Nitrogen-fixingEnterobacter agglomerans andEnterobacter spp. were consistently isolated from the bark beetleDendroctonus terebrans. Large populations of nitrogen-fixing bacteria were found with the beetle, although no in situ acetylene reduction was demonstrated. The constant occurrence of nitrogenfixing bacteria withD. terebrans suggests a symbiotic relationship. Nitrogen-fixing bacteria were also isolated from the bark beetlesDendroctonus frontalis andIps avulsus.

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1. Tarsonemus mites phoretic on southern pine beetles were shown to be hypervectors of bluestain fungus, Ceratocystis minor (Hedgcock 1906).2 . Beetles with phoretic mites had significantly more C.minor than did mitefree beetles.3. Over 90% of tarsonemid mites collected from beetle-infested inner bark and 59% of mites phoretic on emerging beetles carried C.minor spores.4. This association is an interesting example of a three-way mutualism among insects, mites and fungi.

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Amount of bluestain caused by Ceratocystis minor (Hedgcock) Hunt in trees infested with the southern pine beetle (SPB), Dendroctonus frontalis Zimmermann, was measured in three Texas and Louisiana forests. It was significantly correlated with number of Tarsonemus krantzi Smiley & Moser, a mite phoretic on SPB. Significantly less bluestain and significantly fewer mites were found in certain Texas infestations where SPB outbreak was most severe. KEY WORDS Dendroctonus fron talis, Tarsonemus kmn tzf, Tarsonemus tps, Cera towstis minor References Cited Sam Houston 8.3 k I6.6a 4.9 k 18.2a Bridges, J. R. 1985. Relationship of symbiotic fungi Sabine 9.7 2 16.9a 6.5 + l4.3ab to southern pine beetle population trends. In S. J. Kisatchie 20.2 k 23.9a 20.8 2 31.8b Branham L R. C. Thatcher [eds.l Integrated pest management research symposium: the proceedings. Means within a column not followed by the same letter are USDA For. Ser., South. For. Exp. Stn. Gen. Tech. significantly different (P < 0.05; Kruskal-Wallis test). Rep. SO-56: 127-135.