Interspecific competition of a new invasive mosquito, Culex coronator, and two container mosquitoes, Aedes albopictus and Cx. quinquefasciatus (Diptera: Culicidae), across different detritus environments

Integrating pyriproxyfen into the incompatible insect technique enhances mosquito population suppression efficiency and eliminates the risk of population replacement

BACKGROUND

The incompatible insect technique (IIT) has been used for Aedes mosquito population suppression to curb the transmission of dengue. However, its wide application is limited owing to the low output of male mosquitoes and the risk of population replacement from the release of fertile Wolbachia-infected females. This study aims to improve IIT efficiency for broader adoption.

RESULTS

We assessed the impact of 10% pyriproxyfen (PPF) sticky powder exposure on Wolbachia (from Culex molestus)-transinfected Aedes albopictus Guangzhou line (GUA line) (GC) mosquitoes. We found that the exposure caused chronic toxicity in adult mosquitoes without affecting the cytoplasmic incompatibility (CI)-inducing capability of males. The PPF-contaminated GC females exhibited significant sterilization and the ability to disseminate lethal doses of PPF to breeding sites. Subsequently, we conducted a field trial combining PPF with IIT aiming to suppress the Ae. albopictus population. This combined approach, termed boosted IIT (BIIT), showed a notable enhancement in population suppression efficiency. The improved efficacy of BIIT was attributed to the dispersion of PPF particles in the field via the released PPF-contaminated male mosquitoes. During the BIIT field trial, no Wolbachia wPip-positive Ae. albopictus larvae were detected, indicating the effective elimination of the risk of Wolbachia-induced population replacement. Additionally, the field trial of BIIT against Ae. albopictus resulted in the suppression of the nontarget mosquito species Culex quinquefasciatus.

CONCLUSION

Our results highlight the remarkable efficiency and feasibility of combining IIT with PPF in suppressing mosquito populations, facilitating the widespread implementation of IIT-based management of mosquito-borne diseases. © 2024 Society of Chemical Industry.

Habitat Segregation Patterns of Container Breeding Mosquitos: The Role of Urban Heat Islands, Vegetation Cover, and Income Disparity in Cemeteries of New Orleans

Aedes aegypti and Aedes albopictus are important pathogen-carrying vectors that broadly exhibit similar habitat suitability, but that differ at fine spatial scales in terms of competitive advantage and tolerance to urban driven environmental parameters. This study evaluated how spatial and temporal patterns drive the assemblages of these competing species in cemeteries of New Orleans, LA, applying indicators of climatic variability, vegetation, and heat that may drive habitat selection at multiple scales. We found that Ae. aegypti was well predicted by urban heat islands (UHI) at the cemetery scale and by canopy cover directly above the cemetery vase. As predicted, UHI positively correlate to Ae. aegypti, but contrary to predictions, Ae. aegypti, was more often found under the canopy of trees in high heat cemeteries. Ae. albopictus was most often found in low heat cemeteries, but this relationship was not statistically significant, and their overall abundances in the city were lower than Ae. aegypti. Culex quinquefasciatus, another important disease vector, was also an abundant mosquito species during the sampling year, but we found that it was temporally segregated from Aedes species, showing a negative association to the climatic variables of maximum and minimum temperature, and these factors positively correlated to its more direct competitor Ae. albopictus. These findings help us understand the mechanism by which these three important vectors segregate both spatially and temporally across the city. Our study found that UHI at the cemetery scale was highly predictive of Ae. aegypti and strongly correlated to income level, with low-income cemeteries having higher UHI levels. Therefore, the effect of excessive heat, and the proliferation of the highly competent mosquito vector, Ae. aegypti, may represent an unequal disease burden for low-income neighborhoods of New Orleans that should be explored further. Our study highlights the importance of considering socioeconomic aspects as indirectly shaping spatial segregation dynamics of urban mosquito species.

Distribution of Culex coronator in Texas

The distribution of Culex coronator Dyar and Knab by county in Texas was updated by combining data from peer-reviewed literature, military and government reports, and university and private collections, and by collecting specimens from counties where data had not been reported. With 254 counties in Texas, the initial collection effort was focused on counties east of US Highway 277, which runs from Val Verde County on the US and Mexico border to Wichita County on the Texas and Oklahoma border. The study resulted in 127 counties with Cx. coronator presence data. The remaining 127 counties need to be surveyed for this species.

Complex Effects of Superior Competitors and Resources on Culex restuans (Diptera: Culicidae) Oviposition

A growing body of literature on mosquito oviposition behavior supports the hypothesis that females place eggs in habitats that provide best available opportunity for growth, development, and maturation of their offspring. We conducted a field experiment to evaluate Culex oviposition behavior in response to the interspecific competitor Aedes triseriatus (Say) (Diptera: Culicidae) larvae, and resources in the form of quantity of plant detritus, and dissolved nitrogen (TN) and phosphorus (TP) derived from that detritus. We tested a set of specific predictions: 1) As a poorer competitor, Culex will avoid ovipositing in containers with superior interspecific competitors; 2) Culex choose oviposition habitats that contain greater amount of resources for the microbial food of their offspring; 3) Sufficiently high resource abundance can override avoidance of oviposition in containers with interspecific competitors. Culex restuans Theobald (Diptera: Culicidae) was the only species ovipositing, and the oviposition responses changed over time. The effect of resources was more important in driving oviposition decisions at the beginning and end of the experiment. The amount of resources, as manifest by TN and TP concentrations, had differential effects on oviposition. At the beginning females laid more eggs in containers with low detritus, which had the highest TN. After that, females preferred those containers with high detritus, which had low TN and high TP. The effect of competitors was important only during the middle of the experiment. Paradoxically, even as a poorer competitor Cx. restuans preferentially oviposited in containers with late-instar Ae. triseriatus, suggesting that the presence of successful heterospecifics indicates a good quality larval habitat.

Temporal Variations of Microbiota Associated with the Immature Stages of Two Florida Culex Mosquito Vectors

Microbiota associated with mosquito vector populations impact several traits of mosquitoes, including survival, reproduction, control, and immunity against pathogens. The influence of seasonal variations and mosquito species on mosquito gut microbiota is poorly understood. We sought to determine whether the mosquito microbiota associated with immature stages of two congeners (Culex coronator and Culex nigripalpus) differ temporally and between the two species. Using high throughput 16S rRNA gene sequence analysis, we characterized bacterial and archaeal communities found in the immature stages of the two Culex mosquito species sampled over three seasons to compare the diversity of bacteria between the two species. Beta diversity analyses of the larval microbiota sequences revealed that the two Culex species differed significantly, both temporally within each species and between the two species. Bacteria in Cx. coronator larvae were dominated by Alphaproteobacteria, mainly associated with Roseoccocus and unidentified species of Rhizobiales, and two unidentified species of Cyanobacteria. In contrast, Cx. nigripalpus was dominated by Thorsellia anophelis (Gammaproteobacteria), Clostridium, an unidentified species of Ruminococcacae (Clostridiales), and additional unidentified species associated with Erysipelotrichaceae (Erysipelotrichales), Bacteroidales, and Mollicutes. Results of our study revealed both seasonal and interspecies differences in bacterial community composition associated with the immature stages of Cx. coronator and Cx. nigripalpus vector populations in Florida. These results have important implications for our understanding of the underlying factors of variations in disease transmission among seasons, susceptibility to various pesticides, and other biotic factors, including the role of the microbiota on the spread of invasive species. In addition, our results suggest close associations of certain bacteria species with each of the two Culex species that will be further targeted for their potential in the development of microbial-based control strategies.

Data-driven identification of potential Zika virus vectors

Zika is an emerging virus whose rapid spread is of great public health concern. Knowledge about transmission remains incomplete, especially concerning potential transmission in geographic areas in which it has not yet been introduced. To identify unknown vectors of Zika, we developed a data-driven model linking vector species and the Zika virus via vector-virus trait combinations that confer a propensity toward associations in an ecological network connecting flaviviruses and their mosquito vectors. Our model predicts that thirty-five species may be able to transmit the virus, seven of which are found in the continental United States, including Culex quinquefasciatus and Cx. pipiens. We suggest that empirical studies prioritize these species to confirm predictions of vector competence, enabling the correct identification of populations at risk for transmission within the United States.

What Can Larval Ecology Tell Us About the Success of Aedes albopictus (Diptera: Culicidae) Within the United States?

Aedes albopictus (Skuse) was introduced in the United States approximately 30 years ago, and since has become an important pest and vector of disease. This species uses small water-holding containers as sites for oviposition and larval development. Larvae can consume a wide range of detritus-based energy sources, including microorganisms, and as such the type and quantity of detritus that enters these systems have been studied for the effects on adult populations. This review examines the documented responses of Ae. albopictus to different larval environments within the United States, and some of its unique ecology that may lead to a better understanding of its spread and success. Field surveys generally find larvae in shaded containers with high amounts of organic detritus. Larvae have higher survival and population growth under high amounts of detritus and microorganisms, but they also can outcompete other species when nutrients are limiting. Allocation of time to feeding by larvae is greater and more focused compared with resident species. These latter two points also may explain differences in carbon and nitrogen composition (nutrient stoichiometry), which point to a lower need for nitrogen. Combined, these facts suggest that the Ae. albopictus is a species with a relatively wide niche that had been able to exploit container habitats in the United States better than resident species. After 30 yr of research, only a narrow range of detritus types and environmental conditions have been examined. Data on factors affecting the production of adults and its spread and apparent success are still needed.

An Updated Checklist of the Mosquitoes of Oklahoma Including New State Records and West Nile Virus Vectors, 2003-06

The mosquito fauna of Oklahoma has not been evaluated since 1965 and no report has been published concerning species associated with urban areas in the state. Mosquito collections were conducted as part of the West Nile virus (WNV) surveillance program between April and November from 2003 to 2006, using standard collection methods. A total of 74,756 adults were collected in 26 urban centers in 16 counties of Oklahoma. Altogether, 40 species were recorded during this study period, bringing the total mosquito species recorded in Oklahoma to 62 species in 9 different genera and 18 subgenera. An updated checklist of Oklahoma mosquito fauna is included with a comparison to historical records. New state records include 3 species: Aedes muelleri, Anopheles perplexens, and Culex coronator. In addition to updating the checklist, 12 species of mosquitoes were tested for WNV. Pools of Culex pipiens complex represented the highest proportion testing positive for WNV (134/766, 17.5%), followed by Cx. tarsalis (13/192, 6.8%) and Aedes albopictus (5/215, 2.3%). West Nile virus-positive mosquitoes were detected earliest in June 2005 and latest in November 2004. Infected Cx. pipiens complex testing positive for WNV were more prevalent in the eastern and central areas of Oklahoma, whereas positive Cx. tarsalis were found mainly in the western areas of the state. This distinct geographical difference needs to be monitored and followed up to ensure optimal mosquito control efforts in Oklahoma communities with mosquito control capabilities.

How Diverse Detrital Environments Influence Nutrient Stoichiometry between Males and Females of the Co-Occurring Container Mosquitoes Aedes albopictus, Ae. aegypti, and Culex quinquefasciatus

Allocation patterns of carbon and nitrogen in animals are influenced by food quality and quantity, as well as by inherent metabolic and physiological constraints within organisms. Whole body stoichiometry also may vary between the sexes who differ in development rates and reproductive allocation patterns. In aquatic containers, such as tree holes and tires, detrital inputs, which vary in amounts of carbon and nitrogen, form the basis of the mosquito-dominated food web. Differences in development times and mass between male and female mosquitoes may be the result of different reproductive constraints, which could also influence patterns of nutrient allocation. We examined development time, survival, and adult mass for males and females of three co-occurring species, Aedes albopictus, Ae. aegypti, and Culex quinquefasciatus, across environments with different ratios of animal and leaf detritus. We quantified the contribution of detritus to biomass using stable isotope analysis and measured tissue carbon and nitrogen concentrations among species and between the sexes. Development times were shorter and adults were heavier for Aedes in animal versus leaf-only environments, whereas Culex development times were invariant across detritus types. Aedes displayed similar survival across detritus types whereas C. quinquefasciatus showed decreased survival with increasing leaf detritus. All species had lower values of ¹⁵N and ¹³C in leaf-only detritus compared to animal, however, Aedes generally had lower tissue nitrogen compared to C. quinquefasciatus. There were no differences in the C:N ratio between male and female Aedes, however, Aedes were different than C. quinquefasciatus adults, with male C. quinquefasciatus significantly higher than females. Culex quinquefasciatus was homeostatic across detrital environments. These results allow us to hypothesize an underlying stoichiometric explanation for the variation in performance of different container species under similar detrital environments, and if supported may assist in explaining the production of vector populations in nature.

Mosquito Larvae in Tires from Mississippi, United States: The Efficacy of Abiotic and Biotic Parameters in Predicting Spatial and Temporal Patterns of Mosquito Populations and Communities

Container systems, including discarded vehicle tires, which support populations of mosquitoes, have been of interest for understanding the variables that produce biting adults that serve as both nuisances and as public health threats. We sampled tires in six sites at three times in 2012 across the state of Mississippi to understand the biotic and abiotic variables responsible for explaining patterns of larvae of common species, species richness, and total abundance of mosquitoes. From 498 tires sampled, we collected >58,000 immatures representing 16 species, with the most common species including Aedes albopictus (Skuse), Culex quinquefasciatus (L.), Orthopodomyia signifera (Coquillett), Aedes triseriatus (Say), Toxorhynchites rutilus septentrionalis (Coquillett), and Culex territans (Walker) accounting for ∼97% of all larvae. We also documented 32 new county records for resident species and recent arrivals in the state, including Aedes japonicus japonicus (Theobald) and Culex coronator (Dyar & Knab). Cluster analysis, which was used to associate sites and time periods based on similar mosquito composition, did reveal patterns across the state; however, there also were more general patterns between species and genera and environmental factors. Broadly, Aedes was often associated with factors related to detritus, whereas Culex was frequently associated with habitat variables (e.g., tire size and water volume) and microorganisms. Some Culex did lack factors connecting variation in early and late instars, suggesting differences between environmental determinants of oviposition and survival. General patterns between the tire environment and mosquito larvae do appear to exist, especially at the generic level, and point to inherent differences between genera that may aid in predicting vector locations and populations.