© 2005 The Netherlands Entomological Society Entomologia Experimentalis et Applicata 115: 355–361, 2005 355 Blackwell Publishing, Ltd. Optimization of pheromone dosage for gypsy moth mating disruption Ksenia S. Tcheslavskaia 1 , Kevin W. Thorpe 2 , Carlyle C. Brewster 1 , Alexei A. Sharov 3 , Donna S. Leonard 4 , Richard C. Reardon 5 , Vic C. Mastro 6 , Patricia Sellers 7 & E. Anderson Roberts 1 1 Department of Entomology, Virginia Tech, Blacksburg, VA 24061, USA; 2 USDA, Agricultural Research Service, Beltsville, MD 20705, USA; 3 249 Ullman Road, Pasadena, MD 21122, USA; 4 USDA, Forest Service, Asheville, NC 28802, USA; 5 USDA, Forest Service, Morgantown, WV 26505, USA; 6 USDA, APHIS, Otis ANGB, MA 02542, USA; 7 USDA, Forest Service, Harrisonburg, VA 22801, USA Accepted: 22 December 2004 Key words: Lymantria dispar, Lepidoptera, Lymantriidae, pheromone, Hercon Disrupt® II plastic flakes, disparlure, dosage response, forest pest Abstract The effect of aerial applications of the pheromone disparlure at varying dosages on mating disruption in low-density gypsy moth, Lymantria dispar (L.) (Lepidoptera: Lymantriidae), populations was determined in field plots in Virginia, USA during 2000 and 2002. Six dosages [0.15, 0.75, 3, 15, 37.5, and 75 g active ingredient (AI)/ha] of disparlure were tested during the 2-year study. A strongly positive dose–response relationship was observed between pheromone dosages and mating disruption, as measured by the reduction in male moth capture in pheromone-baited traps and mating successes of females. Dosages of pheromone ≥ 15 g AI/ha (15, 37.5, and 75 g AI/ha) reduced the mating success of females by >99% and significantly reduced male moth catches in pheromone-baited traps compared to untreated plots. Pheromone dosages <15 g AI/ha also reduced trap catch, but to a lesser extent than dosages ≥ 15 g AI/ha. Furthermore, the effectiveness of the lower dosage treatments (0.15, 0.75, and 3 g AI/ha) declined over time, so that by the end of the study, male moth catches in traps were significantly lower in plots treated with pheromone dosages ≥ 15 g AI/ha. The dosage of 75 g AI/ ha was initially replaced by a dosage of 37.5 g AI/ha in the USDA Forest Service Slow-the-Spread (STS) of the Gypsy Moth management program, but the program is currently making the transition to a dosage of 15 g AI/ha. These changes in applied dosages have resulted in a reduction in the cost of gypsy moth mating disruption treatments. Introduction The management of populations of the gypsy moth, Lymantria dispar (L.) (Lepidoptera: Lymantriidae), by mating disruption has been attempted since 1971 (Stevens & Beroza, 1972; Schwalbe et al., 1974; Granett & Doane, 1975). During the last 20 years extensive research has been conducted towards finding an appropriate formulation (e.g., Plimmer et al., 1982; Thorpe et al., 1999) and dosage (e.g., Webb et al., 1988) of the gypsy moth pheromone, disparlure, for use in mating disruption. Studies have shown that for mating disruption to be successful, the pheromone must be released slowly at a constant rate and be present in the air in sufficient quantities for the entire period during which the moths are sexually active (Cardé et al., 1975; Howse et al., 1998; Reardon et al., 1998). Thus far, the Hercon Disrupt® II plastic flake formulation of disparlure is a gypsy moth mating disruption product that satisfies the above criteria, and this formulation is therefore currently in use in the USDA Forest Service Slow-the-Spread (STS) of the Gypsy Moth program (Reardon et al., 1998; Sharov et al., 2002b). In one of the earliest dose–response experiments to be conducted (Webb et al., 1988), Hercon Disrupt® II was applied aerially at dosages of 7.5, 30, and 75 g active ingredient (AI)/ ha. A strong negative relationship was observed between pheromone dosage and male moth response to pheromone- baited traps and females. The large number of males that were trapped suggested that the study was conducted in an * Correspondence: Department of Entomology, 202 Price Hall, Virginia Tech, Blacksburg, VA 24061-0319, USA. Tel.: +1 540 231 9623; Fax: +1 540 231 9131; E-mail: ktchesla@vt.edu