Byers, J.A., Svihra, P., & Koehler, C.S. 1980. Attraction of elm bark beetles to cut limbs on elm. Journal of Arboriculture 6:245-246.

Scolytus multistriatus feeding in Elm twig crotch
Abstract-- The smaller European elm bark beetle, Scolytus multistriatus, vector of the Dutch elm disease fungus, is attracted to pruned limbs of European and Siberian elm compared to healthy, non-pruned limbs. To minimize the spread of Dutch elm disease it is suggested that pruning of elm limbs be undertaken during the fall and winter when bark beetle activity is reduced or absent. (photo: elm bark beetle feeding in twig crotch of European elm)
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Chemical Ecology