Direct and Indirect Effects of a Large-Scale Application of Nosema locustae (Microsporida: Nosematidae) on Rangeland Grasshoppers (Orthoptera: Acrididae)

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Abstract
In 1988, a study in central Wyoming was done to determine direct and indirect effects of a large-scale (3,250 hal field application of Nosema locustae Canning on rangeland grasshoppers. No clear direct or indirect effects of N. locustae on low-density (N. locustae, high-density (≥9.6 grasshoppers per m2) populations had 40 to 45% higher mortality than controls. However, between 3 and 7 wk after treatment, a natural population crash obscured any further effects. In treated, high-density asemblages, grasshoppers exhibited higher rates of necrophagy and lower fecundity than controls. Treated plots had greater forb, grass, and total plant biomass than untreated plots. Although the highdensity community structure (based on grasshopper subfamilies) was not affected by treatment, the sex ratio shifted significantly; proportionately fewer males were found in treated areas. The rate of development and mean body weight of grasshoppers in high-density treated areas did not differ significantly from that of controls. The relevance of indirect effects of N. locustae to grasshopper management and the conditions accentuating these effects are discussed.