The Effect of Perennial Grasses on Growth, Development and Survival of Grasshopper Nymphs (Orthoptera: Acrididae): Implications for Population Management in Roadsides

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Growth, development and mortality of nymphs of Melanoplus sanguinipes (Fabr.) fed diets of one of 12 species or cultivars of perennial grasses were monitored over a 3-week period in early summer, 1991 and 1992. Mean dry weight of grasshoppers was significantly higher (P < 0.05) on Western wheat grass (cv. S-8580) than any other grass, and lowest on smooth brome grass (cv. Carlton and Signal). Development of grasshoppers was significantly more rapid (P < 0.05) when feeding on Western wheat grass (cv. S-8580) and Intermediate wheat grass (cv. S-9051) than any other grass. Smooth brome grass had the greatest negative impact on grasshopper development. Mortality among grasshoppers fed these grasses was not significantly different over the 21 days. Analysis of historical grasshopper abundance survey data showed that mean grasshopper densities in 15 of 18 years (1975-1992) were significantly lower (P <0.05) in roadsides containing brome grass and alfalfa than in roadsides containing a high proportion of weeds. This relationship also held true for cropland that was adjacent to these respective roadsides. In 11 of 18 years of the adult grasshopper survey, mean grasshopper density was significantly higher (P <0.05) in crops that were next to weedy roadsides compared to those next to brome grass/alfalfa. In no year was the inverse true, that is, grasshopper density in brome grass/alfalfa was never significantly higher than in weedy roadsides. Records from the annual grasshopper abundance survey (1975-1992) indicate that about 30% of roadsides in Saskatchewan are weedy. Grain producers may be able to reduce grasshopper damage if these roadsides were seeded to brome grass or brome grass/alfalfa mixture [