Author
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THORPE, KEVIN |
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Submitted to: Environmental Entomology
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 7/9/1998 Publication Date: N/A Citation: N/A Interpretive Summary: The gypsy moth is considered to be a key pest of hardwood trees in the northeastern United States. Federal, state, and local governments and private interests spend millions of dollars each year to combat this pest. Workers must be able to distinguish between new and old gypsy moth egg masses when measuring gypsy moth population numbers. Two methods are used for egg masses that are out of reach: 1)visual inspection through binoculars or 2) by calculating the percentage of new egg masses at ground level and then 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 25% 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, gypsy moth control specialists, and government agencies decide which method is best suited to their program. Technical Abstract: It is necessary to distinguish between new and old gypsy moth, Lymantria dispar(L.), egg masses when conducting gypsy moth population surveys. Egg masses within reach from the ground are touched to determine if they contain unhatched eggs and thus are considered new. Two methods are used for egg masses not within reach: 1) visual inspection through binoculars or 2) by calculating the percentage of new egg masses at ground level and applying this figure to counts of all egg masses not within reach. To evaluate these methods, egg-mass persistence and color between generations, the proportion of new and old egg masses at ground level and in the canopy, and the ability of observers to visually distinguish new and old egg masses was examined. Fifty-five percent of exposed new egg masses studied were still at least 25% 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 visually discriminating new and old egg masses. With the use of binoculars to visually distinguish 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 the use of either method over the other, benefits and drawbacks to the use of each method are discussed relative to the data presented. |
