INFLUENCE OF OLEORESIN CONSTITUENTS FROM PINUS-PONDEROSA AND PINUS-JEFFREYI ON GROWTH OF MYCANGIAL FUNGI FROM DENDROCTONUS-PONDEROSAE AND DENDROCTONUS-JEFFREYI

Dendroctonus jeffreyi and D. ponderosae are morphologically similar sympatric species of pine bark beetles over portions of their geographic ranges; however, D. jeffreyi is monophagous on P. jeffreyi while D. ponderosae is highly polyphagous. Both species carry a species of mycangial fungi that are also very similar in appearance. Growth of the two mycangial fungi and of the fungus Leptographium terebrantis (associated with the polyphagous and non-tree-killing Dendroctonus valens) in the presence of oleoresin constituents of host and nonhost conifers was tested by placing individual chemicals on agar growth medium and by growing the cultures in saturated atmospheres of the chemicals. The fungus associated with D. jeffreyi showed greater tolerance for chemical constituents placed on the growth medium than the other two fungi, and growth after three days was enhanced by heptane, the dominant constituent of P. jeffreyi oleoresin. Growth of all three species of fungi was reduced by the resin constituents when the chemicals were presented as saturated atmospheres. The results suggest that the influence of the tree on growth of the symbiotic fungi of the bark beetles during the initial attack process may be different than after colonization by the beetles is complete. The difference in the responses of the apparently related species of mycangial fungi may provide some new insight into the evolutionary history of these beetle/mycangial fungus/host tree systems.