Pine Bar^ Beetles 



427 



information useful in developing silvi- 

 cultural practices that will create 

 conditions unfavorable for the develop- 

 ment of outbreaks or minimize damage 

 during an outbreak. 



R. G. BROWN is an entomologist in 

 the Bureau of Entomology and Plant 

 Quarantine. He was graduated from 

 the University of New Hampshire in 

 1922 and has been in the Bureau since 

 1925. In 1935 he was put in charge of 

 the Division of Forest Insect Investi- 

 gations laboratory in New Haven. 



H. J. MACALONEY assists Mr. Brown 

 at New Haven and has charge of stud- 



ies in the application of biological in- 

 formation as it affects silvicultural 

 practices. He was graduated from the 

 New York State College of Forestry 

 at Syracuse University in 1923 and has 

 been in the Division of Forest Insect 

 Investigations since 1925. 



P.B.DowDEN also assists Mr. Brown. 

 He was graduated from Massachusetts 

 State College in 1923 and has been 

 with the Bureau of Entomology and 

 Plant Quarantine since that time. He is 

 in charge of the biological-control in- 

 vestigations on forest insects conducted 

 at the New Haven laboratory in Con- 

 necticut. 



PINE BARK BEETLES 



F. P. KEEN 



Pine bark beetles are small, dark- 

 colored, hard-shelled insects of the size 

 of a grain of rice or a medium-sized 

 bean. They bore under the bark of vari- 

 ous pines and dig egg tunnels, mostly 

 in the inner bark, which cut the cam- 

 bium layer a tree's most vital tissue. 

 Eggs laid along the sides of these tun- 

 nels hatch into small, white, legless 

 grubs. Under the bark also the attack- 

 ing beetles introduce fungi, blue stains, 

 and yeasts, which penetrate the sap- 

 wood and plug the sap stream from 

 roots to foliage. The tree is hurt in the 

 same way that an animal would be in- 

 jured or killed if worms were to bore 

 into it and stop up all veins and arteries. 



When the larvae complete their 

 feeding in the inner bark, they change 

 into pupae, the resting stage, then to 

 new adults. These adults later emerge 

 from the bark and fly off to attack 

 other pines. Thus they perpetuate their 

 species and continue their destructive 

 course. The new adults may attack 

 the green trees nearby, or they may fly 

 several miles to find trees to attack. 



A great many different kinds of 

 beetles work into and under the bark 

 of pines. The most destructive bark 

 beetle enemies of American forest trees 



are the so-called pine beetles (Den- 

 droctonus spp.), which attack primar- 

 ily the more mature trees, and engraver 

 beetles (Ips spp.), which prefer young 

 trees or the tops of older ones. Species 

 of Dendroctonus and Ips are found 

 throughout North America. 



The more important species of 

 Dendroctonus that attack pine are the 

 western pine beetle (D. brevicomis 

 Lee.), which attacks ponderosa pine 

 and Coulter pine in the Pacific States, 

 Idaho, Montana, and British Colum- 

 bia; the southern pine beetle (D. 

 frontalis Zimm.), which attacks all 

 species of pines and spruce from Penn- 

 sylvania south to Florida and west to 

 Arkansas and Texas; the mountain 

 pine beetle (D. monticolae Hopk.), 

 which attacks lodgepole pine, western 

 white pine, sugar pine, and other pines 

 in the Pacific States and northern 

 Rocky Mountain regions; the Black 

 Hills beetle (D. ponderosae Hopk.), 

 which attacks ponderosa and lodgepole 

 pines in the southern and central 

 Rocky Mountain regions and in the 

 Black Hills of South Dakota; the 

 Jeffrey pine beetle (D. jeffreyi Hopk.) , 

 which attacks Jeffrey pine in Califor- 

 nia; and the turpentine beetles (D. 



