Factors influencing the abundance of Japanese encephalitis vectors in ricefields in India--II. Biotic

The relationship of insect predators and phytoplankton with the abundance of Culex tritaeniorhynchus Giles, Cx. vishnui Theobald and Cx. pseudovishnui Colless mosquito larvae and pupae (Diptera: Culicidae) in ricefields was investigated during three rice growing seasons. Notonectids were the most abundant insect predators, whereas diatoms dominated among phytoplankton. Multiple regression analysis showed that the occurrence of notonectids (both nymphs and adults) was negatively associated with larval abundance. Phytoplankton, especially diatoms and blue green algae (BGA), were found to favour abundance of culicine immatures during Navarai and Kuruvai crops, respectively. Larval gut analysis showed that the intake of algae by late instars was high, with 93%, 58% and 24% of diatoms, BGA and green algae, respectively. Filamentous algae may not necessarily be of nutritive value, but they are observed to form mats, which provide protection to the mosquito immatures from the predators.     

Effects of organic and inorganic fertilisers on mosquito populations in rice fields of southern India

The effects of nitrogenous (inorganic) fertilisers, organic manures and blue-green algae (BGA) biofertiliser on mosquito populations (Diptera: Culicidae) were studied in rice fields of Madurai, Tamil Nadu, south India, with particular attention to Culex vishnui Theobald, Cx. pseudovishnui Colless and Cx. tritaeniorhynchus Giles, the vectors of Japanese encephalitis (JE). The application of urea, a nitrogenous fertiliser, in rice fields significantly increased the grain yield and the population densities of mosquito larvae and pupae (anophelines as well as culicines) in a dose-related manner. Fields treated with inorganic fertilisers (N, P, K) had significantly higher population densities of mosquito immatures than fields treated with organic manures (farmyard manure and green manure). Without nitrogenous fertiliser, BGA increased paddy yield without enhancing mosquito production. Therefore, the use of BGA with less nitrogenous fertiliser is recommended, which is beneficial economically and agronomically to the farming community and also significantly reduces mosquito production in rice fields. Increased use of nitrogenous fertiliser over the past two decades may have contributed to the increased severity of Japanese encephalitis epidemics, vectors of which breed in rice fields.     

The role of urea in the oviposition behaviour of Japanese encephalitis vectors in rice fields of South India

The effect of urea on the oviposition behaviour of culicine vectors of Japanese encephalitis was studied in rice fields. Gravid females had a strong preference for oviposition in urea treated areas in rice fields, while no such preference was exhibited in untreated areas. The egg laying declined in the area where urea treated water surface had a mechanical barrier, which allowed volatile fractions to escape, but prevented contact with the water. Urea was shown to act as an oviposition attractant/stimulant for Culex tritaeniorhynchus, but its role was not clear for Cx. vishnui, as the number of egg rafts obtained for the latter species was low.     

Evaluation of various control agents against mosquito larvae in rice paddies in Taiwan.

A field test was conducted in rice paddies adjacent to Wufeng, Taichung County in Central Taiwan to evaluate the efficacy of control agents against mosquito larvae. The agents included Bacillus thuringienesis israelensis (Bti), two Lagenidium giganteum products (Lg product A and T), and temephos. The major mosquito species found in the rice paddies were Culex tritaeniorhynchus/vishnui and Anopheles sinensis. Compared to controls, a 7-day treatment with Bti or Lg products A and T caused overall reductions in the number of immatures (larvae and pupae) of Cx. tritaeniorhynchus/vishnui of 77.5%, 49.7%, and 21.9%, respectively, whereas temephos caused an increase of 66.9%. The overall reductions in An. sinensis were 85.4%, 8.6%, 44.6%, and 92.1%, respectively. There was no significant reduction in the number of mosquito larvae following 42 days of treatment with these agents. In summary, 1-week treatments with both biological control agents produced moderate overall reductions in mosquito larvae in rice paddies. The insecticide temephos, on the other hand, was very effective at suppressing the larvae of An. sinensis but significantly increased the number of Cx. tritaeniorhynchus/vishnui larvae in temephos-treated plots.     

Population interactions between Culex vishnui mosquitoes and their natural enemies in Pondicherry, India.

Population interactions among mosquitoes in the Culex vishnui subgroup, which are vectors of Japanese Encephalitis, and their natural enemies were studied in Pondicherry, India. We tested the hypothesis that the breakdown of interactions between the larvae and their natural enemies due to drought followed by rain was responsible for the sudden increase in the vector population above the threshold for disease transmission during the heavy rainy period. We randomly sampled mosquito larvae and their predators in different breeding habitats and subjected the mean densities of prey, predator, and mosquito larvae infected with parasites/pathogens to covariate analysis to understand the interaction between prey and their natural enemies in relation to environmental factors. In rice fields, neither prey nor predator showed any positive correlation with temperature, RH, or the number of rainy days. However, the pathogen/parasite of mosquito immatures showed a positive correlation with RH. Among the mosquito predators, notonectids exhibited a significant positive correlation with Cx. vishnui larvae. The parasitic Romanomermis iyengari and pathogenic Coelomomyces anopheliscus also showed positive correlations with immatures. No parasites and pathogens of mosquito larvae were recorded in shallow water pools (SWP) or cement tanks (CT) during the study period. Important predators recorded in SWP were notonectids, damselfly nymphs, Diplonychus indicus, and hydrophilids. Dragonfly nymphs, gerrids, and tadpole shrimps were recorded in CT. In CT, prey and their predators were positively correlated with RH and rainy days. In SWP, there was a highly significant correlation between prey, predators and environmental factors. We conclude that rice fields are a stable ecosystem where regular interaction occurs between larvae and their natural enemies and a sudden increase in mosquito populations is uncommon. In transient habitats, no such stability is present and they become more important as breeding habitats in terms of seasonality and number. Shallow water pools should be seriously considered for the control of these vectors.     

Potential vectors of West Nile virus following an equine disease outbreak in Italy

In the late summer of 1998, an outbreak of equine encephalomyelitis due to West Nile virus (WNV) occurred in the Tuscany region of central Italy. The disease was detected in 14 race horses from nine localities in four Provinces: Firenze, Lucca, Pisa and Pistoia. The outbreak area included Fucecchio wetlands (1800 ha), the largest inland marsh in Italy, and the adjacent hilly Cerbaie woodlands with farms breeding horses. To detect potential vectors of WNV, entomological surveys of Fucecchio and Cerbaie were undertaken during 1999-2002 by collecting mosquito larvae from breeding sites and adult mosquitoes by several methods of sampling. Among 6023 mosquitoes (Diptera: Culicidae) collected, 11 species were identified: Aedes albopictus (Skuse), Ae. vexans (Meigen), Anopheles atroparvus Van Thiel, An. maculipennis Meigen s.s., An. plumbeus Stephens, Culex impudicus Ficalbi, Cx. pipiens L., Culiseta longiareolata Macquart), Ochlerotatus caspius (Pallas), Oc. detritus (Haliday) and Oc. geniculatus (Olivier). In Fucecchio marshes, Cx. impudicus predominated with seasonal peak densities in spring and autumn: its greatest abundance during early spring coincides with arrival of migratory birds from Africa. In Cerbaie hills, Cx. pipiens predominated with peak population density in late summer. No viruses were isolated from 665 mosquitoes processed. These findings, plus other data on Italian mosquito bionomics, suggest a possible mode of WNV transmission involving the most abundant Culex in the Fucecchio-Cerbaie areas. Culex impudicus, being partly ornithophilic, might transmit WNV from migratory to non-migratory birds during springtime; Cx. pipiens, having a broader host range, would be more likely to transmit WNV from birds to horses and, perhaps, to humans by late summer.     

Septic tank mosquitoes: competition between species in central Nigeria

Exit traps, placed over the air vents of septic tanks, were used to examine species diversity and relative abundance of mosquitoes breeding in ammonia-rich waters of septic tanks. Of the six species found, Culex decens Theobald and Culex cinereus Theobald appeared to be competing successfully with Culex quinquefasciatus Say during the wet season but not during the long dry season. The seasonal timing of their displacement by Cx quinquefasciatus was variable and did not correlate well with climatic factors. The three other species present, generally during the wet season and early dry season, were Culex tigripes G. & C., Culex horridus Edwards and Aedes aegypt (L.). Experimental bucket ovitraps were used to assess preference towards covered (dark) septic tank water in comparison with sunlit septic tank water, covered and sunlit compost water. These were colonized by Cx quinquefasciatus, Cx decens, Ae. aegypti and Ae. vittatus Bigot. The covered septic tank water was more abundantly colonized by Cx quinquefasciatus and marginally so by the two Aedes species. Cx decens appeared to colonize the exposed compost water more readily in the dry season, but changed to the covered septic tank water in the wet season. The discussion centres around competition between these mosquitos species and concludes that it would be useful to know what environmental factors, or what aspects of competition, lead to severe natural reductions in the abundance of the major pest species Cx quinquefasciatus.     

Temporal distribution of larval Chironomidae (Diptera) in experimental rice fields in Penang,Malaysia

The distribution and abundance of chironomid larvae were investigated in experimental rice fields at the Bukit Merah Agricultural Experimental Research Station, Penang, Northern Malaysia. The mean density of chironomid larvae during the period of the study (including two cultivation seasons) was 121 larvae m^?2. Chironomus kiiensis (48.6%) was the most abundant species, while four other species, Polypedilum trigonus (4.8%), Tanytarsus formosanus (22.6%), Tanypus punctipennis (13.9%), and Clinotanypus sp. (10.1%) occurred less frequently, although they were present during all wet phases of rice cultivation. Generally, water depth, rice plant height, conductivity, and nitrate–nitrogen content of the water only weakly influenced the abundance of the larvae. Other environmental parameters such as pH, dissolved oxygen, daytime water temperature, total suspended solids, phosphate, and sediment total organic matter did not significantly affect larval populations. The community structure of chironomids in this rice agroecosystem followed the dynamic changes of the field including agronomic practices, patterns of water availability, and phases of rice plant growth.     

Mosquito vectors of the 1998-1999 outbreak of Rift Valley Fever and other arboviruses (Bagaza, Sanar, Wesselsbron and West Nile) in Mauritania and Senegal

Following an outbreak of Rift Valley fever (RVF) in south-eastern Mauritania during 1998, entomological investigations were conducted for 2 years in the affected parts of Senegal and Mauritania, spanning the Sénégal River basin. A total of 92 787 mosquitoes (Diptera: Culicidae), belonging to 10 genera and 41 species, were captured in light traps. In Senegal, Culex poicilipes (41%) and Mansonia uniformis (39%) were the most abundant species caught, whereas Aedes vexans (77%) and Cx. poicilipes (15%) predominated in Mauritania. RVF virus was isolated from 63 pools of Cx. poicilipes: 36 from Senegal in 1998 and 27 from Mauritania in 1999. These results are the first field evidence of Cx. poicilipes naturally infected with RVFV, and the first isolations of this virus from mosquitoes in Mauritania - the main West African epidemic and epizootic area. Additional arbovirus isolates comprised 25 strains of Bagaza (BAG) from Aedes fowleri, Culex neavei and Cx. poicilipes; 67 Sanar (ArD 66707) from Cx. poicilipes; 51 Wesselsbron (WSL) from Ae. vexans and 30 strains of West Nile (WN) from Ma. uniformis, showing differential specific virus-vector associations in the circulation activity of these five arboviruses.     

Natural parasitism of Romanomermis iyengari (Welch) (Nematoda: Mermithidae) on various species of mosquitoes breeding in rice fields in Pondicherry,India

Natural habitat of Romanomermis iyengari, an entomophilic mermithid nematode, is rice field. Parasitism of this nematode on mosquito larvae breeding in rice fields in Pondicherry, India, has been studied in 1979. The present study was to find out its persistence in the same habitat, after many years of agricultural practices. Evaluation of parasitism on mosquito larvae was carried out during two rice cultivation seasons at a schedule of 1 week prior, and 1 and 2 weeks after transplantation of paddy. Larval stages of mosquito species such as Culex tritaeniorhynchus, Culex vishnui, Anopheles vagus, and Anopheles subpictus showed parasitism of R. iyengari. Parasitism was the highest on C. tritaeniorhynchus with a maximum of 15.38% during season I and 17.85% during season II. Followed by this, it was on A. vagus (10.82% and 9.43%), C. vishnui (7.37% and 8.69%), and A. subpictus (3.70% and 6.36%). The overall density of mosquito larvae and level of parasitism of R. iyengari on them during season II was significantly higher than that of season I. The parasitism was maximum at 1 week before transplantation and showed a decreasing trend towards 2 weeks after transplantation, during both the seasons. The level of natural parasitism of R. iyengari during the present investigation was higher than that observed in the same ecosystem almost 35 years ago. This is clearly an indication towards the capability of the nematode to withstand several years of agricultural practices, including pesticide and agrichemical application. Hence, if applied at sufficient level and frequency, this nematode could act as a successful biocontrol agent against mosquitoes breeding in rice fields.     

Dynamics and diversity of mosquito vectors of Japanese encephalitis virus in Kandal province,Cambodia

The Japanese encephalitis virus (JEV) is one of the main causes of encephalitis in Asia, including Cambodia. An understanding of the interactions between JEV hosts and vectors (Diptera: Culicidae) remains rare in the context of expanding urbanization. The relative abundance, species diversity and population dynamics of potential JEV vectors were studied between August 2015 and July 2016 on a peri-urban and rural pig farm in Kandal province, Cambodia, where JEV is circulating. Five similar environments in the two farms were selected for mosquito trapping: pig farm, cattle house, river/canals, household/ponds and paddy fields. The main objective was to describe the distribution and the dynamics of the main JEV vector mosquito species. In total, 83,013 mosquitoes from 20 species were caught in rural and peri-urban areas, and 82.3% of the mosquitoes were potential JEV vector species. In peri-urban areas, Culex (Cx.) gelidus was the most abundant species, followed by Cx. vishnui subgroup and Cx. tritaeniorhynchus. In rural areas, the same species were dominant: Cx. vishnui subgroup, Cx. gelidus and Cx. tritaeniorhynchus. The vast majority of mosquitoes (95.9%) were collected in close proximity to pigs and cattle. In conclusion, JEV vectors were present at all study sites and throughout all months of the year, supporting a continuous circulation of JEV in Cambodia.     

Heart and head defects in mice lacking pairs of connexins

Gene ablation studies in mice have revealed roles for gap junction proteins (connexins) in heart development. Of the 20 connexins in vertebrates, four are expressed in developing heart: connexin37 (Cx37), connexin40 (Cx40), connexin43 (Cx43), and connexin45 (Cx45). Although each cardiac connexin has a different pattern of expression, some heart cells coexpress multiple connexins during cardiac morphogenesis. Since different connexins could have overlapping functions, some developmental phenotypes may only become evident when more than one connexin is ablated. In this study, we interbred Cx40(-/-) and Cx43(-/-) mice to generate mice lacking both Cx40 and Cx43. Cx40(-/-)Cx43(-/-) mice die around embryonic day 12.5 (E12.5), much earlier than either Cx40(-/-) or Cx43(-/-) mice, and they exhibit malformed hearts with ventricles that are abnormally rotated, suggesting a looping defect. Some Cx40(-/-)Cx43(-/-) animals also develop head defects characteristic of exencephaly. In addition, we examined mice lacking both Cx40 and Cx37 and found a high incidence of atrial and ventricular septal defects at birth. These results provide further evidence for the importance of gap junctions in embryonic development. Moreover, ablating different pairs of cardiac connexins results in distinct heart defects, suggesting both common and unique functions for Cx40, Cx43, and Cx37 during cardiac morphogenesis.     

Environmental factors associated with the distribution of Anopheles arabiensis and Culex quinquefasciatus in a rice agro-ecosystem in Mwea, Kenya

Studies were conducted between May and June, 2006 to investigate the environmental factors affecting the distribution of An. arabiensis Patton and Culex quinquefasciatus Say in Mwea, Kenya. The sampling unit comprised all non-paddy aquatic habitats and ten randomly selected paddies and canals located within a 200 m radius from the periphery of the study site. Thirteen physico-chemical variables were recorded for each sampling site in each sampling occasion and a sample of mosquito larvae and other aquatic invertebrates collected. The non-paddy aquatic habitats identified included pools and marshes. Morphological identification of 1,974 mosquito larvae yielded four species dominated by Cx. quinquefasciatus (73.2%) and An. arabiensis (25.0%). Pools were associated with significantly higher Cx. quinquefasciatus larval abundance and less diversity of other aquatic invertebrates compared with other habitat types. In contrast, the abundance of An. arabiensis did not differ significantly among habitat types. Culex quinquefasciatus habitats had higher water conductivity and exhibited a higher abundance of other aquatic invertebrates than An. arabiensis habitats. Chi-square analysis indicated that the two species were more likely to coexist in the same habitats than would be expected by chance alone. Anopheles arabiensis larvae were positively associated with dissolved oxygen and adults of family Haliplidae and negatively associated with emergent vegetation and Heptageniidae larvae. Culex quinquefasciatus larvae were positively associated with dissolved oxygen, total dissolved solids, Chironomidae larvae, and Microvelidae adults and negatively associated with emergent vegetation. These findings suggest that both biotic and abiotic factors play a significant role in niche partitioning among Cx. quinquefasciatus and An. arabiensis, a factor that should be considered when designing an integrated vector control program.     

Growth characteristics of the veterinary vaccine candidate ChimeriVax-West Nile (WN) virus in Aedes and Culex mosquitoes

In 1999 West Nile (WN) virus was introduced to North America where this flavivirus has spread rapidly among wildlife (especially birds) transmitted by various species of mosquitoes (Diptera: Culicidae). Increasing numbers of cases and deaths among humans, horses and other domestic animals require development of effective vaccines. 'ChimeriVax-West Nile(vet)' is being developed for use as a veterinary vaccine to protect against WN infection. This chimeric virus contains the pre-membrane (prM) and envelope (E) genes from the wild-type WN NY99 virus (isolated from a flamingo in New York zoo during the 1999 WN epidemic) in the backbone of yellow fever (YF) 17D vaccine virus. Replication kinetics of ChimeriVax-WN(vet) virus were evaluated in mosquito cell culture (Aedes albopictus C6/36), in WN vector mosquitoes [Culex tritaeniorhynchus Giles, Cx. nigripalpus Theobald and Cx. quinquefasciatus Say (Diptera: Culicidae)] and in YF vectors [Aedes aegypti (L) and Ae. albopictus (Skuse)], to determine whether these mosquitoes become infected through feeding on a viraemic vaccine, and their potential infectivity to transmit the virus. Growth of ChimeriVax-WN(vet) virus was found to be restricted in mosquitoes, compared to WN virus in Ae. albopictus C6/36 cells. When inoculated intrathoracically, ChimeriVax-WN(vet) and YF 17D viruses did not replicate in Cx. tritaeniorhynchus or Cx. nigripalpus; replication was very restricted compared to the wild-type WN virus in Cx. quinquefasciatus, Ae. aegypti and Ae. albopictus. When fed on hanging drops with ChimeriVax-WN(vet) virus (7.7 log10 PFU/mL), none of the Culex mosquitoes became infected; one Ae. albopictus and 10% of the Ae. aegypti became infected, but the titre was very low and virus did not disseminate to head tissue. ChimeriVax-WN(vet) virus had a replication profile similar to that of the attenuated vaccine virus YF 17D, which is not transmitted by mosquitoes. These results suggest that the natural mosquito vectors of WN and YF viruses, which may incidentally take a bloodmeal from a vaccinated host, will not become infected with ChimeriVax-WN(vet) virus.     

Influence of successional stage of Eucalyptus regnans (mountain ash) on habitat use by reptiles in the Central Highlands,Victoria

Abstract Eleven sites, representing different successional stages of Eucalyptus regnans-dominated forest in the Central Highlands of Victoria, were selected to identify potentially important habitat variables for heliothermic reptiles, three species (Eulamprus tympanum, Niveoscincus coventryi, Pseudemoia spenceri) of which were common at these sites. Analyses reveal that many forest attributes are strongly correlated with stand age and that some are significant habitat variables for some of these species. ‘One-at-a-time’ modelling of habitat variables reveals that counts of E. tympanum are most strongly correlated with the proportion of grass as substrate (?ve), moss cover of logs (?ve) and litter depth (+ ve); N. coventryi counts are most significantly related to litter depth (?ve), numbers of logs (?ve), log diameter (?ve), the proportion of bare ground as substrate (?ve) and length of sunny patches (+ ve); P. spenceri counts are most significantly related to the number of sunny patches (?ve) and moss cover of logs (?ve). The total reptile count is most significantly correlated with stag diameter (?ve) and log diameter (?ve). Predictive equations for each of the common species are also presented, using measured habitat variables, and these, along with ‘one-at-a-time’ models, indicate that a number of factors determine reptile occurrence or abundance and that no single predictor variable is apparent.     

Transmission Dynamics of the West Nile Virus in Mosquito Vector Populations under the Influence of Weather Factors in the Danube Delta,Romania

EcoHealth - Mosquitoes were collected in the Danube Delta during the active seasons of 2011–2013. For Culex spp. mosquitoes, the abundance was calculated. Culex pipiens (sensu lato), (s.l.)...     

Mosquito species diversity and abundance in relation to land use in a riceland agroecosystem in Mwea, Kenya.

We conducted an entomological survey to determine the mosquito species diversity and abundance in relation to land use in the Mwea rice scheme, Kenya. Adult mosquitoes were collected by indoor spraying of houses and outdoors by CDC light traps in three villages representing planned (Mbuinjeru) and unplanned (Kiamachiri) rice agroecosystems and a non-irrigated agroecosystem (Murinduko). During the 12-month sampling period, a total of 98,708 mosquitoes belonging to five genera and 25 species were collected. The five most common species collected during this study were Anopheles arabiensis Patton (52.5%), Culex quinquefasciatus Say (36.7%), Anopheles pharoensis Theobald (5.2%), Anopheles coustani Laveran (1.4%), and Anopheles funestus Giles (1.3%). Anopheles arabiensis, Cx quinquefasciatus, and An. pharoensis were more abundant in rice agroecosystems than in the non-irrigated agroecosystem, and in planned than in the unplanned rice agroecosystems. In contrast, An. funestus was more abundant in the non-irrigated agroecosystem. The mosquito species diversity (H) and evenness (E(H)) in the non-irrigated agroecosystem (Shannon diversity Index, H = 1.507, EH = 0.503) was significantly higher than in the rice agroecosystems (H) = 0.968, E(H) = 0.313, unplanned; and H= 1.040, E(H) = 0.367 planned). Results of lag cross correlation analysis revealed a strong relationship between rainfall and the abundance of An. arabiensis, and C. quinquefasciatus in the non-irrigated agroecosystem but not in the rice agroecosystems. It is inferred from the data that different levels of habitat perturbations with regard to rice cultivation have different effects on mosquito diversity and abundance. This provides an understanding of how mosquito diversity is impacted by different habitat management and rice cropping strategies.     

Evidence for the Presence of a Free C-Terminal Fragment of Cx43 in Cultured Cells

Migration of the gap junction protein connexin 43 (Cx43) in SDS-PAGE yields 2 to 4 distinct bands, detectable in the 40-47 kDa range. Here, we show that antibodies against the carboxy-terminal domain of Cx43 recognized an additional 20-kDa product. This protein was detected in some culture cell lysates. The presence of the 20-kDa band was not prevented by the use of protease inhibitors (Complete® and phenylmethylsulfonyl fluoride (PMSF), 1-5 mM). The band was absent from cells treated with Cx43-specific RNAi, and from those derived from Cx43-deficient mice, indicating that this Cx43-immunoreactive protein is a product of the Cx43 gene. Treatment of CHO cells with cyclosporin A caused a reduction in the amount of full-length Cx43 and a concomitant increase in the amount of the 20-kDa band. Overall, our data show that a fraction of the Cx43-immunoreactive protein pool within a given cell may correspond to a C-terminal fragment of the protein.     

A quantitative study of calcareous stream and Tintenstriche algae from the Malham district,Northern England

The algal floras of two limestone streams and two calcareous Tintenstrichen are described and compared. The most important factor governing the distribution and abundance of species was the availability of water. Permanently wet stands, dominated by filamentous blue-green algae (Schizothrix calcicola and Phormidium incrustatum) had a greater species diversity than stands subject to frequent drying which were dominated by coccoid blue-green algae (Gloeocapsa spp.).

Significant correlations were found between S. calcicola and water pH (+ve), total species numbers and pH (+ve), filamentous blue-green algae and aufwuchs thickness (+ve) and Calothrix numbers and rock mass colonized (+ve).

The algal flora of the Tintenstrichen and the streams differed, although both developed upon the same limestone formation. The results are discussed with reference to previous work, substratum stability, aufwuchs structure, water chemistry, light and temperature.