Larval habitat for the avian malaria vector Culex quinquefasciatus (Diptera: Culicidae) in altered mid‐elevation mesic‐dry forests in Hawai'i

Effective management of avian malaria (Plasmodium relictum) in Hawai'i's endemic honeycreepers (Drepanidinae) requires the identification and subsequent reduction or treatment of larval habitat for the mosquito vector, Culex quinquefasciatus (Diptera: Culicidae). We conducted ground surveys, treehole surveys, and helicopter aerial surveys from 2001–2003 to identify all potential larval mosquito habitat within two 100+ ha mesic‐dry forest study sites in Hawai'i Volcanoes National Park, Hawai'i; ‘Ainahou Ranch and Mauna Loa Strip Road. At ‘Ainahou Ranch, anthropogenic sites (43%) were more likely to contain mosquitoes than naturally occurring (8%) sites. Larvae of Cx. quinquefasciatus were predominately found in anthropogenic sites while Aedes albopictus larvae occurred less frequently in both anthropogenic sites and naturally‐occurring sites. Additionally, moderate‐size (≈20–22,000 liters) anthropogenic potential larval habitat had >50% probability of mosquito presence compared to larger‐ and smaller‐volume habitat (<50%). Less than 20% of trees surveyed at ‘Ainahou Ranch had treeholes and few mosquito larvae were detected. Aerial surveys at ‘Ainahou Ranch detected 56% (95% CI: 42–68%) of the potential larval habitat identified in ground surveys. At Mauna Loa Strip Road, Cx. quinquefasciatus larvae were only found in the rock holes of small intermittent stream drainages that made up 20% (5 of 25) of the total potential larval habitat. The volume of the potential larval habitat did not influence the probability of mosquito occurrence at Mauna Loa Strip Road. Our results suggest that Cx. quinquefasciatus abundance, and subsequently avian malaria, may be controlled by larval habitat reduction in the mesic‐dry landscapes of Hawai'i where anthropogenic sources predominate.     

Blood‐feeding ecology of mosquitoes in zoos

To determine if the unique host assemblages in zoos influence blood‐feeding by mosquitoes (Diptera: Culicidae), a sampling programme was conducted in Greenville and Riverbanks Zoos, South Carolina, U.S.A., from April 2009 to October 2010. A total of 4355 female mosquitoes of 14 species were collected, of which 106 individuals of nine species were blood‐fed. The most common taxa were Aedes albopictus (Skuse), Aedes triseriatus (Say), Anopheles punctipennis (Say), Culex erraticus (Dyar & Knab), Culex pipiens complex (L.) and Culex restuans (Theobald). Molecular analyses (cytochrome b) of bloodmeals revealed that mosquitoes fed on captive animals, humans and wildlife, and took mixed bloodmeals. Host species included one amphibian, 16 birds, 10 mammals (including humans) and two reptiles. Minimum dispersal distances after feeding on captive hosts ranged from 15.5 m to 327.0 m. Mosquito–host associations generally conformed to previous accounts, indicating that mosquito behaviour inside zoos reflects that outside zoos. However, novel variation in host use, including new, exotic host records, warrants further investigation. Zoos, thus, can be used as experiment environments in which to study mosquito behaviour, and the findings extrapolated to non‐zoo areas, while providing medical and veterinary benefits to zoo animals, employees and patrons.     

The roles of history: age and prior exploitation in aquatic container habitats have immediate and carry‐over effects on mosquito life history

1. Per‐capita resource availability in aquatic habitats is influenced directly by consumer density via resource competition and indirectly via delayed resource competition when temporally non‐overlapping cohorts of larvae exploit the same resources. In detritus‐based systems, resources are likely to be influenced by the age of the aquatic habitat, as detritus changes in quality over time and may be replenished by new inputs. 2. For aquatic insects that exploit detritus‐based habitats, feeding conditions experienced during immature stages can influence fitness directly via effects on development and survivorship, but also indirectly by influencing adult traits such as fecundity and longevity. 3. Larval habitat age and prior resource exploitation were manipulated in a field experiment using the container mosquito Aedes triseriatus. 4. It was found that A. triseriatus from older habitats had greater larval survival, faster development and greater adult longevity. Exploitation of larval habitats by a prior cohort of larvae had a significant negative effect on subsequent cohorts of larvae by delaying development. 5. It is suggested that extended conditioning of detritus probably resulted in conversion of recalcitrant resources to more available forms which improved the quality of the habitat. 6. In a parallel study, evidence was found of carry‐over effects of habitat age and prior exploitation on adult longevity for A. triseriatus and Aedes japonicus collected from unmanipulated aquatic habitats. 7. These results indicate the importance of detritus dynamics and the discontinuous nature of resource competition in these mosquito‐dominated aquatic systems.     

Transgenerational effect of infection in Plasmodium-infected mosquitoes

Transgenerational effects of infection have a huge potential to influence the prevalence and intensity of infections in vectors and, by extension, disease epidemiology. These transgenerational effects may increase the fitness of offspring through the transfer of protective immune factors. Alternatively, however, infected mothers may transfer the costs of infection to their offspring. Although transgenerational immune protection has been described in a dozen invertebrate species, we still lack a complete picture of the incidence and importance of transgenerational effects of infection in most invertebrate groups. The existence of transgenerational infection effects in mosquito vectors is of particular interest because of their potential for influencing parasite prevalence and intensity and, by extension, disease transmission. Here we present what we believe to be the first study on transgenerational infection effects in a mosquito vector infected with malaria parasites. The aim of this experiment was to quantify both the benefits and the costs of having an infected mother. We find no evidence of transgenerational protection in response to a Plasmodium infection. Having an infected mother does, however, entail considerable fecundity costs for the offspring: fecundity loss is three times higher in infected offspring issued from infected mothers than in infected offspring issued from uninfected mothers. We discuss the implications of our results and we call for more studies looking at transgenerational effects of infection in disease vectors.     

Characterisation of Culex quinquefasciatus (Diptera: Culicidae) larval habitats at ground level and temporal fluctuations of larval abundance in Córdoba, Argentina

The aims of this study were to characterise the ground-level larval habitats of the mosquito Culex quinquefasciatus, to determine the relationships between habitat characteristics and larval abundance and to examine seasonal larval-stage variations in Córdoba city. Every two weeks for two years, 15 larval habitats (natural and artificial water bodies, including shallow wells, drains, retention ponds, canals and ditches) were visited and sampled for larval mosquitoes. Data regarding the water depth, temperature and pH, permanence, the presence of aquatic vegetation and the density of collected mosquito larvae were recorded. Data on the average air temperatures and accumulated precipitation during the 15 days prior to each sampling date were also obtained. Cx. quinquefasciatus larvae were collected throughout the study period and were generally most abundant in the summer season. Generalised linear mixed models indicated the average air temperature and presence of dicotyledonous aquatic vegetation as variables that served as important predictors of larval densities. Additionally, permanent breeding sites supported high larval densities. In Córdoba city and possibly in other highly populated cities at the same latitude with the same environmental conditions, control programs should focus on permanent larval habitats with aquatic vegetation during the early spring, when the Cx. quinquefasciatus population begins to increase.     

Cytoplasmic incompatibilities in the mosquito Culex pipiens: How to explain a cytotype polymorphism?*

Although cytoplasmic incompatibilities have been used as a means of eradicating the mosquito Culex pipiens, the population dynamics of these sterilities in relation to the coexistence of multiple incompatible cytotypes in a single area has not been investigated, except in the case of two unidirectionally incompatible cytotypes. An analytical model of the evolution of n cytotypes in an infinite panmictic population has been developed in order to investigate polymorphic equilibrium. A necessary criterion for the stability of such an equilibrium is established; it is shown that a stable polymorphism cannot exist between incompatible cytotypes. This result is discussed in the light of population dynamics and genetics of Culex pipiens, and of our present knowledge on incompatibilities. The consequences of a geographic structuring and of homogamy are considered. A careful reconsideration of previous experimental results disclosed probable nuclear effects and a serious experimental weakness: with the common procedure of backcrossing hybrid females to males of constant genotype it is not possible to rule out probable nuclear effects with paternal expression. It is concluded that incompatibilities in Culex pipiens may have a nuclear-cytoplasmic determinism.     

Mosquitoes and West Nile virus along a river corridor from prairie to montane habitats in eastern Colorado

We conducted studies on mosquitoes and West Nile virus (WNV) along a riparian corridor following the South Platte River and Big Thompson River in northeastern Colorado and extending from an elevation of 1,215 m in the prairie landscape of the eastern Colorado plains to 1,840 m in low montane areas at the eastern edge of the Rocky Mountains in the central part of the state. Mosquito collection during June‐September 2007 in 20 sites along this riparian corridor yielded a total of 199,833 identifiable mosquitoes of 17 species. The most commonly collected mosquitoes were, in descending order: Aedes vexans, Culex tarsalis, Ae. dorsalis, Ae. trivittatus, Ae. melanimon, Cx. pipiens, and Culiseta inornata. Species richness was higher in the plains than in foothills‐montane areas, and abundances of several individual species, including the WNV vectors Cx. tarsalis and Cx. pipiens and the nuisance‐biter and potential secondary WNV vector Ae. vexans, decreased dramatically from the plains (1,215‐1,487 m) to foothills‐montane areas (1,524‐1,840 m). Ae. vexans and Cx. tarsalis had a striking pattern of uniformly high abundances between 1,200‐1,450 m followed by a gradual decrease in abundance above 1,450 m to reach very low numbers above 1,550 m. Culex species were commonly infected with WNV in the plains portion of the riparian corridor in 2007, with 14 of 16 sites yielding WNV‐infected Cx. tarsalis and infection rates for Cx. tarsalis females exceeding 2.0 per 1,000 individuals in ten of the sites. The Vector Index for abundance of WNV‐infected Cx. tarsalis females during June‐September exceeded 0.5 in six plains sites along the South Platte River but was uniformly low (0–0.1) in plains, foothills and montane sites above 1,500 m along the Big Thompson River. A population genetic analysis of Cx. tarsalis revealed that all collections from the ≈190 km riparian transect in northeastern Colorado were genetically uniform but that these collections were genetically distinct from collections from Delta County on the western slope of the Continental Divide. This suggests that major waterways in the Great Plains serve as important dispersal corridors for Cx. tarsalis but that the Continental Divide is a formidable barrier to this WNV vector.     

Diel activity patterns of blood-seeking anthropophilic mosquitoes in central Sweden

1. Blood-seeking diel activity cycles of mosquitoes are described from 24 h landing catches on human bait in a field and a forest habitat during June-August in central Sweden. 2. Daytime activity in the field was low or absent, whilst in the forest activity was relatively even throughout the diel. 3. In both habitats, activity peaks generally occurred about sunset and sunrise and were more distinct in the field than in the forest. 4. Data from this and other studies show that, in general, Aedes cinereus Meigen feeds at night in field-type habitats and Ae.communis (DeGeer) during the diurnal-crepuscular period in forest and woodland habitats. 5. Although abundant in the study area, Anopheles maculipennis Meigen sensu lato, Culex pipiens L., Cx torrentium Martini and Culiseta morsitans (Theobald) were not caught on the human bait. This is because, in central Sweden, An.maculipennis s.l. is mainly feeding in animal sheds whereas the others are ornithophagous. 6. Ae.geniculatus (Olivier) was recorded from central Sweden for the first time. 7. Blood feeding success (proportion of mosquitoes that managed to obtain blood from the human bait) was significantly greater in Ae.cinereus (14.9%) than in Ae.punctor (Kirby), Ae.communis and Ae.annulipes (Meigen) (2.8-0.7%). 8. The data are interpreted in relation to the transmission of Ockelbo disease (caused by Sindbis virus) and tularaemia in Sweden.     

Preliminary report of knockdown resistance in Culex pipiens pallens and Aedes koreicus from Korea

Pyrethroid insecticides have been effective and powerful for controlling mosquitoes. However, abuse of these insecticides increases the number of resistant mosquitoes. In this study, Culex pipiens pallens and Aedes koreicus were collected from an artificial reservoir in the vicinity of a populated area in Korea, which is also a migratory bird catchment area. To monitor resistance to pyrethroid insecticides in mosquitoes, genomic DNA from the collected mosquitoes was sequenced for the kdr mutation in the voltage‐gated sodium channel (VGSC) gene. As a result, three samples with homozygous resistance (17.6%) and one with heterozygous resistance (5.9%) were found among 17 Cx. pipiens pallens specimens. One of the samples had a unique sequence at the amplified VGSC region. Of the 15 Ae. koreicus, no insecticide resistant individuals were found. In Korea, this is the first report of kdr genetic traits in Ae. koreicus and Cx. pipiens pallens and of a unique VGSC allele in Cx. pipiens pallens. Further investigation is needed to monitor the kdr resistance of these species in Korea and to determine how the unique sequence found in Cx. pipiens pallens is related to insecticide resistance.