Browsing by Author "Le Sueur, David."

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The ecology, over-wintering and population dynamics of the pre-imaginal stages of the Anopheles gambiae Giles complex (Diptera : culicidae) in northern Natal, South Africa.
(1991) Le Sueur, David.; Appleton, Christopher Charles.
This study investigated aspects of the breeding biology, ecophysiology, morphology, over-wintering and population dynamics of the pre-imaginal stages of members of the Anopheles gambiae complex in northern Natal, South Africa, Investigation of the breeding biology, concentrated on breeding site utilisation by the different members of the Anopheles gambiae complex. Surveillance personnel were unable to locate the breeding sites of Anopheles arabiensis and postulated that location and description of these would offer a unique opportunity for control. The difficulty in locating the breeding sites of An. arabiensis at certain localities was found to be a product of their low density, presumably as a result of the intra-domiciliary, residual insecticide spray programme. The effect of temperature on larval physiology and adult morphology was investigated. terms of their implications Anopheles gambiae complex. The findings are discussed in for anopheline taxonomy and the The effect of temperature on larval growth rates was investigated in both the field and laboratory. The finding of this part of the study indicate that the larval stages play an important role in the over-wintering of populations within the region. The control implications of these findings and winter breeding site localisation are discussed. A theory for the so called 'late season transmission i.e. Apri-May, within the province and southern Africa is proposed. The population dynamics of An. merus were investigated, together with the effect of abiotic factors such as temperature, salinity and rainfall. The effect of sampling bias due to factors such as behavioural avoidance were studied.
Effects of temperature on members of the Anopheles gambiae complex (Diptera: Culicidae) in South Africa : implications for malaria transmission and control.
(1996) Maharaj, Rajendra.; Appleton, Christopher Charles.; Le Sueur, David.
This study investigated the effects of temperature and relative humidity (both controlled and natural) on the lifecyle and morphology of adults of members of the Anopheles gambiae complex in northern KwaZulu-Natal, South Africa. Laboratory investigations into the effects of simulated temperature and relative humidity regimes concentrated on seasonal differences in longevity, egg hatchability, reproductive potential and adult survivorship of An. arabiensis. Differences were found in the life table parameters when these mosquitoes were reared under conditions of seasonal temperature and relative humidity. During the cool season the lifespan and adult survivorship of mosquitoes were greater than those reared during the warm season. In summer, the egg hatchability and reproductive potential were greatest whereas in winter An. arabiensis underwent gonotrophic dissociation although these females were found to take blood meals readily. The influence of seasonal temperature and relative humidity on the body size of An. arabiensis was investigated, both in the laboratory and under field conditions. In both environments, these factors were found to significantly influence body size. In winter, there was a 13% increase in wing size compared to summer bred mosquitoes. A comparison of body size of An. arabiensis, An. merus and An. gambiae reared under laboratory conditions of seasonal temperature and relative humidity showed that the wing size of An. arabiensis was greater than that of An. merus and An. gambiae. The effect of temperature and relative humidity on morphological criteria used in species separation was also investigated. Seasonal differences in wing spot size were compared for An. arabiensis, An. merus and An. gambiae. From this investigation it was concluded that the pale and dark spots on the wing of Anopheles mosquitoes could not be used in species identification due to the large degree of inter-species overlap in the wing spot measurements. The measurement of the pale band at the junction of the 3rd and 4th tarsomere on the hind leg was also investigated for its use in species separation and were found to be useful within the An. gambiae complex. The implications of this study on the transmission and control of malaria are discussed with reference to the late season transmission during March to May that is characteristic of the region.
Malaria vector populations associated with the agricultural development at Mamfene, Northern KwaZulu-Natal, South Africa.
(1995) Obala, Andrew Ambogo.; Appleton, Christopher Charles.; Sharp, Brian Leslie.; Le Sueur, David.
The irrigation farming methods on the Makhathini Flats are thought to be responsible for recent increase in malaria cases in the Mamfene area of northern KwaZulu-Natal despite ongoing malaria control activities. Their coincidence with the period of intensive fanning is an interesting one. This study was therefore carried out to determine the relationship between larval habitats and adult mosquito population in malaria transmission using Geographic Information System (GIS). Four types of breeding sites were utilised by malaria vectors in Mamfene, viz; types 1, II, III and IV. Habitat type I was tap pools, type II was irrigation spillage in agricultural land, type III was spillage outside but adjacent to the agricultural land and type IV was depression pools located both in the Balamhlanga swamp and inland. The cumulative larval density in all habitats peaked in March 1995 (20/man-hr), with irrigation spillage (type III) recording the highest density index (33/man-hr) as compared to tap pools (type I) which recorded 32.8/man-hr while other waterbodies recorded I3 .4/man-hr (type II) and O.5/man-hr (type IV) respectively. Subsamples of both larvae and adults of An. gambiae group were identified by the Polymerase Chain Reaction (PCR) technique. Of the larvae identified, 94.1 % and 5.9% (n=289) were An. arabiensis and An. quadriannulatus respectively while in the adult component, the composition was 98.7% and 1.3% (n=303) for An. arabiensis and An. quadriannulatus respectively. This confirmed An. arabiensis as the dominant malaria vector in Mamfene area while the exophilic behaviour of An. quadriannulatus was portrayed. Of the An. gambiae group dissected for parity, 51 .5%) were found parous. This is an indication that the population was old and was able to maintain transmission locally despite ongoing vector control measures. The Global Positioning System (GPS) was used to position larval and adult mosquito sampling sites. The spatial distribution of adult mosquitoes from the breeding sites were plotted using GIS soft ware (Map Info ) and the distance between the breeding sites and study houses were measured using a utility distance tool. With the aid of GIS, the adult mosquito density in houses could be used as an indicator to locate the breeding sites in the vicinity. The importance of these findings in terms of application in cost-effective malaria control cannot be over-emphasized.