Direct and indirect effects of a large-scale application of Nosema locustae (Microsporida: Nosematidae) on rangeland grasshoppers (Orthoptera: Acrididae).
Lockwood J.A. | Debrey L.D.
In 1988, a study in central Wyoming was done to determine direct and indirect effects of a large-scale (3,250 ha) field application of Nosema locustae Canning on rangeland grasshoppers. No clear direct or indirect effects of N. locustae on low-density (<9.6 grasshoppers per m2) populations were apparent compared with controls. In the 3 wk after application of N. locustae, high-density (greater than or equal to 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 assemblages, 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 high-density 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.
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