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23R W. A. Smirnoffand O. N. Morris
Background
A. Field Development of Bacillus thuringiensis Berliner
in Eastern Canada, 1970-80
W.A. SMIRNOFF and O.N. MORRIS
Bacillus Ihuringiensis var. kurslaki, (B.I.) is a bacterium registered in Canada for control
of agricultural and forest pests. The registered preparations, derived from cultures of the
serotype 3a, 3b, are a mixture of dormant endospores and endotoxin crystals suspended
in a liquid carrier.
Forest protection agencies have found spraying to be more expensive with B.I. than
with chemical insecticides, yet B.I. remains a desirable alternative because its toxicity is
confined to lepidopterous larvae and its use rarely arouses public antagonism. The
Canadian experience of B.I. aerially applied against spruce budworm, Chorisloneura
fumiferana (Clem.) is that its efficacy is variable. Field trials have indicated differences
among commercial products, varying efficacies among field formulations, uncertainties
over dosages, technical difficulties in spraying methods, weaknesses in means of measuring
deposits, and inadequacies in techniques of assessing the agent's effectiveness in reducing
larval populations and protecting foliage.
Research into these problems was conducted in the 1970s, in two main areas, by two
laboratories of the Canadian Forestry Service (C.F.S.): (a) in Quebec, where the
Laurentian Forest Research Centre collaborated with the Quebec Department of Lands
and Forests, and (b) in Ontario and the Atlantic Provinces, where the Forest Pest
Management Institute participated in provincial-federal field trials. This paper collates
the results from both laboratories.
Mode of action
B. Ihuringiensis serotype 3a, 3b is a bacterium that is pathogenic to lepidopterous
larvae. On spruce budworm and other tortricids the commercial formulations cause
enterotoxicosis by the action of the crystal-like parasporal inclusions (= delta endotoxin),
followed by septicaemia from the action of their spores (Smirnoff & Valero 1979, Fast
1981). The mode of action of the crystal toxin is described by Cooksey (1971).
The pathogenic action of 8.1. on spruce budworm depends on the dose ingested. the
age and physiological state of the larvae, the temperature, and possibly on the presence
of natural infections by microsporidia. The optimal temperature for this action is
20-22°C (Smirnoff 1967). Young larvae are more susceptible to B.I. than fifth- and sixthinstar
larvae (Morris 1973).
Formulations
Initially B.I. was tested against spruce budworm in New Brunswick in 1960. The
material used was Thuricide® SO-75 (Bioferm Corp.), based on the Berliner serotype.
Next, a small-scale aerial application of Thuricide® 90T was made in 1969, using both
suspensions in water and water-in-oil emulsion (Morris el al. 1975). Assessment of
population density reduction and foliage protection was inconclusive owing to clogging
of the spray nozzles and poor distribution of the active ingredient.
Improved commercial preparations of B.I. became available for testing between 1970
and 1980, namely Thuricide® 24B, Thuricide® 32B, Dipel® 36B (Abbot Ltd.), and
Novabac® 32B (Cyanamid Canada) or Novabac® wettable powder titrating 80 000