Larval Habitat Diversity and Ecology of Anopheline Larvae in Eritrea

Abstract

Studies on the spatial distribution of anopheline mosquito larvae were conducted in 302 villages over two transmission seasons in Eritrea. Additional longitudinal studies were also conducted at eight villages over a 24-mo period to determine the seasonal variation in anopheline larval densities. Eight anopheline species were identified with Anopheles arabiensis predominating in most of the habitats. Other species collected included: An. cinereus, An. pretoriensis, An. d'thali, An. funestus, An. squamosus, An. adenensis, and An. demeilloni. An. arabiensis was found in five of the six aquatic habitats found positive for anopheline larvae during the survey. Anopheles larvae were sampled predominantly from stream edges and streambed pools, with samples from this habitat type representing 91.2% (n = 9481) of the total anopheline larval collection in the spatial distribution survey. Other important anopheline habitats included rain pools, ponds, dams, swamps, and drainage channels at communal water supply points. Anopheline larvae were abundant in habitats that were shallow, slow flowing and had clear water. The presence of vegetation, intensity of shade, and permanence of aquatic habitats were not significant determinants of larval distribution and abundance. Larval density was positively correlated with water temperature. Larval abundance increased during the wet season and decreased in the dry season but the timing of peak densities was variable among habitat types and zones. Anopheline larvae were collected all year round with the dry season larval production restricted mainly to artificial aquatic habitats such as drainage channels at communal water supply points. This study provides important information on seasonal patterns of anopheline larval production and larval habitat diversity on a countrywide scale that will be useful in guiding larval control operations in Eritrea.

High Seasonal Variation in Entomologic Inoculation Rates in Eritrea, a Semi-Arid Region of Unstable Malaria in Africa

“…11 Recent studies indicate that vector production in Eritrea is associated with roadside ditches, ponds, and drainage channels, which form as soon as the rains begin, and streambed pools that persist into the dry season on a number of intermittent streams that drain through or close to the study villages. 12 The mean sporozoite rates for the combined villages per zone were two times higher in the villages in the Gash Barka zone than in the Debub and Anseba zones, and were significantly higher during the wet season (June to September) and the period soon after the rains (October to December). It is likely that the scarcity of rainfall during the dry season and the cold temperatures associated with the high altitude areas could have influenced geographic variations in survival rates and parasite development.…”

The effect of physical water quality and water level changes on the occurrence and density of <i>Anopheles</i> mosquito larvae around the shoreline of the Koka reservoir, central Ethiopia

“…It was lowered below the water surface and left for two minutes for the thermometer reading to stabilize. It was then withdrawn without touching the bulb end and the temperature was recorded (Minakawa et al, 1999;Shillilu et al, 2003;Yohannes et al, 2005). The turbidity of the larval breeding water was categorized by taking a small sample of water in a glass test tube and comparing it with a white background.…”

“…Other parameters, including surface area, exposure to sunlight, presence and types of vegetation and type of substratum (i.e. muddy or rocky) were observed and recorded (Minakawa et al, 1999;Shillilu et al, 2003;Yohannes et al, 2005).…”

Integrated malaria vector control with microbial larvicides and insecticide-treated nets in western Kenya: a controlled trial

“…[9][10][11] While ITNs are currently the priority strategy, there is growing interest in attacking the aquatic stages of malaria vectors with microbial larvicides, in conjunction with environmental management. 5,6,[12][13][14][15][16][17][18][19][20][21] Presently, microbial larvicides are being used in an operational context only in Dar es Salaam, in the United Republic of Tanzania. 22,23 However, in the future larvicide application will be expanded to many of the 15 countries included in the President's Malaria Initiative and this interest is likely to spread to other African countries.…”