Root-Inhabiting Bark Beetles (Coleoptera: Curculionidae) and their Fungal Associates Breeding in Dying Loblolly Pine in Alabama

Abstract

Root feeding bark beetles in the genus Hylastes Hylastes breeding in loblolly pine across 3 crown (Coleoptera: Curculionidae: Scolytinae) commoncondition classes (healthy, dying, dead). Addition ly carry ophiostomatoid fungi (Ophistomatales: ally, the relationship between ophiostomatoid Ophistomataceae)and collectively contribute to species, their Hylastes species vectors, and tree root disorders of Pinus species around the world condition were investigated. (Jacobs & Wingfield 2001). One of the most damLoblolly pine stands across central Alabama aging root disorders is black-stain root disease have experienced high mortality rates, character of conifers in the Western United States, caused ized by scattered stand mortality with a distinct by the fungal species Leptographium wageneri lack of above-ground pests (Brown & McDowell Kendrick and its primary beetle vector H. nig1968). During an investigation of one stand in rinus (Mannerheim) (Witcosky et al. 1986). ReMay 2008 in central Alabama, dying trees were cently, Hylastes salebrosus Eichhoff and H. tenuis found to be infested with root-inhabiting beetles Eichhoff have been associated with loblolly pine and their associated ophiostomatoid fungi. Six (Pinus taeda L.) decline (Eckhardt et al. 2007), trees were selected based on crown condition, in which is considered an emerging forest health iseluding 2 with green, healthy crowns (healthy), sue in the southeastern United States (Eckhardt 2 with severely chlorotic and thinning crowns et al. 2010). (dying), and 2 with red crowns (dead). Two pri Loblolly pine decline (LPD) is a tree disease mary lateral roots were randomly selected and complex that is characterized by symptoms that excavated to approximately 3 meters from the include thinning tree crowns, growth reductions root collar. Roots were removed from trees and (Eckhardt et al. 2007) and premature mortality in carefully dissected. All insects, including imma localized areas (Brown and McDowell 1968). Eviture stages, were collected from roots and adult dence suggests the complex is the result of interbeetles were identified to species. Root tissue was acting abiotic (Eckhardt & Menard 2008) and biobtained from each brood gallery for the isolation otic (Eckhardt et al. 2007) stress factors. Hylastes of ophiostomatoid fungal species using methods species vector a variety of root-infecting ophiostodescribed in Eckhardt et al. (2007). Following matoid fungi (Klebzig et al. 1991, 1995; Eckhardt surface sterilization, tissue was placed on CSMA et al. 2007; Zanzot et al. 2010) which are patho(malt extract agar containing 800 mg/L of cyclo genic to loblolly pine (Matusick & Eckhardt 2010; heximide and 200 mg/1 of streptomycin sulfate) Matusick et al. 2011). Hylastes beetles and their selective nutrient agar (Jacobs & Wingfield 2001). associated fungi are thought to collectively contribEach adult insect was also rolled on CSMA to re ute to LPD by causing root damage through fungal cover ophiostomatoid fungi from insect bodies infection and insect feeding (Eckhardt et al. 2007). (Zanzot et al. 2010). Isolated ophiostomatoid fun Root and lower stem feeding beetle species (Colegal species were identified using morphological optera: Curculionidae) includingH. salebrosus and characters and established keys. Unknown iso H. tenuis are found in increased numbers within lates were sequenced and confirmed as new spe LPD-affected stands, compared to healthy stands cies by M. Wingfield (Forestry and Agricultural (Eckhardt et al. 2007, Menard 2007). A recent Biotechnology Institute, Pretoria, South Africa), study has found Hylastes to be the most common A total of 157 adult beetles (Coleoptera: Cur bark beetle genus observed in loblolly pine stands culionidae) were collected from roots, most from in central Alabama (Thompson 2011), illustrating dying trees (Table 1). A majority of the beetles col their dominance in this ecosystem. Despite their lected were Hylastes species, including a total of dominance and potential for damage in loblolly 113 H. salebrosus (all from dying trees) and 34 pine, the breeding behavior of Hylastes species in H. tenuis (31 from dying and 3 from dead trees), the southeastern United States is not well underIn addition, H. salebrosus larvae and pupae were stood. In the current study, observational methcollected from dying trees. Other adult insect spe ods were used to investigate the potential for cies collected include the black turpentine beetle