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

Abstract

Bacillus thuringiensis (Bt) is a naturally occurring bacterium that is now widely used for control of spruce budworm and several other defoliating forest insects in Canada. It took more than 25 years of research and development to bring Bt from first experimental use in the early 1960s into full operational use in the mid 1980s. Critical to this process was the adoption of HD-1 for commercial use, the standardization of formulations based on international units, and the development of higher potency products. An increase in product potency from 4 BIU/L in the early 1970s to 16.9 BIU/L in the mid 1980s, concomittant with improvements in formulation and application technology, reduced treatment costs while at the same time improving reliability of efficacy. A shift in political climate pushed Bt into operational use by 1985. Since then, Bt has been used in more than half of all spruce budworm control programs. The use of high-potency formulations (12.7 to 16.9 BIU/L) applied undiluted at 30 BIU in 2.4 L/ha or less has significantly reduced but not eliminated initial constraints of high treatment costs and inconsistent efficacy. Current research is focussed on further reducing these constraints. In the short term, registration of formulations containing 25 BIU/L or more is expected to permit application of reduced dosages in less than 1 L/ha and to clear the way for adoption of a split application scheme to increase reliability of efficacy. Selection and commercialization of more effective strains and the enhancement of natural strains by genetic or genetic engineering techniques offer exciting prospects for improvements in the longer term.