Biomedical subjects
Publications and source records attributed to Y Mekuria.
Published information on the distribution of Aedes albopictus in South Carolina is limited and fragmentary. This paper draws on various published and unpublished sources and presents synoptic information on the occurrence of the mosquito in 17 counties. Additional surveys are required to establish the infestation status of the other 29 counties in the state.
In an effort to develop a more effective measure for use in emergency control of the dengue vector Aedes aegypti. applications of a combination of a larvicide (Bacillus thuringiensis israelensis [B.t.i.]) and an adulticide (permethrin) were made using a truck-mounted forced-air generator (Scorpion 20) and evaluated in the Dominican Republic. This method has the potential to simultaneously control adults and larvae. In bioassay cages placed in household water containers at the time of application, larval mortalities were 95.1 and 100% for 2 application rates of permethrin mixed with B.t.i. Adult mortalities were not as impressive, probably because of resistance to permethrin. Higher adult mortality in caged specimens (78.5%) and a substantial reduction in the natural population (68.4%) of Ae. aegypti were obtained following a 2.1-g AI/ha application of deltamethrin alone.
Susceptibility tests were conducted using the World Health Organization diagnostic test procedure on strains of Aedes taeniorhynchus, Aedes sollicitans, Aedes vexans, and Culex nigripalpus collected from several localities in Charleston and Georgetown counties of South Carolina. Aedes taeniorhynchus was resistant to malathion (mortality 1.0-54.4%) but not to propoxur, permethrin, or fenitrothion. There also were indications that Ae. sollicitans and Cx. nigripalpus were resistant to malathion, but to a lesser extent than Ae. taeniorhynchus (mortalities: 72.1-81.0%, and 46.2%, respectively). Aedes vexans was susceptible to malathion (mortality 98.6%). In field tests using ULV application of malathion and field-collected Ae. taeniorhynchus, and susceptible Ae. aegypti and Ae. taeniorhynchus, a noticeably lower mortality also was obtained in the wild mosquitoes.
The insecticide susceptibility of Aedes aegypti adults and larvae from Santo Domingo, Dominican Republic, was investigated using World Health Organization standard procedures. A field strain was more resistant to insecticides than a colony strain that originated from the same place. Larvae produced from ovitrap-collected eggs were resistant to temephos (78.2% mortality on exposure to 0.025 mg/liter). Mortality rates after exposure of adults to discriminating concentrations showed that wild populations were resistant to DDT, malathion, propoxur, permethrin and deltamethrin. The problem of resistance was considered serious enough to warrant consideration of control measures other than the use of chemicals.
A field and laboratory study was conducted to determine some of the parameters relevant to malaria transmission by Anopheles mosquitoes in Dajabon Province, Dominican Republic. Although all 4 species occurring in the area, i.e., An. albimanus, An. crucians, An. grabhamii and An. vestitipennis, were included in the investigations, most of the work focused on the first and last named species because of their abundance. Gonotrophic cycles were determined to be 2.6 and 3.2 days for An. albimanus and An. vestitipennis, respectively. Mean parity rates for the 2 species were 37.3 and 20.7%, respectively, in outdoor samples. The human blood index, as determined by ELISA, was 0.08 for An. albimanus and 0.12 for An. vestitipennis. Only An. albimanus was confirmed positive for Plasmodium falciparum circumsporozoite protein, using ELISA. The vectorial capacity of An. albimanus was determined to be 0.019 and that of An. vestitipennis 0.005.
Polytene chromosome analysis was carried out in samples of Anopheles arabiensis from two colonies originating from different sites in the Rift Valley, Ethiopia. Both colonies were found to maintain the main chromosomal inversion variations existing in wild populations. Changes in karyotype frequencies were documented as well as excesses of heterokaryotypes.
Insecticide susceptibility of Anopheles albimanus and An. vestitipennis in Dajabon Province, Dominican Republic, was investigated. Only 74.3% of An. albimanus exposed to 4% DDT for 1 h died. The mortality in this species following exposure for 1 h to 0.25% permethrin was also 74.3%. However, this species was susceptible to malathion, fenitrothion and propoxur. The mortality obtained following exposure of An. vestitipennis to 4% DDT and 0.1% propoxur, both for 1 h, was 71% and 100%, respectively. However, the number of specimens exposed to propoxur was small.
Field studies of Dajabon Province, Dominican Republic, revealed that Anopheles albimanus and An. vestitipennis were the most abundant anopheline species followed by An. crucians and An. grabhamii. Three of the species were collected as adults and larvae whereas An. grabhamii was found only in the adult stage. Perennial ponds and rice fields were the most important larval habitats. The anophelines were predominantly exophilic and exophagic; however, outdoor resting sites could not be identified. Large numbers of mosquitoes were collected from corrals at night and also by using an animal-baited net trap and UV light traps. Man-biting collections showed an early evening peak of biting activity by An. albimanus and An. vestitipennis. Only 23% and 13% of the bites by the 2 species, respectively, occurred indoors.
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Blood fed female mosquitoes were collected from human dwellings in the Awash Valley, Ethiopia. Those identified morphologically as A. gambiae s.l. were preserved in Carnoy's fixative for later ovarian polytene chromosomes examination. Only one member of the A. gambiae complex, A. arabiensis, was found by such examination. The polymorphic inversions identified were 2Rb and 3Ra. The frequencies of these inversions were variable in different localities and the former inversion was found to form an altitudinal cline.
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