A field trial was carried out to quantify the observation that the presence of the aquatic fern Salvinia auriculata is determined to the production of Anopheles albimanus by transplanting the fern to natural ponds and sampling larval populations on a weekly basis. Intact mats of Salvinia had a marked inhibitory effect on Anopheline breeding. Cage tests in the laboratory indicated that the plant can be an oviposition barrier to gravid An. albimanus. The suggestion is made that the plant might be considered as a naturalistic vector control measure in certain types of breeding places.