Large-Scale Test of Control of Grasshoppers on Rangeland with Nosema locustae123

Abstract

Nosema locustae Canning was applied to rangeland by aircraft at dosage rates of 2.1 × 109 and 2.1 × 108 spores per ha when the major grasshopper species, Melanoplus Sanguinipes (F.), were mostly 3rd instars. These treatments were compared with a standard rangeland insecticide treatment with 560 ml of 95% technical malathion per ha, and compared with no treatment. Each plot was 2,332 ha, and each treatment was replicated four times. The high level of N. locustae caused significant reductions in grasshopper densities during the season of treatment (1975). A panzootic among grasshoppers caused by the fungus Entomophthora grylli Fresenius occurred early in the second season and reduced the potential for expression of subsequent effects by N. locustae . Nevertheless, the high level caused significant reductions, and the low level appeared to cause slight but not significant reductions in grasshopper densities during the two subsequent seasons (1976 and 1977). Parasitism of grasshoppers by entomophagous flies and nematodes decreased sharply in malathion plots, but tended to increase in N. locustae and untreated plots.