pdf, 57.71Mb - Entomological Society of Canada

354 D. G. Embree and I. S. Olvos
Releases and Recoveries
Agrypon fla.-eo/atum
(Grav.)
(Hymenoptera:
Ichneumonidae)
Cyzenis a1bicans
(FaIl.) (Dlptera:
Tachinidae)
wind patterns develop. Winter moth hatching is synchronized to this pattern of wind
movement, with hatching beginning at dawn and virtually ceasing by mid-morning. By
this efficient means larvae are transported from hatching sites in crevices and lichens on
the lower tree trunks to the tree crowns. Once there, the larvae either survive or die
depending on whether the buds have opened. The wind may also transport the larvae
several miles, but once established on the foliage, they do not dislodge easily until the
late fifth instar in early summer, when they drop to the ground to pupate (Embree 1970).
No other means of dispersal exists because the females, which are active in November
and December, have vestigial wings and are flightless.
No releases of parasitoids have been made in the maritimes since 1965 (Embree 1971b).
Releases of parasitoids in British Columbia were conducted in 1979 and 1980 and are
listed in Table 91.
The British Columbia operation was financed and administered by the Crop Protection
Branch (formerly Entomology and Plant Pathology Branch) of the British Columbia
Ministry of Agriculture and Food in co-operation with the Pacific and Maritimes Forest
Research Centres of the Canadian Forestry Service. Collections of last instar larvae
were made in apple orchards in Nova Scotia in 1978 and 1979. Collections were also
made in Germany by the Commonwealth Institute of Biological Control.
Winter moth pupae were sent to the Biocontrol Unit of the Research Branch of
Agriculture Canada in Ottawa, where pupae were cold-treated and then reared under
quarantine conditions. Only the adult parasitoids were shipped to British Columbia from
the German collection but about two-thirds of the Nova Scotia collection were sent to
Victoria for parasitoid rearing. The remainder were reared in Ottawa and the adults of
the two parasitoids were sent to Victoria.
Based on studies in Nova Scotia, the control strategy in British Columbia has been to
treat the infested area with repeated releases, each consisting of a minimum of 50 mated
females of each species.
This parasitoid beromes decreasingly effective as host densities increase, and is therefore most
effective at low population density (Embree 1966). The adult parasitoids develop in
winter moth pupae and emerge the following spring to parasitize early instars of host
larvae.
The first introduction of A. Jlaveolatum was in 1979 when a total of 1654 males and
1 700 females was released at 33 locations in the greater Victoria area in stands infested
with winter moth. Fifty pairs of parasitoids were released in each location after being
held in mating cages for 1-3 days. The parasitoids in the cages were provided with twigs
of cherry blossoms and bottles of sugared water with feeding wicks. In 1980 an additional
2213 males and 2 813 females were released at 25 locations; of these a small proportion
came from Germany, and the rest from Nova Scotia. This parasitoid has not yet been
recovered in British Columbia.
This parasitoid exhibits a sigmoid functional response curve and is most effective at high
host densities (Embree 1966). The female, which can lay as many as 1300 eggs, oviposits
in the vicinity of feeding damage by defoliators. Associated species such as the fall
cankerworm, Alsophila pometaria (Harr.), which are resistant to parasitism by C.
albicans, also consume the parasitoid eggs. With increasing winter moth populations C.
albicans becomes increasingly effective.