypti larvae was around 13%.     

Laboratory evaluation of Mesocyclops annulatus (Wierzejski, 1892) (Copepoda: Cyclopidea) as a predator of container-breeding mosquitoes in Argentina

In laboratory bioassays we tested the predatory capacity of the copepod Mesocyclops annulatus on Aedes aegypti and Culex pipiens larvae. A single adult female of M. annulatus caused 51.6% and 52.3% mortality of 50 first instar larvae of Ae. aegypti and Cx. pipiens respectively, in a 72 h test period. When alternative food was added to the containers, mortality rates declined to 16% and 10.3% for Ae. aegypti and Cx. pipiens respectively. When 50 first instar larvae of each of the two mosquito species tested were placed together with a single adult female of M. annulatus, mortality rates were 75.5% for Ae. aegypti larvae and 23.5% for Cx. pipiens larvae in a three day test period. Different density of adult females of M. annulatus ranged from 5 to 25 females produced mortality rates of Ae. aegypti first instar larvae from 50% to 100% respectively. When a single adult female of M. annulatus was exposed to an increasing number of first-instar Ae. aegypti larvae ranging from 10 to 100, 100% mortality was recorded from 1 to 25 larvae, then mortality declined to 30% with 100 larvae. The average larvae killed per 24 h period by a single copepod were 29.     

The influence of larval density, food stress, and parasitism on the bionomics of the dengue vector Aedes aegypti (Diptera: Culicidae): implications for integrated vector management

New larval control strategies for integrated vector management of Aedes aegypti are in high demand, including the use of biological control agents. Exposure of Aedes aegypti to parasites, starvation, and overcrowded conditions during larval development reduces the probability of survival to eclosion, can directly affect fitness parameters such as adult size and fecundity, and can affect the size, provisioning, and viability of eggs produced by females. We compared these parameters after exposing larvae to 1) abundant food at low larval densities, 2) food deprivation and high larval density, and 2) infection with the endoparasite Plagiorchis elegans, an entomopathogenic digenean trematode. Female mosquitoes that eclosed from larval conditions of starvation and overcrowding were smaller and laid fewer and smaller eggs than controls. The proportion of females to complete an oviposition cycle was reduced in the P. elegans-infected treatment group. Parasite load was negatively correlated with wing length and egg size. Infection of Ae. aegypti with P. elegans has sublethal effects and may reduce population-level reproductive output, but one-time low-density P. elegans exposure does not have sufficient effect on Ae. aegypti fitness parameters to be considered a viable biocontrol option.     

Influence of shading and pedestrian traffic on the preference of Aedes (Stegomyia) aegypti (Diptera: Culicidae) for oviposition microenvironments

Aedes aegypti mosquitoes are highly adaptable to abiotic stimuli. To evaluate the influence of shading and pedestrian traffic on the preference of Ae. aegypti for oviposition microenvironments, 20 sites were sampled weekly using ovitraps within the perimeter of Universidade Federal do Espírito Santo, located in São Mateus, Espírito Santo, Brazil. A spatial and statistical analysis was performed in order to assess the relationship between shading time, pedestrian traffic, and the presence of biological forms of Ae. aegypti. A temporal analysis of temperature and precipitation influence on oviposition was also made. Between June, 2013 and June, 2014, 7,362 Ae. aegypti eggs were collected. Over a 12‐month period, we made weekly collections of Ae. aegypti eggs from ovitraps. Pedestrian traffic and shading time influenced the number of positive ovitraps; precipitation and temperature were correlated with the number of positive ovitraps (p <0.05). We conclude that the influence of temperature and precipitation was not significant for the oviposition index, and the frequency of oviposition was directly proportional to the number of individuals moving close to the traps during periods of greater shading.     

Laboratory and field evaluation of insect repellents as oviposition deterrents against the mosquito Aedes albopictus

Three experimental approaches were used to evaluate the oviposition deterrency of three insect repellents, AI3-35765, AI3-37220 (piperidine compounds), and the standard N,N-diethyl-3-methylbenzamide (deet) to the mosquito Aedes albopictus Skuse (Diptera: Culicidae). Against laboratory-reared Ae. albopictus gravid females, the EC50 values of AI3-37220, AI3-35765 and deet were 0.004%, 0.008% and 0.011% in laboratory cages and 0.004%, 0.01% and 0.009% in an outdoor screened cage. For a natural population of Ae. albopictus tested in the field, the EC50 values were determined as 0.004%, 0.008% and 0.001%, respectively. Ageing concentrations of 0.1% of each repellent provided >50% effective oviposition deterrency against the laboratory population of Ae. albopictus for 13 days in laboratory cages, for 15 days in the outdoor cage, and for 21 days against field population of Ae. albopictus in Florida. These topical skin repellents are effective oviposition deterrents for Ae. albopictus when employed at relatively low application rates.     

Laboratory evaluation of Toxorhynchites splendens (Diptera: Culicidae) for predation of Aedes albopictus mosquito larvae

Biology of the mosquito Toxorhynchites splendens (Wiedemann) was studied in the laboratory to provide baseline data for using the predatory larvae of this species against those of Aedes albopictus (Skuse) in a biological control programme. The mean incubation time of Tx.splendens eggs was 43.8 h and the time required for newly-hatched larvae to initiate predation was 2.5 h. Mean numbers of prey larvae consumed and killed by each Tx.splendens larva totalled 389 and 345 respectively. The larval period of Tx.splendens was not significantly different for rearing individually or in groups of nine, with equal prey density, and duration of larval development was proportional to prey density. In mass rearing, larval cannibalism was usually observed during days 1-3 post-eclosion. The incidence of cannibalism decreased sharply on the fourth day after hatching when some larvae became fourth-instar. Adult female Tx.splendens usually commenced oviposition on day 4 after emergence. The number of eggs laid daily increased on day 7 and the peak oviposition of 6.3 eggs/female/day occurred on day 11. When oviposition containers were provided only intermittently, gravid females of Tx.splendens scattered most of their eggs on the dry floor of the cage. Viability of eggs laid by females aged 4-14 days was high (60-90%) but decreased to less than 40% as the females aged.     

Polarotaxis in egg-laying yellow fever mosquitoes Aedes (Stegomyia) aegypti is masked due to infochemicals

Aquatic and water-associated insects need to locate suitable bodies of water to lay their eggs in and allow their aquatic larvae to develop. More than 300 species are known to solve this task by positive polarotaxis, relying primarily on the horizontally polarized light reflected from the water surface. The yellow fever mosquito Aedes (Stegomyia) aegypti has been thought to be an exception, locating its breeding habitats by chemical cues like odour of conspecifics, their eggs, or water vapour. We now demonstrate through dual-choice experiments that horizontally polarized light can also attract ovipositing Ae. aegypti females when the latter are deprived of chemical cues: water-filled transparent egg-trays illuminated by horizontally polarized light from below gained a 94.2% higher total number of eggs than trays exposed to unpolarized light, but only when no chemical substances capable of functioning as cues were present. Ae. aegypti is the first known water-associated insect in which polarotaxis exists, but does not play a dominant role in locating water bodies and can be constrained in the presence of chemical cues.