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Pest Status
Background
Chapter 19
Releases and Recoveries in Ontario
Oulema melanopus (L.), Cereal
Leaf Beetle (Coleoptera: Chrysomelidae)
D.G. HARCOURT, J.e. GUPPY and C.R. ELLIS
During the early and mid 1970s, the cereal leaf beetle (eLB), Oulema melanopus (L.),
began to threaten the production of small grains in Ontario. Following its initial
discovery in Essex County near the border of Michigan in 1965, it spread rapidly
eastward and by 1975 it had occupied most of Ontario south of Hwy 17. Populations
reached economic levels in 1973, and in 1974 chemical treatment was required in ca. 75
fields within the triangular area bounded by the counties of Lincoln, Grey, and
Durham (Bereza 1974). In 1976, it occurred in damaging numbers on Manitoulin Island
and, in 1977, it was found north of Lake Huron in the districts of Algoma, Sudbury,
and Nipissing (Ellis et al. 1979).
Like many of our introduced pests, the cereal leaf beetle is rarely troublesome in its
native Europe where it is attacked by a complex of natural enemies. One of these, the
larval cndoparasitoid Tetrastichus julis (Walker) was introduced against the beetle by
research workers in Michigan in 1967. It was recovered in low numbers in 1969 (Stehr
1970) and was extensively recolonized in 1971, when further releases were made in
Michigan, Indiana, Ohio, West Virginia, and New York (Dysart et 01. 1973).
T. julis is mostly bivoltine in Michigan (Gage & Haynes 1975). It emerges from its
overwintering sites in late May and flies to nearby grain fields where it deposits its eggs
in the first host larvae that appear. The gregarious parasitoid larvae grow slowly within
their host while it is feeding. As soon as the host larva enters the soil and forms its
pupal cell, the parasitoids quickly complete their development and form naked pupae
within the cell. Diapause is facultative, but the incidence increases as the season
progresses. Some adults emerge in early summer and give rise to a second generation.
The remainder of the first generation and all of the second overwinter as last instar
larvae inside the pupal cells of their hosts. In Michigan, roughly 80% of the population
enters a second generation; this generation is poorly synchronized with populations of
its host since at the time of emergence relatively few beetle larvae are available for the
adults to attack (Gage & Haynes 1975).
Studies in Michigan during the early seventies indicated that T. julis had poor
powers of dispersal (Haynes et -al. 1974). Natural spread was slow and rates of
parasitism in the United States midwest remained well below that needed to maintain
populations at subeconomic levels.
Large-scale releases of T. julis were made at 4 sites in southcentral Ontario in June
1974 when parasitized host larvae were set out in fields of oats and barley (Harcourt et
al. 1977). This has been the only parasitoid released in the province.
In 1975, life table studies of the host in the Quinte area of southern Ontario showed
that 55% and 43% respectively of the pupal cells in study plots in Northumberland and
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