Differentiation of Competitive vs. Non-competitive Mechanisms Mediating Disruption of Moth Sexual Communication by Point Sources of Sex Pheromone (Part 2): Case Studies

Abstract

Eleven out of 13 disruption profiles (plots of dispenser density vs. male catch) from moth sex pheromone literature were consistent with a competitive-attraction mechanism, in which dispensers attract males and thereby divert them from females. Mean dispenser activity (D(a)) across all competitive-attraction cases was 0.04 +/- 0.06 (SD); values ranged from 0.0005 for a tiny laminated flake dispenser of racemic disparlure targeting gypsy moth to 0.2 for polyethylene tube dispensers used against lightbrown apple moth. A dispenser application activity (D(Aa)) can be calculated by multiplying D(a) by the number of such dispensers applied per hectare of crop. The highest dispenser application activity (D(Aa)) values approached 200 and corresponded to >99% inhibition of catches of male moths in monitoring traps. Relative to the D(Aa) scale, % inhibition of catches of male moths compressed and obscured large differences in D(Aa) when % disruption exceeded 90%. For cases of competitive attraction, these two efficacy scales can be interconverted by using the formula: D(Aa) approximately = 100/(100 minus % disruption). When disruptive point sources of pheromone were directly observed, male moths were seen approaching pheromone dispensers whose disruption profiles matched competitive attraction. Two cases fit non-competitive disruption mechanisms, which include camouflage, desensitization (adaptation and/or habituation), and sensory imbalance. In these cases, pheromone was released at rates higher than for cases of disruption by competitive attraction. Practical ramifications of the finding that competitive attraction appears to be the prevalent mechanism for moth mating disruption by pheromone point sources are listed. We believe that the congruence of diverse sets of mating disruption field data with explicit a priori predictions validates competitive-attraction theory. The analytical tools and principles governing competitive attraction that were uncovered during this study of mating disruption of moths should be generally applicable to competitive-attraction phenomena.