Graduate Thesis Or Dissertation
 

Insect parasites of the omnivorous leaf tier, Cnephasia longana (Haworth) in Oregon

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  • The purpose of this study was to determine the present status of introduced parasites of the omnivorous leaf tier, Cnephasia longana (Haworth) in Oregon. The omnivorous leaf tier is native to Europe. It was introduced into North America around 1929 and became a serious pest of economic crops such as strawberry, Dutch iris and flax in Oregon. Its life history, habits, host plants and control measures have been investigated by several workers. Fourteen species of parasites from France were introduced against this pest in Oregon during the years 1951 to 1954, Three of the introduced species were recovered during 1955 and 1956. They were: Bracon stabilis Wesmael, Bracon piger Wesmael, and Itoplectis maculator (F.), but none of these were recovered during a 1957 study. Since 1957, the status of these released parasites has not been investigated. The study of introduced parasites during the present research was carried out at nine localities, including four previous release and recovery sites within the Willamette Valley of Oregon. The host larvae and pupae were collected and reared under insectary conditions at the OSU Entomology Department laboratory. The current study revealed that none of the introduced species have become established in the study areas. Factors preventing establishment are not known, but the physical factors, especially low winter temperatures and hot, dry summer conditions in Oregon, may have been detrimental to the introduced parasites. Although the research was primarily concerned with investigating the present status of introduced parasites, four species of native parasites were recovered. They were: Enytus eureka (Ashm. ), Itoplectis conquisitor (Say), Phytodietus burgessi (Cress.), and a hyperparasite, Mesochorus sp. All of these were reared from leaf tier larvar infesting vetch plants. Of these four species, E. eureka was found in the highest numbers. Its parasitism of C. longana was 17.14 percent. Investigations of feeding habits of host larvae upon plantain, Plantago lanceolata L., and vetch, Vicia villosa Roth, were carried out under field conditions at Dallas, Oregon. The study confirmed that the first and second instar larvae feed as leaf-miners on plantain. The second instar migrates to vetch or other host plants and the remaining instars feed on the tender tips within webbed leaves. A study of seasonal populations of host larvae was conducted in the field near Mt. Angel. The study revealed that the stages or instars of larval development were overlapping but that C. longana has only one generation a year in Western Oregon. The emergence dates of the adult parasite, E. eureka, and moths were observed in the laboratory. The parasite started to emerge on June 6 which was nine days earlier than the host emergence. The peak emergence of the parasite was reached on June 18 while that of the host was reached on June 28. It would appear that none of the introduced parasites have become established. Although as many as 14 species of native parasites have been recovered in Oregon. The results of this study suggest that the scattered distribution and low level of parasitism is probably not an important biological control agent in regulating omnivorous leaf tier population in Western Oregon.
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