Canada. The outbreak became evident in 1930 and tree destruction reached 

 a peak by 1938. That year, spruce forests in Vermont and New Hampshire 

 also were heavily infested. By 1940, the outbreak subsided, due to a 

 disease that eventually brought about a tremendous kill. Canadian insect 

 pathologists had identified the helpful agent as a virus. Laboratory tests 

 showed that the virus was extremely virulent to the sawfly during its 

 younger caterpillar stages. Infected larvae died in a week or two. In the 

 spruce forests, the virus 1 victory came slowly, because for years the 

 sawfly reproduced armies of hungry caterpillars faster than the virus 

 could spread and kill. 



Since 1940, the European spruce sawfly has been common in Canada 

 and the Northeastern United States, but has not been a serious pest. If it 

 should resume massive destruction, entomologists have a tested weapon-- 

 a virus spray developed in Canada that can be mass-produced and applied 

 for a strong initial attack. 



Two Pine Sawflies 



Finding a virus deadly to a spruce sawfly encouraged entomologists to 

 seek viruses for killing pine sawflies. 



First success was attained with a virus that kills the European pine 

 sawfly, a costly pest of pines in Canada and the United States. Canadian 

 entomologists could find no virus foe of this pest in their part of the world, 

 but they got one from Sweden in 1949. Using the gift- -a few virus -killed 

 larvae of the European pine sawfly- -they developed a dilute spray and 

 applied it successfully in 1950. 



In 1951, they shared 100 gallons with the U. S. Department of Agri- 

 culture. Using this, Federal and New Jersey State scientists jointly tested 

 treatments on Scotch and red pine infested with the European pine sawfly 

 and got excellent results from either ground or air spraying. Ground spray 

 tests, similarly successful, were made in Illinois by Federal forest ento- 

 mologists and Illinois State forestry specialists. 



This virus from Sweden has gained considerable practical use in 

 Eastern and Central United States, in fighting the European pine sawfly 

 under scientific guidance. The virus has not been commercially produced, 

 but a bank of the virus extract from insect sources has been started re- 

 cently at the Forest Insect Laboratory of the Forest Service, in New 

 Haven, Conn. From experiments in Ohio, it is known that the virus in 

 suspension can be stored at least 5 years without losing effectiveness. 

 The bank enables the Forest Service to provide starter materials of the 

 virus and a few other pathogens to research scientists, State pest control 

 officials, and others who can mass-produce and process a supply. One 

 virus spraying of trees infested with the European pine sawfly generally 

 keeps this pest down for 6 or 7 years, provided the spray is applied at the 

 right time in spring. A gallon of spray generally is enough for an acre 

 and the strength allows for some pests to survive to enable the disease 

 to persist. 



A virus for killing the Virginia pine sawfly was discovered in Mary- 

 land in 1954, when USDA scientists were examining severely infested pine 

 trees. They took dead larvae samples for disease tests, and found a virus 

 in 30 larvae. Using this, they developed a spray and tried it at larval 

 season in pinewoods infested with the Virginia pine sawfly. In a typical 

 test, the spray killed about 77 percent of the larvae in 1 1 days. 



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