Preliminary Evaluation of a Granular Trimethacarb Formulation for Deterring Grazing by American Coots

In a 0.2 ha flight pen, groups of 4 American coots were tested to determine if their grazing activity could be affected by application of a registered granular-trimethacarb insecticide. In the 3 days following treatment (3 kg/ha, a.i.), grazing activity in the treated portions of the 200 m experimental plots was reduced an average of 47X. Overall use of the treated areas followed a similar pattern but was less consistent among groups. The addition of methylpyrazine, a strong odorant, produced a strong initial suppression of grazing activity in the treated halves of the plots. However, subsequent rain and a change in the coots' grazing behavior prevented a definitive evaluation of the methylpyrazine treatment. Two birds that died during the trimethacarb-only portion of the study did not have abnormally low levels of brain cholinesterase. However, this finding does not preclude the possibility that they were unable to distinguish treated from untreated grass and consumed lethal amounts of trimethacarb. Additional investigation of methylpyrazine appears warranted; such materials may act to decrease the likelihood that birds will ingest lethal quantities of repellent.