OLFACTORY BASIS OF CANNIBALISM IN GRASSHOPPERS (ORTHOPTERA, ACRIDIDAE) .2. FIELD ASSESSMENT OF ATTRACTANTS

The responses of rangeland grasshoppers to biologically and historically derived attractants were studied in a shortgrass prairie in southeastern Wyoming in July 1990. Seven long-chain fatty acids (C-14-C-20; singly and in combination), grasshopper cadavers, molasses, fruit extracts, and chloroform (solvent control) were tested. Each attractant was applied to filter paper and placed in an arena delimited by a 0.10-m(2) aluminum ring. Grasshoppers were most attracted to linoleic and linolenic acids, with significantly more grasshoppers found in these arenas than in those of the controls or other attractants. These two fatty acids alone and in combination were more attractive at 1 grasshopper equivalent (GE) than at 5 GE. The seed bug, Lygaeus kalmii Stal, and five species of ants were also attracted to these two fatty acids. Molasses had significantly more grasshoppers on the filter paper than did the other attractants, but molasses had significantly fewer grasshoppers in the arena than the fatty acids. Fruit extracts were not effective at attracting grasshoppers. Water extracts of cadavers attracted significantly more grasshoppers to the bait than did chloroform extracts. Because the assayed grasshopper community was dominated by the Gomphocerinae (a subfamily that includes many pest species that do not readily consume wheat bran bait), it may be possible to use fatty acids in conjunction with insecticidal bran baits for increased control of rangeland grasshoppers.