Parasitism of Ascogregarina taiwanensis and Ascogregarina culicis (Apicomplexa: Lecudinidae) in larvae of Aedes albopictus and Aedes aegypti (Diptera: Culicidae) from Manaus, Amazon region, Brazil

Presence of Ascogregarina culicis and Ascogregarina sp. in natural sympatric populations of Aedes aegypti and Ae. albopictus (Diptera: Culicidae) in Argentina

Aedes aegypti is the main vector of the four arboviruses in America which have the greatest impact on human health. The introduction of Aedes albopictus in South America and Argentina acquires importance given the possibility that this species may be a new vector of arboviruses in this region. For this reason, the studies of the biology of their parasites, such as Ascogregarina spp., should be important for the knowledge of the invasive behavior of these vectors. We reported the finding of Ascogregarina culicis in Aedes aegypti and Ascogregarina sp. in Ae. albopictus populations in subtropical Argentina. The prevalence of parasitism by A. culicis in Ae. aegypti and Ascogregrarina sp. in Ae. albopictus was 34.81% (n = 464) and 37.23% (n = 70), respectively, differing between the seasons and habitats. The infection intensity caused by A. culicis and Ascogregarina sp. varied between 1 to 250 and 1 to 327 trophozoites respectively. Ascogregarina culicis was found throughout the all sampling period of Ae. aegypti (June 2016-April 2018). However the presence of Ascogregarina sp. in the midgut of Ae. albopictus was not recorded throughout the whole sampling period despite the presence of the host.

Field Evidence of Mosquito Population Regulation by a Gregarine Parasite

Although parasites are by definition costly to their host, demonstrating that a parasite is regulating its host abundance in the field can be difficult. Here we present an example of a gregarine parasite, Ascogregarina taiwanensis Lien and Levine (Apicomplexa: Lecudinidae), regulating its mosquito host, Aedes albopictus Skuse (Diptera: Culicidae), in Bermuda. We sampled larvae from container habitats over 2 yr, assessed parasite prevalence, and estimated host abundance from egg counts obtained in neighboring ovitraps. We regressed change in average egg count from 1 yr to the next on parasite prevalence and found a significant negative effect of parasite prevalence. We found no evidence of host density affecting parasite prevalence. Our results demonstrate that even for a parasite with moderate virulence, host regulation can occur in the field.

Effects of Ascogregarina culicis (Eugregarinorida: Lecudinidae) on Mosquito Size and Dengue Virus Infection in Aedes aegypti (Diptera: Culicidae)

Dengue virus infection, transmitted via mosquito bites, poses a substantial risk to global public health. Studies suggest that the mosquito's microbial community can profoundly influence vector-borne pathogen transmissions, including dengue virus. Ascogregarina culicis (Ross) of the phylum Apicomplexa is among the most common parasites of Aedes aegypti (Linnaeus), the principal vector of dengue. Despite a high prevalence worldwide, including in the areas where dengue is endemic, the impact of A. culicis on Ae. aegypti vector competence for dengue virus is unknown. This study aimed to investigate the effects of A. culicis infection on mosquito size and fitness, as measured by wing length, and the susceptibility to dengue virus infection in Ae. aegypti. Our results showed that there was no statistically significant difference in wing lengths between Ae. aegypti infected and not infected with A. culicis. Furthermore, A. culicis infection did not significantly affect dengue virus infection or disseminated infection rate. However, there was a significant association between shorter wings and higher dengue virus infection rate, whereby a 0.1-mm increase in wing length decreased the odds of the mosquito being infected by 32%. Thus, based on our result, A. culicis infection does not influence the body size and dengue virus infection in Ae. aegypti. This study helps to shed light on a common but neglected eukaryotic mosquito parasite.

Critical low temperature for the survival of Aedes aegypti in Taiwan

Background

Taiwan is geographically located in a region that spans both tropical and subtropical climates (22–25°N and 120–122°E). The Taiwan Centers for Disease Control have found that the ecological habitat of Aedes aegypti appears only south of 23.5°N. Low temperatures may contribute to this particular habitat distribution of Ae. aegypti under the influence of the East Asian winter monsoon. However, the threshold condition related to critically low temperatures remains unclear because of the lack of large-scale spatial studies. This topic warrants further study, particularly through national entomological surveillance and satellite-derived land surface temperature (LST) data.

Methods

We hypothesized that the distribution of Ae. aegypti is highly correlated with the threshold nighttime LST and that a critical low LST limits the survival of Ae. aegypti. A mosquito dataset collected from the Taiwan Centers for Disease Control was utilized in conjunction with image data obtained from the moderate resolution imaging spectroradiometer (MODIS) during 2009–2011. Spatial interpolation and phi coefficient methods were used to analyze the correlation between the distributions of immature forms of Ae. aegypti and threshold LST, which was predicted from MODIS calculations for 348 townships in Taiwan.

Results

According to the evaluation of the correlation between estimated nighttime temperatures and the occurrence of Ae. aegypti, winter had the highest peak phi coefficient, and the corresponding estimated threshold temperatures ranged from 13.7 to 14 °C in the ordinary kriging model, which was the optimal interpolation model in terms of the root mean square error. The mean threshold temperature was determined to be 13.8 °C, which is a critical temperature to limit the occurrence of Ae. aegypti.

Conclusions

An LST of 13.8 °C was found to be the critical temperature for Ae. aegypti larvae, which results in the near disappearance of Ae. aegypti during winter in the subtropical regions of Taiwan under the influence of the prevailing East Asian winter monsoon.

Differential response to mosquito host sex and parasite dosage suggest mixed dispersal strategies in the parasite Ascogregarina taiwanensis

Mixed dispersal strategies are a form of bet hedging in which a species or population utilizes different dispersal strategies dependent upon biotic or abiotic conditions. Here we provide an example of a mixed dispersal strategy in the Aedes albopictus / Ascogregarina taiwanensis host/parasite system, wherein upon host emergence, the gregarine parasite is either carried with an adult mosquito leaving the larval habitat, or released back into the larval habitat. We show that the parasite invests a larger proportion of its dispersing (oocyst) life stage into adult female mosquitoes as opposed to adult male mosquitoes at low parasite exposure levels. However, as the exposure level of parasite increases, so does the parasite investment in adult males, whereas there is no change in the proportion of oocysts in the adult female, regardless of dose. Thus, A. taiwanensis is utilizing several dispersal strategies, depending upon host sex and intraspecific density. Furthermore, we demonstrate that this parasite reduces body size, increases time to emergence in females, and leads to a reduction in estimates of per capita growth rate of the host.

The Effect of Parasitism and Interpopulation Hybridization on Aedes albopictus (Diptera: Culicidae) Fitness

Recent research in mosquito population genetics suggests that interpopulation hybridization has likely contributed to the rapid spread of the container-breeding mosquitoes. Here, I used laboratory experiments to investigate whether interpopulation Aedes (Stegomyia) albopictus (Skuse) F1 and F2 hybrids exhibit higher fitness than parental populations, and whether hybrid mosquito performance is related to infection by the coevolved protozoan parasite Ascogregarina taiwanensis (Lien and Levine). Overall, there were significant differences in development time, wing length, and survival between the two parental mosquito populations, but no difference in per capita growth rate r. Hybrid mosquitoes were generally intermediate in phenotype to the parentals, except that F2 females were significantly larger than the midparent average. In addition, As. taiwanensis parasites produced fewest oocysts when they were reared in hosts of hybrid origin. These data suggest that hybridization between previously isolated mosquito populations can result in slight increases in potential mosquito reproductive success, via increased hybrid body size, and via the temporary escape from coevolved parasites. These findings are significant because studies have shown that even slight hybrid vigor can have positive fitness consequences for population persistence. Although this was a laboratory experiment extending only to the F2 generation, many other invasive insects also carry coevolved parasites, and thus the patterns seen in this mosquito system may be broadly relevant.

Mosquito and sand fly gregarines of the genus Ascogregarina and Psychodiella (Apicomplexa: Eugregarinorida, Aseptatorina)--overview of their taxonomy, life cycle, host specificity and pathogenicity

Mosquitoes and sand flies are important blood-sucking vectors of human diseases such as malaria or leishmaniasis. Nevertheless, these insects also carry their own parasites, such as gregarines; these monoxenous pathogens are found exclusively in invertebrates, and some of them have been considered useful in biological control. Mosquito and sand fly gregarines originally belonging to a single genus Ascogregarina were recently divided into two genera, Ascogregarina comprising parasites of mosquitoes, bat flies, hump-backed flies and fleas and Psychodiella parasitizing sand flies. Currently, nine mosquito Ascogregarina and five Psychodiella species are described. These gregarines go through an extraordinarily interesting life cycle; the mosquito and sand fly larvae become infected by oocysts, the development continues transtadially through the larval and pupal stages to adults and is followed by transmission to the offspring by genus specific mechanisms. In adult mosquitoes, ascogregarines develop in the Malpighian tubules, and oocysts are defecated, while in the sand flies, the gregarines are located in the body cavity, their oocysts are injected into the accessory glands of females and released during oviposition. These life history differences are strongly supported by phylogenetical study of SSU rDNA proving disparate position of Ascogregarina and Psychodiella gregarines. This work reviews the current knowledge about Ascogregarina and Psychodiella gregarines parasitizing mosquitoes and sand flies, respectively. It gives a comprehensive insight into their taxonomy, life cycle, host specificity and pathogenicity, showing a very close relationship of gregarines with their hosts, which suggests a long and strong parasite-host coevolution.

Prevalence of Acanthamoeba spp. (Sarcomastigophora: Acanthamoebidae) in wild populations of Aedes aegypti (Diptera: Culicidae)

Studies of interrelationship between microorganisms and mosquitoes are of great importance, since it can provide support for better understand related to biology, development and their control. In this way, it is known that mosquito larvae and free-living amoebae (FLA) normally occupy similar aquatic microhabitats. However, few studies have been conducted about such coexistence. For that reason, the objective of the present study was to verify the prevalence of Acanthamoeba spp. in wild populations of Aedes aegypti, as well as to characterize the genotypic lineage, and their possible pathogenicity through thermo- and osmotolerance. Amoebae were investigated in 60 pools, each containing ten larvae of A. aegypti, collected in Porto Alegre (Rio Grande do Sul, Brazil). The Acanthamoeba isolates were morphologically characterized and submitted to the polymerase chain reaction technique to confirm identification of the genus. In addition, genotype analyses as well as tests for presumptive pathogenicity in some samples were performed. Of the 60 pools examined, 54 (90 %) were positive for FLA. Of these isolates, 47 (87 %) belonged to the genus Acanthamoeba. The genotypic groups T4, T3 and T5 were identified, numbering 14 (53.8 %), ten (38.5 %) and two (7.7 %) isolates, respectively. The physiological tests performed with 14 strains showed that 12 (85.7 %) were non-pathogenic, while two (14.3 %) were considered as having low pathogenic potential. These results provide a basis for a better understanding of the interaction between these protozoan and mosquitoes in their natural habitat. This study is the first to report the isolation of Acanthamoeba spp. from wild mosquitoes.

Susceptibility of Aedes aegypti (Diptera: Culicidae) to Acanthamoeba polyphaga (Sarcomastigophora: Acanthamoebidae)

To date there is no report on mosquitoes infected with free-living amoebae. For this reason, the aim of this study was to verify if Aedes aegypti could be susceptible to Acanthamoeba polyphaga under laboratory conditions, so trophozoites were offered as a unique food resource for larvae of first instar. The results show that those amoebae are able to infect and colonize the mosquito gut and could be re-isolated of all stages of the mosquito (larvae, pupae, and adults).