Diet of Migratory Grasshopper (Orthoptera: Acrididae) in a California Native Grassland and the Effect of Prescribed Spring Burning

Abstract

Crop contents of the lesser migratory grasshopper, Melanoplus sanguinipes F., were identified from specimens collected in a California native grassland, an increasingly rare habitat. Samples were taken of late immature stages (early summer 1994 and 1995) and adults (late summer 1994 and 1995) from areas burned in 1992 and 1993. Overall, forbs were the most common vegetation type found in grasshopper diets for late summer 1994 and 1995, and early summer 1995. For all sample dates, native grasses were significantly more abundant in grasshopper diets than exotic grasses. Percentage of cover of forbs (an index of food availability) was lower than cover of both native and exotic grasses in the field; however, forbs were the most abundant vegetation type in grasshopper diets for 3 of 4 samples, indicating a feeding preference for forbs. Time since rangeland burning (1992 versus 1993) had a significant effect on grasshopper diets in both early and late summer 1994, but not in 1995. The proportion of forbs found in grasshopper crops from recently burned areas (1993) in the late summer 1994 sampling period was higher than in areas burned earlier (1992); the burning treatment had the opposite effect on the proportion of native grasses in grasshopper diets. No effects of time since burning treatment were found in 1995. These data support the hypothesis that grasshopper herbivory has a stronger impact on native grasses than exotic grasses in California native grasslands; however, this impact is diluted, because forbs are preferred over both native grasses and exotic grasses. Furthermore, fire alters grasshopper diets 1 yr after a fire, and this effect is undetectable two years after a fire.