found in forest ecosystems; and (3) the insecticide spray should be 

 directed efficiently to the target insect (Schmiege eJt at., 1970). 



Currently, the U.S. Forest Service is evaluating the efficacy of 

 several organophosphate, carbamate insecticides, and insect growth regula- 

 tors for the control of three major insect pests: the gypsy moth 

 {PotitheJyiia cLLbpaA), Douglas-fir tussock moth [Hemciocampa p&eudott>uga£a) , 

 and spruce budworm. All three pests cause defoliation, but the spruce 

 budworm has the most widespread distribution and causes the most damage. 



The gypsy moth was introduced accidentally into North America in 1869 

 at Medford, Massachusetts, by a French naturalist who had intended to 

 cross it with the silkworm [Bombyx monX) . The spread of the gypsy moth 

 from that source occurred in two ways: (1) by windblown dispersal of the 

 newly hatched larvae, and (2) by inadvertent transport. The gypsy moth is 

 now generally distributed in the northeastern and eastern portions of the 

 U.S. It feeds primarily on leaves of hardwood trees (mainly oaks), but 

 the late-instar larvae may also defoliate conifers (USDA, 1973b). 



The Douglas-fir tussock moth is a native insect of western North 

 America and has caused extensive damage to coniferous forests of Canada 

 and the northwestern United States. It prefers to feed on Douglas-fir, 

 white fir, and grand fir. Larvae secondarily attack ponderosa pine, 

 western hemlock, and western larch after the preferred hosts have been de- 

 foliated. The population density of this moth varies tremendously over 

 cycles of 2 or 3 years, probably due to a viral infection of the moth 

 (USDA, 1973a). 



The spruce budworm is also indigenous to North America and has caused 

 extensive damage to conifers in Canada and the United States. In the 

 eastern United States and Canada, balsam fir is the preferred host 

 species, followed by white, red, and black spruce. Spruce budworm popu- 

 lations do not fluctuate as extremely as do those of the Douglas-fir 

 tussock moth (USDA, 1975). In the State of Maine, the area infested with 

 the spruce budworm increased from about 24,000 hectares (60,000 acres) in 

 1968, to 2.8 million hectares (7 million acres) in 1975. Batzer (1973) 

 reported that over a 10-year period, total losses of balsam fir and spruce 

 timber were equivalent to 12.4 cubic meters per hactare per year (1.37 

 cords per acre per year). Craighead (1923) estimated that a total of more 

 than 97 million cubic meters (27 million cords) were destroyed in Maine 

 during the outbreak of 1910 to 1918. According to the U.S. Forest 

 Service, present conditions in northern Maine are similar to those during 

 the budworm epidemic of 1910 to 1918. 



The extensive damage to forests by defoliating insects has become a 

 problem of national significance. The gypsy moth, spruce budworm, and 

 Douglas-fir tussock moth have caused annual losses estimated to be greater 

 than 68 million cubic meters (2.4 billion cubic feet) of lumber, worth 

 about $5,000,000,000, Reforestation of these areas is expected to take 

 more than 20 years. Thus, it is important to protect these resources 

 from excessive insect damage, to protect important wildlife habitat, and 



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