Mosquito larval productivity in rice-fields infested with Azolla in Mvomero District, Tanzania
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Date
2009
Journal Title
Journal ISSN
Volume Title
Publisher
Tanzania Journal of Health Research
Abstract
Azolla (Salviniales: Azollaceae) is known to reduce oviposition and adult emergence of a number
of mosquito species. Several species of Azolla are reportedly indigenous to Tanzania. However, the potential
of Azolla as a biocontrol agent against malaria mosquitoes has not been evaluated in the country. This crosssectional
study was carried out to assess mosquito larval productivity in irrigated rice-fields infested with Azolla
in Mvomero District, Tanzania. A systematic larval sampling covering all open water bodies along designed
transect was carried in rice-fields. Larval density was estimated by dipping water bodies with or without
Azolla. The degree of Azolla coverage was categorized as 0%, <50%, 50%, and >80%. Larvae densities were
categorised as low (<50/m2), medium (50-500/m2) and high (≥500/m2) productivity. A total of 120 water bodies
were surveyed and 105 (87.5%) had Azolla microphyla and A. pinnata at varying degrees of coverage. Of the total
105 water bodies with Azolla, 80 (76.2%) had a green Azolla mat, and 25 (23.8%) a brown Azolla mat. Eightyeight
(73.3%) of the sites were infested with anophelines and 109 (90.8%) with culicine larvae. Seventy percent
of all water bodies contained anophelines and culicines in sympatric breeding, while 20.8% and 3.3% had only
culicines and anophelines, respectively. The majority (82%) of mosquito breeding sites were found in area with
Azolla substrate. Mosquito larva productivity was low in sites with highest (>80%) Azolla coverage. Seventytwo
(81.8%) of the anopheline and 90 (82.6%) culicine breeding sites were infested with Azolla. Water bodies
infested with green Azolla were more productive than those covered by brown coloured Azolla substrates for
both culicines (13%) and anophelines (8%). Of the 1537 field collected larvae that hatched to adult stage, 646
(42.03%) were Anopheles gambiae s.l., 42 (2.73%) were An. funestus and 769 (50.03%) were Culex quinquefasciatus.
These findings suggest that the mosquito productivity is low when the Azolla coverage is high (>80%). The
promotion of Azolla in mosquito control should take into consideration the degree of Azolla coverage.
Description
Research article
Keywords
Azolla, Mosquito, Larval productivity, Rice fields, Tanzania