Techniques for Estimating the Density of Late-Instar Gypsy Moth, Lymantria dispar (Lepidoptera: Lymantriidae), Populations Using Frass Drop and Frass Production Measurements

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Abstract
A technique was developed for estimating larval gypsy moth, Lymantria dispar (L.), densities using simultaneous measurements of the amount of frass produced per larva (frass yield) and the amount of frass falling in the forest per unit area (frass drop). The technique was tested in a postseason experiment in which 6,000 larvae were released in a stand. Frass yield was measured by individually caging several larvae in the field on cut host foliage. The most reliable and efficient method of measuring frass drop was the deployment of several large funnel-shaped frass traps near the forest floor. Number of pellets was found to be superior to frass weight as a unit for quantifying frass yield and drop, because it was not strongly influenced by instar distribution. Density estimates obtained using this method closely matched those expected from the number of larvae released. Frass width measurements provided a method of estimating instar distributions.