Hylastes nigrinus

LeConte, 1868

Hylastes nigrinus is a root-feeding bark beetle in the Curculionidae ( Scolytinae) that breeds in the roots and stumps of Douglas-fir (Pseudotsuga menziesii), particularly in trees killed by Dendroctonus pseudotsugae. The exhibits strong temperature-dependent and light-influenced , with peak activity occurring in late afternoon or early evening. It is a suspected of the Verticicladiella wageneri, which causes black stain root . Development typically spans one year, with five larval instars and by both and mature larvae in galleries.

Pronunciation

How to pronounce Hylastes nigrinus: //hɪˈlæstiːz nɪˈɡrɪnəs//

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Habitat

Breeds in roots and stumps of Douglas-fir (Pseudotsuga menziesii), especially in trees killed by Dendroctonus pseudotsugae. Maturation feeding occurs on small roots of dead, old Douglas-fir and on roots of young Douglas-fir weakened after replanting. Reaches roots by digging through soil.

Distribution

North America: western United States (Oregon, California) and western Canada (British Columbia, Alberta, Yukon Territory, Northwest Territories).

Seasonality

Maximum and occur in late April and early May. Emergence seldom occurs at temperatures below 61°F or above 75°F. Flight peaks at light intensities of 300–1200 ft-c during late afternoon or early evening.

Diet

Phloem of Douglas-fir roots and stumps during larval development.

Host Associations

Pseudotsuga menziesii - primary Douglas-fir; breeding and feeding occur in roots and stumps
Dendroctonus pseudotsugae - facilitator-killed Douglas-fir trees are preferred for breeding

Life Cycle

galleries initiated in June, running parallel with the grain of the wood. Eggs laid from end of June. Five larval instars. and full-grown larvae overwinter in galleries. Majority of completes development in one year.

Behavior

Reaches roots by digging through soil. activity strongly affected by light intensity, peaking at 300–1200 ft-c during late afternoon or early evening. strongly temperature-dependent. Attracted to α-pinene, β-pinene, and Douglas-fir resin; prefers bark of insect-killed trees over cut trees, though healthy Douglas-fir bark becomes attractive after some time.

Ecological Role

Breeds in dead and dying Douglas-fir, contributing to decomposition of root systems. Competes with scolytid, curculionid, cerambycid, and buprestid in stumps and roots. Prey for larvae of Medetera vidua (Dolichopodidae), which can heavily decimate larval . Suspected of Verticicladiella wageneri, the causal agent of black stain root ; activity increases in thinned stands, potentially facilitating disease spread.

Human Relevance

Suspected of black stain root (Verticicladiella wageneri), a significant of Douglas-fir in managed forests. Activity increases following thinning operations, raising concerns for forest health management.