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Biology of Gnathotrichus sulcatus (LeConte 1868) (Col.:Scolytidae) with special emphasis on host colonization and brood production

University of British Columbia

The bionomics of Gnathotrichus sulcatus (LeConte) (Col.: Scolytidae) were studied on eight western hemlock (WH), Tsuga heterophylla (Raf.) Sarg., and eight Douglas-fir (Df), Pseudotsuga menziesii (Mirb.) Franco, trees at the UBC Research Forest, Maple Ridge, B.C. during 1978 and 1979. Natural colonization by associated scolytid beetles was also studied on the same trees, which were felled on May 8, 1978. More attacks occurred on downtrees (with branches.) than on logs (no branches), and on WH stumps, trunks (logs and down-trees) than on Df stumps and trunks. WH was more suitable for colonization and brood production in the first year after felling than Df but no differences could be demonstrated between these two hosts in the second year. Whenever possible five fresh attacks were covered with petri dishes on every stump and trunk. Higher quantities of frass, numbers of brood, pupal niches, deeper penetration and longer galleries were recorded on WH than on Df. Relationships between brood, frass production and length of galleries were established. It was calculated that one hectare of clearcut with 200 WH stumps could produce 714,860 ± 417,020 beetles with 13.7 ± 3.7 brood per gallery (both with 95% confidence limits), within two years after attack, while the estimated total brood production from the 16 trunk/stump combinations was 107,080 from 16,049 attacks. Pupal niches, length and depth of penetration of galleries were studied on attacks initiated two to seventeen months after felling, excluding the winter months. For each of the three factors WH showed higher results than Df. Traps set out in Point Roberts, Washington, captured more beetles when baited with WH sapwood than with WH bark or heartwood. More beetles were captured on traps baited with Df phloem than those baited with Df bark, sapwood or heartwood. These results indicate which tissues might be extracted to determine the identity of primary attractants. It was concluded that WH is preferred as a host tree over Df by G. sulcatus during the first year, but both hosts had similar number of attacks in the second year. Such preference for WH poses a problem for logging managers in coastal British Columbia since WH is 40% of the total volume processed. If G. sulcatus populations are allowed to build up in stumps, they could degrade logs in felled and bucked timber in adjacent areas. WH should be removed as soon as possible after felling (hot logging) and the period in dryland sorts should be minimized as logs remain vulnerable to attack 17 months following felling.

Text

2010-03-30

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http://hdl.handle.net/2429/23038

Forestry

University of British Columbia

Graduate