Frequency of Borer Attacks as Related to Character of Aspen Sucker Stands:A Comparative Study of Oberea schaumii and Saperda inornata12

Abstract

Frequency of oviposition by Saperda inornata Say and Oberea schaumii LeConte was studied in relation to character of aspen sucker stands. Fieldwork took place during 1964, 1965, and 1966 in 5- to 6-year-old aspen, Populus tremuloides Michx., sucker stands situated in the western portion of Michigan's Upper Peninsula. For both species, oviposition frequency per 30-sucker sampling unit conformed satisfactorily to the negative binomial distribution as fitted by the method of maximum likelihood. The observed parameter values, 0.45 ≤ mean ≤ 3.11 and 0.62 ≤ k ≤ 1.66, reflect endemic populations with definite clumping. Of several factors studied, only stand density was consistently correlated with infestation. Populations of the insects were not limited by food supply and, as expected, the total number of S. inornata galls per acre at first increased with sucker density and then ceased to change. However, the situation was more complex with O. schaumii. Its infestations were greatest at sucker densities of 5000–6000/acre, declining with further increases in sucker density. Clear-cutting to achieve maximum density of sucker regeneration should minimize damage from these insects.