Mosquito larval productivity in rice-fields infested with Azolla in Mvomero District, Tanzania.
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 cross-sectional 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 (> or = 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. Eighty-eight (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. Seventy-two (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.
Mwingira
V S
VS
Amani Medical Research Centre, P.O. Box 81, Muheza, Tanzania. mwingirafamily@yahoo.com
Mayala
B K
BK
Senkoro
K P
KP
Rumisha
S F
SF
Shayo
E H
EH
Mlozi
M R S
MR
Mboera
L E G
LE
D000383:Agriculture; D000818:Animals; D000852:Anopheles; D003465:Culex; D017753:Ecosystem; D029624:Ferns; D006801:Humans; D007814:Larva; D009032:Mosquito Control; D012275:Oryza; D010572:Pest Control, Biological; D013636:Tanzania