J. Robert Bridges

Nitrogen-fixing bacteria associated with bark beetles

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.

Hyperphoretic Dispersal of a Pyxidiophora Anamorph

It has been suggested that Thaxteriola species and other minute, nonmycelial fungi associated with arthropods have phylogenetic relationships with the Laboulbeniales. However, direct development of the thallus of Thaxteriola from an ascospore of Pyxidiophora has now been discovered. Thaxteriola is specialized for dispersal by mites carried on pine bark beetles; other fungi dispersed by arthropods in this symbiotic assemblage rely primarily on arthropod specializations.

Ascospore dispersal of Ceratocystiopsis ranaculosus, a mycangial fungus of the southern pine beetle

Ascospores of the heterothallic fungus Cer- atocystiopsis ranaculosus were found in sporothecae of three mite species of the genus Tarsonemus. These mites were phoretic on the coniferous bark beetles Den- droctonus frontalis, D. brevicomis, and Ips acuminatus. Ceratocystiopsis ranaculosus inhabits the mycangium of both Dendroctonus species as conidia in a budding yeast- like form. Ascospores are not known to occur in my- cangia of bark beetles, and the means of ascospore dispersal has not previously been reported. It is pos- tulated that ascospores transported by phoretic mites may be responsible for establishing sexually compat? ible colonies of the fungus in beetle galleries either by themselves or in combination with the mycangial fun? gus type.

Southern Pine Beetles Attack Felled Green Timber

Although Hopkins (1909) briefly mentioned that the southern pine beetle (SPB) (Dendroctonus frontalis Zimmermann) will breed in felled pines (Pinus spp.), this behavior has been thought to be uncommon (Gara and others 1965). MacAndrews (unpublished MS thesis 1926)’ first reported SPB completing a generation in felled logs of shortleaf pine (Pinus echinata Miller) in an “epidemic”situation. In summer and fall he noticed that the logs were attacked simultaneously by SPB and Ips calligraphus (Germar) within 2 days after felling and that the bottoms of logs were colonized more heavily by SPB than the tops. Highest emergence:attack ratio (E/A) (10.4) was in the butt logs where bark was thickest. The average number of beetles was 21 .4/cm2 (198/ft2). In standing timber, the VA was lower (about 8.0), but numbers of emerging SPB were higher (32.41 cm2 or 300/ft2).