430 



In any pine forest a rapid increase of 

 bark beetles may develop in any of 

 these various types of favored food ma- 

 terial. When the supply of susceptible 

 trees becomes exhausted, the beetles 

 are forced to turn to healthy and vigor- 

 ous trees, which they overcome by 

 sheer force of numbers. Bark beetle 

 epidemics, once they develop, continue 

 until brought under control by natural 

 forces or by artificial-control measures. 



THE NATURAL-CONTROL FACTORS 



keep some in check. Besides the limita- 

 tions of food supply, disease, and un- 

 favorable weather that restrict the 

 populations of bark beetles, they have a 

 number of insect enemies. Parasites and 

 predators feed upon and destroy the 

 bark beetles. Also, many species of 

 birds catch beetles when they are in 

 flight. Certain species of woodpeckers 

 go after beetle larvae which are in or 

 under the bark. 



Bark beetles can stand heat up to 

 about 120 F. and so they are rarely 

 killed by hot weather, unless on the top 

 side of a log fully exposed to the sun. 

 But they cannot stand subzero tem- 

 peratures, unless they have had time to 

 acclimatize themselves. Overwintering 

 broods of western pine beetle start to 

 die at about 5 and are hard-hit at 

 -20. 



And so it is that while the vigorous 

 broods, free from too many parasitic 

 insects, predators, and woodpeckers, 

 are necessary for an outbreak, they 

 must also have ample breeding grounds 

 of slash, windfalls, drought-stricken 

 trees, or susceptible stands. If both sets 

 of conditions are favorable, a major 

 epidemic is inevitable, and much tim- 

 ber will be sacrificed to the hungry 

 hordes. 



Fifty years of research has brought 

 real progress in our ability to deal with 

 the infestations. Many control methods 

 have been tried. Some have been ef- 

 fective. Newer methods have been 

 found and put to good use. Most sig- 

 nificant of all advances is the grow- 

 ing interest and activity of private 

 and public owners of pine forests in 



Yearboo^ of Agriculture 1949 



bark beetle control as a conservation 

 measure. 



THE FIRST OFFENSIVES against the 

 beetle infestations were designed to de-r 

 stroy the beetle populations in infested 

 trees and thus to prevent them from 

 emerging and attacking more trees. 

 The strategy was based on the concept 

 that dead beetles cannot kill trees. On 

 an area to be protected, infested trees 

 were located in the fall, winter, and 

 spring when the beetles and their 

 broods were dormant. Then the insects 

 were destroyed, usually by felling the 

 dead trees and burning the bark. 



Beginning with the relatively small 

 project to control the Black Hills bee- 

 tle in 1905, a long series of control 

 campaigns have been carried on. The 

 work has involved nearly all species of 

 pine beetles and pine-producing re- 

 gions. Some of the work has consisted 

 of small routine control jobs, under- 

 taken and completed by local forest 

 officers or owners of summer homes; 

 others have been large cooperative 

 projects over thousands of acres, made 

 possible by many individual owner- 

 ships. During the period of the Civilian 

 Conservation Corps, the battle was 

 carried on as part of the forest-conser- 

 vation program wherever serious in- 

 festations were encountered. Recent 

 outbreaks of mountain pine beetles 

 and Black Hills beetles in the northern 

 Rocky Mountains have again led to 

 the initiation of large-scale projects. 



In their unceasing effort to find 

 new and better ways of disposing of 

 the beetles, entomologists have ex- 

 plored all possibilities from the sim- 

 ple expedient of hitting the beetles 

 with an ax to radio waves and com- 

 plicated electrical traps, from burn- 

 ing the infested bark to hauling 

 infested trees out of the forest area 

 and dunking them in millponds. 



Toxic oils sprayed on infested bark 

 have been used to avoid the costs and 

 fire hazards of peeling and burning it. 

 Fuel-oil solutions of naphthalene, 

 orthodichlorobenzene, and of paradi- 

 chlorobenzene have proved effective 



