436 



Yearbook^ of Agriculture 1949 



Even though this method requires pro- 

 fessional assistance, it is more effective, 

 practicable, and cheaper in destroying 

 heavy, hidden, deep-seated infesta- 

 tions than the use of liquid chemicals 

 or poison dusts or the replacement of 

 infested areas with chemically impreg- 

 nated wood. Fumigation will not pre- 

 vent reinfestation. 



THOMAS E. SNYDER, a senior en- 

 tomologist in the Division of Forest 



Insect Investigations, Bureau of En" 

 tomology and Plant Quarantine, has 

 devoted 40 years to the study of insects 

 that attack forest products and ways 

 to control them. He has published 

 numerous articles on termites, powder- 

 post beetles, ambrosia beetles, and 

 the chemical wood preservatives. Dr. 

 Snyder is an authority on the classifi- 

 cation of termites. He has degrees 

 from Columbia, Yale, and George 

 Washington Universities. 



CONTROLLING THE TUSSOCK MOTH 



PAUL H. ROBERTS, JAMES C. EVENDEN 



In the field headquarters at Moscow, 

 Idaho, a tense group of men were wait- 

 ing for the signal that was to start the 

 greatest of all airplane offensives 

 against an insect. It was 3 o'clock on 

 the morning of May 22, 1947. The sun 

 had not yet limned the mountain maj- 

 esty of northern Idaho and neighbor- 

 ing Washington or the desolation 

 wrought in the forests by the tussock 

 moth. The report came: Weather 

 clear; wind velocity 5 miles an hour. 

 It was relayed to the Laird Park air- 

 strip and the municipal airport at 

 Moscow, the seat of the University of 

 Idaho, and nearby Pullman, the seat 

 of Washington State College. 



At 3 : 20 a. m. the big C-47 trundled 

 onto the runway, roared through a 

 short take-off, then rose and turned 

 toward the rough terrain of Moscow 

 Mountain to spread 1,000 gallons of 

 DDT spray over 1,000 acres of infested 

 fir timber. The Ford trimotors followed. 

 Simultaneously the small planes at the 

 Laird Park airstrip went out, one at a 

 time. 



They were after the Douglas-fir tus- 

 sock moth (Hemerocampa pseudot- 

 sugata McD.), which early in 1946 

 appeared in epidemic proportions 

 throughout a large forest area near 

 Moscow, Idaho. A native of north- 

 western United States and southeast- 

 ern Canada, the small insect can kill 



its preferred hosts, Douglas-fir and the 

 true firs, in a year if it destroys all the 

 foliage; partial defoliation may result 

 in serious top killing and the death of 

 trees if it continues for several years. 



In its life cycle this insect produces 

 but one generation each year. Eggs are 

 laid in August and September and 

 hatch the following spring in late May. 

 The tiny caterpillars are active and will 

 travel relatively long distances in search 

 of food. They become full-grown by 

 late August, pupate, and transform to 

 new adults in about 2 weeks. As the 

 female moths are wingless, eggs are 

 usually laid on or near the pupal case 

 from which the moths have emerged. 

 Any widespread distribution of an in- 

 festation must be by means other than 

 the flight of adult moths. It is known 

 that the young, hairy caterpillars are 

 carried long distances by air currents. 

 When disturbed, they drop from the 

 limbs and hang suspended on a fine 

 silken thread often 5 feet or more in 

 length, which they spin as they fall. 

 This thread and the body hairs of the 

 caterpillar offer considerable wind re- 

 sistance, and air currents of about 10 

 miles an hour will carry them away. 



By early summer of 1946 whole 

 mountainsides appeared brown from 

 defoliation of trees by the insect. In 

 the Idaho territory these brown areas 

 intensified public concern as to reme- 



