Association of Caliciopsis pinea Peck and Matsucoccus macrocicatrices Richards with eastern white pine (Pinus strobus L.) seedling dieback

Matsucoccus macrocicatrices Richards (Hemiptera: Matsucoccidae) is the only species within this genus that feeds and reproduces on eastern white pine (Pinus strobus L.), and at the time of its description, was not observed or known to cause serious damage. With eastern white pine dieback occurring extensively throughout the Appalachian Mountains, researchers are now in search of the contributors to this dieback phenomenon. Since its recent discovery (2007) far outside its historical range, M. macrocicatrices, and cankers associated with Caliciopsis pinea Peck, are regularly present on symptomatic trees throughout the range of eastern white pine. Little is known about the relationship between M. macrocicatrices and the fungal cankers commonly found on eastern white pines expressing dieback symptoms. For this study, we evaluated the relationships between both focal organisms and the extent of dieback symptoms on tree seedlings to identify contributing factors affecting symptomatic trees. We assessed the insect-pathogen complex on 270 eastern white pine seedlings from nine states that include the Appalachian Mountain range. There were positive correlations between M. macrocicatrices and seedling dieback, cankers and seedling dieback, and M. macrocicatrices and cankers in both the southern and northern portions of the Appalachians. About 95% of the observed M. macrocicatrices cysts and shells were associated with cankers, especially C. pinea-dominated cankers, which were exceptionally abundant on severely affected seedlings. The most prevalent fungi isolated from cankers without apparent fruiting bodies of C. pinea were in the genus Phaeomoniella. Trials were conducted to test the pathogenicity of C. pinea and other fungal isolates. Of the 15 fungal species tested, C. pinea was the only pathogenic species that formed girdling cankers on eastern white pine seedlings. We postulate that there is a facultative relationship between M. macrocicatrices and C. pinea, forming an insect-pathogen complex that is contributing to eastern white pine dieback and significantly impacting its regeneration dynamics in North America.