Culex molestus Forskal (Diptera: Culicidae) in Australia: colonisation, stenogamy, autogeny, oviposition and larval development

Interindividual variation among Culex pipiens larvae in terms of thermal response

This study aims to determine the phenological characteristics of thermal responses in the larvae of a Culex pipiens complex field population at the individual level under the influence of thermal regime of its habitat. The analysis is based on a structured population model quantifying the thermal responses of development time and survival under variable conditions and characterising the variety between the larvae (interindividual variety). During the study performed in Turkish Thrace on a monthly basis between May 2021 and June 2022, a total of 3744 larvae were reared as peer larval cohorts and 2330 larvae as siblings in artificial containers to be fully exposed to the natural thermal condition that was recorded hourly. The development process of larvae was monitored daily from egg to adult. As a result, a total of 4788 adult mosquitoes emerged, with a development period ranging from 8 to 52 days in the females and 7 to 50 days in the males, and the survival rate was found to range from 0% to 100%. Both parameters varied by month and individuals, and the variations manifested itself, particularly in the colder periods. The results indicate that the variation between the individuals in terms of thermal response in the larvae of C. pipiens, along with the thermal acclimation ability, appears to be fate determinant in resisting fluctuating thermal regimes, surviving in concurrent climate change and adapting to new conditions with modifications in the seasonal phenology, such as maintaining reproductive dynamics throughout the winter thanks to global warming.

Scoping review of Culex mosquito life history trait heterogeneity in response to temperature

BACKGROUND

Mosquitoes in the genus Culex are primary vectors in the US for West Nile virus (WNV) and other arboviruses. Climatic drivers such as temperature have differential effects on species-specific changes in mosquito range, distribution, and abundance, posing challenges for population modeling, disease forecasting, and subsequent public health decisions. Understanding these differences in underlying biological dynamics is crucial in the face of climate change.

METHODS

We collected empirical data on thermal response for immature development rate, egg viability, oviposition, survival to adulthood, and adult lifespan for Culex pipiens, Cx. quinquefasciatus, Cx. tarsalis, and Cx. restuans from existing literature according to the PRISMA scoping review guidelines.

RESULTS

We observed linear relationships with temperature for development rate and lifespan, and nonlinear relationships for survival and egg viability, with underlying variation between species. Optimal ranges and critical minima and maxima also appeared varied. To illustrate how model output can change with experimental input data from individual Culex species, we applied a modified equation for temperature-dependent mosquito type reproduction number for endemic spread of WNV among mosquitoes and observed different effects.

CONCLUSIONS

Current models often input theoretical parameters estimated from a single vector species; we show the need to implement the real-world heterogeneity in thermal response between species and present a useful data resource for researchers working toward that goal.

Behavioural response of Culex pipiens biotype molestus to oviposition pheromone

Insect behaviour relies on an olfactory sensory system that controls a range of activities, from food choice and mating to oviposition, where pheromones play a central role. In Culex mosquitoes, egg-laying is accompanied by the release of mosquito oviposition pheromone (MOP), which has been shown to affect the oviposition behaviour of conspecifics. Here, we investigated for the first time the effect of MOP on the oviposition rate of Culex pipiens biotype molestus, examining separately males and females, before and after mating and oviposition. Our results demonstrate that MOP is more likely to act as an oviposition stimulant rather than an attractant, since more gravid females laid eggs in its presence, while the number of male or female mosquitoes (virgin or mated) captured on pheromone-treated pots was similar to those treated with control water.

Distribution of insecticide resistance and molecular mechanisms involved in the West Nile vector Culex pipiens in Morocco

BACKGROUND

Mosquitoes of the Culex pipiens complex are the vectors of several arboviruses and are thus subjected to insecticide control worldwide. However, overuse of insecticides selects for resistance. While assessing the resistance status of the vectors is required for effective and sustainable disease control, resistance has so far only been sparsely studied in Morocco. In this study, we establish a first countrywide assessment of the levels of resistance to various insecticides and the potential responsible mechanisms involved. Cx. pipiens larvae were collected from natural populations of five regions of Morocco, and their taxonomic status was determined (molecular forms). The level of their susceptibility to insecticides was assessed by single-diagnostic-dose bioassays. Molecular identification of known resistance alleles was investigated to determine the frequency of target-site mutations.

RESULTS

This study confirms that Moroccan populations are an interbreeding mix of pipiens and molestus forms, with large gene flow for the resistance alleles. We also found that Cx. pipiens mosquitoes are resistant to all insecticide families, all over Morocco: resistance is high for insecticides used in mosquito control, but also present for other pesticides. Resistance alleles are similarly more frequent for mosquito control insecticides. However, their distribution is heterogeneous in the five regions, with significant genetic differentiation between populations, revealing the crucial role of local insecticide treatment practices.

CONCLUSION

This study provides reference countrywide data that highlight the need for further research to refine the distribution of resistance in Morocco and to understand the role of agriculture/urban residuals in its spread. © 2020 Society of Chemical Industry.

Citizen science and smartphone e-entomology enables low-cost upscaling of mosquito surveillance

Mosquito surveillance remains a cornerstone of pest and disease control operations globally but is strongly limited in scale by resources. The use of citizen science to upscale scientific data collection is commonplace, and mosquito surveillance programs have begun to make use of citizen scientists in several countries, particularly for exotic species detection. Here we report on a proof of concept trial in southern Australia for a citizen science mosquito surveillance program characterised by fixed point trapping with BG GAT devices and remote mosquito identification through emailed images, which we term 'e-entomology'. In a study with 126 participants, we detected mosquito seasonality with peak abundance in mid-summer (1.78 mosquitoes per trap per day), weather correlations (positive correlation with maximum temperature, r = 0.41) and a diversity of species (15 of 22 known species in the region) in a metropolitan setting. Whilst we demonstrated that the costs of a citizen science program is only about 20% of a comparable professional surveillance program, the mosquito community sampled by citizen scientists was biased towards container-inhabiting species, particularly Aedes notoscriptus. This is the first time fixed-point mosquito trapping has been combined with citizen science e-entomology to deliver comprehensive surveillance of urban mosquitoes.

Autogeny, Fecundity, and Other Life History Traits of Culex pipiens molestus (Diptera: Culicidae) in Shanghai, China

Culex pipiens molestus Forskål is common in subterranean and aboveground environments in Shanghai, China. However, little is known about its autogeny, fecundity, and other life history traits. In this study, Cx. p. molestus larvae were collected from four different types of underground parking lots and artificially maintained, without blood feeding, in a laboratory. Life history traits parameters were recorded from the F0 to F9 generation. Culex pipiens molestus from Shanghai can autogenously persist for at least 10 generations, and some females can develop more than one egg batch without blood feeding (oviposition rate in Lot C was >100% in some generations). The average number of eggs per raft produced autogenously ranged from 36.94 to 42.19. The average generation time (GT) ranged from 20.06 to 21.30 d, and the pre-oviposition time (POT) ranged from 2.17 to 12.68 d among the generations. Culex pipiens molestus from the four groups had different autogeny, fecundity, and longevity patterns. This variability may result from genetic polymorphism caused by co-occurrence with other Culex pipiens subspecies (Diptera: Culicidae).

Accurate identification of Australian mosquitoes using protein profiling

Australian mosquito species significantly impact human health through nuisance biting and the transmission of endemic and exotic pathogens. Surveillance programmes designed to provide an early warning of mosquito-borne disease risk require reliable identification of mosquitoes. This study aimed to investigate the viability of Matrix-Assisted Laser Desorption/Ionization-Time-of-Flight Mass Spectrometry (MALDI-TOF MS) as a rapid and inexpensive approach to the identification of Australian mosquitoes and was validated using a three-step taxonomic approach. A total of 300 mosquitoes representing 21 species were collected from south-eastern New South Wales and morphologically identified. The legs from the mosquitoes were removed and subjected to MALDI-TOF MS analysis. Fifty-eight mosquitoes were sequenced at the cytochrome c oxidase subunit I (cox1) gene region and genetic relationships were analysed. We create the first MALDI-TOF MS spectra database of Australian mosquito species including 19 species. We clearly demonstrate the accuracy of MALDI-TOF MS for identification of Australian mosquitoes. It is especially useful for assessing gaps in the effectiveness of DNA barcoding by differentiating closely related taxa. Indeed, cox1 DNA barcoding was not able to differentiate members of the Culex pipiens group, Cx. quinquefasciatus and Cx. pipiens molestus, but these specimens were correctly identified using MALDI-TOF MS.

Ecological differentiation of members of the Culex pipiens complex, potential vectors of West Nile virus and Rift Valley fever virus in Algeria

Background

We investigated the ecological differentiation of two members of the Culex pipiens complex, Cx. p. pipiens form pipiens and Cx. p. pipiens form molestus in three sites, El-Kala, M'Sila and Tinerkouk in Algeria. These two forms are the most widespread mosquito vectors in temperate regions exhibiting important behavioural and physiological differences. Nevertheless, this group of potential vectors has been poorly studied, particularly in North Africa.

Methods

Ten larval populations of Cx. p. pipiens were sampled from various above- and underground habitats in three zones representing the three bioclimatic regions in Algeria. The reproduction characteristics were also investigated in the laboratory to define the rates of autogeny and stenogamy. Identification of Cx. p. pipiens members present in Algeria was achieved using a molecular analysis with the microsatellite CQ11 locus.

Results

We detected larvae of Cx. p. pipiens in all areas suggesting that the species is a ubiquitous mosquito well adapted to various environments. To our knowledge, this study provides the first molecular evidence of the presence of the Cx. p. pipiens form molestus and hybrids (molestus/pipiens) in Algeria with a high proportion of molestus form (48.3 %) in comparison with hybrids (36.8 %) and pipiens form (14.9 %).

Conclusions

Some unexpected correlations between the proportion of forms pipiens, molestus and hybrids, and mosquito biological characteristics were observed suggesting some epigenetic effects controlling Cx. p. pipiens mating and reproduction. Consequences for pathogen transmission are discussed.

Electronic supplementary material

The online version of this article (doi:10.1186/s13071-016-1725-9) contains supplementary material, which is available to authorized users.

Age-Stage, Two-Sex Life Table Characteristics of Aedes albopictus and Aedes Aegypti in Penang Island, Malaysia

The life table developmental attributes of laboratory colonies of wild strains of Aedes albopictus and Aedes aegypti were analyzed and compared based on the age-stage, two-sex life table. Findings inclusive in this study are: adult preoviposition periods, total preoviposition period, mean intrinsic rate of increase (r), mean finite rate of increase (λ), net reproductive rates (R0), and mean generation time (T). The total preadult development time was 9.47 days for Ae. albopictus and 8.76 days for Ae. aegypti. The life expectancy was 19.01 days for Ae. albopictus and 19.94 days for Ae. aegypti. Mortality occurred mostly during the adult stage. The mean development time for each stage insignificantly correlated with temperature for Ae. albopictus (r  =  -0.208, P > 0.05) and (r  =  -0.312, P > 0.05) for Ae. aegypti. The population parameters suggest that Ae. albopictus and Ae. aegypti populations are r-strategists characterized by a high r, a large R0, and short T. This present study provides the first report to compare the life parameters of Ae. albopictus and Ae. aegypti strains from Penang island, Malaysia.

The importance of males: larval diet and adult sugar feeding influences reproduction in Culex molestus

Culex molestus is an obligatory autogenous mosquito that is closely associated with subterranean habitats in urban areas. The objective of our study was to investigate the influence of larval and adult nutrition on the role of males in determining the expression of autogeny in Cx. molestus. Mosquitoes raised at low and high larval diets had sex ratio, wing length, mating rates, autogenous egg raft size, and hatching rates recorded. There was a higher ratio of males to females when raised at a low larval diet. Mean wing lengths of both males and females were significantly greater when raised at the high larval diet regime. Regardless of larval or adult diet, males mated with only a single female. Mosquitoes raised at the higher larval diet regimes developed significantly more autogenous eggs. However, the egg raft size was reduced when adult females were denied access to sugar. The results of this study indicate that the performance of males in the reproductive process is influenced by both larval diet and adult sugar feeding.

A review of the status and significance of the species within the Culex pipiens group in Australia

The mosquito known in the northern hemisphere as Culex pipiens (a.k.a. Culex pipiens pipiens or Culex pipiens form pipiens) is not known from Australia. However, there are four species of the Culex pipiens group: two indigenous, Culex australicus and Culex globocoxitus, and two introduced, Culex quinquefasciatus and what is known locally as Culex molestus (? = Culex pipiens molestus or Culex pipiens form molestus), all four being members of the pipiens subgroup (= 'pipiens complex'). The species status of the indigenous Cx. australicus and Cx. globocoxitus in Australia appears to be accepted as legitimate; however, the true identity of the mosquito called 'Cx. molestus' in Australia remains contentious, even as its local profile has been increasing over the past 40 years. This paper provides an overview of the taxonomic and biologic knowledge of these species, and their public health significance as vectors of arboviruses in Australia.

Autogeny in Culex pipiens complex mosquitoes from the San Francisco Bay Area

We surveyed the genetic ancestry and recorded the occurrence of autogeny, the developmental times, and survival rates in families of Culex pipiens in Santa Clara County, CA, at 37°N latitude. Females in 95% of the families produced fertile egg rafts without access to blood (= autogeny) after mating in stenogamous conditions. Developmental time, survival, and egg raft production were closely correlated to temperature. Male DV/D ratios overwhelmingly matched Cx. pipiens but a microsatellite analysis revealed these were Cx. pipiens form molestus hybridized with Culex quinquefasciatus and to a lesser extent to Cx. pipiens form pipiens, a genetic mix heretofore not recorded elsewhere. Greater DV/D ratios and larger proportions of genetic ancestry from Cx. quinquefasciatus were negatively correlated to autogeny. The combination of multiple overwintering strategies and widespread autogeny in females arising from aboveground larval sites supports the hypothesis that some North American populations of Cx. pipiens complex mosquitoes express unusual phenologies.