Bionomics of the hop cyst nematode, Heterodera humuli Filipjev, 1934 (Nematoda : Heteroderidae) Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/cr56n359t

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  • The hop cyst nematode, Heterodera humuli Filipjev, 1934 was first reported from Europe in 1894, however, very little is known with respect to the biology and economic importance of this pest. Abundant material from Oregon hop yards provided an excellent opportunity to add additional details concerning the bionomics of this pest, and from the taxonomic viewpoint, to amend the existing descriptions of larvae and males. Second -stage larvae (larvae that hatch from eggs) were reared at various temperatures on hop plants (Humulus lupulus L. ) to determine the length of time needed to complete a life - cycle. As the temperature increased, time required to complete a life -cycle decreased and vice versa. No development took place beyond 80 °F. Thirty different kinds of plants were tested to determine their susceptibility to H. humuli. Host range of this nematode was noted to be predominently in the Urticaceae family. H. humuli also will infect plants in Cruciferae, Cucurbitaceae, Leguminosae and Moraceae families. Tests to determine the effect of temperature, moisture and soil upon the survival of the nematode indicated that H. humuli stored in wet soil withstood the longest storage period. Nematodes stored at 15 °C survived longer than storage in other temperatures. Twenty -three chemicals, consisting of acids, alcohols, amino acids, esters and lactones, heterocycles, phenols, miscellaneous organic and inorganic compounds were tested to investigate hatching stimuli. Highest hatch was obtained by urea (1840 larvae were liberated) and lowest by n -butyl alcohol (25 larvae were liberated). Ascorbic acid, citric acid, pyruvic acid and thiourea also had an efficient hatching effect. Inorganic compounds were poor hatching stimulators. It also was observed that a pH range of 5 to 7. 5 was suitable for H. humuli larval emergence. Tests to determine the relation between growth of hop seedlings and density of H. humuli indicated that the tolerance limit of hop seedlings to H. humuli is between 50 and 100 eggs per gram of soil. The effect of different population levels of H. humuli on cyst production indicated that the number of cysts increased at every inoculum level. Ratio of increase at highest inoculum level (256 cysts), however, was only 1.47, while lowest inoculum level (1 cyst) was 4. Highest ratio of increase (13.2) was obtained at the inoculum level of 16 cysts. Initial egg numbers (empty eggs) appeared to be directly correlated with the number of larvae that hatched over a period of time, and that had taken part in plant invasion. Approximately 34 empty eggs per cyst disappeared during the eight month storage period. Bionomical investigation conducted in controlled environments indicate that the hop cyst nematode is well adapted to the climatic and edaphic conditions of Western Oregon hop yards. Serious injury to Oregon hops does not appear imminent because the population density in the hops does not approach the level required to produce the symptoms observed in the greenhouse. Since hop crowns lie dormant for several weeks each year and weed control measures destroy alternate hosts, destruction by H. humuli is impeded.
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