Spodoptera exigua: Mating disruption, measurement of airborne concentration of pheromone, and use of specialist receptor cell responses for comparison to female pheromone emission

Field experiments were conducted to evaluate Shin-Etsu Yoto-con-S(R) 'rope' pheromone dispensers applied at different site densities in cotton to dete rmine efficacy in disrupting sexual communication and mating of beet armywo rm moths, Spodoptera exigua (Hubner); obtain atmospheric measurements of th e disruptant pheromone components in and away from treated areas; and relat e this information to estimates of the concentration of pheromone in the ne ar vicinity of a calling virgin female moth. The number of pheromone-dispen sing sites/ha ranged from 25 with 20 ropes/site up to a total of 247 sites with 2 ropes each. A total of 112 g pheromone of a 70:30 blend of (Z,E)-9,1 2-tetradecadien-1- ol acetate (ZETA) and (Z)-tetradecen-1-ol (Z9-14:OH) was applied/ ha. As few as 25 sites/ha effectively disrupted sexual communicat ion by 91%, as measured by reductions of moth captures in traps baited with pheromone lures, and mating by beet armyworm females by 94% for at least 1 0 weeks post-treatment. The results compared favorably to an earlier large- scale field experiment in which beet armyworm larval populations were reduc ed 95% using 500 pheromone-dispensing sites/ha (two ropes/site) and 160 g t otal pheromone/ha. The airborne concentration of ZETA and Z9-14:OH measured within the pheromone-treated plots that disrupted mating was 1.5 x 10(-13) M and 1.2 x 10(-13) M, respectively. The airborne concentration of ZETA an d Z9-14:OH in the vicinity of a female was estimated (by excision and elect rophysiological methods) to range between 2.1 x 10(-11) M and 2.4 x 10(-12) M, respectively, in a 1.6 km / h (1 mph) wind speed. Thus, the average ZET A concentration in the treated plots was about 140 times less than that exp ected from a single female; the average Z9-14:OH in the treated plots was a bout 20 times less. The data support an argument that disruption of mating by beet armyworm resulted from an imbalance in sensory input because mating was almost completely disrupted in all of the plots for at least 10 weeks with a mixture of ZETA:Z9-14:OH that differed significantly with that from excised female sex pheromone glands. Estimates of these parameters provide a benchmark for the requisite pheromone concentration in the atmosphere to achieve a high level of mating disruption for beet armyworm and possibly ot her insect pest species.