REDUCTION OF GRASSHOPPER POPULATIONS FOLLOWING FIELD APPLICATION OF THE FUNGUS BEAUVERIA-BASSIANA

Conidia of the Hyphomycete fungus Beauveria bassiana (Bals.) were appl ied in an attempt to reduce field populations of grasshoppers, primari ly the migratory grasshopper Melanoplus sanguinipes (Fabricius). Dry s pores were applied with wheat bran carrier to three fallow fields at a rate of 2.0 x 10(13) spores ha-1 in 10 kg bait ha-1. Examination of c ulture plates that had been placed in the field to capture spores and of bran carrier with scanning electron microscopy indicated that a sub stantial portion of the B. bassiana colony-forming units (spores and c lumps of spores) did not adhere to the bran and were applied in the fi eld as free particles. Grasshoppers collected from the treated plots a t intervals after application were assayed for infection by B. bassian a. The observed rate of mycosis in the treated populations was 70% of those collected after 2 days, declining to 41% by 13 days and 5% by 19 days after application. Analysis of reductions in population density gave results in agreement with the infection data. Treated populations declined 60% and 33% by 9 and 15 days after application respectively. The reductions were significant on both post-treatment sampling dates (p < 0.05) and the three replicated fields gave comparable results. T his is the first field demonstration of effectiveness of this fungus a s a microbial control agent of grasshoppers.