pdf, 57.71Mb - Entomological Society of Canada

270 1. W. Varty
Lissonola sp.
(Hymenoptera:
Ichneumonidae)
Trichogramma
minutum Riley
(Hymenoptera:
Chalcidoidea)
The biology of this ichneumonid species from C. diversana hosts on todo fir in Japan has
been reported by Zw61fer (1972, personal communication). Shipments were air-freighted
from Hokkaido to New Brunswick in 1972, 1973, and 1975 (Tables 73 and 74). Females
mated soon after emergence from the cocoon, and were maintained on a diet of sugar,
honey, and water for up to a month in insectary cages. No responses were observed to
the presence of free-moving first-instar or spun-up second-instar spruce budworm.
However, large samples dissected in winter revealed parasitism rates of 7% in 1972 and
1% in 1973. No more than one egg shell was dissected from anyone host, although
heavy superparasitism is the rule in C. diversana hosts. Although many thousands of
spruce budworm hosts were exposed, only one parasitoid emerged as a pre-pupa, and
it failed to pupate. Three more mature larvae were dissected frot:T\ dead hosts, but no
evidence of encapsulation or of tissue absorption of the parasitoids was found. Thus
Lissonola sp. appears to be incompatible with spruce budworm because of low ovipositional
stimulus to the parasitoid and some innate resistance by the host.
The object ofthis study in Quebec in 1970-75 (F.W. Quednau 1974, personal communication,
unpublished work reported to the Annual Review of Spruce Budworm Research,
Canadian Forestry Service) was to explore the potential of this egg parasitoid for
inundative release against rising spruce budworm populations in local epicentres. This
native chalcidoid wasp is already present in all eastern North American forests, attacking
eggs of scores of species, and typically contributing 5-25% parasitism of spruce budworm
eggs. Apparently, scarcity of alternate hosts prevents the numerical response that T.
m;nulUm might otherwise make to rising budworm density. Quednau believed that about
2.5 x 10" female parasitoids per hectare would be needed for effective release in epicentres.
The research problems facing the Laurentian Forest Research Centre were: (l)the
maintenance of year-round research cultures of the parasitoids and suitable hosts;
(2)comparison of commercial strains and arboreal ecotypes, and the selection of a
type most responsive to laboratory rearing and the spruce budworm forest habitat;
(3)determination of the parasitoid female's functional response to host density;
(4)refinement of a mass-culture method, and (5)development of techniques for
inundative release and assessment of efficacy.
From 1970 to 1975 considerable biological knowledge and research experience was
gained in the first three problems. Methods of air-freighting stock from the United States
and Mexico were established, and techniques for small-scale rearing and storage of
parasitoids and host eggs were developed (Table 74). However, the application of
American commercial techniques of mass-rearing was thwarted by quarantine regulations,
which prevented the utilization of the angoumois grain moth, Silotroga cerea/ella
(Olivier), the most suitable host for Trichogramma cultures. Moreover, there were
worker health problems (allergies) associated with mass-rearing.
Progress was made in the selection of a Canadian ecotype well adapted to the forest
environment and with superior host-finding potential. However, T. m;nulum was shown
to have only a weak functional response to density of spruce budworm egg-masses; that
is, in caged-tree experiments with varying parasitoid densities and host densities, the
number of attacked host eggs per individual parasitoid was greater when egg-mass
density was increased. However, increased density of parasitoids tended to lower
success in finding hosts, perhaps because of mutual interference and increased superparasitism.
Parasitism greater than 50% was not attained in cage experiments. Thus the
prospects for useful impact on spruce budworm dynamics appear low, because only a
drastic change in egg parasitism could have any significant effect on generation survival
in spruce budworm outbreak densities (Morris 1963).
The research was terminated in 1975 without definitive assessment of the feasibility of
application to spruce budworm control.