Mosquito species collected from a marsh in western Kenya during the long rains.

A total of 475,431 mosquitoes representing 8 genera and 43 species were collected from a marsh in the western Kenya highlands to determine species composition and succession in relation to the epidemiology of Rift Valley fever virus. Culex pipiens was the most common species, totalling 92.3% of the collection, followed by Cx. zombaensis (2.2%), Anopheles coustani (1.1%), An. squamosus (0.8%), Mansonia uniformis (0.6%), Coquillettidia microannulatus (0.5%), Uranotaenia mashonaensis (0.5%), Ma. africana (0.4%) and Cq. aurites (0.4%). Aedes quasiunivittatus was the first floodwater species to emerge from newly flooded areas and was the most abundant Aedes collected, representing 88% of all Aedes specimens. Culex guiarti and Cx. zombaensis colonized newly flooded areas soon after the areas became flooded.

Egg hatching of Aedes mosquitoes during successive floodings in a Rift Valley fever endemic area in Kenya.

Floodwater Aedes breeding habitats in central Kenya were sequentially flooded to determine the numbers of mosquito eggs hatching during each flooding. Approximately 90% of the larvae sampled during 4 floodings emerged during the initial flooding. The number of Aedes eggs hatching during the second flooding was lowest of all 4 floodings, and no significant differences in the amount of egg hatching during floodings 3 and 4 were seen. Unhatched Aedes eggs were present in soil samples collected after the final flooding. The possible implications of these findings with regard to Rift Valley fever virus control are discussed.

Pretreatment of floodwater Aedes habitats (dambos) in Kenya with a sustained-release formulation of methoprene.

Effectiveness of sustained-release Altosid pellets (4% AI methoprene) against floodwater mosquitoes in dambos treated at 5, 3, and 1 wk before and 1 day after flooding was determined. Only 2% of Aedes pupae (primarily Aedes mcintoshi) survived to adults in an area treated 5 wk preflood, and no adult mosquitoes emerged from an area treated 1 day after flooding. In contrast, 12 and 16% of Aedes pupae successfully survived to the adult stage in areas pretreated 3 and 1 wk, respectively, preflood. The effectiveness of the Altosid declined against Culex spp. (primarily Cx. antennatus) collected from dambos 15-31 days after flooding. The potential for using preflood treatment with methoprene to control Aedes vectors of Rift Valley fever virus in endemic areas is discussed.

Application of polar-orbiting, meteorological satellite data to detect flooding of Rift Valley Fever virus vector mosquito habitats in Kenya.

Measurements of green-leaf vegetation dynamics recorded by the advanced very high resolution radiometer instruments onboard National Oceanic and Atmospheric Administration satellites 7 and 9 were used to derive ground moisture and rainfall patterns in Kenya and monitor resultant flooding of mosquito larval habitats (dambos) likely to support Rift Valley Fever virus vector mosquitoes (Aedes and Culex spp.). Satellite-derived data from mid-1981 to December 1988 have been analysed with corresponding rainfall, flooding and vector population data as they relate to Rift Valley Fever virus ecology. Single (7 x 7 km) and multiple grid-cell image analysis (200 x 300 km) in small localized areas and large geographical regions, respectively, of vegetation data were used to quantify the potential for flooding of mosquito breeding habitats. The ability to detect accurately parameters, such as ground moisture, that determine flooding could provide local officials with sufficient warning to allow for implementation of specific mosquito control measures before a disease outbreak.