A FIELD POPULATION OF MELANOPLUS SANGUINIPES (FAB.) (ORTHOPTERA: ACRIDIDAE) AND ITS PARASITES

Abstract

Nine species of Acrididae were found during a 10-year sampling of a grasshopper population in a pasture field at Chatterton, Ontario, of which Melanoplus sanguinipes (Fab.) constituted 74 to 90% of the specimens. Eight dipterous and one, possibly two, mermithid species were found as primary parasites, and one hymenopteron was found as a secondary parasite; microsporidia were also present. Differences in the annual levels of abundance and rates of mortality of M. sanguinipes were small. Chi-square tests of percentages of parasitism in the semimonthly periods indicate that parasitism by the complex of parasites was not significantly different at the 5% level in many years. A seasonal index of parasitism based on a sequence of parasite attacks is considered an approximation of the percentage by which parasites reduce the numbers of grasshoppers that survive to the end of the season. The 10-year series of indices was positively correlated with the number of hosts parasitized.