- 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
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
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.