Ambrosia beetle (Coleoptera : Scolytidae) species attacking chestnut and captured in ethanol-baited traps in middle Tennessee

Ambrosia beetles can be important pests of nursery production. The beetles are difficult to control with insecticides, requiring that pesticides be cl osely timed before tree attack, applied repeatedly, or have long residual a ctivity. The goal of this project was to improve management decisions for a mbrosia beetle control in nurseries. This study used ethanol-baited traps, field observations of tree attacks, and emergence cages over beetle galleri es to determine the following: (1) composition of ambrosia beetle fauna in middle Tennessee, (2) species responsible for attacks on chestnut (Castanea mollissima Blume), a susceptible tree species, (3) timing of tree attacks and progeny emergence, and (4) the relationship between tree attacks, proge ny emergence, and beetle collections in ethanol-baited traps. Ambrosia beet les were surveyed using ethanol-baited Lindgren traps at the Tennessee Stat e University Nursery Crop Research Station in McMinnville, TN, and at two c ommercial nurseries near Dibrell and Tarlton, TN, during 1998 and 1999. At the Nursery Station, species composition of ambrosia beetles attacking ches tnut trees was determined in 1999. Xyleborinus saxeseni Ratzeburg, Xylosand rus crassiusculus Motschulsky, and Monarthrum fasciatum Say were the domina nt ambrosia beetle species collected in traps. Xyleborinus saxeseni was the dominant species at all three locations when both 1998 and 1999 collection s were totaled. Other commonly trapped species included Monarthrum mali Fit ch, Xyleborus atratus Eichhoff, and Xyleborus pelliculosus Eichhoff. Tree a ttacks began on 2 April before trees broke dormancy. The majority of chestn ut attacks occurred in April and May. Progeny emerged from 48% of the caged galleries, including 35.9, 10.3, 3.3, and 1.1% X. germanus, X. crassiuscul us, Hypothenemus spp., and X. saxeseni, respectively. Beetles exhibited sev eral unusual behaviors during this study, including emergence of female X. germanus from trees the following spring, emergence of live male X. germanu s and X. crassiusculus,a staggered chronology of progeny emergence, and pre sence of multiple beetle species emerging from the same gallery. Xylosandru s crassiusculus and X. germanus were the dominant species attacking chestnu t, but total trap collections of X. germanus were small (less than or equal to 1.7%). Several findings from this study have significance to the nurser y industry. The timing of peak trap collections during April (particularly collections of X. crassiusculus and X. saxeseni) coincided with peak tree a ttacks. The factors responsible for chestnut susceptibility to attack were not measured in this study, but since the majority of trees were attacked b efore dormancy break, tree phenological state probably is an important dete rminant of tree vulnerability. The collection of some species like X. germa nus in trap collections may be a more important indicator of tree attack th an abundance in the trap. Progeny emergence from chestnut trees during June and July did not coincide with increased trap collections or renewed attac ks on chestnut. Therefore, traps may not always indicate ambrosia beetle ab undance. Several new state records were collected during this study, includ ing X. crasiusculus, a species capable of serious economic damage to nurser y stock.