Experimental transmission of Tahyna virus (California group) to wild rabbits (Oryctolagus cuniculus) by mosquitoes.

Two wild rabbits (Oryctolagus cuniculus) were subcutaneously infected with a dose of 2.6 dex. i.c. LD50/0.02 ml of extraneurally passaged Tahyna virus strain "236". During the 24-72 hours interval p.i. viremia was demonstrated in both animals ranging from 1.0 to 3.42 dex. i.e. LD50/0.02. Mosquitoes Aedes vexans, which had fed on them, transmitted the virus to one of three other rabbits. During 24-96 hours interval after terminated feeding of infectious mosquitoes viremia was detected in this animal ranging from 0.49 to 4.08 dex i.c. LD50/0.02 ml. Seroconversion was revealed by means of plaque reduction neutralization test 11 days after infection.     

Virological examination of mosquito larvae from southern Moravia.

254 pools of 4,115 mosquito larvae belonging to nine species were examined by isolation experiments. The larvae were collected in breeding places in an inundated forest--a natural focus of Tahyna virus, in April, June and July 1974 and 1975. Tahyna virus was isolated from one pool of 10 Culiseta annulata larvae collected in July 1974. Ecological questions concerning this finding are discussed.     

Resistance levels of nine mosquito species to 4% DDT in Phnom Penh, Kampuchea.

According to the standard WHO method criteria, the mosquitoes Anopheles campestris and Culex vishnui were found to be susceptible to DDT in the territory of Phnom Penh. An. vagus and An. sinensis were approximately at the limit of susceptibility and the remaining five species (Aedes vexans, Cx. tritaeniorhynchus, Cx. fuscocephala, Cx. gelidus, Cx. bitaeniorhynchus) were found to be more or less resistant. Except for An. vagus, the males of all species were more susceptible than the females.     

DDT-resistant mosquito strains with cross-resistance to pyrethroids

Various DDT-resistant strains of mosquito, comprising 8 strains of Aedes aegypti from the Neotropics (tropical and South America) and one each of Anopheles gambiae and An. quadrimaculatus were tested for resistance to pyrethroids. Susceptibility was measured by LT₅₀ values, after exposure to impregnated papers in the cylinders used in the WHO standardised test for adult mosquitoes. DDT-resistance levels (by comparison with susceptible strains) ranged from × 2 to × 73, with simultaneous low resistance to permethrin (× 1.4 to × 3.4) except in one strain from Guyana which reached × 30. Further comparisons were made with this Guyana strain and one from Salvador with similar DDT-resistance (about × 70) but low permethrin-resistance. Tests with methoxychlor and I,I-di-(4-chlorophenyl)-2-nitropropane and with the synergist I,I-di-(4-chlorophenyl)-2,2,2-trifluoroethanol suggested that a considerable part of the DDT-resistance of both strains was due to a dehydrochlorination mechanism. Tests with the synergist piperonyl butoxide (PB) suggested that microsomal oxidase systems were also involved, especially in the Guyana strain. The cross-resistance in both strains extended to 3 other pyrethroids. Addition of the synergist PB had little effect on the Salvador strain, but substantially reduced permethrin-resistance in the Guyana strain. It is concluded that an unknown mechanism associated with DDT-resistance confers a low level cross-tolerance to pyrethroids; this can be substantially augmented by the development of a microsomal oxidase mechanism, as in the Guyana strain.     

1975—1986年我国小麦品种抗条锈性分小种成株鉴定结果

 本文报道了1975—1986年以我国条锈菌主要流行小种、稀有类型共39个菌系对我国重要小麦品种(系)和抗源进行分小种成株抗性鉴定的结果。明确了条中17—28号小种和洛10、洛13类群各类型的致病特征.对目前在世界范围内广泛应用的“洛类”品种在我国丧失抗条锈性进行了分析,提出了提高其抗性的途径,为抗锈育种和品种布局提供了依据.研究结果支持了我国条锈鉴别寄主的选择和对小种的合理划分.     

Susceptibility of adult Aedes aegypti (L.) and Culex quinquefasciatus Say (Diptera; Culicidae) to DDT in Kampuchea.

The susceptibility to 4% DDT was tested in adult Aedes aegypti and Culex quinquefasciatus mosquitoes collected in houses in Phnom Penh (Kampuchea). It was found that in spite of the fact that insecticide treatment had not been performed for many years, the populations of both species as a whole remained resistant. However, there were some differences in the susceptibility between males and females and between engorged and hungry females. Possible causes of these differences are discussed in the present paper.     

Review of microsporidia-mosquito relationships: from the simple to the complex

Microsporidia in mosquitoes can be divided into two categories based on their life cycles and host-parasite relationships. Some species of microsporidia exhibit simple life cycles with one spore type responsible for oral (horizontal) transmission. They affect only one generation of the mosquito and are not usually host or tissue specific. Brachiola algerae and Vavraia culicis are examples of species isolated from mosquitoes with relatively straightforward life cycles (one spore type) and simple host-parasite relationships. B. algerae and a close relative of V. culicis have also been isolated from a vertebrate (human) host but sources for these infections are unknown. In contrast to B. algerae and V. culicis, polymorphic (heterosporous) microsporidia in mosquitoes are characterized by complex life cycles involving multiple spore types responsible for horizontal and vertical transmission. They affect two generations of the mosquito and some involve an obligate intermediate host. These microsporidia are generally very host and tissue specific with complex developmental sequences comprised of unique stages and events. The microsporidium Edhazardia aedis is a pathogen of Aedes aegypti and does not require an intermediate host. The developmental cycle of E. aedis is characterized by four sporulation sequences, two in the parental host and two in the filial generation. Recent speculation relative to the source of B. algerae human infection have implicated infected mosquitoes and raised concerns about the safety of mosquito microsporidia in general. The subject of this review is to compare and contrast three species of microsporidia from mosquitoes, two with broad host ranges (B. algerae and V. culicis) and one specific to mosquitoes (E. aedis). This review describes features that distinguish mosquito-parasitic microsporidia with simple life cycles and broad host ranges from truly mosquito-specific microsporidian parasites with complex life cycles.     

豫南罗索线虫感染库蚊、伊蚊和阿蚊的实验研究

试验的伊蚊、库蚊和阿蚊,对豫南罗索线虫均表现敏感,当蚊幼与线幼虫数之比为1:5时,4种伊蚊的感染率均在95％以上;致倦库蚊和三带喙库蚊的感染率分别为98.6％和97.1％,骚扰阿蚊为66.4％。线虫在蚊体内发育良好,感染度亦较高,表明此线虫具有应用前景。     

Isolation of a Pseudomonas fluorescens metabolite/exotoxin active against both larvae and pupae of vector mosquitoes

A formulation was developed from the metabolite(s) of a novel Pseudomonas fluorescens Migula strain (VCRC B426) and tested against 4th-instar larvae and pupae of three species of vector mosquitoes, Anopheles stephensi Liston, Culex quinquefasciatus Say and Aedes aegypti (L). The larvae and pupae of An. stephensi were the most susceptible to the formulation, followed by those of C. quinquefasciatus and Ae. aegypti, in that order, and the dosage requirement for pupal mortality was less than that required for larval mortality. The LC50 dosage requirements for larvae of these mosquito species were, respectively, 70.4, 511.5 and 757.3 microg protein ml(-1), whereas for pupae they were, respectively, 2.0, 9.4 and 19.2 microg protein ml(-1). The lethal fraction was purified from the culture broth and its molecular mass, as determined by high performance liquid chromatography, was 44kDa. This is the first report of a microbial formulation acting upon mosquito pupae, a non-feeding stage. Its mode of action and efficacy to control mosquitoes under field conditions need to be studied further.     

Resistance mechanisms to DDT and transpermethrin in Aedes aegypti

Penetration, metabolism and excretion of [¹⁴C]DDT and [³H]transpermethrin were studied in three strains of Aedes aegypti L. after topical application of 10 nl of a solution of the insecticide in 2-ethoxyethanol. The standard susceptible strain was compared with a DDT-selected strain (BKS) and a permethrin-selected strain (BKPM). No significant penetration resistance was observed in either resistant strain, but both showed high DDT-dehydrochlorinase activity which contributed to the DDT resistance. A non-metabolic factor was also involved. Rates of transpermethrin metabolism were very similar in all three strains and substantially higher internal concentrations of transpermethrin were required to produce toxic effects in both BKS and BKPM mosquitoes. By analogy with other insect species, it is concluded that transpermethrin resistance in these strains is of the kdr type, while the DDT resistance is a mixture of kdr and DDT-dehydrochlorinase.     

Serologic examination of human population in South Moravia (Czechoslovakia) on the presence of antibodies to arboviruses of the Alfavirus, Flavivirus, Turlock groups and Bunyamwera supergroup.

A statistically representative group of human population from the South Moravian region (CSSR) was examined on the presence of antibodies against the following arboviruses: Lednice, Sindbis, tick-borne encephalitis, West Nile, Tahyna and Calovo. The ascertained absence of antibodies to the Lednice virus is an evidence that at present this virus is of no epidemiological importance in the region studied. No antibodies to Sindbis, West Nile and Calovo viruses were demonstrated. 17.8 to 42.0% of antibodies to Tahyna virus were detected in all age groups examined. The total infection rate was 26.0%. Antibodies to the tick-borne encephalitis virus occurred primarily in persons over 40 years. The total infection rate was 5.5%.     

Circulation of mosquito-borne viruses in large-scale sheep farms in eastern Slovakia

Samples of blood sera collected from 608 sheep in large farms of the districts of Trebisov, Michalovce, Vranov nad Toplou and Humenné were investigated in hemagglutination-inhibition test for the presence of mosquito-borne viruses Sindbis, West Nile, Tahyna and Calovo. Antibodies to arboviruses Tahyna (11.5%) and Calovo (10.9%) were detected most frequently, while a lower sero-positivity was recorded to the Sindbis (2.3%) and West-Nile (1.0%) viruses. Certain differences were found in the infection rates in the respective districts: the highest frequency of antibodies to Tahyna and Calovo viruses was recorded in sheep of the district of Trebisov and the lowest one in animals of the district of Humenné.     

Repellency of aerosol and cream products containing fennel oil to mosquitoes under laboratory and field conditions

The repellency of fennel (Foeniculum vulgare Miller)-containing products (5% aerosol and 8% cream) against mosquitoes was compared with those of citronella oil, geranium oil and deet, as well as three commercial repellents, Baby Keeper cream containing IR3535, MeiMei cream containing citronella and geranium oils, and Repellan S aerosol containing 19% N,N-diethyl-m-toluamide (deet) under laboratory and field conditions. In a laboratory study with female Aedes aegypti (L), fennel oil exhibited good repellency in a release-in-cage test and repellency in skin and patch tests of the oil was comparable with those of citronella and geranium oils. In paddy field tests with five human volunteers, 5% and 8% fennel oil-containing aerosol and cream produced 84% and 70% repellency, respectively, at 90 min after exposure, whereas Baby Keeper cream and MeiMei cream gave 71% and 57% repellency at 90 min after exposure, respectively, and Repellan S aerosol gave 89% repellency at 210 min. The species and ratio of mosquitoes collected were the genera Culex (44.1%), Anopheles (42.2%), Aedes (7.8%) and Armigeres (5.9%). Fennel oil-containing products could be useful for protection from humans and domestic animals from vector-borne diseases and nuisance caused by mosquitoes.     

Mosquito studies on the Isla de la Juventud, Cuba, at the beginning of rain period

A total of 8418 mosquitoes belonging to 16 species were collected in 11 localities of the Isla de la Juventud. The most abundant species was Aedes taeniorhynchus (92% of specimens collected). The species Wyeomyia vanduzeei and Mansonia nigricans were encountered on the island for the first time.     

两种罗索线虫对不同蚊种的自然感染及实验研究

1984年在河南信阳地区发现两种蚊体寄生索线虫,在同一孳生地内生长繁殖,分别寄生于中华按蚊和致倦库蚊及三带喙库蚊等幼虫体内,自然寄生率为5.48％、4.32％、5.82％。通过人工感染试验,感染率均较高,可达61.5％～95.7％。试验证明两者对按蚊和库蚊具有显然不同的生理特性。这两种罗索线虫在稻田、田沟等多种水体内均有孳生,宿主范围广泛,有应用价值。     

Occurrence of Aedes aegypti (L.) and Culex quinquefasciatus Say (Diptera, Culicidae) in houses of different constructions in Phnom Penh, Kampuchea

The relation between the number of mosquito specimens of the most abundant species Aedes aegypti (L.) and Culex quinquefasciatus Say and the construction of houses which they inhabited was studied. The effect of the building materials and of the height at which the floor was situated above the ground were assessed in five and four localities, respectively. It was found that in the localities having the character of a town the mosquitoes were most abundant in houses constructed from corrugated plate and in those the floor of which was situated 2-3.5 m above the ground. In the locality of a village character, the mosquitoes were most numerous in brick houses with the floors at the ground level.     

A survey on indoor resting mosquito species in Phnom Penh, Kampuchea

Indoor resting mosquitoes were collected in 7 localities (250 houses) of Phnom Penh at various periods. The mosquitoes were collected for 8 min in every house by means of an aspirator and net. A total of 16 species of mosquitoes resting in houses were found, one of them for the first time in Kampuchea. Culex quinquefasciatus was the predominant species in 6 of the localities observed; its predominance in houses was more or less evident; Aedes aegypti prevailed in one locality. The percentage of A. aegypti predominance in houses corresponds with the risk of occurrence of dengue haemorrhagic fever. Anopheles vagus was found resting in higher abundance in houses of one locality. This fact is of little epidemiological significance because of the zoophilic character of An. vagus in Kampuchea. On the other hand even uncommon occurrence of Anopheles subpictus found in houses may signalize a possibility of an endemic occurrence of malaria in Phnom Penh.     

Insecticide resistance in vector mosquitoes in China

Because of their special behaviour, physiology and close relationship with humans, mosquitoes act as one of the most important vectors of human diseases, such as filariasis, Japanese encephalitis, dengue and malaria. The major vector mosquitoes are members of the Culex, Aedes and Anopheles genera. Insecticides play important roles in agricultural production and public health, especially in a country with a huge human population, like China. Large quantities of four classes of insecticides, organochlorines, organophosphates, carbamates and pyrethroids, are applied annually to fields or indoors in China, directly or indirectly bringing heavy selection pressure on vector populations. The seven major species of vector mosquito in China are the Culex pipiens L. complex, C. tritaeniorhynchus Giles, Anopheles sinensis Wied., A. minimus Theobald, A. anthropophagus Xu & Feng, Aedes albopictus (Skuse) and Ae. aegypti L., and all have evolved resistance to all the above types of insecticide except the carbamates. The degree of resistance varies among mosquito species, insecticide classes and regions. This review summarizes the resistance status of these important vector mosquitoes, according to data reported since the 1990s, in order to improve resistance management and epidemic disease control, and to communicate this information from China to the wider community.     

Insecticide resistance and,efficacy of space spraying and larviciding in the control of dengue vectors Aedes aegypti and Aedes albopictus in Sri Lanka

Unprecedented incidence of dengue has been recorded in Sri Lanka in recent times. Source reduction and use of insecticides in space spraying/fogging and larviciding, are the primary means of controlling the vector mosquitoes Aedes aegypti and Ae. albopictus in the island nation. A study was carried out to understand insecticide cross-resistance spectra and mechanisms of insecticide resistance of both these vectors from six administrative districts, i.e. Kandy, Kurunegala, Puttalam, Gampaha, Ratnapura and Jaffna, of Sri Lanka. Efficacy of the recommended dosages of frequently used insecticides in space spraying and larviciding in dengue vector control programmes was also tested.