The effects of Plagiorchis noblei metacercariae on the development and survival of Aedes aegypti larvae in the laboratory

Plagiorchis noblei infections impair the survival and development of fourth instar Aedes aegypti larvae. Mortality during the larval and pupal stages reached 92%, and 60% of the emerging adults were malformed. The metacercariae interfere with pupation and the emergence of adults. Larvae and pupae that fail to transform to the next developmental stage within the normal time characteristically persist for extended periods, but invariably die without transforming. Whereas 82% of the control larvae gave rise to functional adults, only 4% of infected larvae managed to do so. Such effects may facilitate the transmission of the parasite.

[The activity of Culicidae mosquitoes in the primeval highland rain forest of the Ribeira Valley, São Paulo, Brazil]

Relatam-se observações sobre o ciclo diário de atividade culicídea em ambiente primitivo da floresta perenifólia higrófila da encosta, do Sistema da Serra do Mar, no Vale do Ribeira, Estado de São Paulo, Brasil. Com periodicidade bimensal, e no período de dois anos, foram levadas a efeito coletas de vinte e cinco horas ininterruptas com o emprego de isca humana, bem como a utilização de armadilhas tipo Shannon operadas dentro e fora do ambiente florestal. Os resultados evidenciaram acentuada dominancia de An. cruzii, que se manteve durante todos os meses do ano mesmo naqueles de menor atividade culicídea. A influência crepuscular evidenciou-se pela nítida ocorrência de picos endocrepusculares para An. cruzii e An. bellator, seguidos imediatamente por outros, de menor intensidade, caracterizando assim ritmo que se propõe chamar de paracrepuscular. Ambas essas espécies de Kerteszia apresentaram atividade contínua para a isca humana, no período das 24 horas. Cx. sacchettae mostrou-se nitidamente noturna e com ritmo eocrepuscular. Ae. serratus e Ps. ferox revelaram-se essencialmente diurnos, com certa tendência ao ritmo paracrepuscular porém, até onde foi possível observar, de maneira incompleta e limitado ao crepúsculo matutino. A atividade ininterrupta, aliada à densidade e dominância de An. cruzii reafirma sua importância epidemiológica e a torna uma das feições que caracteriza o ambiente primitivo supracitado.

Changes in ribonuclease activity during development of the mosquito, Aedes aegypti

In the mosquito Aedes aegypti, quantitative and qualitative changes have been detected in ribonuclease activity during development. Ribonuclease activity is particularly high in extracts from larvae, relative to that in extracts from pupae or adults. Larval extract is enriched for a ribonuclease that is heat-labile, has an alkaline pH optimum, and is extremely sensitive to the divalent cation, manganese. Extract from adult females is enriched for a heat-stable component that has an acidic pH optimum and is more active at 56 than at 30 degrees C. Throughout the vitellogenic cycle, no major changes in ribonuclease activity were detected in fat body extracts.

[Mosquitoes of the subgenus Edwardsaedes of the fauna of the Palaeoarctic region with a description of the larva of Aedes (Edw.) bekkui]

Two species of the subgenus Edwardsaedes, Ae. (Edw.) pingpaensis Chang and Ae. (Edw.) bekkui Mogi, are spread in the Palaearctic region, the first one being known from China only and the second one from Japan and South Primorye, USSR. The name Ae. (Edw.) antuensis Su, Wang et Li, 1965 should be considered as a synonym of Ae. (Edw.) pingpaensis Chang, 1965; the larva of Ae. (Ochlerotatus) sticticus Mg. has been erroneously described by Su et al. (1978) as larva of Ae. antuensis. The differential diagnosis of the females, male genitalia, and larvae of mosquitoes Ae. pingpaensis and Ae. bekkui, is given. The description of the fourth stage larva of Ae. bekkui from the South Primorye is presented for the first time in the home literature.

Rift Valley fever virus (family Bunyaviridae, genus Phlebovirus). Isolations from Diptera collected during an inter-epizootic period in Kenya

A total of 134 876 Diptera collected in Kenya during a 3-year period were tested in 3383 pools for Rift Valley fever (RVF) virus. Nineteen pools of unengorged mosquitoes were found positive for RVF. All isolations were made from specimens collected at or near the naturally or artificially flooded grassland depressions that serve as the developmental sites for the immature stages of many mosquito species. The isolation of virus from adult male and female A. lineatopennis which had been reared from field-collected larvae and pupae suggests that transovarial transmission of the virus occurs in this species.

Effects of a juvenile hormone analogue on the morphology and biology of Aedes scutellaris malayensis Colless (Diptera: Culicidae)

Effects of 2-methyl-9(4-isopropylphenyl)-2,6-dimethyl nonane, or MV-678, a juvenile hormone analogue, on Aedes scutellaris malayensis Colless were investigated under laboratory conditions (29 degrees +/- 2 degrees C and 86 +/- 3% RH). The MV-678 was tested against the first, second, third and fourth instar larvae. The concentrations used were 0.0032, 0.016, 0.08, 0.4 and 2.0 mg/l. The morphogenetic aberrations were determined and divided into 8 groups, among which they included (1) death larvae, (2) late fourth instar larvae before pupation, (3) larvae with pupae partly emerged, (4) white pupae, (5) brown pupae, (6) elephantoid pupae of which pupae with adults visible inside, (7) pupae with apparently adults partly emerged and (8) death adults. The percentage mortality rates were found to be relatively high in pupal and larval stages when they were treated with 2.0 mg/l. The LC50 values were 0.26, 0.175, 0.06 and 0.032 mg/l for the first, second, third and fourth instar larvae respectively. The effectiveness of MV-678 at 2.0 mg/l was about 11 days under the open air conditions (28 degrees +/- 2 degrees C and 72 +/- 3% RH). When the fourth instar larvae were treated with 0.4 and 2.0 mg/l of MV-678, the LC50 values were 3.1 and 7.1 days respectively.

Paradoxical effects of simulated larviciding on production of adult mosquitoes

We determined whether simulated mortality of larval mosquitoes in food-deprived bodies of water increases emergence of adult females as well as their size by releasing the remaining larvae from competition for food. Removal of larval Aedes aegypti from rearing containers with suboptimal amounts of food increased the number of adults that emerged. Thus, larvicidal measures do not inevitably lead to reduced numbers of mosquito vectors of disease. In food-limiting breeding sites, partially effective anti-larvae measures can be counterproductive, perhaps increasing transmission of vector-borne disease.

[Predatory activity of Helobdella triserialis lineata (Hirudinea: Glossiphonidae) on immature forms of Aedes fluviatilis and Culex quinquefasciatus (Diptera: Culicidae) in the laboratory]

Foi avaliada a atividade predatória, em laboratório, de Helobdella triserialis lineata (Hirudinea: Glossiphonidae) sobre ovos, larvas e pupas de Aedes fluviatilis e Culex quinquefasciatus (Diptera: Culicidae), bem como a influência da presença desses hirudíneos sobre o comportamento de oviposição das fêmeas das duas espécies de mosquitos. Experimentos adicionais foram feitos testando a influência da profundidade da água e da sua salinidade sobre a capacidade predatória dos hirudíneos. Nas condições do experimento, foi observada predação de larvas e pupas, porém não de ovos das duas espécies de dípteros. Número estatisticamente menor de desovas foi depositado por fêmeas de Cx. quinquefasciatus em recipientes que continham hirudíneos, não ocorrendo o mesmo com fêmeas de Ae. fluviatilis. As diferentes profundidades de água testadas não interferiram na atividade predatória de H. t. lineata e somente em concentrações acima de 3% de NaCl essa atividade mostrou-se bastante diminuída.

Glutathione levels during the mosquito life span with emphasis on senescence

Glutathione levels were determined in mosquitoes of all ages of the life span. Specific analyses for reduced (GSH) and oxidized (GSSG) glutathione were used and validated to ensure minimal autoxidation of GSH and conversion of these forms. Indeed GSH accounted for greater than 97% of the total glutathione (GSH + GSSG) content in all samples. Marked changes occurred during the life span, and the highest levels of GSH and total glutathione were found during larval growth and metamorphosis (P less than 0.001). Thereafter the levels decreased in the early adult, plateaued in the mature, and decreased 46% in the old and very old mosquito (P less than 0.001). This aging-specific decrease was a general phenomenon, for it occurred in all body regions of both sexes. Starvation up to 3 days did not affect the GSH levels. The importance of these changes in glutathione is its relationship to the reducing and biosynthetic capacities of different life span stages. Of special interest is the senescence decrease which can lead to lower biosynthetic activity and also impaired detoxification capacity.

The effect of colonization upon aedes aegypti susceptibility to oral infection with yellow fever virus

Two colonies of Aedes aegypti were established from two independent collections from Vero Beach, Florida. Eleven sequential generations of the first colony were tested for variation in oral susceptibility to infection with yellow fever virus (YFV). Each generation was also assayed for genetic variability at seven enzyme loci using electrophoretic techniques. Significant differences in infection rates were detected between some generations. These differences were significantly correlated with genetic variation at the malate dehydrogenase locus. Seven generations from the second colony were examined simultaneously for variation in susceptibility to YFV. Significant differences were also detected between some of these generations. The results suggest that colonization may have an effect on the genetic and phenotypic variation in a mosquito strain, and that genetically based variation for susceptibility to infection with YFV occurs in populations of Ae. aegypti.

Medium for the production of primary powder of Bacillus thuringiensis subsp. israelensis

Five media, formulated from the seeds of five legume varieties, dried cow blood, and mineral salts, were assessed for the growth and production of insecticidal properties of Bacillus thuringiensis subsp. israelensis. Bacterial powders prepared from the broth cultures were assayed against the larvae of Aedes aegypti, Culex quinquefasciatus, and Anopheles gambiae. A standard primary powder of B. thuringiensis subsp. israelensis (IPS78) was included in the assay for comparison. Good growth was obtained in all the media, and all powders were effective against the three types of mosquito larvae. The powder containing ground seeds of Voandzeia subterranean was the most effective and compared favorably with the standard (IPS78). The concentrations required to kill 50% of the larvae of Aedes aegypti, C. quinquefasciatus, and Anopheles gambiae were 1.13 X 10(-2) +/- 1.79 X 10(-3), 1.83 X 10(-2) +/- 2.55 X 10(-3), and 2.25 X 10(-2) +/- 1.88 X 10(-3) micrograms/ml, respectively. This investigation shows that the medium containing V. subterranean can be used for the production of B. thuringiensis subsp. israelensis primary powder.

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.

Glutathione S-transferase activities in the yellow-fever mosquito [Aedes aegypti (Louisville)] during growth and aging

Our previous findings [Hazelton & Lang (1978) Fed. Proc. Fed. Am. Soc. Exp. Biol. 37(6), 2378 (abstr.)] demonstrated aging-specific changes in glutathione concentrations in the yellow-fever mosquito [Aedes aegypti (Louisville)]. A possible mechanism could be increased utilization via glutathione S-transferase. Thus glutathione S-transferase activities were measured in mosquito samples from the entire life span, including growth, maturity and senescence. Methods were validated for the quantitative determination of transferase activities with 1,2-dichloro-4-nitrobenzene (DCNB) and 1-chloro-3,4-dinitrobenzene (CDNB) as second substrates. Marked changes occurred during the life span, and the profiles for both DCNB and CDNB activities were identical. The activities increased throughout larval development and reached a maximum in the metamorphosis stage. The activities decreased at the end of metamorphosis in the 5-day-old adult, reached a plateau during maturity (5-20 days), and then decreased 31% (P less than 0.007) during senescence (after 33 days). This senescence-specific decrease occurred in both sexes and was localized in the abdominal region. Further kinetic analyses indicated that the lower enzyme activities were most likely due to lower amounts of active enzyme rather than a change in kinetic properties. These findings indicate that the capacity for GSH utilization via glutathione S-transferase is diminished with aging. This does not explain our previously observed decreases in GSH, but the results suggest that GSH-linked detoxification would be impaired during senescence.

Glutathione biosynthesis in the aging adult yellow-fever mosquito [Aedes aegypti (Louisville)]

Our previous findings [Hazelton & Lang (1978) Fed. Proc. Fed. Am. Soc. Exp. Biol. 37(6), 2378 (abstr.)] demonstrated a senescence-specific decrease in glutathione (GSH) concentration in the yellow-fever mosquito Aedes aegypti (Louisville)]. As a possible mechanism for this change, GSH biosynthesis was investigated in adult mosquitoes of different ages through the life-span. Biosynthesis was measured as the incorporation rate of [14C]glycine or [14C]cystine into glutathione. Essential information to validate the procedure was also obtained on the precursor-amino-acid pool sizes and kinetic parameters such as lag-time and time course of incorporation. Also, synthesis de novo rather than exchange was verified using buthionine sulphoximine, a specific inhibitor of GSH biosynthesis. The synthetic rates with either amino acid precursor varied throughout the adult life-span, but the patterns for both precursors were essentially identical. Biosynthesis was high in the newly emerged adult and decreased 62-70% (P less than 0.005) to a plateau during maturity. From the mature value there was a decrease of 36-41% (P less than 0.005) to a new plateau during senescence. Glutathione biosynthesis and concentration were correlated throughout maturity and senescence (r = 0.982) and thus biosynthesis was proportional to glutathione content. On this basis we concluded that impaired biosynthesis is the major and perhaps sole mechanism for the aging decrease in glutathione content.

[Fauna and ecology of blood-sucking mosquitoes (Culicidae) in the northern taiga of the Sverdlovsk region]

20 species of blood-sucking mosquitoes were recorded from the northern taiga of Ural (the northern part of the Sverdlovsk region): 15 species of the genus Aedes, 2 species of Culex, 2 species of Culiseta and 1 species of Anopheles. Larvae of Aedes occur in masse in small temporary water bodies. In summer after rains larvae of Culiseta and Culex as well as some species of Aedes appear. In May overhibernated Culiseta alaskaensis, C. bergrothi and An. maculipennis begin the flight of mosquitoes. The peak of the number and specific variety of attacking mosquitoes was recorded in July; in August their activity started to decrease. Aedes communis and A. punctor are mass species, A. excrucians, A. hexodontus and C. bergrothi are rather abundant, the other species are small in number or rare.

Persistence of La Crosse virus (California encephalitis serogroup) in north-central Illinois

La Crosse (LAC) virus was first isolated in Illinois from a pool of 50 female Aedes triseriatus mosquitoes collected in July 1976, in Peoria Heights. From 1978 through 1981, 27 strains (11 from males and 16 from females) of LAC virus were recovered from 888 pools containing 22,021 adult A. triseriatus mosquitoes from the same study area. These mosquitoes had developed from larvae and pupae collected from 50 individually identified treeholes. Of the 14 trees that yielded LAC virus-positive mosquitoes, one was positive in 3 of 4 years and another was positive in all 4 years. The latter tree had minimum mosquito field infection rates (MFIR) ranging from 3.4 to 12.7/1,000. Eight (57%) of the trees with positive mosquitoes were red oak (Quercus rubra) while 10 (71%) were in the oak genus (Quercus). The four most productive treeholes accounted for 30% of mosquitoes tested and 52% of the LAC isolations. In 1979, 6,729 A. triseriatus mosquitoes were collected in man-baits and tested for virus. From 1,282 tested in 259 pools (mean = 5), 13 LAC isolates were made, resulting in a field infection rate (FIR) of 11.4/1,000. The remaining 5,447 were tested in 218 pools (mean = 25) and 48 strains of LAC were isolated for a FIR of 9.9/1,000. The relationship of these findings to the occurrence of human LAC encephalitis cases in Peoria County, Illinois is discussed. Repeated recovery of virus from this study area reflects a stable, yet dynamic, focus of LAC virus transmission.

Transovarial and trans-stadial transmission of California encephalitis virus in Aedes dorsalis and Aedes melanimon

California encephalitis (CE) virus was transmitted transovarially by its natural vectors, Aedes dorsalis and Aedes melanimon following infection by intrathoracic inoculation. Virus was recovered from adult Ae. melanimon reared from eggs that were stored for up to 19 months and exposed to repeated freezing and thawing. Neither time since oviposition nor storage conditions affected infection rates in surviving embryos. Survival rates were highest in eggs stored at 4 degrees C. Transovarial infection with CE virus did not affect survival of embryos, larvae or adults. However, transovarially infected larvae took longer to develop than did their uninfected siblings.

Field evaluation of the microbial insecticide Bacillus thuringiensis serotype H-14 against floodwater mosquitoes

Four experimental formulations of the microbial insecticide Bacillus thuringiensis var. israelensis (serotype H-14) were evaluated in the field against larvae of the floodwater mosquitoes Aedes nigromaculis and Psorophora columbiae with ground and aerial application methods. The formulations included ABG-6108D (Abbott Laboratories, North Chicago, Ill.), a wettable powder containing about 400 IU/mg, Sandoz 402-WDC (Sadoz, Inc., Homestead, Fla.), a flowable concentrate containing 600 IU/mg, and two wettable powder formulations of Bactimos (Biochem Products, Montchanin, Del.), one with 3,000 IU/mg and the other with 6,000 IU/mg. Trials against both species indicated they were similar in susceptibility to B. thuringiensis var. israelensis (serotype H-14), and that by using ground application methods, populations of second and third instars could be reduced by 83 to 100% with ABG-6108 and Sandoz 402-WDC at 0.56 to 1.12 kg/ha and with Bactimos (6,000 IU/mg) at 0.44 kg/ha. When applied aerially, approximately two to three times the ground rates had to be used to obtain similar population reductions. Fourth instars were difficult to control, requiring approximately 1.5 to 2 times the rates required for the earlier instars to obtain 80 to 100% reductions. However, these rates were not sufficient to obtain adequate control if larvae were late fourth instars.

Observations on container-breeding mosquitoes in New Orleans, Louisiana, with an estimate of the population density of Aedes aegypti (L.)

In a survey of containers infested with Aedes aegypti (L.) conducted during September and October 1979 in a substandard residential area of New Orleans, LA, infestation indices were as follows: House--35, Breteau (foci)--85, Receptacle--69, Block--100, and Larval Density--169. A mean of 48.5 water-holding containers were found per block. More than 50% of these receptacles were narrow-mouthed containers, e.g., drink bottles, that held an average of less than 0.03 mosquito immatures each. After exclusion of data on the unproductive narrow-mouthed type, the average container held 7.8 liters of water, 105 1st and 2nd instars, 69 3rd an 4th instars, and 12 pupae. With assumed constant adult survival rates of 0.85-0.90 per day, the number of females per block on any particular day was estimated from pupal production data at 362-558, and the standing crop of females 12 days and older and therefore old enough to transmit dengue fever if they are vector competent was estimated at 51-158 per block.

Studies on the breeding habitats and seasonal prevalence of larval population of Aedes aegypti (L.) and Aedes albopictus (skuse) in Dacca city

An one-year study was conducted on the outdoor breeding habitats and seasonal prevalence of larval populations of Aedes aegypti and Aedes albopictus in ten different locations of Dacca city. Nine locations were found infested with larvae of either one or both species during the rainy season (May to October) of the year. A total of 1898 containers/sites were surveyed out of which 86 (4.53%) were infested with either one or both species. Out of then different kinds of artificial containers and natural habitats surveyed, Ae. albopictus larvae were present in nine including all four natural sites resulting in highest number and per cent (54, 62.8%) of albopictus infested container in the city. Ae aegypti larvae were present in only four kinds of artificial containers. Earthen pot was the most numerous breeding habitat (24.3%, 461) and contributed the highest number of infested container (45.3%, 39) Seasonal variations in the larval population of both species closely followed the fluctuations in rainfall with zero population during the driest three months.

The urban mosquitoes of Suva, Fiji: seasonal incidence and evaluation of environmental sanitation and ULV spraying for their control

Larval surveys and oviposition traps were used to monitor urban mosquito populations in two adjacent transects in Suva, Fiji between May 1978 and August 1979. Populations of Aedes aegypti and Ae. pseudoscutellaris fluctuated seasonally with changes in rainfall, the latter species being most prevalent throughout the year. Populations of these two species were highest between December and July and lowest between August and October. Larval populations of Culex quinquefasciatus did not show a seasonal variation and larval populations of Cx. annulirostris were too low for any conclusions to be made. All species were found breeding most often in miscellaneous containers, with tyres, plant containers and flower vases also being important sources for Ae. aegypti breeding. Through environmental sanitation the Breteau Index for all species was reduced by 88%; Premise Index by 72% and the Container Index by 83%, when compared to a control area. ULV applied malathion was effective in temporarily reducing Ae. pseudoscutellaris populations from 50--100%. Effects on Ae. aegypti were inconclusive. It is concluded that through enforcement of the existing laws and strict monthly surveillance during the periods of highest seasonal density, urban Aedes and Culex populations can be maintained at an acceptable level.

[Population distribution and the dynamics of Aedes caspius development in biotopes of the southern Urals (Culicidae)]

The distribution of populations and dynamics of the development of the most spread species Aedes caspius (Pallas, 1771) was studied from 1977 to 1978 in the biotopes of the South Urals. It has been established that floodplain water bodies are typical hatching sites of these mosquitoes. The hatching of larvae from wintered eggs takes place in the end of March--beginning of April, the emergence of mosquitoes of the 1st generation--in the end of April--beginning of May. Mosquitoes become very abundant by the end of May--beginning of June and in June--July their abundance remains at the same level. The larvae of Ae. caspius are characterized by the agregated type of distribution.

Epidemic dengue hemorrhagic fever in rural Indonesia. III. Entomological studies

Entomological studies were carried out during a dengue hemorrhagic fever epidemic in Central Java in December 1976. Both Aedes aegypti and Aedes albopictus were widely distributed in Bantul, but the latter species was more abundant. Comparative studies on the vector competence of the two species showed that Ae. albopictus had a higher susceptibility than Ae. aegypti to oral infection with all four dengue serotypes. The two species were equally compentent in transmitting the Bantul strain of dengue 3 virus after parenteral infection. The data suggest that Ae. albopictus could have been an important vector in this epidemic, but no direct observations were obtained to define the respective contribution of either Ae. albopictus or Ae. aegypti.