Phloeosinus aubei (Perris, 1855) (the cypress bark beetle), a bark beetle living on Cupressaceae species, was previously recorded in Romania only at Orşova, in the warmest area of Romania, with sub-Mediterranean climate. Recently we found this species on a dying tree of Thuja occidentalis L. (the American arbovitae) in Solca, a locality in northern Romania, with Baltic climatic influences. A piece of 1.05 m long from the lower trunk of that tree was harvested on 24th of July 2012 and maintained in a plank-walled store room with good natural ventilation, at Câmpulung Moldovenesc, until beginning of April 2013. Thereafter it was transferred into laboratory, at room temperature of 18-22oC. We obtained 1644 beetles from that piece, 809 males and 835 females, the sex ratio of the insects from the new generation being close to 1. Under the bark (about 40 dm2) we found 215 gallery systems of which 151 (70%) had only one arm and no nuptial chamber. These were significantly shorter than two-armed egg-galleries (mean ± standard error: 14.9 ± 0.4 mm and 27.7 ± 0.7 mm, respectively; t = 17.087, p < 0.0001). Forty two adults of Metacolus unifasciatus Förster, 1856, one of Eurytoma morio Boheman, 1836, and two unidentified braconids (Hymenoptera) were also obtained from the attacked trunk. The parasitoid-host relations between these two species and P. aubei are new to Romania. The information gathered in the field, as well as under semi-natural and laboratory conditions suggests that P. aubei has one generation per year and that at least some insects of the new generation overwinter as adults. The insects that overwinter under the bark emerge in spring during two months (April-May). In the new location, P. aubei has other parasitoids than in the southern area of the country, with little impact on bark beetle mortality.