The Columbian Timber Beetle, Corthylus columbianus (Coleoptera: Scolytidae). I. Biology of the Beetle1

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Abstract
A technique was developed for rearing Corthylus columbianus Hopkins in the laboratory, and the eggs, larvae, and pupae are described. The maximum developmental period of field-collected eggs was 6 days; the larval period ranged from 12 to 15 days; and the pupal stage required 8–9 days at 75°F. The life cycle took 34–40 days under laboratory conditions, but rearing of field-collected eggs to adults at 75° indicated that a 26- to 30-day period may be possible under natural conditions. This species overwinters in its galleries, both as pupae and as adults. Slight male dominance was indicated by a sex factor of 0.4. Activity of the beetle in the laboratory was strongly influenced by the favorable moisture contents of 104.6%–114.0%, with moisture contents of the test blocks ranging from 89% to 138.4% at 75°F; the favorable temperature range was 70°–85°F. Laboratory tests showed that the beetles are photopositive. The minimum suceptible diameter and age of soft-maple hosts were 1.25 in. (dbh) and 9 years, respectively. Susceptibility of sapling hosts increases with diameters. Attacks were most concentrated (81.8%) in the basal 1 ft of the boles of 102 saplings examined. Cephalobid and aphelenchoidid nematodes, an unidentified mite, and dipterous larvae of the families Ceratopogonidae and Syrphidae were associated with the adult beetles and their galleries.

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