Environmental Factors Associated with Larval Habitats of Anopheline Mosquitoes (Diptera: Culicidae) in Irrigation and Major Drainage Areas Between Adami Tulu and Meki Towns, Central Ethiopia
No Thumbnail Available
Date
2008-07
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Addis Ababa University
Abstract
A study was conducted to characterize larval habitats of anopheline mosquitoes in
irrigation and major drainage areas between Adami Tulu and Meki towns, in the middle
course of the Ethiopian Reft Valley. A total of 22 anopheline larval positive aquatic
habitats were sampled fortnightly from late December 2007 to early June 2008 by using
dipping techniques. Simultaneously, environmental variables of the larval habitats were
also measured/estimated and recorded. A total of 3,439 anopheline and 5,213 culicine
larvae were collected. Microscopic identification of the late instars (3rd and 4th) of
anopheline larvae yielded 47.6% of An. pharoensis, 32.1% An. gambiae s.l. larvae
(presumably An. arabiensis) and only 20.3% other anopheline larval species (An.
squamosus, An. coustani and An. cinereus). Anopheles larvae were sampled
predominantly from natural swamps, irrigation canals and sand pools with samples from
these habitat types representing 88.0% (3025) of the total anopheline larval collection in
the study area. Larvae of the malaria vector species, An. gambiae s.l. (An. arabiensis) and
An. pharoensis were most frequently sampled from sand pools and natural swamps,
respectively. The habitats were characterized based on water temperature, turbidity, water
current, water pH, elevation, aquatic vegetation, habitat permanence, origin of the
habitats (natural or human made), distance to the nearest house, presence of mats of algae,
water depth, intensity of shade, and substrate type. Logistic regression analysis detected
six key environmental variables that were associated with the occurrence/abundance of
anopheline larvae: Water temperature, presence of mats of algae, water depth, and origin
of the habitats, turbidity and water current. Multiple step-up regression analysis further
detected four best predictor variables associated with larval abundance of the malaria
vector species. Accordingly, relative abundance of An. gambiae s.l. larvae was
significantly and inversely associated with aquatic vegetation and water current whereas
that of An. pharoensis larvae were significantly and positively associated with water
temperature and the presence of algae in the water bodies. Dry season anopheline larval
habitats that are created and maintained by perenial water bodies such as the Ethiopian
Rift Valley lakes and rivers and their associated water development projects need to be
considered in vector control operation and further research.
Description
Keywords
Biology