Effects of elevated atmospheric CO2 on competition between the mosquitoes Aedes albopictus and Ae. triseriatus via changes in litter quality and production

Imported tires; a potential source for the entry of Aedes invasive mosquitoes to Iran

INTRODUCTION

International trade of tires has been responsible for the introduction of invasive Aedes species into many countries. The present study aimed to determine the sources and volume of such trading in Iran and to establish and map points of entry for entomological surveillance.

METHOD

A list of tire importers, type and number of tires and source of their shipment was compiled, and the map of the main location(s) of their depot in the country was produced from 2017 to 2018. Contamination of imported tires with mosquito eggs or larvae was also determined. The samples from all parts of the warehouse were taken randomly from 4 to 20 tires every 15 days. In tires with a trace of water inside, the existence of the egg and larva of Aedes mosquitoes was investigated by sticking the glue band to the hot spot of left water inside the unpacked tires.

RESULTS

Approximately one-third of the annual tire requirements of Iran were imported from 15 countries, most of which were endemic to Aedes aegypti and or Ae. albopictus. It is obligatory to import only wrapped tires. About 10% of total country consumption is imported through informal markets and smuggled. However, the unofficially imported tires are usually not wrapped. The majority of tire imports were made through the southern ports of the country. The main sites for depots of imported tires were located in four Iranian provinces, namely Tehran, Isfahan, Fars, and Sistan and Baluchestan. The latter is extremely important given its border with Pakistan. Depot locations were mostly unstructured, and tires were kept in the open air. All these depot locations were at the edge of towns and residential areas. Priority areas for routine entomological surveillance were established. Such as the previous studies, surveillance of imported tires for the presence of Aedes eggs or larvae was negative in this study.

DISCUSSION

Mapping the entry points of imported tires and their origin is crucial to determine and prioritize sites for entomological surveillance of invasive mosquito species. Strengthening collaboration with customs authorities and the association of tire importers is imperative in this effort. The development of national rules and regulations for tire import is necessary to minimize the danger of the introduction of invasive vector species into the country.

How do noncompetent hosts cause dilution of parasitism? Testing hypotheses for native and invasive mosquitoes

Parasite dilution occurs in varied systems, via multiple potential mechanisms. We used laboratory manipulation and field surveys to test for invader-induced parasite dilution via two specific mechanisms: host-host competition and encounter reduction. In the laboratory, single Aedes triseriatus larvae were exposed to one of eight combinations of: parasitic Ascogregarina barretti, +/-1 cohabiting Aedes albopictus larva during parasite exposure, and +/-1 cohabiting A. albopictus larva after infectious parasite removal. Larval infection intensity (predicted to decrease via dilution by encounter reduction) was not significantly affected by A. albopictus. Adult infection prevalence and intensity (predicted to decrease via dilution by host-host competition) were significantly greater with A. albopictus, suggesting parasite amplification by interspecific competition, an effect potentially mediated by competition increasing A. triseriatus development time. In the field, we tested for effects of potential dilution host abundances on prevalence and abundance of A. barretti in A. triseriatus larvae. Piecewise path analysis yielded no evidence of host-host competition impacting parasitism in the field, but instead indicated a significant direct negative effect of Aedes spp. abundance on parasite abundance in A. triseriatus, which is consistent with dilution via encounter reduction in the field, but only in tree holes, not in man-made containers. Our results are consistent with the hypothesis that a noncompetent invader can alter the native host-parasite relationship, but our laboratory and field data yield differing results. This difference is likely due to laboratory experiment testing for per capita effects of dilution hosts on parasitism, but field analysis testing for effects of dilution host abundance on parasitism. Individually, host-host competition with the invader amplifies, rather than dilutes, parasite success. In contrast, our path analysis is consistent with the hypothesis that dilution of parasitism results from increased abundance of noncompetent hosts in the field.

Analysis of the transcription of genes encoding heat shock proteins (hsp) in Aedes aegypti Linnaeus, 1762 (Diptera: Culicidae), maintained under climatic conditions provided by the IPCC (Intergovernmental Panel On Climate Change) for the year 2100

Human actions intensify the greenhouse effect, aggravating climate changes in the Amazon and elsewhere in the world. The Intergovernmental Panel on Climate Change (IPCC) foresees a global increase of up to 4.5 °C and 850 ppm CO₂ (above current levels) by 2100. This will impact the biology of the Aedes aegypti mosquito, vector of Dengue, Zika, urban Yellow Fever and Chikungunya. Heat shock proteins are associated with adaptations to anthropic environments and the interaction of some viruses with the vector. The transcription of the hsp26, hsp83 and hsc70 genes of an A. aegypti population, maintained for more than forty-eight generations, in the Current, Intermediate and Extreme climatic scenario predicted by the IPCC was evaluated with qPCR. In females, highest levels of hsp26, hsp83 and hsc70 expression occurred in the Intermediate scenario, while in males, levels were high only for hsp26 gene in Current and Extreme scenarios. Expression of hsp83 and hsc70 genes in males was low under all climatic scenarios, while in the Extreme scenario females had lower expression than in the Current scenario. The data suggest compensatory or adaptive processes acting on heat shock proteins, which can lead to changes in the mosquito's biology, altering vectorial competence.

Effects of Detritus on the Mosquito Culex pipiens: Phragmites and Schedonorus (Festuca) Invasion Affect Population Performance

Species interactions that influence the performance of the exotic mosquito Culex pipiens can have important effects on the transmission risk of West Nile virus (WNV). Invasive plants that alter the vegetation communities of ephemeral ground pools may facilitate or resist the spread of C. pipiens (L.) by altering allochthonous inputs of detritus in those pools. To test this hypothesis, we combined field surveys of roadside stormwater ditches with a laboratory microcosm experiment to examine relationships between C. pipiens performance and water quality in systems containing detritus from invasive Phragmites australis (Cav.) Trin. Ex Steud., introduced Schedonorusarundinaceus (Schreb.) Dumort., or native Juncus effusus L. or Typha latifolia L. In ditches, C. pipiens abundance was unrelated to detritus species but female C. pipiens were significantly larger from ditches with S. arundinaceus and smaller with J. effusus. Larger and smaller C. pipiens were also produced in microcosms provisioned with S. arundinaceus and J. effusus, respectively, yet the per capita rate of population of change did not vary. Larger females from habitats with S. arundinaceus were likely caused by faster decay rates of S. arundinaceus and resultant increases in microbial food, but lower survival as a result of fouling and higher tannin-lignin concentrations resulted in little changes to overall population performance. Larger female mosquitoes have been shown to have greater potential for transmitting arboviruses. Our findings suggest that changed community-level interactions from plant invasions in urban ephemeral ground pools can affect the fitness of C. pipiens and possibly increase WNV risk.

Predicting the direct and indirect impacts of climate change on malaria in coastal Kenya

Background

The transmission of malaria is highly variable and depends on a range of climatic and anthropogenic factors. This study investigates the combined, i.e. direct and indirect, impacts of climate change on the dynamics of malaria through modifications in: (i) the sporogonic cycle of Plasmodium induced by air temperature increase, and (ii) the life cycle of Anopheles vector triggered by changes in natural breeding habitat arising from the altered moisture dynamics resulting from acclimation responses of vegetation under climate change. The study is performed for a rural region in Kilifi county, Kenya.

Methods and findings

We use a stochastic lattice-based malaria (SLIM) model to make predictions of changes in Anopheles vector abundance, the life cycle of Plasmodium parasites, and thus malaria transmission under projected climate change in the study region. SLIM incorporates a nonlinear temperature-dependence of malaria parasite development to estimate the extrinsic incubation period of Plasmodium. It is also linked with a spatially distributed eco-hydrologic modeling framework to capture the impacts of climate change on soil moisture dynamics, which served as a key determinant for the formation and persistence of mosquito larval habitats on the land surface. Malaria incidence data collected from 2008 to 2013 is used for SLIM model validation. Projections of climate change and human population for the region are used to run the models for prediction scenarios.

Under elevated atmospheric CO₂ concentration ([CO₂]) only, modeled results reveal wetter soil moisture in the root zone due to the suppression of transpiration from vegetation acclimation, which increases the abundance of Anopheles vectors and the risk of malaria. When air temperature increases are also considered along with elevated [CO₂], the life cycle of Anopheles vector and the extrinsic incubation period of Plasmodium parasites are shortened nonlinearly. However, the reduction of soil moisture resulting from higher evapotranspiration due to air temperature increase also reduces the larval habitats of the vector. Our findings show the complicated role of vegetation acclimation under elevated [CO₂] on malaria dynamics and indicate an indirect but ignored impact of air temperature increase on malaria transmission through reduction in larval habitats and vector density.

Conclusions

Vegetation acclimation triggered by elevated [CO₂] under climate change increases the risk of malaria. In addition, air temperature increase under climate change has opposing effects on mosquito larval habitats and the life cycles of both Anopheles vectors and Plasmodium parasites. The indirect impacts of temperature change on soil moisture dynamics are significant and should be weighed together with the direct effects of temperature change on the life cycles of mosquitoes and parasites for future malaria prediction and control.

Effects of tire leachate on the invasive mosquito Aedes albopictus and the native congener Aedes triseriatus

Discarded vehicle tire casings are an important artificial habitat for the developmental stages of numerous vector mosquitoes. Discarded vehicle tires degrade under ultraviolet light and leach numerous soluble metals (e.g., barium, cadmium, zinc) and organic substances (e.g., benzothiazole and its derivatives [BZTs], polyaromatic hydrocarbons [PAHs]) that could affect mosquito larvae that inhabit the tire casing. This study examined the relationship between soluble zinc, a common marker of tire leachate, on mosquito densities in tire habitats in the field, and tested the effects of tire leachate on the survival and development of newly hatched Aedes albopictus and Aedes triseriatus larvae in a controlled laboratory dose-response experiment. In the field, zinc concentrations were as high as 7.26 mg/L in a single tire and averaged as high as 2.39 (SE ± 1.17) mg/L among tires at a single site. Aedes albopictus (37/42 tires, 81.1%) and A. triseriatus (23/42, 54.8%) were the most widespread mosquito species, co-occurred in over half (22/42, 52.4%) of all tires, and A. triseriatus was only collected without A. albopictus in one tire. Aedes triseriatus was more strongly negatively associated with zinc concentration than A. albopictus, and another common mosquito, C. pipiens, which was found in 17 tires. In the laboratory experiment, A. albopictus per capita rate of population change (λ') was over 1.0, indicating positive population growth, from 0-8.9 mg/L zinc concentration (0-10,000 mg/L tire leachate), but steeply declined to zero from 44.50-89.00 mg/L zinc (50,000-100,000 mg/L tire leachate). In contrast, A. triseriatus λ' declined at the lower concentration of 0.05 mg/L zinc (100 mg/L tire leachate), and was zero at 0.45, 8.90, 44.50, and 89.00 mg/L zinc (500, 10,000, 50,000 and 100,000 mg/L tire leachate). These results indicate that tire leachate can have severe negative effects on populations of container-utilizing mosquitoes at concentrations commonly found in the field. Superior tolerance to tire leachate of A. albopictus compared to A. triseriatus, and possibly other native mosquito species, may have facilitated the replacement of these native species as A. albopictus has invaded North America and other regions around the world.

Prior Hydrologic Disturbance Affects Competition between Aedes Mosquitoes via Changes in Leaf Litter

Allochthonous leaf litter is often the main resource base for invertebrate communities in ephemeral water-filled containers, and detritus quality can be affected by hydrologic conditions. The invasive mosquito Aedes albopictus utilizes container habitats for its development where it competes as larvae for detritus and associated microorganisms with the native Aedes triseriatus. Different hydrologic conditions that containers are exposed to prior to mosquito utilization affect litter decay and associated water quality. We tested the hypothesis that larval competition between A. albopictus and A. triseriatus would be differentially affected by prior hydrologic conditions. Experimental microcosms provisioned with Quercus alba L. litter were subjected to one of three different hydrologic treatments prior to the addition of water and mosquito larvae: dry, flooded, and a wet/dry cycle. Interspecific competition between A. albopictus and A. triseriatus was mediated by hydrologic treatment, and was strongest in the dry treatment vs. the flooded or wet/dry treatments. Aedes triseriatus estimated rate of population change (λ') was lowest in the dry treatment. Aedes albopictus λ' was unaffected by hydrologic treatment, and was on average always increasing (i.e., > 1). Aedes triseriatus λ' was affected by the interaction of hydrologic treatment with interspecific competition, and was on average declining (i.e., < 1.0), at the highest interspecific densities in the dry treatment. Dry treatment litter had the slowest decay rate and leached the highest concentration of tannin-lignin, but supported more total bacteria than the other treatments. These results suggest that dry conditions negatively impact A. triseriatus population performance and may result in the competitive exclusion of A. triseriatus by A. albopictus, possibly by reducing microbial taxa that Aedes species browse. Changing rainfall patterns with climate change are likely to affect competition between A. triseriatus and A. albopictus, probably enhancing negative competitive effects of A. albopictus on A. triseriatus in areas that experience drought.

Interspecific Competition between Aedes albopictus and A. sierrensis: potential for Competitive Displacement in the Western United States

The Asian tiger mosquito, Aedes albopictus, was first detected in North America twenty five years ago. It utilizes water-holding container habitats as immature development sites, and has rapidly spread throughout the eastern United States. Aedes albopictus has occasionally been detected in the western United States, but until recently no established populations of A. albopictus were reported. The western tree-hole mosquito, Aedes sierrensis, is the most common tree-hole mosquito throughout the western United States, and is expected to more frequently encounter A. albopictus. In this study, competition between A. albopictus from the eastern United States and A. sierrensis from the western United States was tested in order to better understand the potential for either competitive displacement of A. sierrensis by A. albopictus or competitive resistance of A. sierrensis to A. albopictus. Varying densities of each species were reared with limited resources in a response surface design. Consistent with a prior study, we found that A. albopictus was clearly a superior larval competitor than A. sierrensis. Aedes sierrensis λ' (finite rate of increase) decreased with increasing A. albopictus density, but in contrast, A. albopictus λ' actually increased with increasing A. sierrensis density; a result that was not reflected by individual fitness parameters. These results indicate that A. sierrensis will not be an effective barrier to A. albopictus invasion into tree-holes in the western United States.