United States 

 Department of 

 Agriculture 



Forest Service 



Intermountain 

 Forest and Range 

 Experiment Station 



Research Paper 

 INT-281 



July 1981 



Monoterpenes of 

 Lodgepole Pine 

 Phloem as Related to 

 Mountain Pine Beetles 



Walter E. Cole, E. Park Guymon, and Chester E. Jensen 



INTRODUCTION 



The role of food quantity in mountain pine beetle (MPB) 

 population dynamics in lodgepole pine is well-documented in 

 the literature. The thickness of phloem within trees in a stand 

 determines whether the insect can prosper there. Beetles tend 

 to select trees that possess the thickest phloem in a stand 

 where trees have similar diameters, and they often select that 

 portion of an individual tree having the thickest phloem (Roe 

 and Amman 1970). The mountain pine beetle is food-limited in 

 those stands of lodgepole pine where developmental tempera- 

 tures are optimum (Cole and Amman 1 969). When beetles have 

 killed most of the larger, thick-phloem trees, they are forced to 

 attack and raise brood in the smaller residual trees. These trees 

 have reduced capacity for supporting brood development be- 

 cause of generally thinner phloem. Subsequently, the popula- 

 tion declines (Cole and others 1976). 



While the role of phloem quantity in beetle population dynam- 

 ics is well documented, that of phloem quality is not. Smith 

 (1 965) has shown that vapors of the monoterpenes from west- 

 ern white pine {Pinus ponderosa) vary in toxicity to the western 

 pine beetle (Dendroctonus brevicomis) in the following de- 

 scending order: limonene > As-carene > myrcene > p-pinene 

 ~ p-pinene > control. The monoterpene composition of oleore- 

 sin in lodgepole pine {Pinus contorta var. muriayana) was: 

 p-phellandrene, 69.4 percent; a-pinene, 6.4 percent; A3- 

 carene, 8.9 percent; p-pinene, 5.7 percent; myrcene, 3.9 

 percent; camphene, 0.5 percent; limonene, 2.4 percent; 

 sabinene, 2.1 percent; and a-phellandrene, 0.7 percent (Smith 

 1964). 



In most terpene studies where a variety of pine species were 

 considered, cortical oleoresin differed qualitatively between 

 species but not within species. Coyne and Keith (1972) found 

 no distinct differentiation, either qualitatively or quantitatively, 

 between monoterpene composition of loblolly (P. taeda) and 



slash (P. elliotii) pines within or outside of known southern pine 

 beetle outbreaks. Monoterpenes provide bases for distin- 

 guishing host species but not for distinguishing resistant trees 

 from check trees (Coyne and Critchfield 1974). Hanover (1975) 

 identified an apparent genetic hierarchical regulation of the 

 major terpene fractions in lodgepole pine. These discrete gene- 

 tic variations may relate to pest (insect) behavioral patterns, as 

 indicated by differing resistance levels of trees to their respec- 

 tive pest species. 



A continuing question is whether tree-to-tree differences in 

 phloem constituents, particularly the monoterpenes, are coinci- 

 dent with the characteristic MPB attack and survival pattern. 

 Alpha-pinene has been the usual monoterpene used in experi- 

 mentation with pheromones and beetle behavior. However, 

 Moeck (1980) mentions that u-pinene is not an effective pher- 

 omone component in lodgepole pine. While peripheral informa- 

 tion has been developed in this study, the emphasis has been 

 on monoterpene content of the phloem and its relation to tree 

 characteristics previously found to be linked to MPB population 

 dynamics. 



MATERIALS AND METHODS 



We took three 5.08 by 5.08 cm phloem samples at breast 

 height from each of 86 uninfested trees distributed over 20 

 acres (8.1 ha) on the Cache National Forest in 1975. Trees 

 ranged from 12.7 to 50.8 cm in diameter at breast height 

 (d.b.h.). Samples were taken three times during the season: 

 June 6, July 1 0, and July 31 . The samples were transported to 

 the laboratory and frozen on the same day they were removed 

 from the trees. Two samples per tree were analyzed as de- 

 scribed later, and one sample stored (frozen) as a backup 

 sample. 



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