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 closely timed before tree attack, applied repeatedly, or have long residual activity. The goal of this project was to improve management decisions for ambrosia beetle control in nurseries. This study used ethanol-baited traps, field observations of tree attacks, and emergence cages over beetle galleries 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, progeny emergence, and beetle collections in ethanol-baited traps. Ambrosia beetles were surveyed using ethanol-baited Lindgren traps at the Tennessee State University Nursery Crop Research Station in McMinnville, TN, and at two commercial nurseries near Dibrell and Tarlton, TN, during 1998 and 1999. At the Nursery Station, species composition of ambrosia beetles attacking chestnut trees was determined in 1999. Xyleborinus saxeseni Ratzeburg, Xylosandrus crassiusculus Motschulsky, and Monarthrum fasciatum Say were the dominant ambrosia beetle species collected in traps. Xyleborinus saxeseni was the dominant species at all three locations when both 1998 and 1999 collections were totaled. Other commonly trapped species included Monarthrum mali Fitch, Xyleborus atratus Eichhoff, and Xyleborus pelliculosus Eichhoff. Tree attacks began on 2 April before trees broke dormancy. The majority of chestnut 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. crassiusculus, Hypothenemus spp., and X. saxeseni, respectively. Beetles exhibited several unusual behaviors during this study, including emergence of female X. germanus from trees the following spring, emergence of live male X. germanus and X. crassiusculus,a staggered chronology of progeny emergence, and presence of multiple beetle species emerging from the same gallery. Xylosandrus crassiusculus and X. germanus were the dominant species attacking chestnut, 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 nursery industry. The timing of peak trap collections during April (particularly collections of X. crassiusculus and X. saxeseni) coincided with peak tree attacks. The factors responsible for chestnut susceptibility to attack were not measured in this study, but since the majority of trees were attacked before dormancy break, tree phenological state probably is an important determinant of tree vulnerability. The collection of some species like X. germanus in trap collections may be a more important indicator of tree attack than abundance in the trap. Progeny emergence from chestnut trees during June and July did not coincide with increased trap collections or renewed attacks on chestnut. Therefore, traps may not always indicate ambrosia beetle abundance. Several new state records were collected during this study, including X. crasiusculus, a species capable of serious economic damage to nursery stock.