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A study of the age-composition of populations of Anopheles gambiae Giles and A. funestus Giles in North-Eastern Tanzania

  • M. T. Gillies (a1) and T. J. Wilkes (a1)
Extract

Polovodova's technique for determining the physiological age of mosquitos was used in a study in 1962–64 of the age-composition of populations of Anopheles gambiae Giles and A. funestus Giles resting in houses in two areas of Tanzania. One area was around Muheza, 25 miles from the coast, where the climate is humid and equable, and the other was around Gonja, 80 miles inland, where hardly any rain falls for five months of the year.

It was found that the age-composition was almost identical in populations of A. gambiae and A. funestus at Muheza, about 20 and 23 per cent., respectively, being 3-parous and older and 1 per cent. 7-parous and older in both species. At Gonja, the population of A. gambiae was much younger, 14 per cent, being 3-parous and older and only 0·3 per cent. 7-parous and older. The oldest mosquitos found at Muheza included one 12-parous female of A. gambiae and one female of A. funestus believed to have laid eggs 14 times. No examples of A. gambiae older than 8-parous were found at Gonja.

Dissections to determine the condition of the ovariolar sacs in A. gambiae at Gonja showed that in 87 per cent, of freshly fed parous females an interval of at least 24 hours had occurred since oviposition. At Muheza, 72 per cent, of individuals of this species in the cool season and 52 per cent, in the hot season were in a similar condition.

Marking and recapturing experiments were carried out with females of A. gambiae in order to be able to correlate calendar age with physiological age. The oldest recaptured was 34 days old and was found to have laid eggs 10 times. From data on 60 recaptures, it was concluded that, although there was some irregularity, the first gonotrophic cycle lasted 3–4 days and later cycles 3 days.

Age-specific sporozoite rates in A. gambiae rose from 4·1 per cent, for 3-parous to 32 per cent, for 7-parous and older females, and in A. funestus from 3·2 per cent, for 3-parous to 30 per cent, for 7-parous and older females. Most of the infected 3-parous females were gravid, indicating that few were infective at the beginning of the fourth cycle. On this account it was concluded that some 80 per cent, of malaria infections were transmitted in the fifth, sixth and seventh cycles.

Analysis of the distribution of age-groups indicated that both A. gambiae and A. funestus showed a deficiency of nulliparous females, presumably because greater numbers of this group rested outside houses. From the second to seventh cycles the proportions of successive age-groups in both species at Muheza declined regularly at a rate corresponding to a mortality of 37·8 per cent, per cycle for A. gambiae and 38·6 per cent, for A. funestus, or 14·6 and 15·0 per cent, per day, respectively. Beyond this age the mortality was considerably higher. At Gonja, the population of A. gambiae declined at a rate corresponding to a mortality of 51·5 per cent, per cycle for the second to sixth cycles, or 20·9 per cent, per day. Above this age, the mortality was estimated to be higher still.

From the regression of infectivity on age it was estimated that 6·8 and 6·1 per cent, of A. gambiae and A. funestus, respectively, became infected at each blood-meal.

These findings are discussed in the light of current epidemiological theory.

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References
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Adam, J. P., Hamon, J. & Bailly-Choumara, H. (1961). Observations sur la biologie et le pouvoir vecteur d'une population d'Anopheles gambiae résistante à la dieldrine en Haute-Volta.—Bull. Soc. Path. exot. 53 (1960) pp. 10431053.
Coz, J., Gruchet, H., Chauvet, G. & Coz, M. (1962). Estimation du taux de survie chez les anophèles.—Bull. Soc. Path. exot. 54 (1961) pp. 13531358.
Davidson, G. (1955a). Measurement of the ampulla of the oviduct as a means of determining the natural daily mortality of Anopheles gambiae.—Ann. trop. Med. Parasit. 49 pp. 2436.
Davidson, G. (1955b). Further studies of the basic factors concerned in the transmission of malaria.—Trans. R. Soc. trop. Med. Hyg. 49 pp. 339350.
Davidson, G. & Draper, C. C. (1953). Field studies of some of the basic factors concerned in the transmission of malaria.—Trans. R. Soc. trop. Med. Hyg. 47 pp. 522535.
Davidson, G. & Jackson, C. E. (1962). Incipient speciation in Anopheles gambiae Giles.—Bull. World Hlth Org. 27 pp. 303305.
Detinova, T. S. (1949). Physiological changes in the ovaries of female Anopheles maculipennis. [In Russian.]Med. Parasit., Moscow 18 pp. 410420.
Detinova, T. S. (1953a). The age composition and epidemiological significance of populations of Anopheles maculipennis under the conditions found in the Province of Moscow. [In Russian.]Med. Parasit., Moscow 22 pp. 486495.
Detinova, T. S. (1953b). The duration of the gonotrophic cycle in the mosquito Anopheles maculipennis; the interval of time between oviposition and the next blood meal. [In Russian.]Med. Parasit., Moscow 22 pp. 446449.
Detinova, T. S. (1962). Age-grouping methods in Diptera of medical importance with special reference to some vectors of malaria.—Monogr. Ser. World Hlth Org. no. 47, 216 pp.
Detinova, T. S. & Gillies, M. T. (1964). Observations on the determination of the age composition and epidemiological importance of populations of Anopheles gambiae Giles and Anopheles funestus Giles in Tanganyika.—Bull. World Hlth Org. 30 pp. 2328.
Giglioli, M. E. C. (1963). Aids to ovarian dissection for age determination in mosquitoes.—Mosq. News 23 pp. 156159.
Giglioli, M. E. C. (1964). Some illustrations showing the morphology of the female reproductive organs of Anopheles gambiae melas and the structure of follicular dilatations in some Anophelines.—Trans. R. Soc. trop. Med. Hyg. 58 pp. 56.
Gillies, M. T. (1954). The recognition of age-groups within populations of Anopheles gambiae by the pre-gravid rate and the sporozoite rate.—Ann. trop. Med. Parasit. 48 pp. 5874.
Gillies, M. T. (1957). Age-groups and the biting cycle in Anopheles gambiae. A preliminary investigation.—Bull. ent. Res. 48 pp. 553559.
Gillies, M. T. (1958). A modified technique for the age-grading of populations of Anopheles gambiae.—Ann. trop. Med. Parasit. 52 pp. 261273.
Gillies, M. T. (1961). Studies on the dispersion and survival of Anopheles gambiae Giles in East Africa, by means of marking and release experiments.—Bull. ent. Res. 52 pp. 99127.
Gillies, M. T. (1964). The study of-longevity in biting insects.—Int. Rev. gen. exper. Zool. 1 pp. 4776.
Gillies, M. T. & Wilkes, T. J. (1963). Observations on nulliparous and parous rates in a population of Anopheles funestus in East Africa.—Ann. trop. Med. Parasit. 57 pp. 204213.
Gruchet, H. (1962). Etude de l'âge physiologique des femelles d'Anopheles funestus funestus Giles dans la région de Miandrivazo, Madagascar.—Bull. Soc. Path. exot. 55 pp. 165174.
Hamon, J. (1963). Etude de l'âge physiologique des femelles d'anophèles dans les zones traitées au DDT, et non traitées, de la région de Bobo-Dioulasso, Haute-Volta.—Bull. World Hlth Org. 28 pp. 83109.
Hamon, J., Chauvet, G. & Thélin, L. (1961). Observations sur les méthodes d'évaluation de l'âge physiologique des femelles d'anophèles.—Bull. World Hlth Org. 24 pp. 437443
James, S. P., Nicol, W. D. & Shute, P. G. (1929). Habits of Anopheles in relation to their role in the spread of malaria. Importance of monthly differences in the length of life of A. maculipennis.—Trans. 7th Congr. far east. Ass. trop. Med. 2 pp. 712717.
Macdonald, G. (1952). The analysis of the sporozoite rate.—Trop. Dis. Bull. 49 pp. 569586.
Polovodova, V. P. (1949). The determination of the physiological age of female Anopheles, by the number of gonotrophic cycles completed. [In Russian.]Med. Parasit., Moscow 18 pp. 352355.
Pringle, G. (1965). Estimates of the parasite load carried by naturally-infected Anopheline mosquitoes in a highly malarious area.—Rep. E. Afr. Inst. Malar. 1963–1964 pp. 1113.
Samarawickrema, W. A. (1962). Changes in the ovariole of Mansonia (Mansonioides) mosquitoes in relation to age determination.—Ann. trop. Med. Parasit. 56 pp. 110126.
Shipitsina, N. K. (1962). On the gonotrophic cycle and age condition of populations of bloodsucking flies (Diptera, family Simuliidae) in the vicinity of Krasnoyarsk. Pt. I. Gnus cholodchovskii and Simulium reptans var. galeratum. [In Russian with English summary.]Med. Parasit., Moscow 31 pp. 1829.
Smith, A. (1958). Outdoor cattle feeding and resting of A. gambiae Giles and A. pharoensis Theo. in the Pare-Taveta area of East Africa.—E. Afr. Med. J. 35 pp. 559567.
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Bulletin of Entomological Research
  • ISSN: 0007-4853
  • EISSN: 1475-2670
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