Author
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THORPE, KEVIN |
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Submitted to: Virginia Gypsy Moth Advisors Annual Review
Publication Type: Proceedings Publication Acceptance Date: 9/10/1996 Publication Date: N/A Citation: N/A Interpretive Summary: The gypsy moth is considered to be one of the most important pests of hardwood trees in the northeastern United States. Millions of dollars are spent annually by federal, state, and local governments and by private sources to combat this pest. The ability to reliably distinguish between new and old gypsy moth egg masses is required by workers measuring gypsy moth population numbers. Presently, this is done by touch for egg masses within reach from the ground and visually for egg masses not within reach, or by calculating the percentage of new egg masses at ground level and applying this figure to those egg masses not within reach. The reliability of these two methods was evaluated. Fifty-five percent of the exposed new egg masses studied were at least 75% intact at the time of the next year's egg mass survey. However, the color of the egg masses was markedly lighter, providing a mechanism for vision-based discrimination of new and old egg masses. Experienced workers were able to visually estimate the percentage of new egg masses to within 12 percent in all but one instance. While these data do not support recommending either method over the other, benefits and drawbacks to the use of each method are discussed. This information is intended to help gypsy moth managers decide which method is best suited to their program. Technical Abstract: The ability to reliably distinguish between new and old gypsy moth, Lymantria dispar, egg masses is required by workers conducting gypsy moth population surveys. Presently, this is done by touch for egg masses within reach from the ground and visually for egg masses not within reach, or by calculating the percentage of new egg masses at ground level and applying this figure to those egg masses not within reach. To evaluate these methods, egg mass persistence and color from one generation to the next, the proportion of new and old egg masses at ground level and in the canopy, the distribution of new and old egg masses through time and space, and the ability of workers to visually distinguish new and old egg masses was determined. Fifty-five percent of the exposed new egg masses studied were at least 75% intact at the time of the next year's egg mass survey. However, the color of the egg masses was markedly lighter, providing a mechanism for vision-based discrimination of new and old egg masses. Using binoculars to visually distinguish between new and old egg masses, experienced workers were able to estimate the percentage of new egg masses to within 12 percentiles in all but one instance. While these data do not support recommending either method over the other, benefits and drawbacks to the use of each method are discussed relative to the data presented. |
