Attraction of Scolytus unispinosus bark beetles to ethanol in water-stressed Douglas-fir branches

https://doi.org/10.1016/S0378-1127(00)00387-XGet rights and content

Abstract

Three similar-sized branches on each of seven Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) trees with a southern exposure were selected randomly to receive a water-stress, defoliation, or control treatment. All water-stressed branches were attacked by Scolytus unispinosus LeConte at 12–24 days after imposing the treatments, resulting in a significantly higher mean density of gallery holes (107 m−2) than in the defoliated or control branches, which were not attacked. Needles and woody tissues from stressed branches, sampled after being attacked, contained significantly higher ethanol concentrations (ranging from 2.91 to 15.26 μmol g−1 fresh weight) than tissue from defoliated or control branches (0.005–0.12 μmol g−1 fresh weight). Ethanol concentrations did not differ between defoliated and control branches. The water content in woody tissues and needles of stressed branches was 40.9 and 28.1% of the amount in control branches, respectively, when sampled for ethanol analysis. Woody tissues in defoliated branches remained moist, with 91.3% of the water in controls. Drying needles from water-stressed branches also lost 18.3–33.7% of their total monoterpenes compared to needles on the controls. The mechanism for ethanol synthesis in water-stressed branches appears to be distinctly different from that of logs overwintering on the forest floor. Ethanol synthesis in stressed branches probably was initiated by cytoplasmic acidification as a result of damage to cellular membranes from drying and heating. The ethanol that accumulated in needles and woody tissues of stressed branches functioned as a primary host attractant for S. unispinosus at our Willamette Valley, Oregon, site.

Introduction

The Douglas-fir engraver, Scolytus unispinosus LeConte (Scolytidae), is a non-aggressive or ‘secondary’ bark beetle that typically attacks weakened, dying, or recently dead Douglas-fir and occasionally other species of conifers (McMullen and Atkins, 1962, Furniss and Carolin, 1977). They usually colonize the stem and branches of crowns where the bark is thin, preferring crowns exposed to sunlight over crowns in the shade (Stoszek, 1973). Live trees weakened by drought stress may be attacked by S. unispinosus, depending on the tissue water potentials (Stoszek, 1973). These beetles were attracted to Douglas-fir stems with water potentials of −2.58 MPa, and colonization began at a threshold level of −2.94 MPa. Advanced egg galleries were observed in trees with water potentials exceeding −3.44 MPa. When the water status of drought stressed trees improved after rainfall, the S. unispinosus were trapped or ‘pitched out’ in their galleries by oleoresin flow (Stoszek, 1973).

In July of 1998, while setting up an unrelated experiment, the top 2–3 m from several Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) crowns were cut and left on the ground with full exposure to the sun. One week later we noted these crowns were being attacked by S. unispinosus. We analyzed a few tissue samples from the drying crowns and found high ethanol concentrations. Various species of secondary scolytids are attracted to ethanol, or ethanol plus host monoterpenes (Cade et al., 1970, Moeck, 1970, Klimetzek et al., 1986, Phillips et al., 1988, Chenier and Philogene, 1989, Liu and McLean, 1989, Schroeder and Lindelow, 1989, Lindelow et al., 1993; Kelsey, 1994a, Kelsey, 1994b; Kelsey and Joseph, 1997, Kelsey and Joseph, 1999a). Therefore, we hypothesized that ethanol might play a role in host selection by S. unispinosus. We designed the present experiment to examine the synthesis and accumulation of ethanol in rapidly drying Douglas-fir tissues and to determine whether ethanol is a primary host attractant for S. unispinosus.

Section snippets

Study site

This study was conducted in a Douglas-fir plantation (44°48′N, 123°17′30′′W), approximately 3.4 km south of Monmouth, Oregon. The site was planted in 1985 with 2-0 stock seedlings germinated from seed collected at various populations in western Oregon and Washington. The trees were planted in rows running north–south and east–west. When selected for this experiment they were 3.1 m apart and had a mean diameter of 17.7 cm±0.7 S.E. at breast height.

Treatments

On 31 July 1998, seven trees were selected from the

Ethanol concentrations

The woody tissues from stressed branches contained two and three orders of magnitude more ethanol than defoliated or control branches (both p≤0.002), respectively, whereas ethanol concentrations in the defoliated and control branches did not differ (p=0.382) (Fig. 1). In needles, ethanol was affected by treatment and needle age (Fig. 1). Current- and previous-year needles on stressed branches contained 182 and 24 times more ethanol (p<0.001 and 0.044), respectively, than control branches. On

Discussion

S. unispinosus attacked and colonized water-stressed Douglas-fir branches only if they contained high ethanol concentrations, thus providing strong evidence that ethanol functions as a primary attractant for this bark beetle. On 19 August, there were two stressed branches without beetle attacks, and they contained the lowest ethanol concentrations within this treatment. Five days later these two branches were attacked and the ethanol concentrations in their needles and woody tissues had

Acknowledgements

We thank Dr. R. Silen, PNW Research Station, for allowing us access to the Douglas-fir plantation. We thank Dr. K. Cromack and Dr. D. Ross from Oregon State University for comments and review of the manuscript. The use of trade names is for the information and convenience of the reader and does not constitute endorsement or approval by the US Department of Agriculture.

References (52)

  • R.G. Kelsey et al.

    Sapwood and crown symptoms in ponderosa pine infected with black-stain and annosum root disease

    For. Ecol. Manage.

    (1998)
  • R.C. MacDonald et al.

    Aerobic ethanol production by leaves: evidence for air pollution stress in trees of the Ohio River valley, USA

    Environ. Pollut.

    (1989)
  • J.A. Anderson

    Production of methanol from heat-stressed pepper and corn leaf disks

    J. Am. Soc. Hort. Sci.

    (1994)
  • J.A. Anderson et al.

    Ethylene production from wheat seedlings infested with biotypes of Schizaphis graminum (Homoptera: Aphididae)

    Environ. Entomol.

    (1994)
  • J.A. Beal

    Relation between tree growth and outbreaks of the black hills beetle

    J. For.

    (1943)
  • Bennett, D.C., Freeling, M., 1987. Flooding and the anaerobic stress response. In: Newman, D.W., Wilson, K.G. (Eds.),...
  • S.C. Cade et al.

    Identification of a primary attractant for Gnathotrichus sulcatus isolated from western hemlock logs

    J. Econ. Entomol.

    (1970)
  • J.V.R. Chénier et al.

    Field responses of certain forest Coleoptera to conifer monoterpenes and ethanol

    J. Chem. Ecol.

    (1989)
  • Cleary, B.D., 1971. The effect of plant moisture stress on the physiology and establishment of planted Douglas-fir and...
  • Cobb, Jr., F.W., Parmeter, Jr., J.R., Wood, D.L., Stark, R.W., 1974. Root pathogens as agents predisposing ponderosa...
  • F.C. Craighead

    The Dendroctonus problems

    J. For.

    (1925)
  • F.C. Craighead

    Bark-beetle epidemics and rainfall deficiency

    J. Econ. Entomol.

    (1925)
  • G.T. Ferrell

    Host selection by the fir engraver, Scolytus ventralis (Coleoptera: Scolytidae): Preliminary field studies

    Can. Entomol.

    (1971)
  • G.T. Ferrell

    Moisture stress threshold of susceptibility to fir engraver beetles in pole-size white firs

    For. Sci.

    (1978)
  • Ferrell, G.T., Hall, R.C., 1975. Weather and tree growth associated with white fir mortality caused by fir engraver and...
  • G.T. Ferrell et al.

    Indicators of Fomes annosus root decay and bark beetle susceptibility in sapling white fir

    For. Sci.

    (1976)
  • G.T. Ferrell et al.

    Predicting susceptibility of white fir during a drought-associated outbreak of the fir engraver, Scolytus ventralis, in California

    Can. J. For. Res.

    (1994)
  • Fischer, R.A., 1980. Influence of water stress on crop yield in semiarid regions. In: Turner, N.C., Kramer, P.J....
  • Furniss, R.L., Carolin, V.M., 1977. Western Forest Insects. Miscellaneous Publication No. 1339, USDA Forest Service,...
  • Gaff, D.F., 1980. Protoplasmic tolerance of extreme water stress. In: Turner, N.C., Kramer, P.J. (Eds.), Adaptation of...
  • Goheen, D.J., Hansen, E.M., 1993. Effects of pathogens and bark beetles on forests. In: Schowalter, T.D., Filip, G.M....
  • H.D. Hertert et al.

    Interaction of bark beetles (Coleroptera: Scolytidae) and root-rot pathogens in grand fir in northern Idaho

    Can. Entomol.

    (1975)
  • J.D. Hodges et al.

    Comparison of field techniques for measuring moisture stress in large loblolly pines

    For. Sci.

    (1971)
  • R.G. Kelsey

    Ethanol synthesis in Douglas-fir logs felled in November, January, and March and its relationship to ambrosia beetle attack

    Can. J. For. Res.

    (1994)
  • R.G. Kelsey

    Ethanol and ambrosia beetles in Douglas fir logs with and without branches

    J. Chem. Ecol.

    (1994)
  • R.G. Kelsey et al.

    Ambrosia beetle host selection among logs of Douglas fir, western hemlock, and western red cedar with different ethanol and α-pinene concentrations

    J. Chem. Ecol.

    (1997)
  • Cited by (48)

    • Ethanol and acetone from Douglas-fir roots stressed by Phellinus sulphurascens infection: Implications for detecting diseased trees and for beetle host selection

      2016, Forest Ecology and Management
      Citation Excerpt :

      However, it is important to note that low ethanol concentrations do not explicitly confirm the tree is disease free because of the many interacting factors influencing the rates of synthesis and subsequent dissipation. If ethanol escapes from stressed trees into the atmosphere in sufficient quantities and duration it can function, usually in combination with other volatiles released from the tree, as a signal that attracts various bark or ambrosia beetles to land and attack (Kelsey and Joseph, 2001, 2003; Kelsey et al., 2013, 2014; Ranger et al., 2013). Other compounds occur with ethanol in the headspace analysis of tree tissues and their concentration changes associated with pathogen infections may also function as biomarkers for detecting disease.

    View all citing articles on Scopus
    View full text