Bacillus thuringiensis is one of the most versatile pathogens yet 

 found in insect research. It kills more than 100 species of insects - -notably 

 caterpillars - -that are economic problems, yet does not harm beneficial 

 insects or other forms of life. 



During spore production, the bacillus forms toxic crystals that act as 

 a stomach poison in susceptible insects. When caterpillars feed where the 

 spore material has been spread, some kinds die quickly, some more 

 slowly, but all cease eating within minutes after feeding on treated plants. 

 Some of these caterpillars are highly susceptible when young, and less so 

 in their later larval life. 



The spore material, including crystals, can be commercially produced 

 in artificial media and does not lose virulence when the growth process is 

 repeated. Moreover, the spores in dry storage retain their capacity for 

 killing susceptible insects for 10 years, at least. 



This bacillus has attracted researchers ever since its discovery in 

 1911 in Germany, where it was killing larvae of the Mediterranean flour 

 moth. Up to World War II, European scientists had learned that the bacillus 

 could kill larvae of the European corn borer, the gypsy moth, pink boll- 

 worm, and some other serious pests, but the war interrupted their experi- 

 ments. 



An American bacteriologist got a culture of the bacillus from Germany 

 in 1936 and later sent some to the University of California where it was 

 stored in a refrigerator as historic reference material for 7 years. In 

 1949, E. A. Steinhaus at the University tried the spores, found them still 

 highly active, and experimented with them for killing the alfalfa caterpillar. 

 To fight this pest, one of the most destructive in California, he had been 

 working with a virus, first in the laboratory, later in field testing. Bacillus 

 thuringiensis gave a faster kill than the virus. His practical and repeatable 

 successes in spraying both of these microbial materials on caterpillar - 

 ridden alfalfa in California attracted wide scientific attention. 



Although a good deal is known about the bacillus, USDA scientists and 

 others are still developing working knowledge for managing it in different 

 field situations and weighing its value for specific uses. 



FOREST PROTECTION 



Insects on the rampage are the foremost cause of timber mortality, 

 and forest entomologists are seeking economical ways to cut serious 

 losses. Chemical sprays sometimes pay in emergencies, by giving a fast 

 kill of certain pests. Microbial sprays on infested trees offer opportunity 

 for lasting protection. 



Since the United States and Canada have many tree problems in com- 

 mon, cooperation on microbial research to fight forest pests has been 

 close, as some of the following examples indicate. 



European Spruce Sawfly 



The value of viruses in forest pest control was demonstrated first 

 by Canadian Department of Agriculture scientists when the European 

 spruce sawfly was wrecking thousands of acres of spruce in southeastern 



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