|Abstract or Summary
- 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
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
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.