| Abstract |
- 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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