Twig beetles,Pityophthorusspp. (Coleoptera: Scolytidae), as vectors of the pitch canker pathogen in California

Twig beetles in the genusPityophthorusEichhoff are known to be associated with the pitch canker pathogen,Fusarium circinatum, in California. Phoresy of the pathogen on these species has been reported to occur when insects emerge from diseased branches and when they infest disease-free, cut branch tips. To demonstrate that twig beetles can vector the pathogen, studies of phoresy and transmission were conducted in a native Monterey pine,Pinus radiataD. Don (Pinaceae), forest. Phoresy was confirmed for bothPityophthorus setosusBlackman andPityophthorus carmeliSwaine, andP. setosuswas shown to vector the pitch canker pathogen when contaminated with fungal spores and caged onto Monterey pine branches. When attractive baits were used to increase visitation to Monterey pines byP. setosus, baited trees were more likely to develop pitch canker than unbaited trees even though the beetles did not tunnel into the host to develop egg galleries. Therefore, twig beetles are competent as vectors of the pitch canker pathogen, and their vectoring activity, though requiring a wound, does not require that they establish egg galleries in the host.