Comparative efficacy of two controlled-release gypsy moth mating disruption formulations

The effects of aerial applications of the gypsy moth sex pheromone, disparl ure, on mating disruption and suppression of growth of populations of the g ypsy moth, Lymantria dispar (L.), were investigated. Two formulations of di sparlure, plastic laminate flakes applied in a single application and polym ethacrylate beads applied in two applications, were compared in two separat e tests conducted in 1993 and 1994. The beads were applied in two applicati ons spaced 2 weeks apart because preliminary tests had indicated that they released pheromone too rapidly to maintain adequate emission rates througho ut the period of male flight. In 1993, the flakes were applied at a rate of 50 g a.i./ha, and the beads were applied at a rate of 15 g a.i./ha for eac h application. In 1994, the flakes were applied at a rate of 75 g a.i./ha a nd the beads were applied at rates of 32.5 and 42.5 g a.i./ha for the two a pplications. Beads with larger average particle size were used in 1994 to p rolong disparlure release. The treatments applied in 1993 resulted in > 97% reduction in mating and > 82% suppression of population growth in the foll owing year. Because of a 1995 collapse of gypsy moth populations in the vic inity of the tests, reliable population growth data were not available for the treatments applied in 1994, but significant mating disruption did occur under both treatments. Based on measurements of residual disparlure after field aging, the flakes released 32 and 48% of their disparlure content dur ing the 6 weeks of male moth flight in 1993 and 1994, respectively. The sma ller beads used in 1993 released 75% of their disparlure content, and the l arger beads used in 1994 released 52% of their disparlure content, during t he 6 weeks of male flight. The biological efficacy data suggest that the be ad and flake formulations, as applied in these tests, have similar effects on gypsy moth mating disruption and subsequent population growth. Based on the observed release rates from both 1993 and 1994, a single application of the beads would provide emission rates equal to or greater than those prov ided by the flakes when applied at an equal dose.