Smaller European Elm Bark Beetle Elm Bole Bioassay Tests, 1976

The boles of nursery-grown American elms, Ulmusamericana L., (10-15 cm in dbh) were treated with 4 insecticides from June 7-10, 1976, to determine the percentage of mortality among smaller European elm bark beetles attracted to Multilure (pheromone) baits attached to these boles. The experiment was a 2 x 3 x 8 factorial design. The treatment factors were 2 insecticide concentrations (3 and 12%), 3 beetle exposure times (5, 20, and 60 sec), and 8 bioassay periods (every 2 weeks for 16 weeks). Each combination was replicated 3 times. Insecticides were sprayed on the elm boles to the point of runoff; a Hudson 67609 hand sprayer was used to apply the insecticides. The mean temperature was 16.1°C (range: 2.2 to 35.0°C), and total rainfall was 39.4 cm during the study. At the appropriate posttreatment interval, phototoxicity was determined, the trees were felled, and a 30.5-cm bole section was removed from each tree. Bioassays were conducted by placing 20 newly emerged beetles on each bole section with vacuum forceps (1 beetle at a time for each exposure). After each exposure, beetles were removed, placed on filter paper in plastic petri dishes (15 x 100 mm), and held in darkness for 24 h at 30 - 1°C and 92 - 2% RH before mortality was determined. Mortality was pooled and averaged for all 3 exposure times at each concentration, because there were no significant differences in mortality among exposure times. LC50 and LC90 values were determined by interpolation.