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The crepuscular biting Activity of Insects in the Forest Canopy in Bwamba, Uganda. A Study in Relation to the Sylvan Epidemiology of Yellow Fever

Published online by Cambridge University Press:  10 July 2009

W. H. R. Lumsden
W. H. R. Lumsden
Affiliation:
Virus Research Institute, Entebbe, Uganda.*
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Extract

The results of a series of catches of biting insects at human bait on platforms in the canopy of the forest at Mongiro, Bwamba, Uganda, are reported. The catches were designed to investigate differences in the numbers taken, due to platforms, season and weather, but mainly to study the short-term changes in the activity of biting insects near the time of sunset. Each catch lasted from 3 hours before to 3 hours after sunset, and was divided into 10-minute periods from 30 minutes before to 1 hour after sunset. The main analysis is of catches made on five platforms on each of 100 evenings which covered the end of the dry and beginning and end of the wet season, 1948, and the end of the dry season, 1949.

A list of the species of biting insects encountered is given. Eight species (Anopheles (M.) gambiae, Taeniorhynchus (C.) fuscopennatus, Taeniorhynchus (M.) africanus and uniformis, Aëdes (M.) nigerrimus, Aëdes (S.) apicoargenteus and africanus, and Chrysops centurionis) were found to be abundant and data relating to them has been subject to more or less detailed analysis. The remaining 27 species or groups of species are discussed shortly.

Six of the eight abundant species show statistically significant differences between the catches on the five separate platforms. Arrangement of the five platforms in order of the total numbers taken, for each of these six species, gives results which are practically identical in three species (Anopheles (M.) gambiae, T. (M.) africanus and uniformis) and in two others (Aëdes (S.) apicoargenteus and africanus) ; however, the arrangements in these two species groups differ widely from each other. The arrangement for C. centurionis differs again.

These ordinal arrangements are compared with the obvious characteristics of the platforms and no consistent relationship is found. It is pointed out that the first three species are derived, largely or even entirely, from breeding places outside the forest, in or associated with the adjacent extensive areas of open swamp, while the last three are likely to be completely confined to the forest for breeding ; both the latter two mosquito species breed in tree holes, and dense shade is characteristic of the breeding places of species of Chrysops closely allied to C. centurionis. It is considered most probable that these platform differences in the numbers yielded are due to local differences in the densities of the adult populations which in turn are related to the abundance and proximity of breeding places.

Seasonal variations in the numbers of the abundant species are also studied and are considered to be almost certainly related to the amount and distribution of rainfall affecting the profusion of breeding places at least as far as the mosquito species are concerned. The tree-hole breeding species, however, suffered a reduction in numbers before the end of the wet season, an effect also noted by Mattingly in West Africa.

The amount of the reduction of the numbers of A. (S.) africanus in the dry season is of importance in assessing the possibilities of the survival of yellow fever virus in that mosquito as a host. The estimated reduction in the dry season of 1949 was to less than one twenty-third of the population existing at the end of the previous wet season (November, 1948).

C. centurionis occurred during all the catch series but was extraordinarily abundant in late March and early April, 1948. It is considered probable that this time of increase represents a yearly period into which hatching from the pupa is compressed. This conclusion is supported by the finding that during this period the biting population was composed of two groups one of which tended to bite before, and the other after, sunset.

Evidence is produced to show that the biting activity of Anopheles (M.) gambiae was depressed by wind, that of Aëdes (S.) africanus by wind and rain but that that of C. centurionis was little affected by either of these factors.

Studies of the biting-activity changes in the nine ten-minute periods extending from 30 minutes before to one hour after, sunset are presented. Each of the species which were known to be mainly active by night and which were sufficiently abundant for study, show activity increasing about sunset, rising to a maximum shortly after, and thereafter declining again to moderate levels. This initial peak is very clearly marked in the cases of Anopheles (M.) gambiae, T. (C.) fuscopennatus, T. (M.) africanus, Aedes (S.) africanus and C. centurionis, less so, but still distinct, in T. (M.) uniformis and A. (M.) nigerrimus. Its position differs in different species being earliest in the case of C. centurionis (18.10–18.20 hours) and latest in that of T. (M.) africanus (18.40–18.50 hours). However, in any given species the peak period of biting activity was subject to only slight movement in time in relation to sunset; in analyses of the data by different platforms, by season, and by types of weather it was the exception to find the time of peak activity to be shifted more than one ten-minute period away from the position which it occupied over the whole series. Further, in studies of the curves of biting activity on individual nights, three consecutive ten-minute periods centred on the period which showed the peak over the whole series, included the peak in 21 of the 23 A. (M.) gambiae cases available, in all five of the T. (M.) africanus, in eight of the 11 A. (S.) africanus and in 15 of the 20 C. centurionis, cases. The regularity of the occurrence of the peak period of activity in any given species is considered to indicate that it is largely controlled by changes in light intensity about the time of sunset.

These findings are discussed in relation to the general problem of the mechanism controlling the rhythm of activity in insects biting by night and a hypothesis, which is based on the conception that different population groups may have different biting habits, is advanced to account for the different types of cycle commonly encountered.

Type
Original Articles
Information
Bulletin of Entomological Research , Volume 42 , Issue 4 , January 1952 , pp. 721 - 760
Copyright
Copyright © Cambridge University Press 1952

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References

Bates, M. (1949). The natural history of mosquitoes. New York, Macmillan Co.Google Scholar
Buxton, P. A. (1950). In Discussion following Gordon & others (1950).—Trans. R. Soc. trop. Med. Hyg., 44, pp. 41–42.Google Scholar
Edwards, F. W. (1941). Mosquitoes of the Ethiopian region. III. Culicine adults and pupae. London, Brit. Mus. (Nat. Hist.).Google Scholar
Evans, A. M. (1938). Mosquitoes of the Ethiopian region. II. Anophelini, adults and early stages.—London, Brit. Mus. (Nat. Hist.).Google Scholar
Gillett, J. D. (1946). Notes on the subgenus Coquillettidia Dyar (Diptera, Culicidae).—Bull. ent. Res., 36, pp. 425–438.CrossRefGoogle ScholarPubMed
Gordon, R. M., Chwatt, L. J. & Jones, C. M. (1948). The results of a preliminary entomological survey of loiasis at Kumba, British Cameroons, together with a description of the breeding places of the vector and suggestions for future research and possible methods of control.—Ann. trop. Med. Parasit., 42, pp. 364–376.CrossRefGoogle Scholar
Gordon, R. M., Kershaw, W. E., Crewe, W. & Oldroyd, H. (1950). The problem of loiasis in West Africa with special reference to recent investigations at Kumba in the British Cameroons and at Sapele in Southern Nigeria.—Trans. R. Soc. trop. Med. Hyg., 44, pp. 11–41.CrossRefGoogle ScholarPubMed
Haddow, A. J. (1945). The mosquitoes of Bwamba County, Uganda. II. Biting activity with special reference to the influence of microclimate.—Bull. ent. Res., 36, pp. 33–73.CrossRefGoogle Scholar
Haddow, A. J. & Dick, G. W. A. (1948). Catches of biting Diptera in Uganda, with anaesthetised monkeys as bait.—Ann. trop. Med. Parasit., 42, pp. 271–277.CrossRefGoogle ScholarPubMed
Haddow, A. J., Gillett, J. D. & Highton, R. B. (1947). The mosquitoes of Bwamba County, Uganda. V. The vertical distribution and biting-cycle of mosquitoes in rain-forest with further observations on microclimate.—Bull. ent. Res., 37, pp. 301–330.CrossRefGoogle Scholar
Haddow, A. J., Gillett, J. D., Mahaffy, A. F. & Highton, R. B. (1950). Observations on the biting-habits of some Tabanidae in Uganda, with special reference to arboreal and nocturnal activity.—Bull. ent. Res., 41, pp. 209–221.CrossRefGoogle Scholar
Hopkins, G. H. E. (1936). Mosquitoes of the Ethiopian Region. I. Larval bionomics of mosquitoes and taxonomy of Culicine larvae.—London, Brit. Mus. (Nat. Hist.).Google Scholar
Johnson, C. G. (1950). The comparison of suction trap, sticky trap and tow-net for the quantitative sampling of small airborne insects.—Ann. appl. Biol., 37, pp. 268–285.CrossRefGoogle Scholar
Lewis, D. J. (1942). The early stages of Aёdes taylori Edwards and A. furcifer Edwards (Dipt., Culicidae).—Proc. R. ent. Soc. Lond., (B) 11, pp. 153–154.Google Scholar
Lumsden, W. H. R. (1947). Observations on the effect of microclimate on biting by Aёdes aegypti (L.) (Dipt., Culicid.).—J. exp. Biol., 24, pp. 361–373.CrossRefGoogle Scholar
Lumsden, W. H. R. (1951 a). The night-resting habits of monkeys in a small area on the edge of the Semliki Forest, Uganda. A study in relation to the epidemiology of sylvan yellow fever.—J. Anim. Ecol., 20, pp. 11–30.CrossRefGoogle Scholar
Lumsden, W. H. R. (1951 b). Probable insect vectors of yellow fever virus, from monkey to man, in Bwamba County, Uganda.—Bull. ent. Res., 42, pp. 317–330.CrossRefGoogle Scholar
Lumsden, W. H. R. & Buxton, A. P. (1951). A study of the epidemiology of yellow fever in West Nile District, Uganda.—Trans. R. Soc. trop. Med. Hyg., 45, pp. 53–78.CrossRefGoogle ScholarPubMed
Mattingly, P. F. (1949 a). Studies on West African forest mosquitoes. Part I. The seasonal distribution, biting cycle and vertical distribution of four of the principal species.—Bull. ent. Res., 40, pp. 149–168.CrossRefGoogle Scholar
Mattingly, P. F. (1949 b). Studies on West African forest mosquitoes. Part II. The less commonly occurring species.—Bull. ent. Res., 40, pp. 387–402.CrossRefGoogle Scholar
Mellanby, K. (1940). The daily rhythm of activity of the cockroach, Blatta orientalis L. II. Observations and experiments on a natural infestation.—J. exp. Biol., 17, pp. 278–285.CrossRefGoogle Scholar
Nautical Almanac and Astronomical Ephemeris for the Year 1949. London, H.M. Stationery Office.Google Scholar
Pitman, E. J. G. (1938). Significance tests which may be applied to samples from any populations. III. The analysis of variance test.—Biometrika, 29, pp. 322–335.Google Scholar
Russell, P. F. & Ramachandra Rao, T. (1942). Observations on longevity of Anopheles culicifacies imagines.—Amer. J. trop. Med., 22, pp. 517–533.CrossRefGoogle Scholar
Simpson, G. G. & Roe, A. (1939). Quantitative zoology. New York, McGraw-Hill Book Co.Google Scholar
Smithburn, K. C., Haddow, A. J. & Lumsden, W. H. R. (1949). An outbreak of sylvan yellow fever in Uganda with Aёdes (Stegomyia) africanus Theobald as principal vector and insect host of the virus.—Ann. trop. Med. Parasit., 43, pp. 74–89.CrossRefGoogle Scholar
Thomson, R. C. M. (1938). The reactions of mosquitoes to temperature and humidity.—Bull. ent. Res., 29, pp. 125–140.CrossRefGoogle Scholar
Williams, C. B. (1937). The use of logarithms in the interpretation of certain entomological problems.—Ann. appl. Biol., 24, pp. 404–414.CrossRefGoogle Scholar