Response of the european elm bark beetle,Scolytus multistriatus, to host bacterial isolates.

The response of the European elm bark beetle,Scolytus multistriatus, to host bacterial isolates was studied qualitatively under field conditions. Initial experiments indicated that such isolates were attractive to in-flight beetles. These isolates, identified asBacillus subtilis (five strains),B. pumilus, andEnterobacter cloacae, were grown on nutrient agar in glass vials and attached to sticky traps in elm woods. Although beetles were caught on the bacterial isolate-baited traps, the catches were variable, inconsistent, and often contradictory from one experiment to another. High numbers ofS. multistriatus were caught on traps baited with three strains ofB. subtilis, but in addition to thesubtilis strains, there were also aerial contaminants in the treatments, namelyE. aerogenes, Corynebacterium sp., andFlavobacterium sp. Also, relatively high catches were recorded on nutrient agar controls. When elm wood-bark plugs, sterilized (by gamma irradiation) and unsterilized, were placed in vials with the host bacterial isolates, the presence or absence of fresh elm, gamma irradiated or not, had no noticeable effect on beetle attractancy.