Response of Lutz, Sitka, and White Spruce to Attack by Dendroctonus rufipennis (Coleoptera: Scolytidae) and Blue Stain Fungi

Abstract

Mechanical wounding and wounding plus inoculation with a blue-stain fungus, Leptographium abietinum (Peck), associated with the spruce beetle, Dendroctonus rufipennis (Kirby), caused an induced reaction zone or lesion around the wound sites in Lutz spruce, Picea lutzii Little, Sitka spruce, P. sitchensis (Bong.) Carr., and white spruce, P. glauca (Moench) Voss, in south-central Alaska. The effects of tree species on lesion length were nonsignificant; however, the effects of wounding versus wounding plus blue-stain inoculate were highly significant. Lesion length was significantly longer in high-flow Lutz spruce compared with low-flow trees that were wounded. There was a significant change in monoterpene composition in the induced reaction zones of wounded phloem compared with unwounded phloem. The total percentage of potential toxic monoterpenes such as limonene, myrcene, 3-carene, and beta phellandrene increased in all three host species. Egg gallery length and the area of phloem consumed by larvae outside of lesions was significantly less for trees with wounds caused by fungal inoculation compared with mechanical wounds only. Trees with fungal inoculations appeared to deter larval feeding. Hydroxystilbenes were not found in the three species of spruce; however, differences were found in the chemical content of the reaction and the nonreaction zones. Two unknown chemicals present in nonreaction zones were not found in the induced reaction zone. One chemical appears to be a dimer with a carbohydrate moeity. A low molecular weight chemical found in the induced reaction zone could not be identified by mass spectroscopy.