Ecology of the malaria vector Anopheles arabiensis Patton (Diptera: Culicidae) by the nile in northern Sudan

  • Dukeen M
  • Omer S
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Abstract

In 1942 Anopheles arabiensis, a serious African malaria vector, invaded Upper Egypt from the Sudan and caused a significant malaria epidemic in that country. With the completion of the Aswan Dam in 1969, and the creation of a large lake which extended both north and south of the border between the 2 countries, and a renewed fear of a further invasion, it was agreed between the 2 governments that a thorough watch for the malaria vector would be maintained between Dongola (in the Sudan) and Wadi Halfa (on the Egyptian border), a distance of 320 miles, and control measures put into effect if it was found. In fact in part of the area houses have been sprayed with DDT and breeding places treated with temephos since 1971. Malaria has been recorded throughout the area and in every month of the year. Records from 5 hospital clinics from Wadi Halfa in the north to Burgeig in the south, for 1973-81, show a total of 7450 cases. Previous surveys had suggested the virtual disappearance of An. arabiensis during the period of annual flood of the Nile (July-October). It was suggested in fact that the rise in river level "flushed out" the marginal breeding and that the species maintained itself, until the water-level receded and re-presented suitable, marginal breeding places, in a state of aestivation as an adult.

This study made between August 1978 and October 1979 records regular monthly observations made at 4 localities (3 in the sprayed area and 1 south of it) on larval breeding and adult occurrence and behaviour. Breeding was shown to be continuous throughout the year but during the river flood period it seemed to be confined to more obscure water collections away from the river edge. Gonoactive adults (which when held oviposited quite readily in the expected time after a blood meal) could also be collected throughout the year. Minimum and maximum larval densities were recorded in July to November and in March, respectively. The lowest numbers of adults were found between August and September and the highest (up to 13 per house) in March.

The conclusion arrived at is that "For an arbitrary critical mosquito density of one A. arabiensis female per house, the associated critical level of the river is about 13 m. This River Nile level could be considered as the threshold at which breeding sites may either start or disappear".

[This is a longish article, worth reading in full for its wealth of observational detail, by those directly interested. However, some confusion arises from the use of local terms such as mataras, khors, wadis, jammams etc. which are inadequately defined.]

G. DavidsonADDITIONAL ABSTRACT:In order to understand how the malaria vector Anopheles arabiensis exists in the extremely hot and arid environment (mean annual rainfall 21 mm) in Northern Province, Sudan, regular sampling from breeding places and resting sites was undertaken during 1978 and 1979 at 4 villages along the River Nile downstream (i.e. northwards) from Dongola. The population density of A. arabiensis was lowest during the flood season (July-October) and increased as the river flow decreased during November-June. Thus there was an inverse relationship between the Nile water level and A. arabiensis production. Prolific breeding in riverside pools was the main source of A. arabiensis as the river receded. During the annual flood, when riverside pools were all inundated, A. arabiensis continued breeding at low densities in sheltered sites such as wells and pits. Breeding also occurred in all months in association with the weed Potamogeton crispus in slow reaches of the river. Adult females fed regularly on blood, with gonotrophic concordance in all months, and there was no evidence of aestivation. Outdoor biting activity occurred throughout the night, with a peak between 21.00 and 05.00 h. Daytime searches indoors and oudoors indicated that resting females of A. arabiensis are almost entirely endophilic in the s

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Authors

  • Mustafa Y.H. Dukeen

  • S. M. Omer

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