Mortality of mountain pine beetle larvae, Dendroctonus ponderosae (Coleoptera: Scolytidae) in logs of lodgepole pine (Pinus contorta var. latifolia) at constant low temperatures

Abstract

Mortality of mountain pine beetle larvae (Dendroctonus ponderosae Hopkins) in naturally in rested logs of lodgepole pine (Pinus contorta var. latifolia Douglas) held at constant low temperatures was investigated. The logs were brought to the laboratory in mid-fall and stored at -6.6°C for 10 weeks, then at -12.2°C for 2 weeks prior to the start of the experiments to allow the larvae to acquire maximum cold hardiness. The logs were exposed to constant temperatures or -1 7.8, -23.3, -28.8, and -34.4°C for 1, 2, 4, 8, 16, and 32 days. Mortality of larvae was recorded for two size classes: 1st- and 2nd-instar larvae and 3rd- and 4th-instar larvae. Mortality in logs stored at -12.2°C served as control. Mortality was negatively correlated with log diameter, bark thickness, brood density, and gallery length per m2, but only the correlation with log diameter was statistically significant. Mortality in both small and large larvae was inversely related to temperature and directly related to duration of treatment. Mortality of the small larvae was positively correlated to mortality of large larvae but mortality of the latter was significantly lower. Multiple regression was used to describe the relationship between temperature, duration of treatment, and log diameter for both larval groups. Results are discussed in relation to published in formation.

Key words: Dendroctonus monticolae; Scolytidae; Pinus contorta; mortality; low temperature; cold hardiness