Sap-feeding nitidulid beetles were trapped for 15 months at four oak wilt centers in central Texas and assayed for the presence of Ceratocystis fagacearum. Levels of contamination with the pathogen ranged 0.3% (Kerrville) -2.0% (Austin); also detected were G. piceae at slightly higher levels and a low number of beetles carrying C. pluriannulata. The percentages of contaminated beetles were similar to those reported for other parts of the oak wilt range in the USA, but probable species differences in Texas were detected.

Genetic diversity in the oak wilt pathogen Ceratocystis fagacearum was assessed using restriction fragment length polymorphisms (RFLPs) of the mitochondrial DNA (mtDNA) and anonymous RFLP loci in the nuclear DNA (nuDNA). No genetic variation was detected in the mtDNA among 27 isolates sampled from a broad geographical area. Southern hybridization to 100 anonymous, random, nuDNA probes detected a low level of variation among nine of the isolates. Only 35 out of 437 probe-enzyme combinations detected RFLPs. Most of the RFLPs appeared to result from insertions and deletions of less than 200 bp. A composite multilocus haplotype based on hybridization to six anonymous probes could differentiate each of the nine isolates tested, suggesting that these probes may be useful for further studies of the population biology and epidemiology of this pathogen. Hypotheses are presented to account for the low level of genetic variation.