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

The responses of rangeland grasshoppers to biologically and historical ly derived attractants were studied in a shortgrass prairie in southea stern Wyoming in July 1990. Seven long-chain fatty acids (C-14-C-20; s ingly and in combination), grasshopper cadavers, molasses, fruit extra cts, 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 lin olenic acids, with significantly more grasshoppers found in these aren as 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 f ive species of ants were also attracted to these two fatty acids. Mola sses had significantly more grasshoppers on the filter paper than did the other attractants, but molasses had significantly fewer grasshoppe rs in the arena than the fatty acids. Fruit extracts were not effectiv e at attracting grasshoppers. Water extracts of cadavers attracted sig nificantly more grasshoppers to the bait than did chloroform extracts. Because the assayed grasshopper community was dominated by the Gompho cerinae (a subfamily that includes many pest species that do not readi ly consume wheat bran bait), it may be possible to use fatty acids in conjunction with insecticidal bran baits for increased control of rang eland grasshoppers.