Development of a novel bioassay for estimation of median lethal concentrations (LC50) and doses (LD50) of the entomopathogenic fungus Beauveria bassiana, against western Xower thrips, Frankliniella occidentalis

To conduct laboratory experiments aimed at quantifying secondary acquisition of fungal conidia by western Xower thrips (Frankliniella occidentalis), an eYcient assay technique using Beauveria bassiana as the model fungus was developed. Various application protocols were tested and it was determined that the percent mortality did not vary among protocols. Peak mortality of secondinstar nymphs, under constant exposure to conidia, occurred 5 days post-inoculation. Second-instar thrips that were exposed to conidia within 24 h of the molt to second instar were more susceptible to Beauveria bassiana than thrips exposed after times greater than 24 h post-molt. Conidia eYcacy, which was monitored at 24 h intervals, did not diVer signiWcantly within 72 h. A test of the Wnal bioassay system was conducted in a series of assays aimed at determining the LD50 of B. bassiana technical powder against secondinstar western Xower thrips. It was determined that B. bassiana (strain GHA) is highly eVective at very low doses (LD50 of 33–66 conidia/insect).  2005 Elsevier Inc. All rights reserved.