Satyrization and satyrization‐resistance in competitive displacements of invasive mosquito species

Competitive displacements or reductions of resident populations of insects, often effected by a related species, may be caused by a variety of mechanisms. Satyrization is a form of mating interference in which males of one species mate with females of another species, significantly decreasing their fitness and not generating hybrids. Satyrization has been established to be the probable cause of competitive displacements of resident mosquitoes by invasive species, especially of Aedes aegypti by Aedes albopictus, two important vectors of dengue and chikungunya viruses. Mathematical models predict that even low levels of asymmetric mating interference are capable of producing competitive displacements or reductions. Couplings of virgin Ae. aegypti females with Ae. albopictus males effectively sterilize these females through the monogamizing actions of male accessory gland products, but the converse interspecific mating does not impact the future reproduction of Ae. albopictus females. Populations of Ae. aegypti exposed to satyrization quickly evolve resistance to interspecific mating, which is believed to ameliorate reproductive interference from, and promote co‐existence with, Ae. albopictus. The evolution of satyrization resistance among Ae. aegypti in laboratory cages is accompanied by fitness costs, such as reduced fecundity and slower receptivity to conspecific males. Cage experiments and field observations indicate that Ae. albopictus males are capable of satyrizing females of other species of the Stegomyia subgenus, potentially leading to competitive displacements, and possible extinctions, especially of endemic species on islands. Examination of other examples of reproductive interference in insects reveals few parallels to the mechanism and outcomes of satyrization by Ae. albopictus. We conclude by posing the hypothesis that satyrization may favor the ecological success of Ae. albopictus, and suggest many lines for future research on this phenomenon.     

Oviposition substrate selection by Florida mosquitoes in response to pathogen‐infected conspecific larvae

The impact of the presence of larval mosquito pathogens with potential for biological control on oviposition choice was evaluated for three mosquito species/pathogen pairs present in Florida. These included Aedes aegypti infected with Edhazardia aedis, Aedes albopictus infected with Vavraia culicis, and Culex quinquefasciatus infected with Culex nigripalpus nucleopolyhedrovirus (CuniNPV). Two‐choice oviposition bioassays were performed on each host and pathogen species with one oviposition cup containing infected larvae and the other cup containing uninfected larvae (control). Both uninfected and E. aedis‐infected female Ae. aegypti laid significantly fewer eggs in oviposition cups containing infected larvae. Uninfected gravid female Ae. albopictus and Cx. quinquefasciatus oviposited equally in cups containing uninfected larvae or containing larvae infected with V. culicis or CuniNPV, respectively. Gravid female Ae. albopictus infected with V. culicis did not display ovarian development and did not lay eggs. The decreased oviposition by gravid Ae. aegypti in containers containing E. aedis‐infected larvae may indicate that the infected larvae produce chemicals deterring oviposition.     

The effect of photoperiod on life history and blood‐feeding activity in Aedes albopictus and Aedes aegypti (Diptera: Culicidae)

Several studies have examined how climatic variables such as temperature and precipitation may affect life history traits in mosquitoes that are important to disease transmission. Despite its importance as a seasonal cue in nature, studies investigating the influence of photoperiod on such traits are relatively few. This study aims to investigate how photoperiod alters life history traits, survival, and blood‐feeding activity in Aedes albopictus (Skuse) and Aedes aegypti (Linnaeus). We performed three experiments that tested the effects of day length on female survival, development time, adult size, fecundity, adult life span, and propensity to blood feed in Ae. albopictus and Ae. aegypti. Each experiment had three photoperiod treatments: 1) short‐day (10L:14D), 2) control (12L:12D), and 3) long‐day (14L:10D). Aedes albopictus adult females were consistently larger in size when reared in short‐day conditions. Aedes aegypti adult females from short‐day treatments lived longer and were more likely to take a blood meal compared to other treatments. We discuss how species‐specific responses may reflect alternative strategies evolved to increase survival during unfavorable conditions. We review the potential impacts of these responses on seasonal transmission patterns, such as potentially increasing vectorial capacity of Ae. aegypti during periods of shorter day lengths.     

State‐wide survey of Aedes aegypti and Aedes albopictus (Diptera: Culicidae) in Florida

Aedes aegypti and Aedes albopictus are invasive mosquito species with geographic ranges that have oscillated within Florida since their presence was first documented. Local transmission of dengue, chikungunya, and Zika viruses serves as evidence of the public health importance of these two species. It is important to have detailed knowledge of their distribution to aid in mosquito control efforts and understand the risk of arbovirus transmission to humans. Through a partnership involving the University of Florida Institute of Food and Agricultural Sciences Cooperative Extension Service and the Florida Medical Entomology Laboratory; the Florida Department of Health; and mosquito control agencies throughout Florida, a container mosquito surveillance program involving all life stages was launched in the summer of 2016 to detect the presence of Ae. aegypti and Ae. albopictus. Results from this survey were mapped to provide a picture of the current known distribution of Ae. aegypti and Ae. albopictus in Florida. Aedes aegypti and/or Ae. albopictus were detected in the 56 counties that were part of the survey. Only Aedes albopictus was detected in 26 counties, primarily in the panhandle region of Florida. The results of this work underscore the importance of maintaining container mosquito surveillance in a state where chikungunya, dengue, and Zika viruses are present and where there is continued risk for exotic arbovirus introductions.     

The mosquitoes of eastern Tennessee: studies on abundance,habitat preferences,and host‐seeking behaviors

A significant increase in the number of reported cases of La Crosse virus (LACV) infections in eastern Tennessee has occurred in the last ten years. The objective of this study was to determine the abundance and habitat preferences of the potential vectors of LACV in this region. Adult host‐seeking mosquitoes were collected using CO₂‐baited CDC light traps and a series of human‐landing catches in eastern Tennessee from 2004 to 2006. A total of 4,200 female mosquitoes of 23 species was collected by CO₂‐baited CDC trapping at ten sites during the study period. Aedes albopictus (Skuse) was the most abundant mosquito collected at all sites and vegetation types, with the ratios of total Ae. albopictus to Ae. triseriatus (Say) females collected being 2.1:1 in 2004, 3.8:1 in 2005, and 4.9:1 in 2006. Ten species were collected during a series of human‐landing catches made at four different sites; one probable and three confirmed case sites of LACV infections, totaling 528 female mosquitoes. Aedes albopictus was the most abundant species collected, with a 4:1 ratio of Ae. albopictus to Ae. triseriatus females. Aedes albopictus exhibited two clear peaks of “landing” activity, one in the early morning and one in the late afternoon or early evening. Simple and multiple regression analyses of the predictors of the number of mosquitoes collected showed that populations of Ae. albopictus were three times more likely to be collected overall than Ae. triseriatus. Species (Ae. albopictus), vegetation (residential), and the previous cumulative precipitation for the four weeks prior to collection were significantly (P < 0.05) associated with the number of mosquitoes collected by CO₂‐baited CDC trapping. Aedes albopictus was also more likely to be collected than Ae. triseriatus at confirmed cases of LACV infections.     

The challenge of invasive mosquito vectors in the U.K. during 2016–2018: a summary of the surveillance and control of Aedes albopictus

Mosquito‐borne diseases resulting from the expansion of two key vectors, Aedes aegypti and Aedes albopictus (Diptera: Culicidae), continue to challenge whole regions and continents around the globe. In recent years there have been human cases of disease associated with Chikungunya, dengue and Zika viruses. In Europe, the expansion of Ae. albopictus has resulted in local transmission of Chikungunya and dengue viruses. This paper considers the risk that Ae. aegypti and Ae. albopictus represent for the U.K. and details the results of mosquito surveillance activities. Surveillance was conducted at 34 points of entry, 12 sites serving vehicular traffic and two sites of used tyre importers. The most common native mosquito recorded was Culex pipiens s.l. (Diptera: Culicidae). The invasive mosquito Ae. albopictus was detected on three occasions in southern England (September 2016, July 2017 and July 2018) and subsequent control strategies were conducted. These latest surveillance results demonstrate ongoing incursions of Ae. albopictus into the U.K. via ground vehicular traffic, which can be expected to continue and increase as populations in nearby countries expand, particularly in France, which is the main source of ex‐continental traffic.     

Spatial and temporal patterns of abundance of Aedes aegypti L. (Stegomyia aegypti) and Aedes albopictus (Skuse) [Stegomyia albopictus (Skuse)] in southern Florida

Invasion by mosquito vectors of disease may impact the distribution of resident mosquitoes, resulting in novel patterns of vectors and concomitant risk for disease. One example of such an impact is the invasion by Aedes albopictus (Skuse) [Stegomyia albopictus (Skuse)] (Diptera: Culicidae) of North America and this species' interaction with Aedes aegypti L. (Stegomyia aegypti L). We hypothesized that Ae. aegypti would be found in urban, coastal areas that experience hotter and drier conditions, whereas Ae. albopictus would be more commonly found in suburban and rural areas that are cooler and wetter. In addition, we hypothesized that Ae. aegypti would be more abundant early in the wet season, whereas Ae. albopictus would be more abundant later in the wet season. Urban areas were drier, hotter and contained more Ae. aegypti than suburban or rural areas. Aedes aegypti was relatively more abundant early in the wet season, whereas Ae. albopictus was more abundant in both the late wet season and the dry season. The spatial patterns of inter‐ and intraspecific encounters between these species were also described. The distribution of these mosquitoes is correlated with abiotic conditions, and with temperature, humidity and the relative availability of rain‐filled containers. Understanding the ecological determinants of species distribution can provide insight into the biology of these vectors and important information for their appropriate control.     

Frequency of pyrethroid resistance in Aedes aegypti and Aedes albopictus (Diptera: Culicidae) in Thailand

Thirty‐two Aedes aegypti populations collected throughout Thailand and five populations of Aedes albopictus from southern Thailand were subjected to standard WHO contact bioassays to assess susceptibility to three commonly used synthetic pyrethroids: permethrin, deltamethrin, and lambda‐cyhalothrin. A wide degree of physiological response to permethrin was detected in Ae. aegypti, ranging from 56.5% survival (Lampang, northern Thailand) to only 4% (Kalasin in northeastern and Phuket in southern Thailand). All 32 populations of Ae. aegypti were found to have evidence of incipient resistance (62.5%) or levels of survival deemed resistant (37.5%) to permethrin. Four populations of Ae. albopictus were found with incipient resistance (97 – 80% mortality) and one with resistance (< 80%) to permethrin. The majority of Ae. aegypti populations (68.7%) was susceptible (> 98% mortality) to deltamethrin, with incipient resistance (observed 97–82% mortality) in other localities. In contrast, all populations of Ae. aegypti were completely susceptible (100% mortality) to the recommended operational dosage of lambda‐cyhalothrin. All five populations of Ae. albopictus were found completely susceptible to both deltamethrin and lambda‐cyhalothrin. Evidence of defined incipient or resistance to synthetic pyrethroids mandates appropriate response and countermeasures to mitigate further development and spread of resistance. In light of these findings, we conclude that routine and comprehensive susceptibility monitoring of dengue mosquito vectors to synthetic pyrethroids should be a required component of resistance management policies and disease control activities.     

Susceptibility of Florida Aedes aegypti and Aedes albopictus to dengue viruses from Puerto Rico

Locally acquired dengue cases in the continental U.S. are rare. However, outbreaks of dengue‐1 during 2009, 2010, and 2013 in Florida and dengue‐1 and −2 in Texas suggest vulnerability to transmission. Travel and commerce between Puerto Rico and the U.S. mainland is common, which may pose a risk for traveler‐imported dengue cases. Mosquitoes were collected in Florida and used to evaluate their susceptibility to dengue viruses (DENV) from Puerto Rico. Aedes aegypti and Ae. albopictus were susceptible to virus infection with DENV‐1 and −2. No significant differences were observed in rates of midgut infection or dissemination between Ae. aegypti or Ae. albopictus for DENV‐1 (6–14%). Aedes aegypti was significantly more susceptible to midgut infection with DENV‐2 than Ae. albopictus (Ae. aegypti, ∼28%; Ae. albopictus, ∼9%). The dissemination rate with dengue‐2 virus for Ae. aegypti (23%) was greater than Ae. albopictus (0%), suggesting that Ae. albopictus is not likely to be an important transmitter of the DENV‐2 isolate from Puerto Rico. These results are discussed in light of Florida's vulnerability to DENV transmission.     

Geographic and ecological distribution of the dengue and chikungunya virus vectors Aedes aegypti and Aedes albopictus in three major Cameroonian towns

Aedes albopictus (Diptera: Culicidae) was first reported in Central Africa in 2000, together with the indigenous mosquito species Aedes aegypti (Diptera: Culicidae). Because Ae. albopictus can also transmit arboviruses, its introduction is a public health concern. We undertook a comparative study in three Cameroonian towns (Sahelian domain: Garoua; equatorial domain: Douala and Yaoundé) in order to document infestation by the two species and their ecological preferences. High and variable levels of pre‐imaginal Ae. aegypti and Ae. albopictus infestation were detected. Only Ae. aegypti was encountered in Garoua, whereas both species were found in Douala and Yaoundé, albeit with significant differences in their relative prevalence. Peridomestic water containers were the most strongly colonized and productive larval habitats for both species. No major differences in types of larval habitat were found, but Ae. albopictus preferentially bred in containers containing plant debris or surrounded by vegetation, whereas Ae. aegypti tended to breed in containers located in environments with a high density of buildings. These findings may have important implications for vector control strategies.     

Temperature and photoperiod effects on dormancy status and life cycle parameters in Aedes albopictus and Aedes aegypti from subtropical Argentina

Aedes albopictus (Diptera: Culicidae) distribution is bounded to a subtropical area in Argentina, while Aedes aegypti (Diptera: Culicidae) covers both temperate and subtropical regions. We assessed thermal and photoperiod conditions on dormancy status, development time and mortality for these species from subtropical Argentina. Short days (8 light : 16 dark) significantly increased larval development time for both species, an effect previously linked to diapause incidence. Aedes albopictus showed higher mortality than Ae. aegypti at 16 °C under long day treatments (16 light : 8 dark), which could indicate a lower tolerance to a sudden temperature decrease during the summer season. Aedes albopictus showed a slightly higher percentage of dormant eggs from females exposed to a short day, relative to previous research in Brazilian populations. Since we employed more hours of darkness, this could suggest a relationship between day‐length and dormancy intensity. Interestingly, local Ae. aegypti presented dormancy similar to Ae. albopictus, in accordance with temperate populations. The minimum dormancy in Ae. albopictus would not be sufficient to extend its bounded distribution. We believe that these findings represent a novel contribution to current knowledge about the ecophysiology of Ae. albopictus and Ae. aegypti, two species with great epidemiological relevance in this subtropical region.     

Ecological interactions in Aedes species on Reunion Island

Two invasive, container‐breeding mosquito species, Aedes aegypti (Stegomyia aegypti) and Aedes albopictus (Stegomyia albopicta) (Diptera: Culicidae), have different distribution patterns on Reunion Island. Aedes albopictus occurs in all areas and Ae. aegypti colonizes only some restricted areas already occupied by Ae. albopictus. This study investigates the abiotic and biotic ecological mechanisms that determine the distribution of Aedes species on Reunion Island. Life history traits (duration of immature stages, survivorship, fecundity, estimated finite rate of increase) in Ae. aegypti and Ae. albopictus were compared at different temperatures. These fitness measures were characterized in both species in response to competitive interactions among larvae. Aedes aegypti was drastically affected by temperature, performing well only at around 25 °C, at which it achieved its highest survivorship and greatest estimated rate of increase. The narrow distribution of this species in the field on Reunion Island may thus relate to its poor ability to cope with unfavourable temperatures. Aedes aegypti was also more negatively affected by high population densities and to some extent by interactions with Ae. albopictus, particularly in the context of limited food supplies. Aedes albopictus exhibited better population performance across a range of environmental conditions. Its ecological plasticity and its superior competitive ability relative to its congener may further enhance its invasion success on Reunion Island.     

Spatial repellency and other effects of transfluthrin and linalool on Aedes aegypti and Aedes albopictus

In the present study, the effects of two spatial repellents (SR) were determined for Aedes aegypti and Ae albopictus, the main vectors of dengue, Chikungunya, and Zika fever. The modular high‐throughput screening system (HITSS ) was used to evaluate the response of both species to transfluthrin and linalool SR at different concentrations. The highest spatial repellency results for Ae. aegypti were obtained by transfluthrin to 0.001% with 37.50 ± 4.33%, and for linalool to 10% with 77.50 ± 3.90%. For Ae. albopictus, the highest spatial repellency percentages for transfluthrin 0.01% were 45.00 ± 3.78%, and linalool at 1% and 10% were 56.25 ± 7.06% and 56.25 ± 6.46%, respectively. Transfluthrin caused high levels of mortality with 71.25 ± 6.66%, 79.75 ± 8.65%, and 100% to Ae. aegypti and 70.00 ± 5.98% and 98.75 ± 0.82% to Aedes albopcitus. With the results of this study, we concluded that both the transfluthrin and linalool could be used as protection measures against the bite of Ae. aegypti and Ae. albopictus in the integral strategies for the control of vectors in Mexico.     

Behavioral responses of Aedes aegypti,Aedes albopictus,Culex quinquefasciatus,and Anopheles minimus against various synthetic and natural repellent compounds

The behavioral responses of colony populations of Aedes aegypti, Aedes albopictus, Culex quinquefasciatus, and Anopheles minimus to four essential oils (citronella, hairy basil, catnip, and vetiver), two standard repellents (DEET and picaridin), and two synthetic pyrethroids (deltamethrin and permethrin) were conducted in the laboratory using an excito‐repellency test system. Results revealed that Cx. quinquefasciatus and An. minimus exhibited much stronger behavioral responses to all test compounds (65–98% escape for contact, 21.4–94.4% escape for non‐contact) compared to Ae. aegypti (3.7–72.2% escape (contact), 0–31.7% (non‐contact)) and Ae. albopictus (3.5–94.4% escape (contact), 11.2–63.7% (non‐contact)). In brief, essential oil from vetiver elicited the greatest irritant responses in Cx. quinquefasciatus (96.6%) and An. minimus (96.5%) compared to the other compounds tested. The synthetic pyrethroids caused a stronger contact irritant response (65–97.8% escape) than non‐contact repellents (0–50.8% escape for non‐contact) across all four mosquito species. Picaridin had the least effect on all mosquito species. Findings from the current study continue to support the screening of essential oils from various plant sources for protective properties against field mosquitoes.     

Effects of intraspecific larval competition on adult longevity in the mosquitoes Aedes aegypti and Aedes albopictus

Abstract Larval competition is common in container‐breeding mosquitoes. The impact of competition on larval growth has been thoroughly examined and findings that larval competition can lead to density‐dependent effects on adult body size have been documented. The effects of larval competition on adult longevity have been less well explored. The effects of intraspecific larval densities on the longevity of adults maintained under relatively harsh environmental conditions were tested in the laboratory by measuring the longevity of adult Aedes aegypti (L.) and Aedes albopictus (Skuse) (Diptera: Culicidae) that had been reared under a range of larval densities and subsequently maintained in high‐ or low‐humidity regimes (85% or 35% relative humidity [RH], respectively) as adults. We found significant negative effects of competition on adult longevity in Ae. aegypti, but not in Ae. albopictus. Multivariate analysis of variance suggested that the negative effect of the larval environment on the longevity of Ae. aegypti adults was most strongly associated with increased development time and decreased wing length as adults. Understanding how larval competition affects adult longevity under a range of environmental conditions is important in establishing the relationship between models of mosquito population regulation and epidemiological models of vector‐borne disease transmission.     

Oviposition habitat selection by container‐dwelling mosquitoes: responses to cues of larval and detritus abundances in the field

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Oviposition by Aedes aegypti and Aedes albopictus: Influence of congeners and of oviposition site characteristics

We investigated the oviposition behavior of Ae. aegypti and Ae. albopictus. In particular we examined whether small‐scale site characteristics and the presence of conspecifics or congeners altered oviposition by these mosquitoes. Various combinations of females of the two species were allowed to oviposit inside cages among either vegetation (potted plants) or structural components (wood and concrete blocks). Numbers of eggs deposited per female were compared between species, sides, and treatments. Most significant differences between treatments and species involved differences between single species and mixed species treatments. Ae. aegypti deposited more eggs/female in the vegetation side than in the structure side whereas the opposite pattern was evident for Ae. albopictus. Ae. aegypti females had higher frequency of skip oviposition than Ae. albopictus. An average of 63% of the containers in the two‐species treatments contained eggs of both species, with more frequent joint occurrences observed in the treatment with three females of each species than in the treatments with one of each. Our results point to the existence of various interactions between gravid Ae. aegypti and Ae. albopictus females at or near the oviposition sites but further experimental work is necessary to fully characterize the interactions and their specific mechanisms.     

Electrophysiological and behavioural response of Aedes albopictus to n‐heinecosane,an ovipositional pheromone of Aedes aegypti

Aedes aegypti (L.) and Aedes albopictus (Skuse) (Diptera: Culicidae) are highly anthropophilic mosquito species and potential vectors of dengue and yellow fever. The location of suitable sites for oviposition requires a set of visual, tactile, and olfactory cues that influence females before they lay their eggs. In this study, the effect of n‐heneicosane, a recognized oviposition pheromone of Ae. aegypti, on the olfactory receptors of the antennae of Ae. aegypti and Ae. albopictus was studied using electroantennographic detection coupled to gas chromatography (GC‐EAD). A significant electroantennographic response to n‐heneicosane in adult females of both mosquito species was observed. In addition, gravid Ae. albopictus females laid more eggs in substrate treated with n‐heneicosane at 0.1, 1, or 10 p.p.m. than in the control, denoting oviposition attractancy. Conversely, at 30, 50, 100, and 200 p.p.m., more eggs were laid in the control substrate, indicating oviposition repellency. Analysis of the larval cuticle by GC and mass spectrometry confirmed the presence of n‐heneicosane in the cuticles of Ae. albopictus larvae. The species‐specific role of n‐heneicosane as an oviposition pheromone in Ae. aegypti and its significance as a behaviour modifier of Ae. albopictus in breeding sites is discussed.     

Entomological surveillance,spatial distribution,and diversity of Culicidae (Diptera) immatures in a rural area of the Atlantic Forest biome,State of São Paulo,Brazil

Because of the high adaptive capacity of mosquitoes, studies that focus on transitional environments become very important, such as those in rural areas, which are considered as bridges between wild diseases and human populations of urban areas. In this study, a survey of the existing species of mosquitoes was performed in an Atlantic Forest area of the city of Santa Bárbara d'Oeste, São Paulo state, Brazil, using traps for immatures and analyzing the frequency and distribution of these insects over the sampling months. Five mosquito species were found: Aedes albopictus (the most frequent species), Aedes aegypti, Aedes fluviatilis, Culex quinquefasciatus, and Toxorhynchites theobaldi. The 4,524 eggs collected in ovitraps showed the presence of the tribe Aedini. Aedes aegypti and Ae. albopictus were identified after larval hatching in the laboratory, with different spatial distributions: the first of which coincides with the area of greatest diversity calculated using the Simpson index, while the second does not. The association of ecological analysis of spatial diversity with simple methods of data collection enables the identification of possible epidemiological risk situations and is a strategy that may be implemented to monitor ecological processes resulting from the interaction among different species of mosquitoes.