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A 160-acre pasture near Belle Fourche, SD was chosen for evaluating the efficacy of Dimilin (diflubenzuron) 1.0% bait to rangeland grasshoppers. Major forage species in the site were cool and warm-season perennial grasses. Basal coverage by all plants ranged from 50 to 70%. The site was divided into 16 contiguous plots of ten acres. Pre- and posttreatment densities were assessed by grasshopper counts in 40, 0.1 m2 rings arranged in a circle in the center of the plot. Before the treatments, Aulocara elliotti were 50% 2nd and 30% 3rd instars, M. confusus were 10% 3rd, 20% 4th and 50% 5th instars, and M. bivittatus were 60% 2nd instars. These three species respectively constituted 60, 15, and 10% of the grasshopper population in the site. Treatments were replicated 4 times in a RCB. The 16 plots were grouped into four blocks using 1-day pretreatment counts. The bait was applied on 14-15 Jun. The delivery system consisted of a Brie-Mar Model 60 bran applicator mounted on a pickup truck and provided a 13 m swath. Grasshopper counts were conducted 7, 14, 21, 28, and 60 DAT. Natural change in grasshopper densities was determined by counts from untreated plots. Posttreatment survival rates based on pretreatment counts on the same treated plots were adjusted for natural population fluctuations by a modified Abbott's formula and expressed as percent grasshopper reduction. Prior to treatment, the average grasshopper density in untreated plots was lower than that in plots to be treated.

Two toxicants on wheat bran bait were compared in field cages for their efficacies against the bigheaded grasshopper, Aulocara elliotti in Belle Fourche, S. Dak. The dense vegetation in the test site was dominated by western wheatgrass, Agropyron smithii Rydb., blue gramma, Bouteloua gracilis (H. B. K.) and buffalograss, Buchloe dactyloides (Nutt.) Engelm. Field cages (1 m2) were placed on the test site and freed of grasshoppers and other predators. Lorsban (chlorpyrifos), formulated as 1 and 3% bran bait, and Carbaryl, formulated as 2% bran bait, were applied on 31 Jul to the cages at rates equivalent to 2 or 4 lb of bran flakes/acre to simulate field application. Each cage was then stocked with 20 females (ca. 10-d old adults) of Aulocara elliotti which had been starved for 24 h after being collected in the vicinity of the study site. Eight cages were used for each treatment and 16 for the untreated control. Grasshopper mortalities were recorded 5 DAT and the data were transformed using arcsin x prior to analysis.

Low profit potential of land used in the crop reserve program is sometimes exasperated by the needs to treat grasshopper outbreaks which have the potential of moving into adjacent row crops. To determine an effective and economically acceptable rate of insecticide, we established plots (63.7 by 63.7 m; 0.4 ha) with several rates of proven grasshopper insecticides (28 Aug) with an untreated check arranged in checkerboard fashion, which allowed grasshopper immigration into treated plots from all four directions. Applications were made with Broyhill sprayer delivering 10 gal/acre at 40 psi using Teejet 8002 nozzles. A randomized complete block design was used with 4 replications. Forty rings (0.1 m2) were placed in 4 parallel rows in the central portion of each plot. Grasshopper counts (0, 7, 14, 21 and 28 DAT) were used to calculate the percent reduction. No significant differences were detected between compounds, or application rates during the 28 DAT. The control offered by all insecticides and rates was highly successful, which suggests that the residual of these pesticides remains effective even at the lowest rates. Therefore, the lower rates are favorable to the farmers needs for control and economy.