Anopheles gambiae complex egg-stage survival in dry soil from larval development sites in western Kenya

The potential for Anopheles egg survival in dry soil from larval development sites was investigated in western Kenya. A total of 230 dry soil samples collected in 1987, 1988 and 1989 yielded 126 first-instar Anopheles gambiae s.l. larvae from 2 to 5 days after flooding with water. These larvae were from dried animal hoofprints along streams (57.9%), from dried edges of permanent and temporary pools (41.3%) and from dried stream beds (0.8%). Larval density was 1.2 larvae/kg of soil from positive microhabitats in 1987 and 2.4 larvae/kg in 1988. Thirteen larvae from the 1989 soil samples, reared to adults, were identified by DNA probes as Anopheles gambiae sensu strictu (n = 6) and Anopheles arabiensis (n = 7). Experimentally, eggs from field-collected females remained viable up to 12 days for An. gambiae s.l. and 10 days for An. funestus. In western Kenya, egg viability in dry soil may represent a significant, short-term survival mechanism for 2 species of the An. gambiae complex.