FOREST AND RANGE RESOURCES OF UTAH 



75 



INSECTS 



The principal insect enemies of live trees in Utah are the bark 

 beetles. (Fig. 41.) These are usually about the size of the head of a 

 small match and have hard wing coverings. They live for a period 

 of about one year, and during that time spend all but a day or two 

 between the bark and the wood of a tree. Although they are well 

 equipped to fly, they make use of their wings only once during their 

 lives, and that is to fly from the tree where they were hatched to 

 another tree which they are going to attack. Immediately the female 

 begins boring a hole through the 

 bark of the new tree and excavating 

 a gallery between the bark and 

 the wood. Her mate follows her 

 in, and the two eat out a gallery 

 a little larger than the size of a 

 match and more or less in a ver- 

 tical position. After that they ex- 

 cavate an inch or two of this gal- 

 lery, and eggs are deposited along 

 the sides. The eggs are nearly 

 white bodies about the size of the 

 head of a very small pin. In a few 

 days these eggs hatch, and the 

 larvae begin eating small galleries 

 in a horizontal direction around 

 the tree. Their food is obtained 

 from the cambium layer, between 

 the bark and the growing part of 

 the tree, in which are contained 

 the cells that transport the food 

 and water for the tree. When 

 enough of these bark beetles infest 

 a tree, the entire growing surface 

 in an area completely around the 

 tree is consumed, so that neither 

 the leaves of the tree nor the roots 

 are able to function, and the tree 

 is killed. The effect of the bark- 

 beetle work is exactly the same as 

 that of girdling the tree with an 

 ax; although, when a tree is heavily 

 infested with bark beetles, they do 

 a more effective job of girdling 

 than is usually done with an ax and the tree dies within a period of 

 one year. 



During a period of several months the larv&e gradually change to 

 what are called pupae. These do no feeding at all. As time goes on, 

 legs, wings, head, and body are formed, and in just about a year 

 after the egg was laid the pupa develops into an adult beetle with 

 hard wings. The adult beetles are of different colors, but all of 

 those which infest trees in Utah are either brown or black. The 

 adult beetles that excavated the long vertical gallery die in it. 



In Utah the Black Hills beetle infests nothing but western yellow 

 pine. This is a black beetle, and was named the Black Hills beetle 











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Figure 41. — A bark beetle's signature 

 on the growing wood, the death war- 

 rant of the tree 



