White Pine Weevil Resistance Comparison
Donald P. Connola
Selected exotic white pines were tested against eastern white pine for resistance to white pine weevil attack. They included Balkan, Korean, Swiss stone, western and southwestern white pines. All were more resistant than eastern white pine but were slower growing. Balkan and western white pines appeared to be the best candidates for an eastern white pine alternative or for use in a hybridization program with eastern white pine.
Painter (1951) describes the mechanisms of insect resistance in a plant as divided into three categories: (1) Non-preference for oviposition, food or shelter; (2) Antibiosis or the adverse effect of the plant on the biology of the insect; (3) Tolerance or ability of the plant to withstand the insect attack. Using his classification for describing resistance, our observations on the experimental trees as described here show that, although both eastern and non eastern white pines have the tolerance to withstand attack and damage (depending on the size of the tree), the western white pine and particularly the Balkan white pine suffered less damage to the main stem than the other pines when tested in our cage tests. Western white pine appeared to possess more non-preference to attack whereas Balkan white pine appeared to possess more antibiotic properties judging from its more copious flow of pitch when attacked and the large amount of scar tissue it formed in an attempt to repair damage caused by weevil attack to the leader.
Judging from the results in the small cage tests, it appears that Korean white pine and Swiss stone pine are not as resistant to weevil attack as western white pine and particularly Balkan white pine. The randomized block tests seem to bear this out at least with Swiss stone pine. Tests with Southwestern white pine in both the large cage tests and the randomized block tests indicate that this species is also less resistant to weevil attack than Balkan and western white pines.
Therefore, on the basis of our findings it appears that western white pine and Balkan white pine are the best choices as resistant alternatives to eastern white pine or as candidate species for a hybridization program with eastern white pine. Both species readily hybridize with eastern white pine, (Wright, 1970) and it would be expected that the hybrid would grow faster than either exotic white pine and at the same time be more resistant to weevil attack. Western white pine is more susceptible to white pine blister rust, Cronartium ribicola, J. C. Fisher ex Rabh, another serious pest of white pines. However, blister rust resistant stock like Source X-251 could be used in a hybridization program. Also, the western white pine in our studies suffered winter burning. This disadvantage could also be overcome in hybridization with eastern white pine which is hardy.
Balkan white pine, on the other hand, is winter hardy but in our studies was subject to needle blight complex to a greater extent than was found in our eastern white pine. This weakness could be overcome in hybridizing it with resistant eastern white pine. However, a Balkan white pine advantage is its greater resistance to white pine blister rust than eastern white pine (Bingham, 1967).
Thus with the proper choice of eastern white pine showing good growth, good form and some indication of resistance to white pine weevil attack, and preferably from blister rust resistant stock such as X-239, hybridization with either or both western and Balkan white pine with good growth and form could produce a white pine hybrid with satisfactory resistance to the white pine weevil and possibly blister rust also.