Factors Affecting Suitability ofQuercus rubraas Hosts forEnaphalodes rufulus(Coleoptera: Cerambycidae)

Abstract

Epidemic populations of Enaphalodes rufulus (Haldeman), red oak borer, a native longhorned wood boring beetle, were implicated as a major contributor to a recent widespread oak mortality event in the Ozark National Forest of Arkansas. We assessed potential factors affecting suitability of a primary host Quercus rubra L., northern red oak, which experienced dieback and mortality throughout two successive borer cohorts. We sampled trees with various E. rufulus infestation levels during 2001-2003 when populations were at outbreak levels and 2003-2005 when borer numbers were declining. We measured phloem thickness and calculated a vigor index; the ratio of the past 5-yr basal area increment to sapwood area. We also counted established first year larval feeding galleries and outer-bark adult emergence holes and measured surface area of feeding galleries on a subset of Q. rubra to assess the importance of host susceptibility versus suitability. Phloem thickness did not exhibit any patterns among hosts of varying infestation levels and was therefore not likely an important factor limiting larval success. Less vigorous Q. rubra appeared to be the most suitable hosts, although it is unclear whether reduced vigor was initially caused by stress of E. rufulus infestation or environmental factors. Host suitability seems to be more important than host susceptibility, as numbers of initiated galleries were not consistently different among host infestation classes and between both cohorts, whereas numbers of emerging adults did differ predictably among host infestation classes.

Emergent insects, pathogens and drought shape changing patterns in oak decline in North America and Europe

“…Oaks with low C reserves were more attractive to and readily colonized by A. bilineatus (Dunn et al, 1987(Dunn et al, , 1990. Oaks with poor vigor (Haavik et al, 2010), and reduced capacity for compartmentalization and formation of callus tissue (wound periderm), were most likely to be colonized by E. rufulus . Vigorous growth to tolerate attack by biotic agents, formation of tyloses, and other mechanisms used by hardwoods to compartmentalize and heal wounded vascular tissue could require substantial C investment, certainly in excess of that needed for maintenance and repair processes following drought.…”

“…2000), and, associated with these conditions, specific variables that were investigated. Haavik et al (2010Haavik et al ( , 2008, Haavik and Stephen (2011) severe'' infestation), likely as a consequence of extensive feeding by E. rufulus larvae in phloem and xylem tissues (Haavik et al, 2008).…”

Stand and individual tree characteristics associated with Enaphalodes rufulus (Haldeman) (Coleoptera: Cerambycidae) infestations within the Ozark and Ouachita National Forests

“…Larval galleries leave exactly dateable scars within host tree-rings (Muzika and Guyette, 2004;Haavik and Stephen, submitted for publication), and counts of these scars dated to the outbreak time period were used to estimate infestation at the site level. To determine individual tree infestation densities, counts of scars or an indicator of second year larval survival may be useful as host suitability is likely to be more important during larval development within trees than susceptibility at initial colonization (Haavik et al, 2010).…”

Fertilization of lodgepole pine trees increased diameter growth but reduced root carbohydrate concentrations

“…They argued that high concentrations of soluble carbohydrates have been measured in the sapwood of stressed lodegepole pine trees despite very low radial growth rates (Webb, 1981) and therefore stem growth must be a lower priority than storage (Waring and Pitman, 1985;Waring and Schlesinger, 1985). On this basis, vigor index and growth efficiency have been widely used to predict and explain tree susceptibility to insects and pathogens (Coops et al, 2009;Haavik et al, 2010;Lieutier et al, 1993;Waring and Pitman, 1985;Waring et al, 1992).…”