Predicting Numbers of Eggs in Jack Pine Budworm and Spruce Budworm (Lepidoptera: Tortricidae) Egg Masses in Michigan

Abstract

Simple linear regression equations were developed to predict numbers of eggs in jack pine budworm (JPBW), Choristoneura pinus pinus Freeman, and spruce budworm (SBW), Choristoneura fumiferana (Clemens), egg masses in Michigan as a function of egg mass length for two-row, two-row+ (two rows with a partial third row), and three-row egg masses. Regressions based on data collected from different stands and different years were significantly different for each egg row type of each species. However, all data sets for each species were pooled separately to develop prediction models for general application in Michigan. All regression lines for each insect were significant, and the two regression lines for the two insects were significantly different for each egg-row type. For each species, numbers of eggs per egg mass and egg-mass length increased as row number increased. JPBW egg masses had ca. 1.9-fold as many eggs per egg mass and were ca. 2-fold as long as SBW egg masses. Numbers of eggs per millimeter of egg-mass length were somewhat higher for SBW egg masses. Prediction models yielded average absolute errors ranging from 3.2 to 6.7 eggs and from 2.4 to 3.5 eggs, and average relative errors ranging from -3.6 to 1.2% and from 2.3 to 2.5%, for JPBW and SBW egg masses, respectively.