In an article entitled, “Additive genetic variation in resistance traits of an exotic pine species: little evidence for constraints on the evolution of resistance against native herbivores,” published online in Heredity,  Dec. 12, ’12,  Moreira X and Zas R and Sampedro L at the department of Department of Ecology and Evolutionary Biology, University of California, Irvine, CA, USA and at two research institutes at  Galicia, Spain have adduced evidences to show that the apparent failure of alien pines to invade Europe is due the ability of herbivores to recognize the new guest pine species  and eliminate it before its establishment.  In the above paper, the authors examined genetic variation for constitutive and induced chemical defenses  as measured in terms of amount of non-volatile resin in the stem and total phenolics in the needles. Another important factor  is the inability of exotic pine species to colonize Europe is its vulnerability to  the attack of two insect species: the phloem feeder (Hylobius abietus) and the defoliator, Thaumetopoea pityocampa) to which native P. radiata is immune.  However, an analysis of the present data suggests that in the future the exotic Pinus species may become invasive.