Graduate Thesis Or Dissertation


Biological attributes and alteration of the habitat to manipulate populations of Labops hesperius Uhler (Heteroptera:Miridae) Public Deposited

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  • Biological attributes and alteration of the habitat of Labops hesperius Uhler were investigated on rangeland seeded to crested wheatgrass near Vale, Oregon, and on rangeland seeded to crested and intermediate wheatgrass near Seneca, Oregon. Nymphs and adults were present at Vale from late March until mid-June and at Seneca from early April until late June or early July. Females at the Vale site preferred to oviposit in dry culms of crested wheatgrass and in Sandberg's bluegrass but they also oviposited in cheatgrass and green calms of crested wheatgrass. Females at a Seneca site oviposited in green intermediate wheatgrass. Population density at the Vale site was positively correlated with the total weight of dry wheatgrass and ground litter present at different locations because the straw provided oviposition sites or protection for the bugs. The obligatory egg diapause was investigated by subjecting eggs collected in September to different temperature treatments in the laboratory. Diapause was terminated after a minimum of 60 days exposure to 3° or 9° C and about two weeks incubation in 15°C and 16-hour photophase. Eggs survived temperatures as low as -15° C, and one temperature treatment resulted in 87% hatch. A 30 day acclimation temperature of 9° or 3° C before exposing the eggs to 3° or -15°C, respectively, resulted in a higher egg-hatch percentage. Egg diapause in L. hesperius differed from that in other mirids because the embryo of the former diapaused at a more advanced stage of embryogenesis. Sticky traps, pitfall traps, and a marking technique were used to study dispersal capabilities of L. hesperius at the Vale site. The bugs were capable of moving 7. 8 meters by walking on the ground and 23. 2 meters by a combination of flying and walking. The bugs could perceive red, yellow, and blue traps, but not white traps, at an altitude of 1. 52 meters, which was the common flight altitude. Macropterous females attained sexual maturity later than brachypterous females indicating that the former are specialized for migration. Males flew but the trap data did not indicate whether the nature of their flight was dispersal or trivial. The low percentage of macropterous females in the population might explain the slow dispersal rate of L. hesperius. Another mirid, Irbisia brachycera Uhler, was also captured in large numbers on sticky traps. Feeding damage to wheatgrass plants was studied by visual evaluation and chemical analysis of the damaged leaves. Chemical analysis indicated that feeding damage caused a decrease in plant cell contents but an increase in digestibility of the cell-wall constituents. However, a damage level of only 25% caused a relative increase in cell-wall constituents to an extent that would probably decrease the voluntary intake of wheatgrass by ruminants. Various range cultural and management practices were investigated to determine whether they could be used to reduce the population density of L. hesperius. Fertilizer treatments that included nitrogen significantly increased the density of L. hesperius but none of the fertilizer treatments significantly decreased the density. The bug density did not increase in proportion to the increase in herbage yield expected from fertilizing wheatgrass with nitrogen. The herbicide Paraquat indirectly killed nymphs and adults of L. hesperius by prematurely curing the wheatgrass which resulted in starvation of the bugs. The egg density was also reduced because the females starved to death before they were able to oviposit. Paraquat reduced the herbage yield as expected but increased the quality of the herbage. Prematurely curing wheatgrass with Paraquat will be an economical method of controlling L. hesperius provided that the spray can be timed to both reduce the bug population and increase the feed value of the forage. Mechanical removal of herbage during the egg stage reduced the bug population density by directly destroying the eggs or by exposing them to more harsh winter conditions or both. Mechanical removal during the nymphal and adult stages did not directly affect the population density since the bugs were able to find sufficient food for survival in the stubble. However, mechanical removal of herbage during the nymphal stages can reduce bug density in populations that are relatively dense originally, and removal immediately before oviposition prevents the females from laying eggs. Field burning, hay crop removal, and grazing are cultural practices that might control L. hesperius by mechanically removing the herbage. Hay crop removal, grazing during the nymphal and early adult stages, and grazing during the egg stage should each prove useful for controlling L. hesperius on different types of pasture infested with bugs.
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