Highlight: Large areas of Utah's rangeland have been seeded to introduced wheatgrasses, and many of these areas are now infested with the black grass bug (Labops hesperius). A study of the effects of this insect pest on several native and introduced grasses was conducted on three experimental study plots in southwestern Utah. The data revealed that the six introduced grass species studied, growing in small monocultures, contained considerably more black grass bugs than did the native range grasses in nearby areas. Thus, the six monoculture grass species were more susceptible to grass bug damage than were the native range grasses. Moreover, variations in black grass bug populations within the six grass monocultures also revealed differences in susceptibility. Phenology comparison data revealed there was no correlation between the phenological stage of plant development and the stage of black grass bug instar development, therefore ruling out an accurate means of determining time of spraying in relation to plant maturation. About 89% of Utah is considered rangeland (Nielsen 1967). Large areas of this rangeland have been seeded to grasses for livestock forage and watershed stabilization. Much of the springfall range in southern Utah has been seeded to introduced wheatgrasses, and many of these seeded areas are now infested with the black grass bug (Labops hesperius Uhler). This insect pest damages range grasses, especially Authors are land specialist, Division of State Lands,
SiyiRunt differences in plant resistance to larvae of the bluegrass billbug, .Sphenophorus ptwwdus Gyllenhal (Coleopten: Curculionidae), were found among and within range gnss species and interspecific hybridsinnurseriesnt the Decker,Mont.,surface mine and on a site near Miles City, Mont. Slender wheatgrass (Elymus trachycazdus) and related species were particularly susceptible. Crested wheatgrass (Agropyron cristatum and A. desertorum), thickspike wheatgrass (E. lonceotatus), Russian rildrye (Psathyrostachys juncea), and salinn wildrye (Leymus saIimw) were among the species with P relatively high degree of resistance to the insect. Clonnl lines of the Et. repens X Et. spicata hybrid differed signiticnntly in resistance. Over 50% of the total phenotypic variation among the hybrid lines was attributed to genetic effects, indicating that selection for resistance would be effective.
Highlight: Black grass bugs (Labops hesperius) at a population density of 156 bugs per square meter did not affect herbage yields of intermediate wheatgrass but depressed seedhead production 56%. They caused a small but significant increase in concentrations of crude protein and a slight decrease in cellular contents.An important question in the management of wheatgrass monocultures during recent years has been the effect of the grass bug Labops spp. (Hemiptera: Miridae) on forage yields, forage quality, and stand longevity. Grass bugs occur throughout the Intermountain and adjacent areas (Bohning and Currier 1967; Denning 1948;Todd and Kamm 1974) and have been reported to cause extensive damage to crested wheatgrass (Agropyron cristatum) and intermediate wheatgrass (A. inter-medium) stands in some areas (Knowlton 1967;Haws et al. 1973). Their effect on nutritional quality of forage has remained virtually unknown, although Todd and Kamm ( 1974) inferred significant short-term losses in a recent Oregon study.The study reported here was initiated to determine the effects of relatively low population densities of black grass bugs (Labops hesperius) on yield and nutritional quality of intermediate wheatgrass. Methods and MaterialsTwo intermediate wheatgrass seedings were selected as study areas in the spring of 1974. Major criteria used in selection of these areas included uniformity of soils, topography, and grass stands and presence of grass bug populations that were large enough to impart the characteristic yellowing of the grass leaves, commonly attributed to feeding activities.
Large ares (6 million ha) of the United States and Canada, ciassified as range, have an enormous impact on the economy and environment through grass production. Production is often drastically reduced by infestations of grass-feeding insects. Although the literature is voluminous with references dealing with responses of agronomic crop plants to attacks by these insects, iittle research has been conducted on range grasses. The black grass bugs,Labops spp and Irbisia spp (Hemiptera: Miridae), are economically important on rangeland of the Intermountain West. The recognized mechanisms of plant resistance to insects are nonpreference, toierante, and antibiods. Trichome length and density within species of wheatgrasses (Agropyron sp) are negatively correiated with feeding behavior of the early instars of Labops hesperius Uhier, but not with older instars or adults. Certain species of wheatgrasses show varying degrees of tolerance to feeding by L. hesperius. Approximately 3,000 chemical compounds afford piants some protection against insects. During their long co-evolution with plants, however, insects overcame the toxic effects of many chemical compounds. Essentially no plant breeding has been done to develop range grass cultivars that are resistant to black grass bugs. Nevertheless, the opportunities are as great as the need that must be met if western rangelands are to satisfy multiple demands the future is likely to impose on them.Seeding vast areas (more than 6 million ha) in the western United States and Canada (Dewey and Asay 1975, Rogler and Lorenz 1983) with adapted species of wheatgrasses (Agropyron sp.) has aided immeasurably in supplementing native vegetation and lengthening the grazing season. As Hagen et al. (1971) have poignantly reaffirmed, very little is known about range insects and their association with plants.
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