Mosquito Larval Density Research Articles

Effect of Rice Plant Covering on the Density of Mosquito Larvae and Other Insects in Rice Fields

The larval densities of Culex tritaeniorhynchus, Anopheles sinensis and other insects were compared in fields with and without rice plants, and in fields with short and tall rice plants The density of C. tritaeniorhynchus was higher in unplanted an short rice planted sections of the rice fields. In the case of A. sinensis, a higher larval density was observed only in unplanted sections. Among the 7 families comprising 11 to 13 species of other insects, 5 species were more abundant in unplanted section. The difference in larval densities among sections in rice fields was possibly due to oviposition preferences of females.

Changes in the populations ofBacillus thuringiensis H-14 andBacillus sphaericus applied to vector breeding sites

A dark brown mutant ofBacillus thuringiensis H-14 (BT-MB24) and a macrofibre mutant ofBacillus sphaericus H5 ab (BS-MS3) were applied to mosquito breeding habitats such as rain-water pools, casuarina garden pits, paddy fields and cesspits. The population of these bacilli in the water and soil of these habitats was monitored. The results show that the population of the two bacteria recovered from the water decrease with simultaneous increase in the soil populations within one hour of application: by day 19, the bacilli are virtually absent from the water. Only a few cells remain viable in the water for up to 200 days and in the soil for up to 270 days. Even though both these bacilli persist in the waters for a long time at about 100 CFU mL−1 they do not cause any significant reduction in the mosquito larval density.

Productivité en larves de moustiques (Diptera: Culicidae) des milieux aquatiques peu profonds d'un secteur du Moyen-Nord Québécois (LG-1, Territoire de la Baie de James)

The LG-1 area (53°46′ N; 77°30′ W) is located on La Grande Rivière, 28 km upstream of its mouth at James Bay. It is a Middle Subarctic landscape. The ecological distribution of mosquito larval populations of 21 species is analyzed. For each ecological unit the following data are taken into account: the density of the larval community (larvae per metre cubed) and relative frequency (percentage) of the species per sample.The larval productivity of snowmelt Aedes mosquitoes is evaluated for each ecological unit from the percentage of the area covered by water (percentage), the average depth of the shallow pools (in metres) and the mosquito larval density. The mean number of larvae (log x) per hectare and the standard error of mean range from 4.77 ± 0.255 (33 000 < 59 000 < 106 000) in the Carex rostrata unit with peat bog substrate up to 7.12 ± 0.413 (5.1 × 106 < 1.3 × 107 < 3.4 × 107) in the silty Carex aquatilis unit. The mapping of a typical area of 2 500 ha in which 626 ha are mosquito-productive wetlands, shows an average productivity (log x) of 5.29 ± 0.146 (140 000 < 200 000 < 280 000). These data are compared with quantitative results published from similar northern localities.

水質汚濁が原因と思われるアカイエカの大発生例とその防除対策

1. In the late spring of 1968,nuisance and biting problems by an unusually great number of adult mosquitoes took place in a suburban area of Kagamigahara City, Gifu Prefecture, Central Japan. Through a request of the city authorities, a series of field investigations were made on the population dynamics of the pest mosquitoes. Chemical and environmental control measures were also planned. 2. A pool which was receiving most of the raw wastes of a starch and woolen factories was found to be the main breeding source of the bothering mosquitoes. This pool was located at the river beach neighboring the residential quarter and had an extent of approximately 80 ares and an average depth of 0.2 meters. Population density of mosquito larvae and pupae at the station P selected in the pool was estimated by the removal method, and age structure of these aquatic stages was also analyzed. Imaginal population size in the residential district about 200 meters apart from the breeding source was estimated with light trap collections. These investigations were continued on the weekly basis during the period from June to November, 1968. 3. As the results, it was known that the overall species composition of mosquitoes of this area was very unusual for such a typical suburban habitat surrounded by many paddy fields; more than 90 percent of the collected adults and larvae were the house mosquitoes, Culex pipiens pallens Coquillett. This uncommonness was further ascertained by the comparison with the results of our mosquito surveys simultaneously performed in other two areas with similar topographical features. For the correct identification of the species, examinations were made of ommatidial number in females as well as DV/D value in males randomly sampled from the above "C. pipiens pallens" population. The results revealed that the autogenous house mosquito, C. pipiens molestus, was not intermixed. 4. Population dynamics of the C. pipiens pallens was studied by analyzing the seasonal change of larval population size and age structure. It was presumed that the adults had four definite peaks of emergence in late June, mid and late July, and early August on the bases of precursory ageing in the larval population. The actual number of adults collected by light traps and the above presumption were proven to be in good agreement. 5. Details of the control measures taken to cope with the outbreak were described, and several problems in the planning of insecticide application along with the merit and demerit of the environmental control of the pest mosquitoes, particularly of the construction of drainages, were discussed in relation to the pollution of inland water.

Disabling effects and control of filariasis.

SummaryThis report reviews the distribution and prevalence of clinical filariasis and of microfilaremia in the Pacific, in Africa and in Asia; discusses the disabling effects of filariasis and outlines a control program that is working satisfactorily in the Society Islands, French Oceania.In collecting epidemiologic data for the maps, a lack of standardization in clinical, blood and mosquito surveys was apparent, and comparison had to be limited to prevalence rates for elephantiasis and microfilaremia. Even here, representative numbers in standard age groups and from all segments of the population were seldom available and suitable correction factors had to be employed to adjust the figures to represent the population as a whole.Procedures for performing and reporting standardized clinical, blood and mosquito surveys are recommended and tables are presented which show summaries of certain of these results from the Society Islands before the filariasis control program began. Seven per cent of the population demonstrated elephantiasis 7% of the males had hydrocele and 12% experienced attacks of lymphangitis. A total of 26% of the whole population showed clinical signs of filariasis, and 32% demonstrated microfilaremia.The disabling aspects of filariasis are difficult to evaluate exactly in terms of man-days of work lost annually in a community, but it is concluded that the social and economic aspects of filariasis are such as to constitute a major public health problem in many parts of the tropics.A correlation between prevalence of elephantiasis and microfilaremia in a population as a whole could not always be shown in the south Pacific. A low prevalence of microfilaremia was associated with a low prevalence of elephantiasis but areas with high microfilaremia rates did not always show high elephantiasis rates. However, when the density of microfilariae per unit of blood was calculated, it was found that a definite correlation existed. It is suggested, for at least that part of the Pacific where non-periodic filariasis occurs, that the density of microfilariae in an area may be used as an index to estimate the amount of elephantiasis in that same area.A filariasis control program now in progress in the Society Islands, which combines mosquito control with parasite control by mass treatment with diethylcarbamazine, shows that when practiced thoroughly, these measures reduce microfilaremia, microfilarial density, the mosquito population and larval density in mosquitoes to a minimum. Primary acute filariasis is rare; new cases of elephantiasis together with other forms of chronic filariasis fail to develop; and transmission is reduced to a low point, in some instances to zero.