In 1975, the western treehole mosquito, Aedes sierrensis (Ludlow), infested all 6 fabricated treeholes in an egg-laying test; and another treehole mosquito, Orthopodomyia signifera (Coquillett), also infested the 5 holes that had continuous standing water in them. In 1976, both Ae. sierrensis and Or. signifera infested all of the 8 holes in an egg-laying test. Oviposition in the holes by Ae. sierrensis began in late April 1976, peaked in May, and continued through September 27; oviposition by Or. signifera began in late May, peaked in August, and continued through September 27.