S. multistriatus, the smaller European elm bark beetle (EBB) may be the more significant of these two species (over the native elm bark beetle; EBB) due to reproductive advantages this species has over our native counterpart (and subsequently higher populations). The adult smaller European EBB is 1.9-3.1 mm. in length, although our native EBB (H. rufipes) is 2.2-2.5 mm. long. The European EBB is shiny and reddish-brown in color. Our native EBB is duller in color, brown, with a rough appearance to the body. Although the European species is referred to as the smaller European EBB, when in relation to our native species, it is actually larger. (The adult.) The eggs, larvae, and pupae of both species are indistinguishable in the field unless well developed galleries are present and can be compared. The egg-laying galleries of our native elm bark beetle cross the grain of the wood whereas those of the European elm bark beetle follow parallel to the grain of the wood. The native EBB can overwinter as a fully mature larva in dying trees or as an adult in the bark of the trunk or larger branches in living elm trees. Adults appear in May and construct egg-laying galleries in dying or recently dead trees. 2+ generations may occur per year. The European EBB was first detected in 1904 near Boston and has since spread across the US and Canada. This non-native insect can overwinter as a nearly to full-grown larva in the inner bark of its host. Larvae develop and pupate by mid-May. Adults will emerge over an extended period of time, lasting several weeks. Adults preferentially feed in the crotches of young branches. Mature females will seek stressed elm trees to lay their eggs in. The female will bore into bark of the trunk or larger branches and prepares her egg laying gallery. Two or more generations of the European EBB can occur per year, except in the furthest north locations where the European EBB has dispersed, where only one generation may occur per year.
Most significantly, these two species are vectors of the pathogen of Dutch Elm Disease, Ophiostoma novo-ulmi. The smaller European elm bark beetle may be capable of more damage to the host. This species prefers open-grown trees in parks, streets, and residential landscapes. Beetles prefer feeding in the crown in the bark of twig crotches, particularly on rapidly growing trees. Also bark of elm trunks. Healthy and declining plants will be attacked, although those with recently pruned limbs, broken branches, or suffering drought stress may be prioritized. Terminal shoots wilt and yellow, dieback occurs, and galleries are seen beneath the bark.
Pheromone traps are available for monitoring adult activity from certain retailers. It is suggested that they should be hung by March 1st to begin monitoring. Visual inspection of the crowns of elm trees for yellowing, flagging, or dieback can be done in May.
Remove dead and diseased elms and destroy prior to beetle emergence. Beetles can breed in elm logs. Prune out any infested branches displaying yellowing and flagging. Routine pruning should occur in the dormant season to prevent attraction of beetles to wounds. Maintain tree health, watering and fertilizing as necessary. Trees showing symptoms of Dutch Elm Disease need immediate treatment (see: UMass Extension's Professional Management Guide for Diseases of Trees and Shrubs).
Certain American elm cultivars are reported as resistant to Dutch Elm Disease, including but not limited to: 'New Harmony', 'Valley Forge', and 'Princeton'.
No effective parasites are reported. Past efforts to establish biological control organisms for the smaller European elm bark beetle (Scolytus multistriatus) have occurred. In 1965, a braconid wasp, Dendrosoter protuberans, was introduced from Europe. Millions of individuals were released in infested areas, and the species was considered to be widely established.
Additional natural enemies of Scolytus multistriatus have been reported in Europe. The species is susceptible in the laboratory to many different pathogenic fungi and nematodes. In laboratory and field studies, pathogenic nematodes are capable of killing all stages of the smaller European elm bark beetle, and certain nematode species sterilize the adults. Additional braconid wasps, either Coeloides scolyticida or D. protuberans, have been identified as the principal parasitoids in Europe.
Abamectin (NL)
Azadirachtin (NL)
Beauveria bassiana (NL)
Bifenthrin (NL)
Carbaryl (L)
Chlorpyrifos (N)
Cyantraniliprole (NL)
Cypermethrin (NL)
Deltamethrin (L)
Emamectin benzoate (L)
Flonicamid+cyclaniliprole (N)
Imidacloprid (L)
Isaria (paecilomyces) fumosoroseus (NL)
Lambda-cyhalothrin (L)
Neem oil (NL)
Permethrin (L)
Tau-fluvalinate (NL)
Zeta-cypermethrin (L)
Make insecticide applications after bloom to protect pollinators.
Active ingredients that may be applied systemically include: abamectin (injection), cyantraniliprole (soil drench, soil injection), neem oil (soil drench), and emamectin benzoate (injection).
Applications at times of the day and temperatures when pollinators are less likely to be active can also reduce the risk of impacting their populations.
Note: Beginning July 1, 2022 neonicotinoid insecticides are classified as state restricted use for use on tree and shrub insect pests in Massachusetts. For more information, visit the MA Department of Agricultural Resources Pesticide Program.
