Male origin determines satyrization potential of Aedes aegypti by invasive Aedes albopictus

Culicidae assemblages of artificial containers and possible biotic interactions affecting Aedes albopictus (Diptera: Culicidae) in Argentina

In Argentina, the distribution of Aedes albopictus (Skuse) is limited to two provinces with a subtropical climate and few records. This study aims to describe and compare assemblies of Culicidae that breed in artificial containers in two areas with different degrees of urbanisation where Ae. albopictus is present and to evaluate possible biotic interactions. We sampled container larval habitats of an urban (Eldorado city) and a rural environment (Colonia Aurora village). We performed generalized linear mixed models to evaluate which variables (containers characteristics or environment) are associated with the presence and abundance of Ae. albopictus, Aedes aegypti Linneaus and Culex quinquefasciatus Say, and the presence of mosquito predators (Lutzia bigoti (Bellardi) and Toxorhynchites spp.). Also, the relationship between the most abundant species was quantified in each environment using Hurlbert's C8 association coefficient. Ae. aegypti was the most abundant species in the urban environment, while Cx. quinquefasciatus and Ae. albopictus were the most abundant in the rural area. Predators were more present in the rural environment and affected the abundance of Aedes mosquitoes. Regarding the C8 index, Ae. aegypti was negatively associated with Ae. albopictus in the urban area, whereas in the rural area these species presented a significantly positive relationship. These results show that in urban environments the high abundance of Ae. aegypti could be affecting the Asian tiger mosquito as evidenced by local studies of food larval competition. Also a greater presence of predators could be affecting Ae. albopictus in rural environments.

Larval Competition Between Aedes albopictus and Aedes aegypti (Diptera: Culicidae) in Argentina: Coexistence and Implications in the Distribution of the Asian Tiger Mosquito

Aedes aegypti (Linnaeus) and Aedes albopictus (Skuse) are worldwide vectors of dengue and yellow fever viruses. These species coexist in many countries and the biotic interactions between them can influence their abundances and distributions. In Argentina, Ae. aegypti is widely distributed in the north and center regions of the country, with temperate and subtropical climate, while both are sympatric only in the northeastern area of the subtropical region. Interspecific and intraspecific larval competition for food was evaluated to assess if their interaction influences on patterns of abundance and distribution. Finite rates of increase and survivorship for each species were estimated and the effects of mosquito density ratio and detritus availability were determined. The Lambda (λ´) index of population performance of both showed there is no competitive exclusion pattern. However, survival of Ae. albopictus was negatively affected by the presence of Ae. aegypti. These results suggest one possible explanation for the codominance pattern of both species display in rural regions of the southernmost distribution of Ae. albopictus in South America. They also show Ae. aegypti as a potential biotic barrier for the expansion of Ae. albopictus as was reported in regions of the United States.

Insemination in Aedes aegypti and Aedes albopictus

Aedes mosquitoes are the vectors of several arboviruses that cause human disease. A better understanding of their reproduction helps to improve their management and contributes insights into the fundamental biology of mosquitoes. During mating, inseminated mosquito females receive seminal fluids and sperm from males that they then store in the spermathecae. In Aedes aegypti and Aedes albopictus, most mated females become resistant to further insemination within 2 h of initial insemination. Although the male seminal fluids are known to be involved in initiating the resistance of inseminated females to further insemination, the mechanism underlying this resistance is not well-understood. The determination of insemination status is a key step in investigating the behavioral and molecular interactions between males and females and for exploring the proximate influences and evolutionary implications of interspecific copulations. Several methods exist for determining insemination status, as discussed here. The choice of method depends on the research question and the availability of resources.

Reproductive interference and Satyrisation: mechanisms, outcomes and potential use for insect control

Reproductive Interference occurs when interactions between individuals from different species disrupt reproductive processes, resulting in a fitness cost to one or both parties involved. It is typically observed between individuals of closely related species, often upon secondary contact. In both vertebrates and invertebrates, Reproductive Interference is frequently referred to as 'Satyrisation'. It can manifest in various ways, ranging from blocking or reducing the efficacy of mating signals, through to negative effects of heterospecific copulations and the production of sterile or infertile hybrid offspring. The negative fitness effects of Satyrisation in reciprocal matings between species are often asymmetric and it is this aspect, which is most relevant to, and can offer utility in, pest management. In this review, we focus on Satyrisation and outline the mechanisms through which it can operate. We illustrate this by using test cases, and we consider the underlying reasons why the reproductive interactions that comprise Satyrisation occur. We synthesise the key factors affecting the expression of Satyrisation and explore how they have potential utility in developing new routes for the management and control of harmful insects. We consider how Satyrisation might interact with other control mechanisms, and conclude by outlining a framework for its use in control, highlighting some of the important next steps.

The concomitant effects of self-limiting insect releases and behavioural interference on patterns of coexistence and exclusion of competing mosquitoes

Aedes aegypti is the dominant vector of dengue, a potentially fatal virus whose incidence has increased eightfold in the last two decades. As dengue has no widely available vaccine, vector control is key to reducing the global public health burden. A promising method is the release of self-limiting Ae. aegypti, which mate with wild Ae. aegypti and produce non-viable offspring. The resultant decrease in Ae. aegypti population size may impact coexistence with Ae. albopictus, another vector of dengue. A behavioural mechanism influencing coexistence between these species is reproductive interference, where incomplete species recognition results in heterospecifics engaging in mating activities. We develop a theoretical framework to investigate the interaction between self-limiting Ae. aegypti releases and reproductive interference between Ae. aegypti and Ae. albopictus on patterns of coexistence. In the absence of self-limiting Ae. aegypti release, coexistence can occur when the strength of reproductive interference experienced by both species is low. Results show that substantial overflooding with self-limiting Ae. aegypti prevents coexistence. For lower release ratios, as the release ratio increases, coexistence can occur when the strength of reproductive interference is increasingly high for Ae. albopictus and increasingly low for Ae. aegypti. This emphasizes the importance of including behavioural ecological processes into population models to evaluate the efficacy of vector control.

Interspecific Mating Effects on Locomotor Activity Rhythms and Refractoriness of Aedes albopictus (Diptera: Culicidae) Females

This study tests the hypotheses that the locomotor activity of Ae. albopictus females is not significantly altered by the presence of accessory gland (AG) extracts from conspecific and heterospecific males, and that Ae. albopictus females remain receptive to mating with conspecific males even after receiving AG of Ae. aegypti males. Virgin Ae. albopictus females were injected with saline (control group), AG extracts of Ae. aegypti males (aegMAG) or AG extracts of Ae. albopictus males (albMAG). Locomotor activity was evaluated under 12 h of light and 12 h of darkness at 25 °C. All live Ae. albopictus females were subsequently exposed to conspecific males for 48 h, and their spermathecae were dissected for the presence of sperm. Females injected with aegMAG and albMAG showed significant decreases in total, diurnal and diurnal without lights-on Period activities. Females injected with aegMAG showed significant decreases in nocturnal and nocturnal without lights-off period activities. Females injected with albMAG showed significant decreases in lights-off activity. A total of 83% of Ae. albopictus females injected with aegMAG and 10% of females injected with albMAG were inseminated by conspecific males. These results, coupled with our previous paper on MAG and interspecific mating effects on female Ae. aegypti, demonstrate contrasting outcomes on locomotor activities and loss of sexual receptivity, both conspecific and heterospecific MAGs capable of sterilizing virgin Ae. aegypti, but only conspecific MAGs sterilizing Ae. albopictus, whereas locomotor activities were depressed in females of both species after heterospecific and conspecific injections or treatments.

Into the woods: Changes in mosquito community composition and presence of key vectors at increasing distances from the urban edge in urban forest parks in Manaus, Brazil

Mosquito-borne Zika virus (ZIKV) was recently introduced into the Americas and now has the potential to spill back into a sylvatic cycle in the region, likely involving non-human primates and Aedes, Haemagogus, and Sabethes species mosquitoes. We investigated potential routes of mosquito-borne virus exchange between urban and sylvatic transmission cycles by characterizing mosquito communities in three urban forest parks that receive heavy traffic from both humans and monkeys in Manaus, Brazil. Parks were stratified by both distance from the urban-forest edge (0, 50, 100, and 500 m) and relative Normalized Difference Vegetation Index (NDVI) (low, medium, or high), and mosquitoes were sampled at randomly selected sites within each stratum using BG-Sentinel traps. Additionally, temperature, relative humidity, and other environmental data were collected at each site. A total of 1,172 mosquitoes were collected from 184 sites sampled in 2018, of which 98 sites were resampled in 2019. Using park as the unit of replication (i.e. 3 replicates per sampling stratum), a two-way ANOVA showed no effect of distance or NDVI on the mean number of identified species (P > 0.05 for both comparisons) or on species diversity as measured by the Shannon-Wiener diversity index (P > 0.10 for both comparisons). However, the Morisita overlap index revealed that mosquito communities changed substantially with increasing distance from edge, with communities at 0 m and 500 m being quite distinct. Aedes albopictus and Ae. aegypti penetrated at least 100 m into the forest, while forest specialists including Haemagogus janthinomys, Sabethes glaucodaemon, and Sa. tridentatus were detected in low numbers within 100 m from the forest edge. Trichoprosopon digitatum and Psorophora amazonica were among the most abundant species collected, and both showed distributions extending from the forest edge to its interior. Our results show overlapping distributions of urban and forest mosquitoes at park edges, which highlights the risk of arbovirus exchange via multiple bridge vectors in Brazilian urban forest parks. These parks may also provide refugia for both Ae. albopictus and Ae. aegypti from mosquito control programs.

The Asian tiger mosquito in Brazil: Observations on biology and ecological interactions since its first detection in 1986

Aedes (Stegomyia) albopictus is a mosquito originating from the Asian continent, which was detected in the Americas in 1985 and Brazil in 1986. Due to its rapid expansion throughout Brazil, this species has already been reported in 26 of the 27 federative units of Brazil. In this review, we evaluate some of the biological, epidemiological and ecological characteristics of Ae. albopictus through critical analysis of their importance in the pathogen transmission dynamics, since its first record in the country. We show that immature forms of this species are frequently found in artificial breeding sites whereas females exhibit anthropophilic behavior despite its eclecticism on blood feeding. In addition, Ae. albopictus shows advantages in interspecific competition with Ae. aegypti for both immature and adult stages. Taking together, these aspects as well as its vector competence indicate that Ae. albopictus could act as a bridge vector between sylvatic and urban pathogen transmission cycles. We conclude by pointing to the need of continuous surveillance of Ae. albopictus in Brazil and raise several questions that still need to be answered.

Demonstration of resistance to satyrization behavior in Aedes aegypti from La Réunion island

Aedes aegypti and Aedes albopictus are competent vectors of arboviruses such as dengue and chikungunya viruses which co-exist in some areas, including La Réunion island, Indian Ocean. A type of reproductive interference called satyrization has been described in sympatric species where dominant species mating fails to produce hybrids and thus reduces the fitness and tends to control the spread of the other species. Here, we investigated satyrization in laboratory experiments to provide insights on the potential impact on Ae. aegypti of a control campaign including a sterile insect technique component against Ae. albopictus. Different mating crosses were used to test sympatric, conspecific-interspecific and allopatric effects of irradiated and non-irradiated male Ae. albopictus on female Ae. aegypti, including in a situation of skewed male ratio. Our results suggest that there was only a low level of satyrization between sympatric populations of Ae. aegypti and Ae. albopictus colonized from La Réunion island. A male Ae. albopictus to female Ae. aegypti ratio of 3:1 did not increase the level of satyrization. Female Ae. aegypti previously mated to male Ae. albopictus were not prevented from being inseminated by conspecific males. A satyrization effect was not seen between allopatric Ae. albopictus and Ae. aegypti strains from La Réunion Island either. The tested Ae. aegypti strain from La Réunion island has therefore developed full resistance to satyrization and so releasing sterile male Ae. albopictus may not suppress Ae. aegypti populations if an overflooding of irradiated male Ae. albopictus leads to similar results. The management strategy of two competent species in a sympatric area is discussed.

Gene expression profile of Aedes aegypti females in courtship and mating

Aedes aegypti is the most synanthropic and anthropophilic mosquito of Culicidae. This species always cohabits with humans and is extremely opportunistic. Vector dispersal is directly related to the ability of the females on successfully finding a mate in a generally patchy urban scenario. In the present work, we investigate transcriptional changes in Ae. aegypti females during the courtship process and after mating. We observe a substantial alteration in gene expression triggered just upon contact with Ae. aegypti males, which in turn was not fully correlated to the changes triggered by the contact. After analysing shared significant differentially regulated genes between conspecific contact and insemination, the major part of the observed transcriptomic change triggered by contact is reversed after mating, indicating an intermediary situation between naive and mating conditions that we hypothesize to be crucial for mating success. Upon contact, several chemosensory related genes are repressed, especially odorant binding proteins. Most of these genes return to higher expression rates after mating. None of these genes are significantly regulated by the encounter of a different species, Aedes albopictus. The results presented here might be applied to an innovative control approach focusing on the semiochemical systems of mosquitoes in an effort to disrupt undesirable host–insect interaction to reduce the risk of pathogen transmission to humans.

Where Vectors Collide: The Importance of Mechanisms Shaping the Realized Niche for Modeling Ranges of Invasive Aedes Mosquitoes

The vector mosquitoes Aedes aegypti (L.), native to Africa, and Aedes albopictus (Skuse), native to Asia, are widespread invasives whose spatial distributions frequently overlap. Predictive models of their distributions are typically correlative rather than mechanistic, and based on only abiotic variables describing putative environmental requirements despite extensive evidence of competitive interactions leading to displacements. Here we review putative roles of competition contributing to distribution changes where the two species meet. The strongest evidence for competitive displacements comes from multiple examples of habitat segregation where the two species co-occur and massive reductions in the range and abundance of A. aegypti attributable to A. albopictus invasions in the southeastern U.S.A. and Bermuda (U.K). We summarize evidence to support the primacy of asymmetric reproductive interference, or satyrization, and larval resource competition, both favoring A. albopictus, as displacement mechanisms. Where evidence of satyrization or interspecific resource competition is weak, differences in local environments or alternative ecologies or behaviors of these Aedes spp. may explain local variation in the outcomes of invasions. Predictive distribution modeling for both these major disease vectors needs to incorporate species interactions between them as an important process that is likely to limit their realized niches and future distributions. Experimental tests of satyrization and resource competition are needed across the broad ranges of these species, as are models that incorporate both reproductive interference and resource competition to evaluate interaction strengths and mechanisms. These vectors exemplify how fundamental principles of community ecology may influence distributions of invasive species.