AN ELM BARK BEETLE BIOASSAY FOR RESIDUAL EFFICACY OF CHLORPYRIFOS ANDCYPERMETHRIN USED FOR THE CONTROL OF DUTCH ELM DISEASE IN MANITOBA

The basal 1 m of the elm trunks were treated with 0.48% (active ingred ient, Al) Dursban aqueous solution (chlorpyrifos) or 0.1% (Al) Ripcord aqueous solution (cypermethrin) for control of overwintering native e lm bark beetle, Hylurgopinus rufipes, the vector of Dutch elm disease, Ophiostoma (Ceratocystis) ulmi, at Beaudry Provincial Park, near Winn ipeg, Manitoba, Canada. A simple and effective bioassay method was dev eloped to determine insecticidal persistence against the native elm ba rk beetle. Beetles reared in naturally infested elm logs were confined to the surface of elm bark circles taken from the treated trees. Bark circles were cut at various times after treatment using a cordless ho le saw and stored at - 32 degrees C until the beetles were available. Mortality/morbidity data for the two treatments were suitable for use in the comparison of the action of the two insecticides over a two-yea r period.