Can Bacillus Thuringiensis Replace Chemical Insecticides in the Control of Spruce Budworm?

Abstract

Recent demands by citizen groups calling for replacement of chemical insecticides by Bacillus thuringiensis (B.t.), a microbial insecticide, for the control of spruce budworm have received considerable publicity. Effects of chemical spray operations on the forest environment are discussed, and progress made to date with trial applications of B.t. against spruce budworm is reported. Although great caution should be exercised in the aerial application of insecticides, there is no evidence that these chemical compounds at conventional dosages cause serious damage to the forest environment. Although a desirable substitute for chemicals, B.t. still presents many drawbacks and requires further experimentation before it can be recommended as an economic alternative for effective reduction of damage by spruce budworm. ResumePlusieurs groupes de citoyens du Quebec demandent que la lutte chimique contre la tordeuse des bourgeons de IVpinette soit remplacee par des pulv6risations I'aide du Bacillus thuringiensis (B.t.),, un insecticide microbien. Les effets sur I'environnement des traitements aux insecticides chimiques contre la tordeuse, et les progrbs accomplis jusqu'a ce jour au cours de divers essais avec le B.t. sont discutes. D'une part, il n'est pas apparent que I'application d'insecticides chimiques cause des deglts serieux a I'environnernent. D'autre part, le B.t. bien qu'etant un substitut souhaitable aux insecticides chimiques contre la tordeuse, offre encore plusieurs inconvenients et de nouveaux essais sur le terrain devront dtre effectues afin de determiner si ce produit est vraiment efficace.During the past 3 years several articles have appeared in Quebec newspapers blaming the authorities for the continued use of chemical insecticides against spruce budworm. These articles have suggested that the insecticides used caused damage to forest fauna and that it should be replaced by Bacillus thuringiensis (B.t.1, a microbial insecticide supposedly effective against spruce budworm, and which causes no damage to forms of life other than the target insect. As a consequence of this publicity, the Quebec Department of Lands and Forests has been receiving many petitions and letters asking that chemical insecticides be replaced by B.t. In the fall of 1975 the "Association forestiere des Cantons de I'Est" (ACFE), an organization representing hundreds of 1The paper was presented at a "Symposlum on Mlcroblal Control of Spruce Budworrn" held in Montreal, January 20-22. 1976.

Development and Current Status of Bacillus thuringiensis for Control of Defoliating Forest Insects

“…Various aircraft and delivery systems were tested, ranging from helicopters and single-engine biplanes equipped with rotary atomizers to four-engine aircraft fitted with boom and nozzles (Smirnoff and Morris 1982). Although effectiveness of Bt showed marked improvement during those trials, results remained inconsistent with cost of treatment up to four times higher than chemical insecticide treatment (Blais 1976).…”

“…The general conclusion was that 20 BIUIha was effective only under optimum conditions and against low populations, whereas 30 BIUIha produced much more consistent results, even against populations exceeding 30 larvae per 45-cm branch (Morris 1982a;Carrow 1983;Dorais 1985 Availability of concentrated formulations permitted application of the higher dosage in a lower volume. The initial call for concentrated products was based on the desire to reduce shipping costs and volume application rates (Blais 1976). Pioneering work in this area was done by Smirnoff, who developed a concentrated formulation (Futura) that could be applied at 20 BIUIha in a final volume of 2.5 L. Trials at that rate were conducted as early as 1978 (Smirnoff 1980).…”