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White Pine Weevil Report

SummaryWhite pine weevil

This study investigates the hypothesis that there is a genetic difference in the susceptibility of eastern white pine to white pine weevil attack associated with differences in the geographic origin of the host. The authors tested this hypothesis four ways using wild seedlings and seedlings of known seed sources, three supposedly resistant and one supposedly susceptible to weevil attack by:

  1. Exposing non-weeviled, wild trees averaging 5 feet tall dug in part from an area where trees were heavily weeviled and in equal part from an area where trees were sparsely weeviled. These were potted in 5 gallon pails in their native 24 ft. X 8 ft. outdoor cages and exposed to 160 weevils per cage.

    In tests run the first year, 49 percent of the trees were weeviled. Of the weeviled trees, 81 percent were from the heavily weeviled area and 19 percent from the sparsely weeviled area. Trees that were not weeviled in the tests were retested two years later using the same method. Results showed little change with only two more trees from the heavily weeviled area being attacked. The non-weeviled trees were subsequently out planted in a small field plot to observe any interaction between a nonnative environment and weevil attack. Observations over the next nine years showed that more than 50 percent of the trees had been weeviled with no significant difference between the tree sources.

    As an additional test of environmental interaction, an experiment of similar design as the cage tests above was run except that the potted tree sources, which were the same, were out planted in a small field plot adjacent to the above, a year after they were dug. Observations over the next 10 years showed that more than 50 percent of the trees had been weeviled with no significant difference between the tree sources.
  2. Exposing eastern white pine seedlings, grown singly in pots, from seeds of the 4 known seed sources, one from a heavily weeviled area and the others from sparsely weeviled areas. When the seedlings were 16 in. to 20 in. tall, a potted tree of each source was placed in small 20 in. X 20 in. X 32 in. cages with six male and six female weevils per cage. There was no significant difference in the rate of weeviling among the sources.
  3. Planting seedlings of the 4 known seed sources in the large outdoor cages used previously in the potted wild tree tests. When the trees were about 5 feet tall, they were exposed to weevil attack similar to trial A above. Results showed no significant differences in the susceptibility of the seedling sources to weevil attack.
  4. Planting seedlings of the 4 known seed sources in field plots in three locations in the state: one in an area of sparse weeviling, another of moderate weeviling and the third in an area of heavy weeviling. Weeviling data collected in the plots to the time the trees were six to seven feet tall showed no significant differences in weevil attack among the seedling sources. The sources planted in the sparsely weeviled area were sparsely weeviled, those in the moderately weeviled area were lightly to moderately weeviled, and those in the heavily weeviled area were heavily weeviled.

The results of the various tests indicate that the environment is the overall controlling factor in the incidence of weeviling. Within this, conditions exist which determine the weevil population and the extent of its damage. Site and particularly the soil in which the trees are growing is important. Poor internal soil drainage and thick bark on the leaders of the trees are conducive to weevil attack. When the two factors occur together in an area of adequate weevil population, damage to the trees and stand is usually severe.

Thus, on the basis of our findings, genetic resistance in eastern white pine does not appear to exist in any geographic ecotype, but rather must be sought in individual trees which are making good growth and have not succumbed to attack amongst heavy weeviling on comparable trees in the stand. Vegetative propagation from such trees has begun and the propagates are being tested.

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