Date of Award:

5-1982

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Plants, Soils, and Climate

Department name when degree awarded

Plant Science

Committee Chair(s)

William F. Campbell

Committee

William F. Campbell

Committee

Austin B. Haws

Committee

Kay H. Asay

Abstract

Large populations of black grass bugs, Labops hesperius Uhler, have been observed on extensive acreages of range lands. These bugs cause severe damage to the range grasses, lowering their palatability and productivity. This study was to determine whether morphological differences among breeding lines of grass species or interspecific hybrids could be correlated with the feeding behavior of black grass bugs. If so, plant breeders should be able to develop resistant cultivars. To explore this possibility, cultivars and synthetics of range grasses, representing the genera, Agropyron, Dactylis, Phalaris and Poa, were exposed to different instar stages (II and III; IV and V) under laboratory conditions with greenhouse grown plants. Bromus and Elymus, in addition to the above genera were observed in the field where adult bugs were fed. A rating scale of the percent damage (visual determination of necrosis and leaf discoloration caused by Labops feeding) of the total leaf area was utilized to determine the degree of grass preference by the nymphs and adults forfaield studies. Leaf morphology (pubescence) was examined under a scanning electron microscope. Leaf pubescence (trichomes) varied in density and size and appeared to be associated with resistance of plants in the genera, Agropyron, to the Labops nymphs (instar stages II and III) but had no relation with the feeding behavior of adult black grass bugs. Plant leaves of the general, Dactylis and Phalaris, were smooth (few and small if any trichomes) and were the least preferred of any of the grasses by all stages of the bugs. Trichomes on leaves of other genera were varied in density and size. Based on percent damage, preference by the nymphs was for the species with intermediate sized trichomes. The adult bugs showed no discrimination in their feeding behavior. Field grown plants developed more trichomes per unit leaf area and appeared to have thicker surface waxes than the same species grown in the greenhouse. For this reason, nymph feeding habits may be different in the field than in the greenhouse. Future studies should perhaps investigate (1) first stage nymph activity on field plants and (2) palatability and/or chemical differences of the grasses.

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