A NEW BIOASSAY FOR TESTING-PLANT EXTRACTS AND PURE COMPOUNDS USING RED FLOUR BEETLE TRIBOLIUM-CASTANEUM HERBST

We designed a new bioassay to test plant extract activity against stored product pests. Plant compounds were added to feed disks composed of wheat flour and yeast and fed to the red flour beetle (Tribolium castaneum). By measuring insect mass, disk mass, and insect mortality over time it was possible to calculate a phagodepression index, an antifeedant index, the amount of treatment chemical ingested by the beetles, the mortality rate, and the efficiency of conversion of ingested food. The assay was performed for 60 hr to allow for possible habituation effects and to discriminate between phagodeterrency and physiological stress caused by treatments. Alpha- and beta-pinene, eugenol, kaurenic acid, sparteine, essential oils of Minthostachis mollis and Melaleuca quinquenervia, and extracts of Sapindus saponaria were tested. Using this assay we detected the presence of both phagodepressant and phagostimulant compounds in S. saponaria extracts, and we quantified the pronounced effects of sparteine on T. castaneum.