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Releases and Recoveries
Olesicampe benefactor
Hinz.
(Hymenoptera:
Ichneumonidae)
Pri.slip/lOra erichsonii (Hartig), 373
parasitoid has been released. Rates of hyperparasitism by M. dimidiatus usually increase
rapidly and there is reason to be concerned about the future effectiveness of O. benefactor.
The masked shrew, S. cinereus cinereus, was successfully introduced into Newfoundland
in 1958, when 12 females and 10 males were released near St. George's. Most of the
individuals in the initial release survived the first winter and their progeny have prospered
and spread and now probably occupy most of the suitable habitats throughout the island.
Biological control studies of the larch sawfly during the period 1969 to 1980 have
consisted of the redistribution of O. benefactor and Mesoleius tenthredinis, plus follow-up
studies of these parasitoids and of the masked shrew in Newfoundland.
Most of the redistributions of parasitoids involved O. benefactor (Table 95). The
population increase and dispersal of O. benefactor are discussed in detail by Muldrew
(in press). He has incorporated additional data that were not analysed by Turnock &
Muldrew (1971a), so that his values for maximum dispersal in 1966 and 1967 are greater.
He reports that the rate of dispersal was about 1 km after 4 years, 3 km after 5 years, and
5 km after 6 years. Follow-up sampling until 1974 showed that the rate of dispersal
increased dramatically between 1969 and 1971 (Fig. 19). In 1969. the maximum recorded
distance was 87 km (at the Rennie life-table plot). Sampling in 1970 was inadequate for
assessing dispersal but O. benefactor was recovered in northern Minnesota 293 km
south of the release point (Kulman et al. 1974, Thompson & Kulman 1976). Extensive
sampling by Muldrew in 1971 detected O. benefactor at Ignace, Ontario, 357 km from
the release point. The maximum detected dispersal distance by 1972 was 476 km.
However, larch sawfly populations began declining throughout the area in 1972, while
hyperparasitism by Mesochorus dimidiatus increased. Apparently these factors influence
the rate of spread, as the maximum recorded distance increased by only 64 km, to 540 km,
by 1974.
The dotted lines in Fig. 19 show the approximate maximum rates of parasitism at
different distances from the release point. Until 1969 , the points are clustered around the
lines, but the scatter increases for 1971, 1972, and 1974. Part of this increased variability
was attributable to the relatively slow spread of O. benefactor into southern Manitoba.
Muldrew (in press) surmised that the direction of the prevailing winds and abundance of
tamarack may have been the main reasons for the slow dispersal into this area. However
by 1974 the rates of parasitism in southern Manitoba had increased considerably, and
there was already some indication of a relative decline in rates of parasitism elsewhere,
possibly due to hyperparasitism by M. dimidiatus. Although not shown in Fig. 19 the
rates of M. dimidiatus parasitism increased dramatically from 1969 to 1974. In 1969,
about 80% of O. benefactor near the release point were parasitized by M. dimidiatus. In
1971, high rates of hyperparasitization had extended to nearly 200 km from the release
point. By 1972, the high levels of M. dimidiatus attack had extended to over 300 km.
Muldrew (personal communication) indicatedM. dimidiatus probably transferred to O.
benefactor at a number of locations. The apparently rapid rate of dispersal between 1969
and 1971, and the variable levels of hyperparasitism from 1971 to 1974 both agree with
this hypothesis. There was little additional increase of M. dimidiatus parasitism in 1974,
but the apparent decrease in O. benefactor parasitism is probably attributable to the
hyperparasitoid.
Information on increases in parasitism and dispersal from other release points is
rather limited. A release of 694 males and 737 females was made near The Pas, Manitoba