Anopheles Melas Research Articles

The height and direction of non-host oriented flight, and the age, of Anopheles melas in relation to wind direction in The Gambia, West Africa

The height and direction of non-host oriented flight, and the age, of Anopheles melas in relation to wind direction in The Gambia, West Africa

Oviposition by Anopheles melas and its effect on egg survival during the dry season in the Gambia, West Africa.

Anopheles melas Theobald oviposits after dark in the first half of the night, on damp mud under Avicennia mangrove during neaptides in the Gambia. During oviposition the abdomen is usually slanted, with the eighth segment held vertical to the substrate. Eggs appear rhythmically every 10–12 sec, in 2 distinct movements of extrusion and ejection; 8–10 sec elapse between these 2 movements, during which the egg is inseminated. Eggs are laid on clamp substrate rather than surface waters, in 3 characteristic patterns, of which egg clumps produced by stationary females afford the least chance of egg survival under the desiccating conditions of the dry season.

Preliminary experiments on the hybridization of Anopheles gambiae Giles and Anopheles melas Theobald.

SummaryWhen Anopheles gambiae males were allowed to mate with Anopheles melas females (X-2), hybrids were produced. The sex ratio was 23 males to one female and the hatch was fairly low (22.9%). In the reciprocal cross (X-6) the hatch was greater (51.6%) and the sex ratio approximately 1:1. In each cross the per cent of larvae pupating was about the same and the males appeared to be sterile.One of the hybrid colonies, X-4 (X-6 females and A. gambiae males), was inbred for three filial generations during which the per cent of eggs hatching increased from 5.3 to 83.3, thus establishing a hybrid strain. When the males of these third generation hybrids were back-crossed to A. gambiae females the results were normal, but when back-crossed to A. melas females the progeny were predominantly male, as in X-2, the only other group containing female A. melas heritage.

Comparative susceptibility of Anopheles gambiae Theo. and Anopheles melas Giles to infection by Plasmodium falciparum in Liberia, West Africa.

"Comparative Susceptibility of Anopheles Gambiae Theo. and Anopheles Melas Giles to Infection by Plasmodium Falciparum in Liberia, West Africa" published on Nov 1960 by The American Society of Tropical Medicine and Hygiene.

Anopheles gambias giles and anopheles melas Theobald in a coastal area of Liberia, West Africa

1. (1) The bionomics of Anopheles melas and Anopheles gambiae were studied in Marshall Territory, a rural, coastal district of Liberia, West Africa, from January, 1952, through July, 1953. 2. (2) The A. melas - A. gambiae complex constitutes the most abundant group of mosquitoes in this area, as well as being the main vectors of malaria and bancroftian filariasis. 3. (3) A. melas and A. gambiae are distinct though closely related species, separable by well marked and constant characters in the egg and larval stages. Adults cannot be identified directly. 4. (4) The over-all infection rate for malaria (salivary gland dissections) was 5.7 per cent. in A. gambiae and 1.4 per cent. in A. melas; for filariasis it was 19.5 per cent. in A. gambiae and 27.1 per cent. in A. melas. 5. (5) There was a marked seasonal periodicity in both species in Marshall Territory, A. melas being most abundant in the late dry season and early rains (January - June), and A. gambiae being most abundant during the rains (June - November). The seasonal incidence is a local characteristic and will probably vary from place to place in Liberia. 6. (6) A. melas was restricted to coastal districts. It probably does not occur inland beyond two miles from brackish water, and, in Marshall Territory, was not common beyond three-four miles from the mouth of the Du River, although it occurred in small numbers at least 10 miles upriver. 7. (7) Both species fed readily outdoors but entered human habitations without hesitation. Feeding occurred at all hours of the night, from dusk to dawn. A. melas was shown to be markedly anthropophilic. 8. (8) Window exit trap studies showed that 90 per cent. of the A. melas females feeding in a but during the night left for outdoor resting places by dawn, the majority at dawn. Of those remaining, 90–95 per cent. left at dusk later the same day. For A. gambiae, the figures were 40 per cent. and 85 per cent. Few females of either species spent the entire gonotrophic cycle indoors. 9. (9) Outdoor resting places could not be located in Marshall Territory.In Monrovia, freshly-fed and gravid A. melas females were found abundantly on the buttressed trunks of kapok -trees and in old termite hills. 10. (10) Routine adult collections of A. melas showed a marked correlation of peaks in the adult population with tidal fluctuations, population peaks occurring about 11 days after each “spring” tide in the dry season. With the onset of the rains, the effect of the tides was reinforced. During the height of the rains, the river rose, tidal influence vanished, and the population of A. melas declined. 11. (11) The larvae of A. melas breed almost exclusively in brackish water, conditions being optimal in the zone of salt-marsh grass which is flooded only by the bi-monthly spring tides, The larvae of A. gambiae breed exclusively in fresh-water — small, open, sunlit pools forming the most suitable places. 12. (12) A comparison of adult collecting techniques showed that night-bait collections, human-baited hut traps, and morning collections in huts are all valid sampling methods for following the seasonal variations in incidence of the A. melas - A. gambiae complex.

Filariasis in Liberia.

SummaryThere was very little difference between the number of patients demonstrated to have microfilariae of Wuchereria bancrofti or in the number of microfilaria per smear as measured by scarification or by ordinary thick blood smears. Hourly thick blood smears using 20 cmm. of blood made on 12 subjects demonstrated that the most satisfactory time for making night blood examinations was between 9 and 11 pm. The concentration of microfilariae on night smears was about six times that on day smears in the periodicity examination, but about 15 times the day rate in actual practice. Forty-two or 3.0% of 1395 day smears and 53 or 10.2% of 520 night smears contained microfilariae of Wuchereria bancrofti. No Loa loa was observed but six had Acanthocheilonema perstans. Parasitemia due to W. bancrofti was much commoner along the coast than in the interior locations. This may be dependent upon the presence of the brackish-water-breeding Anopheles melas along the coast which has been demonstrated to have a very much higher filarial infection rate than other potential vectors.

Studies on the vectors of Wuchereria bancrofti in Liberia.

SummaryFrom January, 1952, through April, 1953, a series of dissections of wild-caught anthropophilic mosquitoes for larval worms resembling Wuchereria bancrofti was performed in Marshall Territory, Liberia. Advanced-stage infections were found in Anopheles gambiae, A. melas, and A. hancocki. In addition, natural infections have been found in A. funestus in a nearby locality in Liberia. No advanced-stage infections were found naturally in any culicine mosquito.Five species of laboratory-reared indigenous mosquitoes were fed on a human donor with microfilariae of W. bancrofti. A. gambiae, A. melas, and Culex thallasius were readily infected and carried the infection to maturity within thirteen to fourteen days. Culex fatigans and Aedes aegypti became infected in a much lower percentage, and development of the worms tended to be slower. In all three culicine species, many young nondeveloping larvae were noted in the thoracic muscles.In the small series reported here, Anopheles melas was more heavily infected with the intermediate stages of W. bancrofti in nature than Anopheles gambiae.

Anopheline Life-Cycles and Population Fluctuations

INVESTIGATION of a population of adult Anopheles melas (=A.gambiœ var. melas), conducted during 1941, showed that their numbers underwent regular fluctuations, with very marked peaks at eight-day intervals, and that the only exceptions to this rule were when the rhythm was broken by the dominating influence of tides1. At the time it was difficult to suggest a reason for the fluctuations, because work on both A. melas and its close relative A. gambiœ, by various people, indicated that the life-cycle must occupy at least ten days. Similar fluctuations were found in an A. funestus population at twelve- to fourteen-day intervals, although the supposed time for its complete life-cycle was about twenty days. I tentatively suggested that the fluctuations might be due to intraspecific competition, although this explanation seemed most unlikely.