Labops hesperius Uhler : biology and impact of Oregon rangelands (Hemiptera: Miridae) Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/6w924f024

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  • The seasonal development and habits of Labops hesperius Uhler were studied in rangeland seeded to intermediate wheatgrass (Agropyron intermediurn (Host) Beauv. ) in Baker County, Oregon, The first nymphs appeared on March 22, and required about one week to complete each of the five nymphal stadia. Most small nymphs stayed on the ground beneath the straw and litter during daylight and fed on the leaf blades of grasses at night. Fifth instars and adults fed on the leaf blades during both the day and night. The adults began to emerge on April 26, and the preoviposition period of the females lasted about two weeks. A maximum of 48 eggs was found in the ovaries of a single female, but the mean number of eggs laid per female was estimated at twenty-one and nine eggs, respectively, at two study sites. Most eggs had been laid by June 15, and the eggs remained dormant until March of the following year. Thus L. hesperius completed its development and reproduction in about 2 1/2 months and had an obligatory diapause that lasted about 9 1/2 months. Labops hesperius was found in a variety of habitats, but the greatest numbers were found in two dense stands of intermediate wheatgrass which had received little or no grazing during the past 12 years. Other grasses used as food included Agropyron desertorum (Fisch. ) Schult., A. repens (L. ) Beauv., A. spicatum (Pursh) Scribn. and Smith, A. trichophorum (Link) Richt. , Bromus carinatus Hook and Arn., B. tectorum L., Dactylis glomerata L. , Festuca idahoensis Elmer. Hordeum vulgare L. , Koeleria cristata (L. ) Pers. , Poa bulbosa L. , P. pratensis L., Secale cereale L., and Stipa lemmonii (Vasey) Scribn. Females usually oviposited in dry straws of grass that had been produced during the previous season, because oviposition was completed before straws suitable for oviposition were produced. However, dry straws of bulbous bluegrass (Poa bulbosa L. ) were used for oviposition during the same season in which they grew, since bulbous bluegrass matured earlier than other grasses and had dried before oviposition was completed. Straws of bulbous bluegrass were the preferred oviposition site although bulbous bluegrass was rare in most ranges. Straws of Agropyron desertorum, A. intermedium, and A. spicatum were also readily used for oviposition. The effect of feeding injury by L. hesperius on the yield and composition of wheatgrass was determined by chemical analysis of forage samples from sprayed and unsprayed plots. Feeding injury reduced the yield and nutritional value of wheatgrass by removing the cell contents from the leaves. The loss of forage production was about 18 percent in May when feeding injury was most severe. However, the grass continued to grow because of adequate moisture and when the grass reached maturity near the end of July, the loss of forage production was only about two percent of the total forage production. Exploratory tests suggested that field burning, removal of a hay crop, and grazing might reduce densities of L. hesperius by destroying the overwintering eggs and the straw used for oviposition. Insecticidal control did not appear to be economical, since the return per acre from rangelands was small and since frequently the cost of treatment would have been greater than the value of the forage lost to L. hesperius.
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