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Agria housei Shewell
(Diptera: Sareophagidae)
Native parasitoids of
spruce budwonn larvae
Recommendations
D. Testing of parasitoids 271
The native sarcophagid fly, Agria housei, has long been recorded as a pre-pupal and pupal
parasitoid of spruce budworm and western spruce budworm, usually at low percentage
parasitism. However, it merits consideration for inundative release because it is one of
the few budworm parasitoids that can be laboratory-produced in large quantities at
acceptable costs; it can be reared directly on pork liver without an intermediate insect
host. It has other characteristics that enhance its prospective application to the spruce
budworm problem. However, the laboratory stock available for experimentation had
been reared for many generations under artificial conditions, causing loss of cold hardiness
and diapause induction (House 1967). Therefore there were doubts about the responsiveness
of this stock to spruce budworm hosts and about its capacity to revert to univoltine
reproduction.
Field and laboratory tests were conducted in 1971 to gain experience in handling the
species and to test its response to larval and pupal spruce budworm hosts (Tables 73 and
74). The fly stock was provided by the Agriculture Canada Research Institute, Belleville,
Ontario. Laboratory cage experiments designed to test hostlparasitoid densities failed
to elicit any apparent interaction, and no parasitoid progeny issued. However, some 2800
adult flies (34% female) were freely released into a balsam fir, Abies balsamea (L.) Mill.,
stand highly infested with spruce budworm pupae, at Fundy National Park. From a
sample of 1114 pupae collected within 10 days of release and within 7S m of release point,
14 A. housei puparia were recovered. Based on estimates of the density of available
hosts, this rate of recovery indicated an excellent response by the introduced stock. No
further specimens were recovered from samples of host pupae in 1972 and 1973, but
given the poor cold hardiness inheritance of the stock and the dispersal characteristics of
the species, detectable persistence at the release point was not expected. The potential
for applied biological control under appropriate pre-outbreak conditions remains unassessed.
The Canadian Forestry Service has maintained a sporadic surveillance of the effectiveness
of native parasitoids attacking spruce budworm, especially G. fumiferanae and
Apanteles fumiferanae Vier., which parasitize overwintering larvae. A study at the
Maritimes Forest Research Centre was conducted from 1977 to 1980 on the premise that
an understanding of the factors limiting parasitoid effectiveness might lead to methods
of managing the forest habitat to stimulate parasitoid regulation of spruce budworm. The
study was directed to the behavioural biology of adults of these two species (feeding
habits, flight periodicity, distribution in the canopy), but did not reveal any clear avenue
for practical application (R.S. Forbes 1980, unpublished work, Canadian Forestry
Service).
It is recommended that the Canadian Forestry Service (a) maintain contacts with
CIBC concerning collection opportunities abroad; (b) investigate the compatibilities
of a range of non-indigenous parasitoids with spruce budworm hosts; (c) develop
rearing, release, and assessment skills and facilities; and (d) assess opportunities for
incorporating parasitoid manipulation in integrated pest management programmes based
on spruce budworm population dynamics.