Evaluation of the Fungus Beauveria Bassiana with Selected Insecticide Stressors for Control of Unconfined Rangeland Grasshoppers, 1995

The Mycotrol GH oil formulation of Beauveria bassiana and 4 insecticide stressors (Dimilin, Sevin 4-Oil, Orthene and Fyfanon) were each aerially applied to 10 acre plots of rangeland approximately 5 miles SSW of Bayard, NE, on 8-9 Jul. Stressors (sub-lethal doses of grasshopper-active insecticides used to weaken the target insect) were formulated at 0.1 to 0.01 of the usual recommended dose with spores of B. bassiana. All treatments were applied at a volume of one gpa (oil diluent) with a Cessna Ag-Truck aircraft equipped with 8006 flat fan nozzle tips operating at 40 psi and 120 mph and an assigned swath width of 100 ft. Plot boundaries were separated from one another by 100 yd. An untreated plot was included in the study for comparison. Grasshopper densities were estimated by counting grasshoppers in 0.1 m2 rings (4 rows of 10) located in the center of each quadrant of each plot. At each evaluation site, rings were separated from each other by 5 yd. Grasshopper counts were taken at 0, 5, 8, 11 and 14 DAT. Species and age composition of the grasshopper populations was determined at each plot by taking a sweep net sample comprised of 200 sweeps from the southwest quadrant. The above species were predominantly in the 3rd through 5th instar stages of development and comprised 44.1%, 21.4%, 9.3% and 6.9% of the grasshopper population, respectively, listed above. Data were recorded as surviving grasshoppers/site, 4 sites/treatment and analyzed using the Kruskal-Wallis test with tied ranks.