Smaller European elm bark beetle galleries
James Solomon, USDA Forest Service
Smaller European Elm Bark Beetle
Overland spread of Dutch elm disease (DED) is closely linked to the life cycles of the native elm bark beetle and the smaller European elm bark beetle. Both beetles are attracted to stressed, dying, or dead elm wood to complete the breeding stage of their life cycle
Keywords: beetle, Coleoptera, elm, Ulmus species, Dutch elm disease, fungus, sticky spores, Ophiostoma ulmi, galleries
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Smaller European elm bark beetles overwinter as larvae or adults within the stem of the tree where they hatched. They emerge as adults in spring to feed in twig crotches of healthy trees, where they can introduce spores of the DED fungus (Ophiostoma ulmi) to the crown. High numbers of beetles frequently will feed in a single tree, resulting in multiple points of infection. The cycle is repeated when beetles then seek out diseased and dying wood to breed in throughout the growing season, completing two or more generations per year. Adults tunnel into the bark and lay their eggs in inner bark galleries. The eggs hatch and larvae feed in the inner bark and sapwood. If the DED fungus was present in the wood that the beetles infested, the fungus produces sticky spores in the beetle galleries. Spores of the DED fungus are eaten by or stick to the adult beetles as they emerge from diseased trees. Once the DED fungus is introduced into the upper crown of healthy elms by bark beetles, it slowly moves downward, killing the branch as it goes. Disease progression may occur rapidly, killing the tree by the end of the growing season, or may progress gradually over a period of two or more years.