Immature Stages Of Mosquitoes Research Articles

Characterization of Mosquito Breeding Sites in and in the Vicinity of Tigray Microdams

Malaria vector control in Ethiopia has a history of more than 50 years, but malaria remains a major cause of morbidity and mortality in Ethiopia. Thus, targeting the control program on the larval stage is of paramount importance. This study aimed to characterize the aquatic habitats of vector mosquito larvae associated with micro-dams. Cross-sectional larval survey was conducted on six micro-dams in Tigray, Northern Ethiopia in 2005/06. The study area on each dam was divided into eight zones. Immature stages of mosquitoes were collected using standard dippers. The physico-chemical characteristics of the aquatic habitats were measured onsite. A total of 301 aquatic habitats were surveyed for mosquito larvae; in 32.56% (n=301) only Anopheles, in 27.91% only Culex, both genera were found mixed in 21.59% and no mosquito larvae were found in 17.94%. The findings depicted that dissolved oxygen (r = 0.34, p =0.04), pH (r = 0.35, p =0.03), conductivity (r = 0.36, p =0.03), vegetation (F = 3.54, p =0.002), microhabitat (F = 2.65, p =0.04), fauna and bottom surface of the water body were positively associated and important in explaining the presence and abundance of Culex. On the other hand, dissolved oxygen (r = 0.39, p =0.02), pH (r = 0.42, p =0.008), vegetation (F = 5.6, p =0.000), water transparency (F = 2.72, p =0.00), rainfall (F = 2.22, p = 0.027) and fauna were positively associated and important in explaining the presence and abundance of Anopheles. The findings of this study suggest that both biotic (vegetation and fauna) and abiotic (chemical and physical) factors play a significant role in larvae's habitat preference in both Culex and Anopheles.

Seasonal Occurrence of Immature Mosquitoes in Swimming Pools in Buenos Aires, Argentina

The seasonal variation in the density of swimming pools and the occurrence of immature mosquitoes in these habitats were studied in the temperate city of Buenos Aires, Argentina. The density of swimming pools was highest in the summer (6.0 pools/ha) when temporal pools predominated; it was lowest in the winter (0.9 pools/ha) when only permanent pools were recorded. The presence of immature stages of mosquitoes was mainly associated with the lack of use and maintenance of the pools in the fall season, when temporal pools were still assembled but not intensively used. Seven mosquito species were recorded, among which Culex pipiens and Culex apicinus were the most frequent.

Use of the neotropical fish Cnesterodon decemmaculatus for long-term control of Culex pipiens L. in Argentina

We released the native mosquito fish, Cnesterodon decemmaculatus, into suburban drainage ditches to evaluate its potential as a long-acting agent for the control of Culex pipiens larvae in natural breeding sites. The inoculation of predatory fish was conducted in nine ditches at three densities: 1, 7, and 13 fish/m 2 during a 2-year period (2006–2008). The number of immature stages of Cx. pipiens was recorded before and after release. On a monthly basis, the digestive-tract contents of some fish and the average number of offspring from the females was recorded. Fifteen weeks after release, a 99% reduction in the number of immature mosquito stages was recorded in the drainage ditches containing 13 fish/m 2, while at 22 weeks, a 99% reduction was also observed in those with 7 fish/m 2. The ditches with 1 fish/m 2 had lower densities of immature mosquito stages relative to the controls, but over the entire experiment these observations did not prove statistically significant. The number of offspring per adult C. decemmaculatus female ranged from 4 ± 1.4 (mean ± SD) to 7.4 ± 0.9. Larval remains were detected in the fish collected in January, February, March, June, and September of 2006.

Landscape and Land Cover Factors Influence the Presence of <I>Aedes</I> and <I>Anopheles</I> Larvae

The objective of this study was to test for associations between land cover data and the presence of mosquito larvae of the genera Aedes Meigen and Anopheles Meigen in northern Thailand at the landscape scale. These associations were compared with associations between larval habitat variables and the presence of mosquito larvae at a finer spatial scale. Collection data for the larvae of one Aedes species and three species-groups of Anopheles, all of which are involved in pathogen transmission, were used. A variety of northern Thai landscapes were included, such as upland villages, lowland villages and peri-urban areas. Logistic regression was used to evaluate associations. Generally, land cover and landscape variables explained the presence of larvae as well as did larval habitat variables. Results were best for species/species-groups with specific habitat requirements. Land cover variables act as proxies for the types of habitat available and their attributes. Good knowledge of the habitat requirements of the immature stages of mosquitoes is necessary for interpreting the effects of land cover.

Nutritional quality of leaf detritus altered by elevated atmospheric CO2: effects on development of mosquito larvae

Summary1. Populus tremuloides leaf litter was produced under elevated (ELEV = 720 ppm) and ambient (AMB = 360 ppm) atmospheric CO2 conditions. Leaf chemical quality was significantly altered by CO2 enrichment. ELEV leaves had significantly higher concentrations of phenolic compounds and lignins, and higher C : N ratios than AMB.2. Leaf litter was incubated in a headwater stream for 14 days to become colonised by microorganisms; aquatic bacterial productivity was significantly lower on ELEV than on AMB leaf litter. Colonised leaves were fed to four species of detritivorous mosquito larvae to assess their survivorship and development rates.3. Larval mortality was 2.2 times higher for Aedes albopictus fed ELEV litter when compared with AMB. Although mortality of A. triseriatus, A. aegypti and Armigeres subalbatus was not affected by treatment, larval development rate was delayed by 78, 25 and 27%, respectively, when fed ELEV litter.4. Increased mosquito mortality and/or delayed larval development rates are more likely to have negative implications for food web structure and productivity in ecosystems where immature stages of mosquitoes are an important food source of predators.

Advantages of larval control for African malaria vectors: Low mobility and behavioural responsiveness of immature mosquito stages allow high effective coverage

BackgroundBased on sensitivity analysis of the MacDonald-Ross model, it has long been argued that the best way to reduce malaria transmission is to target adult female mosquitoes with insecticides that can reduce the longevity and human-feeding frequency of vectors. However, these analyses have ignored a fundamental biological difference between mosquito adults and the immature stages that precede them: adults are highly mobile flying insects that can readily detect and avoid many intervention measures whereas mosquito eggs, larvae and pupae are confined within relatively small aquatic habitats and cannot readily escape control measures.Presentation of the hypothesisWe hypothesize that the control of adult but not immature mosquitoes is compromised by their ability to avoid interventions such as excito-repellant insecticides.Testing the hypothesisWe apply a simple model of intervention avoidance by mosquitoes and demonstrate that this can substantially reduce effective coverage, in terms of the proportion of the vector population that is covered, and overall impact on malaria transmission. We review historical evidence that larval control of African malaria vectors can be effective and conclude that the only limitations to the effective coverage of larval control are practical rather than fundamental.Implications of the hypothesisLarval control strategies against the vectors of malaria in sub-Saharan Africa could be highly effective, complementary to adult control interventions, and should be prioritized for further development, evaluation and implementation as an integral part of Rolling Back Malaria.

Frequency of Aedes aegypti and Aedes albopictus larvae and pupae in traps, Brazil

To evaluate the monthly frequency of larvae and pupae of Aedes albopictus, Aedes aegypti and other mosquitoe species in tires, and the influence of environmental factors on that. The immature stages of mosquitoes were collected monthly from four tires in the municipality of Nova Iguaçu, Brazil, from November 1997 to October 1998. The following variables were measured: rainfall, temperature, water volume, water pH. The tires were arranged in a pyramid, one at the base (tire 1) and 3 others (2,3 e 4) laying over it. Were collected 10,310 larvae and 612 pupae. Aedes albopictus was the most common species in both the larval and pupal stages. Aedes aegypti and Aedes albopictus were collected throughout the year but were more frequent during in the rainy season. The number of Aedes aegypti was significantly correlated with the temperature, rainfall and water volume of the tires. The correlation between water pH and number of larvae was not significant. Aedes albopictus larvae were more frequent in tires left in the shade. Aedes albopictus was more abundant in tires than Aedes aegypti. Discarded tires seem to be an important source of both Aedes species throughout the year. The favored environmental conditions of the tires, such as water volume and exposure to sunlight differ for Aedes albopictus and Aedes aegypti.

Long-term dynamics of a predator used for biological control and decoupling from mosquito prey in a subtropical treehole ecosystem.

We identified, staged and counted the immature stages of mosquitoes from 1,826 censuses (with replacement) of the aquatic contents of ten treeholes surveyed every 2 weeks between 1978 and 1993. These time series were used to examine the population dynamics and effect on prey of the predatory mosquito Toxorhynchites rutilus. The mean annual frequency of occurrence of T. rutilus ranged from 0.02 to 0.67 among holes, and no fourth instars were recovered during a 30-month dry period. Oviposition and pupation by this species were recorded in all months, but most commonly in the spring. Overwintering larvae of the predator increased in weight during the prolonged fourth instar that preceded pupation in the spring. Time series analyses showed that the presence of a fourth instar T. rutilus significantly reduced the abundances of late-stage Aedes triseriatus mosquitoes. Pupal numbers of this prey species were more negatively affected by T. rutilus than were numbers of fourth instar A. triseriatus. Long-term declines in mean annual abundance of A. triseriatus prey during 16 years of observations on two holes were not correlated with increases in the mean annual frequencies of T. rutilus. Local extinctions of the aquatic stages of A. triseriatus within treeholes were common, but in most holes not significantly associated with the presence of T. rutilus, suggesting that predation does not routinely drive mosquito prey locally extinct in this ecosystem. The decoupling of T. rutilus and A. triseriatus, as revealed through these complete and long-term censuses, is contrasted with other reports of generalist predators causing extinctions of mosquito prey. Discrepancies among reported outcomes probably result from differences in duration of sampling periods and statistical procedures along with real differences in the intensity of predation among systems and sites.

Prospects and problems of intermittent irrigation for control of vector breeding in rice fields in southern India.

The impact of water management on the abundance and interaction of aquatic stages of mosquitoes and some important groups of their predators was studied in a 22.3-ha plot of rice in southern India. Many pools persisted even in a year when intermittent irrigation (II) was properly implemented (fields being re-irrigated as soon as they were dry) and these acted as microrefuges for the immature stages of mosquitoes and for their predators. Although the abundance of all predators, particularly of Notonectidae, was reduced by II in this year, increased predation efficiency in the confined spaces of the persistent pools resulted in a 75%-88% reduction in the abundance of mosquito pupae, as measured by two independent sampling methods. In another year there was insufficient irrigation water for proper II and re-irrigation took place whenever water was available rather than when it was required, frequently resulting in only partial drying. This reduced predator populations without enhancing their efficiency, and so mosquito abundance was slightly higher than in conventionally irrigated fields. The implications for vector control are discussed.

Immature stages of mosquitoes (Diptera: Culicidae) Collected during the autumn-winter period in Cordoba Province, Argentina

Eggs, immature mosquito collections were made at Cosquin, La Calera ( Chaco phytogeographic region), Villa Allende and Villa del Rosario (Espinal phytogeographic region) during April/September of two consecutive years 1989, 1990. Specific immature habitats in each locality were identified and sampled monthly. Eggs and/or immatures of Aedes albifasciatus, Ae. fluviatilis, Anopheles albitarsis, culex acharistus, Cx. apicinus, Cx. bidens, Cx. coronator, Cx. chidesteri, Cx. dolosus, Cx. maxi, Cx. quinquefasciatus, Cx. saltanensis, Psorophora ciliata and Uranotaenia lowii were collected. Three species (Cx. acharistus, Cx. dolosus and Cx. quinquefasciatus) were collected during the sampling period for all developmental stages. This suggests that immature of these species do not overwinter but continue to develop throughout the cold autumn and winter seasons.

Japanese encephalitis virus infection in mosquitoes reared from field-collected immatures and in wild-caught males.

Immature stages of mosquitoes collected in JE endemic areas of Karnataka, India between 1985 and 1987 were reared to adults and processed for the detection and isolation of Japanese encephalitis (JE) virus in an attempt to find naturally occurring vertical transmission of the virus. Males collected during 1985-1986 were also processed. A total of 15,785 adults reared from immatures and divided into 445 pools and 1,756 wild-collected males divided into 128 pools were processed using mosquito inoculation and immunofluorescence techniques. JE virus antigen was detected in 9 pools, 4 of which yielded JE virus. These were 2 pools of males and 1 pool of female Culex tritaeniorhynchus and 1 pool of male C. pseudovishnui, suggesting vertical transmission of JE virus in the mosquitoes.

THE DIFFERENCE IN THE INSTAR COMPOSITION OF IMMATURE MOSQUITOES SAMPLED BY THREE SAMPLING TECHNIQUES

Three techniques, namely a ladle, a metal quadrat and a D-shaped aquatic net, were used for comparison to sample immature stages of mosquitoes in woodland pools in northern England. The quadrat proved to be more reliable in giving a more accurate representation of the different instar proportions in the ponds than the ladle and aquatic net. The ladle showed bias of undersampling the earlier instars. Similar but not so severe bias also occurred for the D-net.

Field Studies on the Effects of Insecticides on Some Aquatic Wildlife Species1

The effect of 29 insecticides at multiple dosages in the field was studied on the mosquito fish Gambusia affinis (Baird & Girard). This fish is considered one of the most important predators of immature stages of mosquitoes. At mosquito larvicidal rates, 11 experimental compounds plus naled (formerly known as Dibrom), methyl parathion and ronnel were nontoxic to the fish; the remaining 10 experimental materials plus Guthion® (O, O-dimethyl S-(4-oxo-1,2,3-benzotriazin-3-(4H) ylmethyl) phosphorodithioate), ethyl Guthion® (O, O-diethyl S-(4-oxo-1,2,3-benzotriazin-3(4H)-ylmethy1) phosphorodithioate), diazinon, parathion, and carbophenothion (formerly designated Trithion) manifested varying degrees of toxicity. Eighteen materials were tested against pollywogs (aquatic larval stages) of the bullfrog Rana catesbeiana, western toad Bufo boreas, and Hammond’s spade foot toad Scaphiopushammondi. Of the 11 materials tested against the first named species, Bayer 38920 (6,7,8,9,10, 10-hexachloro-1,5,5a,6,9,9a-hexahydro-3-methyl-6,9-methano-2A-benzodioxepin) (at 0.5 and 2.0 pounds per acre), carbophenothion (at 0.4 and 1.6 pounds per acre) and GC-3582 (O, O-diethyl-1-(2,5-dichlorophenyl)-2,2-dichlorovinyl phosphate) (at 0.4 and 1.6 pounds per acre) were highly toxic. The remaiming six experimental materials plus naled and ethyl Guthion were nontoxic to this species. The seven materials including parathion, Guthion, methyl parathion, ronnel and there experimental compounds tested against B. boreas and S. hammondi were all nontoxic for 24 hours after application.

A Revised Nomenclature for the Chaetotaxy of the Mosquito Larva (Diptera: Culicidae)

The recent recognition of species complexes within populations formerly believed to represent a single species has focused the attention of students of mosquitoes to a reexamination of characters previously used in the separation of species and to a search for new morphological features useful in diagnosis. The immature stages of mosquitoes offer a greater variety of morphological characters which can be studied quantitatively, analyzed, and used for recognition of species than do the adults. Until recently almost all the attention was paid to the head, a few thoracic and abdominal hairs and the terminal abdominal segments of the larva, and the trumpets, paddles and a few abPom,nal hairs of the pupa. The larval characters used have not been entirely satisfactory and in the last few years the pupal stage has attracted more attention in the search for additional diagnostic characters. This interest in the pupa has culminated in the work of Knight and 'Chamberlain (1948) who made a comparative study, devised a new nomenclature, and illustrated the complete chaetotaxy of representatives of practically all the genera. The study of the larva has not progressed as rapidly, perhaps because of the greater complexity of the chaetotaxy, since the larva has upward of 200 pairs of hairs while the pupa appears to have about 105 pairs. The complete larval chaetotaxy for the majority of the genera is still unknown. In the course of a study on the genus Uranotaenia from the Solomon Islands, the complete larval chaetotaxy of seven species was described and figured by the author. In the preparation of descriptions it became evident that the existing nomenclatures were not entirely satisfactory as various combinations of numerical, alphabetical and nominal terminologies have been used by different workers according to their individual preferences and no system used all the elements of the larval chaetotaxy known at the present time. It seemed advisable, therefore, to prepare a uniform nomenclature which would (1) take into account all the established elements of the chaetotaxy of the fourth instar mosquito larva, (2) allow for the later inclusion of certain elements now poorly known, (3) show homologies where they have been established, (4) be equally suitable for anophelines and culicines, and (5) be easy to use in descriptions.