Mating Disruption of Gypsy Moth (Lepidoptera: Lymantriidae) Following Repeated Ground Application of Racemic Disparlure

Studies were conducted in Maryland between 1984 and 1988 using racemic disparlure to manage gypsy moth, Lymantria dispar (L.), populations at low levels. Laminated plastic dispensers were manually applied in 1984, 1986, and 1988 at a dose rate of 50 g (AI)/ha (release rate of 12.0 g/ha/yr; 100 release points/hal. Biological effects were measured as reduction of male trap catch in (+)-disparlure traps and mating of monitor females. Efficacy was measured by intensive annual egg mass surveys. Significant reductions in male trap catch and mating of females clearly demonstrated that the disruptant remained biologically active for two consecutive seasons. Nevertheless, egg mass surveys showed that repeated applications of racemic disparlure failed to maintain gypsy moth populations at low levels over the 5-yr period. We attributed lack of efficacy to inadequate levels of mating disruption during peak male activity, ineffective permeation of disruptant throughout the upper canopy of trees, and close proximity of treated woodlots to dense gypsy moth populations. Improvements in the efficacy of this technique might be achieved by higher application rates of plastic laminated tape, identification of formulations which deliver higher release rates (particularly during peak male flight) and use of this tactic only on isolated populations.