The Effect of Agricultural Development on the Grasshopper Populations of the Red River Valley of Manitoba, Canada

Abstract

The Red River Valley was originally a wet prairie and marsh. Drainage commenced in 1899 and was basically complete by 1907. Intensive grain farming developed. The area was periodically invaded by the Rocky Mountain grasshopper, Melanoplus spretus (Walsh), for over 100 years, until 1902, at which time this species apparently became extinct. Local grasshoppers did not become pests until about 1900, after agriculture was well established. The clear-winged grasshopper, Camnula pellucida (Scudder), and the two-striped grasshopper Melanoplus bivittatus (Say), then became abundant. These grasshoppers bred on the roadsides surrounding each square mile. Road-building and ditching produced slopes of ground favorable for oviposition. The destruction of native vegetation and its replacement by introduced grasses, cereal crops and weeds provided attractive and nutritious food plants and oviposition sites. C. pellucida reached its highest population in 1940 when there was an abundance of Poa pratensis L. and Phleum pratense L. on the roadsides. These grasses are attractive food plants. Poa pratensis is known to be highly nutritious. Both species along with Agropyron smithii Rydb. provided favored egg-laying sites. Although C. pellucida has maintained populations capable of damaging crops and peaks occurred in 1950 and 1961 numbers have not again been as high. This may have been related to a marked reduction in P. pratense and A. smithii. M. bivittatus continued at a high population level because of the abundance of oviposition sites and of preferred food plants. Being a general feeder it was not adversely affected by the change in grass species but benefited by an abundance of the lactiferous weeds, Sonchus arvensis Bieb., Lactuca pulchella (Purse) DC. and Taraxacum officinale Weber.