The Association between the Distribution of Resin Beads and the Emergence of Sirex noctilio on Red Pine in North America

SIMPLE SUMMARY: The European woodwasp, Sirex noctilio, is an invasive pest in North America. The presence of resin beads as signs of female ovipositor activity has been effectively used in ground surveillance. Improving our understanding of the relationship between resin bead density and the number of emerging S. noctilio, its parasitoid, and native woodwasp strengthens integrated pest management programs. We also investigated the resin bead density associated with the height, diameter, or cardinal direction on red pines. Results indicated resin bead density was significantly associated with only the emergence of S. noctilio, not the emergence of its parasitoid, or native woodwasp. Resin beads were also most abundant on the north, east, and south sides of logs at 4.5 m above the ground. This study supports the use of resin beads as a first visible sign of S. noctilio colonization of host trees in North America. ABSTRACT: This study examined the relationships of the abundance and distribution of resin beads (signs of Sirex noctilio parent female ovipositor activity) with the abundance and distribution of emerging progeny of S. noctilio, S. nigricornis and their parasitoid Ibalia leucospoides. S. noctilio is native to Europe and is an invasive pest of pines in the Southern Hemisphere and North America; S. nigricornis is native to North America and is a secondary pest of dying pines. I. leucospoides is a parasitoid that has been widely deployed for biological control of S. noctilio. This study aimed to determine if the distribution of resin beads is associated with the height, diameter, or cardinal direction on red pines, Pinus resinosa, as well as the distribution of wood wasp and parasitoid emergence. Our results showed that among log sections taken at five heights, resin beads were most abundant on the north, east, and south sides of logs and mid log at 4.5 m above the ground. Emergence of S. noctilio was most abundant only from logs with more than five resin beads per square meter, while diameter and height were not contributing factor. None of variables evaluated (resin bead densities, height, and diameter) had significant effects on the emergence of S. nigricornis and I. leucospoides. These findings help clarify the biological significance of resin beads as indicators of S. noctilio colonization of host trees in North America.