Studies of the Vertical Distribution of the Clover Root Borer in Roots of Red Clover in Relation to Progression of the Season

Abstract

Red clover roots were sampled periodically from a first-harvest-year field, cut into ½-inch segments starting at the top of each root, and examined for numbers of the clover root borer, Hylastinus obscurus (Marsh.) (Coleoptera: Scolytidae). For the period June 12 to October 12, 1957, the seasonal average depths were: larvae, 0.76 inch; pupae, 0.84 inch; and adults, taken after the first callow individual appeared, 0.82 inch. The pooled average depth of these stages increased in a linear manner as the season progressed. Using head-capsule width as a criterion of size, the depth of larvae collected on August 22 was directly proportional to their size. Temperature appeared not to be a controlling factor for the depth at which the combined stages were found. In the absence of a temperature effect, maturity seemed to be the factor that had the greatest influence on the depth at which larvae were located.