Factors Guiding the Orientation of Nymphal Spotted Lanternfly, Lycorma delicatula

SIMPLE SUMMARY: The spotted lanternfly, Lycorma delicatula White (Hemiptera: Fulgoridae), has recently emerged as a destructive invasive pest that is a great challenge to control. To develop and improve trapping, detection, and mitigation tools, it is crucial to understand what factors guide their behavior. Recent studies show that SLF aggregate, but the mechanisms driving aggregation behavior are poorly understood. This study evaluated the orientation behavior of SLF nymphs in the field when offered specific combinations of three factors: trees with different densities of SLF, tree size, and the presence of a semiochemical lure. When evaluated as a choice between two opposite characteristics while controlling for the two other factors, preferences were discernable, and all three factors were found to be attractive to SLF nymphs. Larger tree sizes and higher densities of SLF were highly attractive, and when forced to choose between them, only first instars revealed a preference for higher SLF density over larger-sized trees. When these two factors were controlled, methyl salicylate lures demonstrated four weeks of efficacy in the field but could not outcompete the draw of larger tree size or higher SLF density. ABSTRACT: A mark–release–recapture experiment was conducted to evaluate the orientation of spotted lanternfly (SLF) Lycorma delicatula White (Hemiptera: Fulgoridae) nymphs when released equidistant between two trees. The experiment was repeated weekly for eight weeks in a heavily infested area with mature tree-of-heaven Ailanthus altissima (Mill.) Swingle (Sapindales: Simaroubaceae) planted in rows as ornamental street trees in Beijing, China. One tree in each pair received a methyl salicylate lure, and the lure was rotated between trees every week as it aged. Two additional independent variables for each tree were also analyzed: size and SLF population density. Marked–released SLF significantly chose trees with higher SLF population density over trees with lower density populations, and they also chose larger trees significantly more than smaller trees. Population density and tree size were better predictors of attraction than lures, but when those factors were controlled, SLF significantly chose trees with methyl salicylate lures over control trees for the first 4 weeks of lure life. Wild SLF distribution was assessed weekly, revealing strong aggregation in first and second instars that diminished with development to the third and fourth instars. Thus, nymphal SLF aggregate, and orientation is strongly guided by the presence of other SLF and tree size.