Influence of Soil Fertility on Infestation of Jack Pine Plantations by the Pine Root Weevil

The influence of soil fertility on the root weevil ( Hylobius rhizophagus Millers) was investigated at 4 infested jack pine plantations and 4 adjacent noninfested jack pine stands in central Wisconsin. Weevil-infested plantations had significantly less total nitrogen and more available phosphorus than adjacent noninfested stands. Elemental content of roots varied within paired study areas, but the differences were inconsistent except for root nitrogen content. In the laboratory, weevil larvae showed differences in response to rates of feeding and survival on roots from infested and noninfested stands. Addition of ammonium nitrate (250 lb/acre 33½-0-0) resulted in significant increases in root moisture content and root nitrogen levels. Phosphorus (150 lb/acre 0-46-0) did not increase root moisture. Larval feeding trials employing roots from replicated check, nitrogen, phosphorus, and N + P treatments, plus roots from an adjacent noninfested stand, revealed that nitrogen and N + P treatments were reflected in drastically reduced rates of larval feeding and development and in increased mortality. Larvae subjected to nitrogen-rich roots from the noninfested stand were influenced in a similar manner. Nitrogen levels appear directly responsible for these responses. Forest Sci. 18:139-147.