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Pest Status
Use of Bacillus thuringiensis
Chapter 5
Field Plot Introductions of Viruses
Artogeia rapae (L.), Imported
Cabbageworm (Lepidoptera: Pieridae),
Trichoplusia ni (Hiibner), Cabbage
Looper (Lepidoptera: Noctuidae) and
Plutella xylostella (L.), Diamondback
Moth (Lepidoptera: Plutellidae)
R.P. JAQUES and J.E. LAING
Artogeia rapae (L.), the imported cabbageworm, causes damage to cole crops
practically wherever these crops are grown in Canada. The pest is quite susceptible to
certain chemical insecticides and to insecticides containing Bacillus thuringiensis
Berliner and, therefore, populations of larvae are usually retained at acceptable
densities by recommended control programmes. Trichoplusia ni (Hiibner), the cabbage
looper, is not as widespread but, because it is less susceptible than A. rapae to
registered insecticides, it is considered to be the more important pest of cole crops,
especially in southern Ontario. Plutella xylostella (L.) is not considered to overwinter
in Canada and thus does not become a pest on cole crops until late in the season.
Formulations of B. thuring;ensis (B.t.) containing B. thuringiensis var. kurstaki, a
high-potency strain of B.t., were registered in Canada in 1972 for use against A. rapae,
T. ni, and P. xylostella on cole crops and other crops. The new formulations (Thuricide®
HPC, Sandoz Crop Protection Inc.; and Dipel® HD-l, Abbott Laboratories Ltd.)
replacing formulations registered previously, protected cole crops equally as well as or
better than did chemical insecticides. These formulations of B.I. are now used quite
extensively.
The native parasitoid complex of the imported cabbageworm (Michalowicz 1980)
and the diamondback moth (Butts 1979, Bolter 1982) have been studied intensively.
Two species, Apanteles rubecula Marsh. which parasitizes A. rapae and Apanleles
plulellae (Kurdj.) a parasitoid of diamondback moth, have been imported and released
in southwestern Ontario.
The granulosis virus of A. rapae (ARGV), a naturally occurring virus (Jaques &
Harcourt 1971) that often causes high mortality in populations of larvae of A. rapae
late in the growing season, was evaluated by bioassays and plot tests as an introduced
pathogen. In addition, three viruses that kill larvae of T. ni were assessed in laboratory
and field studies. Two of these viruses, the single-embedded nuclear polyhedrosis
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