| Shrnutí: | Fifty-one species of plants from the state of Oaxaca, Mexico, were evaluated for toxicity: 39 as water extracts at 5 and 15% and 21 at 25% and three species as acetone extracts in five doses (0.1, 0.01, 0.001, 0.0001 and 0.00001%). Also tested were eight vegetable oils in three doses (0.1, 0.01 and 0.001%) and 11 commercial vegetable essences in four doses (0.1, 0.01, 0.001 and 0.0001%). The bioassays consisted in placing 20, early IV instar larvae of the mosquito, Culex quinquefasciatus, in a plastic container with 100 ml of water with 1 ml of each dose of the extract preparations. The plants that presented the greatest larvacidal action as water and acetone extracts were anona seed (Annona squamosa L.), the huizache vine (Acacia farneciana L.), and bark from the guamuchil tree (Pithecellobium dulce Roxb.). The CL50 and CL95 of the acetone extract of A. squamosa seed was of 0.00025 and 0.00701% respectively. The vegetable oils produced a maximum mortality rate of 20% and the commercial essences produced mortality rates between 65% and 100%.
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