The Canadian Entomologist 128: 353-354 (1996) Detoxicative enzyme systems, such as the cytochrome P450 monooxygenases, gluthione S-hansferases, and general esterases, have been widely studied in holometabolous insects (e.g. Lepidoptera, Diptera, and Coleoptera). These, and other enzyme systems, play important roles in insecticide resistance, but are also important in insect-host plant relationships, because host range can partially depend on the ability of an insect to cope with putatively toxic allelochemicals in an otherwise suitable host plant (e.g. Lindroth 1989). In some cases, differences in the relative activities of these enzymes between closely related insect taxa can have significant biological consequences (Siegfried and Mullin 1989).These enzyme systems have been far less extensively studied in hemimetabolous insects, but we recently investigated the tissue distribution and development changes in detoxicative enzymes in the migratory grasshopper, Melanoplus sanguinipes (Fab.), a major pest of rangelands and cereal crops in western Canada. However, M. sanguinipes is only one member of a melanopline grasshopper community in western North America, consisting of about 10 common Melanoplus species and additional species in related genera (Vicke~y and Kevan 1985). Many A of these species apparently have a wide host range including grasses and forbs, and in some years several species constitute significant pests of cereal and oilseed crops in the Prairie Provinces. At present, grasshopper control is based on aerial and ground-sprayer applications of pyrethroid, carbamate andorganophosphate insecticides (WCCP 1995).Herein we report analyses of detoxicative enzyme systems in five species of melanopline grasshoppers collected in southern Alberta, to determine if interspecific differences occur. Such information could be useful in predicting relative susceptibilities to certain types of insecticides.Adult grasshoppers of the following species were collected with sweepnets in mixed wheat and pasture at Turin, Alberta, in July 1994: M. sanguinipes, M. bivittatus (Say), M. gladstoni Scudder, M. packardii Scudder, and Phoetaliotes nebrascensis (Thomas). The collection site was selected because it contains a mixed grasshopper community from which all of the aforementioned species can be collected simultaneously. More importantly, this site has not been heated with insecticides in the past 4 years. Therefore potential interspecific differences are not confounded by prior pesticide exposure or diet. Grasshoppers were shipped by air to the University of British Columbia where they were maintained in 40-by 28-by 28-cm cages and fed seedling wheat and dry wheat bran for 24 h prior to dissection.Grasshoppers were dissected in cold 0.15 M NaCl solution and their midguts, including the gastric caeca, removed, rinsed, and homogenized as previously described (Feng and Isman 1994). These tissues were previously found to have the highest levels of detoxicating enzymes in M. sanguinipes. Homogenates were prepared using midguts...