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.

Patterns of genetic divergence among populations of Aedes aegypti L. (Diptera: Culicidae) in the southeastern USA

Background

The yellow fever mosquito, Aedes aegypti is a public health concern in the USA, especially in the wake of emergent diseases such as Zika and chikungunya. Aedes aegypti populations dwindled after the invasion of Aedes albopictus in the 1980s and many populations were extirpated. However, in some areas Ae. aegypti persisted in small populations and there are reports of recent resurgences of Ae. aegypti in Florida, Louisiana, Nevada and California. We assessed the population genetic structure of Ae. aegypti in Florida and Georgia, which has concomitant consequences related to mosquito dispersal, pesticide resistance and vectorial capacity.

Methods

We collected Ae. aegypti across Florida and in Georgia using ovitraps. We hatched the eggs and reared them to adults, and after sacrifice we extracted their DNA. We then probed each individual for variation in 6 microsatellite markers, which we used to address population genetic characteristics.

Results

We collected Ae. aegypti and genotyped seven Florida populations and one Georgia population using microsatellite markers. We found evidence of isolation by distance model of gene flow supported by driving distance among cities within Florida and two theoretic genetic clusters.

Conclusions

Significant genetic structure between some populations with substantial gene flow between geographically distant cities suggests regional genetic structuring of Ae. aegypti in Florida. This study provides information on the genetic exchange between populations of Ae. aegypti in the southeastern USA and suggests potential routes of spread of this species.

Widespread evidence for interspecific mating between Aedes aegypti and Aedes albopictus (Diptera: Culicidae) in nature

Aedes aegypti and Aedes albopictus, two important vectors of the dengue and chikungunya viruses to humans, often come in contact in their invasive ranges. In these circumstances, a number of factors are thought to influence their population dynamics, including resource competition among the larval stages, prevailing environmental conditions and reproductive interference in the form of satyrization. As the distribution and abundance of Ae. aegypti and Ae. albopictus have profound epidemiological implications, understanding the competitive interactions that influence these patterns in nature is important. While evidence for resource competition and environmental factors had been gathered from the field, the evidence for reproductive interference, though strongly inferred through laboratory trials, remained sparse (one small-scale field trial). In this paper we demonstrate that low rates (1.12-3.73%) of interspecific mating occur in nature among populations of these species that have co-existed sympatrically from 3 to 150yrs. Finally this report contributes a new species-specific primer set for identifying the paternity of sperm extracted from field collected specimens.