Semi-field life-table studies of Aedes albopictus (Diptera: Culicidae) in Guangzhou, China.
ABSTRACT: BACKGROUND:Aedes albopictus is a major vector for several tropical infectious diseases. Characterization of Ae. albopictus development under natural conditions is crucial for monitoring vector population expansion, dengue virus transmission, and disease outbreak preparedness. METHODS:This study employed mosquito traits as a proxy to understanding life-table traits in mosquitoes using a semi-field study. Ae. albopictus larval and adult life-table experiments were conducted using microcosms under semi-field conditions in Guangzhou. Stage-specific development times and survivorship rates were determined and compared under semi-field conditions in different seasons from early summer (June) to winter (January), to determine the lower temperature limit for larval development and adult survivorship and reproductivity. RESULTS:The average egg- hatching rate was 60.1%, with the highest recorded in October (77.1%; mid-autumn). The larval development time was on average 13.2 days (range, 8.5-24.1 days), with the shortest time observed in September(8.7 days; early autumn) and longest in November (22.8 days). The pupation rates of Ae. albopictus larvae were on average 88.9% (range, 81.6-93.4%); they were stable from June to September but decreased from October to November. The adult emergence rates were on average 82.5% (range, 76.8-87.9%) and decreased from July to November. The median survival time of Ae. albopictus adults was on average 7.4 (range, 4.5-9.8), with the shortest time recorded in September. The average lifetime egg mass under semi-field conditions was 37.84 eggs/female. The larvae could develop into adults at temperatures as low as 12.3°C, and the adults could survive for 30.0 days at 16.3°C and still produce eggs. Overall, correlation analysis found that mean temperature and relative humidity were variables significantly affecting larval development and adult survivorship. CONCLUSION:Ae. albopictus larvae could develop and emerge and the adults could survive and produce eggs in early winter in Guangzhou. The major impact of changes in ambient temperature, relative humidity, and light intensity was on the egg hatching rates, adult survival time, and egg mass production, rather than on pupation or adult emergence rates.
Project description:Within 2 yr of the arrival of the invasive container mosquito Aedes albopictus (Skuse), the previously dominant invasive mosquito Aedes aegypti (L.) disappeared from many Florida cemeteries. At some cemeteries, however, Ae. aegypti populations seem stable despite Ae. albopictus invasion. We sought to understand this variation in the outcome (exclusion, coexistence) of this invasion, given that previous experiments show that Ae. albopictus is the superior larval competitor. We tested experimentally the hypothesis that climate-dependent egg survivorship differs between exclusion and coexistence cemeteries and that differences in invasion outcome are associated with microclimate. Viability of eggs oviposited in the laboratory and suspended in vases at six cemeteries was significantly greater for Ae. aegypti than for Ae. albopictus, and greater in 2001 than in 2006. Cemeteries differed significantly in egg survivorship of Ae. albopictus, but not of Ae. aegypti, which is consistent with the hypothesis that Ae. albopictus suffers site-specific, climate-driven egg mortality that mitigates the competitive superiority of larval Ae. albopictus. Principal component (PC) analysis of microclimate records from vases during the experiments yielded three PCs accounting for >96% of the variance in both years of experiments. Multivariate analysis of variance of the three PCs revealed significant microclimate differences among the six cemeteries and between exclusion versus coexistence cemeteries. Stepwise logistic regression of egg survivorship versus microclimate PCs yielded significant fits for both species, and twice as much variance explained for Ae. albopictus as for Ae. aegypti in both years. Higher mortalities in 2006 were associated with high average daily maximum temperatures in vases, with lethal thresholds for both species at ?40°C. From 1990 to 2007, vase occupancy by Ae. albopictus increased and that by Ae. aegypti decreased, with increasing seasonal precipitation at one well-sampled cemetery. Results support the hypothesis that locally variable climate-driven mortality of Ae. albopictus eggs contributes to patterns of exclusion of, or coexistence with, Ae. aegypti.
Project description:In this article, data on the demographic parameters of the Aedes albopictus were collected from those areas in Shah Alam, Malaysia that had experienced a dengue outbreak. The surveys were conducted from March to December 2017. The eggs of the Ae. albopictus were collected using ovitraps, and were analysed based on the demographic parameters in a controlled environment in an insectarium. The data were comprised of four types of biological information on the life demographic parameters of the Ae. albopictus that were monitored based on specific localities. The data were inferred information regarding egg productivity (n), egg development (%), immature development (days), and survivorship (days).
Project description:Previous studies have shown that the negative effects of density of Ae. albopictus on Ae. aegypti exceed those of Ae. aegypti on Ae. albopictus for population growth, adult size, survivorship, and developmental rate. This competitive superiority has been invoked to explain the displacement of Ae. aegypti by Ae. albopictus in the southeastern USA. In Brazil, these species coexist in many vegetated suburban and rural areas. We investigated a related, but less-well-studied question: do effects of Ae. albopictus on Ae. aegypti larval development and survival occur under field conditions at realistic densities across multiple seasons in Brazil? We conducted additive competition experiments in a vegetated area of Rio de Janeiro where these species coexist. We tested the hypothesis that Ae. aegypti (the focal species, at a fixed density) suffers negative effects on development and survivorship across a gradient of increasing densities of Ae. albopictus (the associate species) in three seasons. The results showed statistically significant effects of both season and larval density on Ae. aegypti survivorship, and significant effects of season on development rate, with no significant season-density interactions. Densities of Aedes larvae in these habitats differed among seasons by a factor of up to 7x. Overall, Spring was the most favorable season for Ae. aegypti survivorship and development. Results showed that under natural conditions the negative competitive effects of Ae. albopictus on Ae. aegypti were expressed primarily as lower survivorship. Coexistence between Ae. aegypti and Ae. albopictus in vegetated areas is likely affected by seasonal environmental differences, such as detrital resource levels or egg desiccation, which can influence competition between these species. Interactions between these Aedes are important in Brazil, where both species are well established and widely distributed and vector dengue, Zika and chikungunya viruses.
Project description:<h4>Objectives</h4>Larval indices have been used for Ae. albopictus surveillance for many years, while there is limited use in assessing dengue transmission risk and adult mosquito emergence. This study is aimed to explore the relationships between larval indices and the Ae. albopictus density captured by BG-mosquito trap (BG-trap) method, with considering the meteorological factors.<h4>Methods</h4>Data on larval density, adult mosquito density and meteorology factors were collected in an entomological survey carried out in Quzhou City, Zhejiang Province of China in 2018. The Spearman's rank correlation and Pearson correlation were used for the analysis on the correlation of density indices. Generalized additive models were established to analyze the influencing factors of mosquito density.<h4>Results</h4>Breteau index (BI), House index (HI) and Container index (CI) were highly correlated with each other (r>0.7, p<0.05). The Ae. albopictus density was significantly correlated with CI (rs = 0.260, p<0.05), CI pre one week (rs = 0.259, p<0.05), and CI pre three weeks (rs = 0.329, p<0.05). BI was correlated with female Ae. albopictus density pre 4 weeks (r = -0.299, p<0.05). Female Ae. albopictus density was correlated with CI pre 3 weeks (rs = 0.303, p<0.05). The influencing factors of BI were average wind speed pre 1 week, average temperature and female Ae. albopictus density pre 4 weeks. The influencing factors of CI were average humidity pre 3 weeks and average temperature. The influencing factors of HI were average temperature and precipitation pre 4 weeks. The influencing factor of Ae. albopictus density and female Ae. albopictus density was temperature.<h4>Conclusions</h4>The adult Ae. albopictus density had low correlation with certain larval indices. Some of the meteorology factors played significant roles in the density of adult Ae. albopictus and larva with or without a time lag.
Project description:Mass egg production is an important component of Aedes albopictus mosquito control programs, such as the sterile insect technique and incompatible insect technique, which requires the releases of large number of sterile males. Developing standard operating procedures and optimized cages for adult maintenance of Ae. albopictus can improve the mass rearing efficiency.Three different sex ratios of females to males with a total number of 4,000 mosquitoes were tested by evaluating the insemination rate, egg production (total number of eggs per cage), female fecundity and egg hatch rate in small cage (30 × 30 × 30 cm). Blood meals with adenosine triphosphate (ATP, 0.05 g/ml), cage structures (Big cage A: 90 × 30 × 30 cm; Big cage B: 90 × 30 × 50 cm or 90 × 50 × 30 cm) and rearing densities (12,000, 16,000 and 20,000 mosquitoes, corresponding to 0.9 cm2/mosquito, 0.675 cm2/mosquito and 0.54 cm2/mosquito, respectively) were also tested and evaluated on the basis of egg production, female fecundity and egg hatch rate. An adult rearing unit holding 15 of Big cage A with optimal egg production was designed to produce 10 million eggs per rearing cycle in a 1.8 m2 space.Female to male ratios at 3:1 in small cages resulted in higher egg production but did not affect insemination rate, female fecundity and egg hatch rate. A concentration of 0.05 g/ml of ATP added to blood meals improved the blood-feeding frequency and thus increased the overall egg production per cage. Cage structures affected the egg production per cage, but not egg hatch rate. A medium rearing density at 0.675 cm2/mosquito (16,000 mosquitoes) resulted in higher egg production compared to both low and high densities. An adult rearing unit for Ae. albopictus on the basis of Big cage A has been developed with the capacity of producing 10 million eggs within 15 days.Our results have indicated that the adult rearing methods and adult maintenance unit are recommended for Ae. albopictus mass rearing in support of the establishment of a medium-sized mosquito factory.
Project description:Background:The Mosq-ovitrap (MOT) is currently used for routine surveillance of container-breeding Aedes in China. However, the effectiveness of monitoring Aedes albopictus using the MOT and other mosquito monitoring methods, such as the Ovitrap (OT) and the CO2-light trap (CLT), have not been extensively compared. Moreover, little is known about the spatial-temporal correlations of eggs with adult Ae. albopictus abundance among these three types of traps. Methods:Comparative field evaluation of MOT, OT and CLT for Ae. albopictus monitoring was conducted simultaneously at two city parks and three residential neighborhoods in downtown Shanghai for 8 months from April 21 to December 21, 2017. Results:Significantly more Ae. albopictus eggs were collected from both MOTs and OTs when traps remained in the field for 10 d or 7 d compared with 3 d (MOT: 50.16, 34.15 vs. 12.38 per trap, P < 0.001; OT: 3.98, 2.92 vs. 0.63 per trap, P < 0.001). Egg collections of MOTs were significantly greater than OTs for all three exposure durations (Percent positive: X 2 = 72.251, 52.420 and 51.429, P value all < 0.001; egg collections: t = 8.068, 8.517 and 10.021, P value all <0.001). Significant temporal correlations were observed between yields of MOT and CLT in all sampling locations and 3 different MOT exposure durations (correlation coefficient r ranged from 0.439 to 0.850, P values all < 0.05). However, great variation was found in the spatial distributions of Ae. albopictus density between MOT and CLT. MOT considerably underestimated Ae. albopictus abundances in areas with high Ae. albopictus density (>25.56 per day ? trap by CLT). Conclusion:The MOT was more efficient than the OT in percent positive scores and egg collections of Ae. albopictus. The minimum length of time that MOTs are deployed in the field should not be less than 7 d, as Ae. albopictus collections during this period were much greater than for 3 d of monitoring. MOT considerably underestimated Ae. albopictus abundance in areas with high Aedes albopictus density compared to CLT. In areas with moderate Aedes albopictus densities, MOT results were significantly correlated with CLT catches.
Project description:Despite the growing awareness that larval competition can influence adult mosquito life history traits including susceptibility to pathogens, the net effect of larval competition on human risk of exposure to mosquito-borne pathogens remains poorly understood. We examined how intraspecific larval competition affects dengue-2 virus (DENV-2) extrinsic incubation period and vectorial capacity of its natural vector Aedes albopictus. Adult Ae. albopictus from low and high-larval density conditions were orally challenged with DENV-2 and then assayed for virus infection and dissemination rates following a 6, 9, or 12-day incubation period using real-time quantitative reverse transcription PCR. We then modeled the effect of larval competition on vectorial capacity using parameter estimates obtained from peer-reviewed field and laboratory studies. Larval competition resulted in significantly longer development times, lower emergence rates, and smaller adults, but did not significantly affect the extrinsic incubation period of DENV-2 in Ae. albopictus. Our vectorial capacity models suggest that the effect of larval competition on adult mosquito longevity likely has a greater influence on vectorial capacity relative to any competition-induced changes in vector competence. Furthermore, we found that large increases in the viral dissemination rate may be necessary to compensate for small competition-induced reductions in daily survivorship. Our results indicate that mosquito populations that experience stress from larval competition are likely to have a reduced vectorial capacity, even when susceptibility to pathogens is enhanced.
Project description:Insect symbionts are major manipulators of host's behavior. Their effect on parameters such as fecundity, male mating competitiveness, and biological quality in general, can have a major influence on the effectiveness of the sterile insect technique (SIT). SIT is currently being developed and applied against human disease vectors, including Ae. albopictus, as an environment-friendly method of population suppression, therefore there is a renewed interest on both the characterization of gut microbiota and their exploitation in artificial rearing. In the present study, bacterial communities of eggs, larvae, and adults (both males and females) of artificially reared Ae. albopictus, were characterized using both culture-dependent and culture-independent approaches. Mosquito-associated bacteria corresponding to thirteen and five bacteria genera were isolated from the larval food and the sugar solution (adult food), respectively. The symbiont community of the females was affected by the provision of a blood meal. Pseudomonas and Enterobacter were either introduced or enhanced with the blood meal, whereas Serratia were relatively stable during the adult stage of females. Maintenance of these taxa in female guts is probably related with blood digestion. Gut-associated microbiota of males and females were different, starting early after emergence and continuing in older stages. Our results indicate that eggs contained bacteria from more than fifteen genera including Bacillus, Chryseobacterium, and Escherichia-Shigella, which were also main components of gut microbiota of female adults before and after blood feeding, indicating potential transmission among generations. Our results provided a thorough study of the egg- and gut-associated bacteria of artificially reared Ae. albopictus, which can be important for further studies using probiotic bacteria to improve the effectiveness of mosquito artificial rearing and SIT applications.
Project description:Temperature-food interactions in the larval environment can affect life history and population growth of container mosquitoes Aedes aegypti (L.) and Aedes albopictus Skuse, the primary vectors of chikungunya and dengue viruses. We used Ae. aegypti, Ae. albopictus, and dengue-1 virus (DENV-1) from Florida to investigate whether larval rearing temperature can alter the effects of larval food levels on Ae. aegypti and Ae. albopictus life history and DENV-1 infection and vertical transmission. Although we found no effect of larval treatments on survivorship to adulthood, DENV-1 titer, or DENV-1 vertical transmission, rates of vertical transmission up to 16-24% were observed in Ae. albopictus and Ae. aegypti, which may contribute to maintenance of this virus in nature. Larval treatments had no effect on number of progeny and DENV-1 infection in Ae. aegypti, but the interaction between temperature and food affected number of progeny and DENV-1 infection of the female Ae. albopictus parent. The cooler temperature (24°C) yielded the most progeny and this effect was accentuated by high food relative to the other conditions. Low and high food led to the highest (?90%) and lowest (?65%) parental infection at the cooler temperature, respectively, whereas intermediate infection rates (?75-80%) were observed for all food conditions at the elevated temperature. These results suggest that temperature and food availability have minimal influence on rate of vertical transmission and a stronger influence on adults of Ae. albopictus than of Ae. aegypti, which could have consequences for dengue virus epidemiology.
Project description:The sterile insect technique (SIT) may offer a means to control the transmission of mosquito borne diseases. SIT involves the release of male insects that have been sterilized by exposure to ionizing radiation. We determined the effects of different doses of radiation on the survival and reproductive capacity of local strains of Aedes aegypti and Ae. albopictus in southern Mexico. The survival of irradiated pupae was invariably greater than 90% and did not differ significantly in either sex for either species. Irradiation had no significant adverse effects on the flight ability (capacity to fly out of a test device) of male mosquitoes, which consistently exceeded 91% in Ae. aegypti and 96% in Ae. albopictus. The average number of eggs laid per female was significantly reduced in Ae. aegypti at doses of 15 and 30 Gy and no eggs were laid by females that had been exposed to 50 Gy. Similarly, in Ae. albopictus, egg production was reduced at doses of 15 and 25 Gy and was eliminated at 35 Gy. In Ae. aegypti, fertility in males was eliminated at 70 Gy and was eliminated at 30 Gy in females, whereas in Ae. albopictus, the fertility of males that mated with untreated females was almost zero (0.1%) in the 50 Gy treatment and female fertility was eliminated at 35 Gy. Irradiation treatments resulted in reduced ovary length and fewer follicles in both species. The adult median survival time of both species was reduced by irradiation in a dose-dependent manner. However, sterilizing doses of 35 Gy and 50 Gy resulted in little reduction in survival times of males of Ae. albopictus and Ae. aegypti, respectively, indicating that these doses should be suitable for future evaluations of SIT-based control of these species. The results of the present study will be applied to studies of male sexual competitiveness and to stepwise evaluations of the sterile insect technique for population suppression of these vectors in Mexico.