Lewis and Macaulay“ studied the nature of the pheromone plume emitted by several trap designs by using smoke plumes and determined the relative efficacy of the trap plumes by pheromone trapping of the pea moth, Cydia nigricana (Stephens). In general, the longer the plume emitted by a trap, the greater the catch.
Of five designs, a triangular trap caught the most moths. However, all traps, including the triangular design, were quite inefficient, capturing only 20 to 30% of males landing on them. Using night vision equipment, Lingren et al.”‘ made repeated direct observations of males of several species of Lepidoptera as they interacted with pheromone plumes released from pheromone traps according to gay pheromones review 2016 | http://pheromones-planet.com
Males flew crosswind until they encountered a plume, and then flew upwind to the trap. Maximum effective plume length seemed to be about 15 m when conditions were favorable, but the effective length varied with meteorological conditions, such as wind and relative humidity. Pheromone rap efficiency varied with moth species, trap design, and pheromone source used but was always low according to http://thongchaimedical.org/?p=176
No more than 34% of male moths orienting to a pheromone trap were caught by the trap, and at least one combination yielded an efficiency of only 0.4%. However, this work was usually done when populations were high, and short range searching may be more important, making traps less efficient. The pheromone dose received by a moth is related to the concentration of the pheromone and the rate of flow across its antennas.
There is evidence that each particular species of moth responds to an optimum concentration of pheromone, and that the range of concentrations evoking similar responses might be large. As pointed out by Cardé,‘ gross increases of pheromone concentrations may result in only slight increases in moth catch or can possibly even decrease catches. As an example for the bertha armyworm, Mamestra configurata Walker, the active space may have a radius of only 10 to 20 m.“‘° The optimum pheromone concentration must be relatively high for this species. On the other hand, Bossert and Wilson” have calculated that, at an optimum windspeed of I00 cm/sec, a pheromone plume from a single gypsy moth can reach 4560 m downwind. Although the assumptions of Bossert and Wilson have been challenged,”’ the wide range of concentration of pheromone that produces equivalent trap catch“ indicates that the active space of a pheromone trap for this species may extend a considerable distance. Jahn”“ found that males of the closely related “nun moth” Lymantria monacha (L.) were lured to females from as far as 85 m and were attracted by synthetic racemic pheromones from as far as 200 m. Wind speed profoundly affects the active space of a trap. Learn at http://weebly.com/
Interestingly. these workers found that the active space increased proportionally with increased emission rate of pheromone. Therefore, in theory, it should be simple to create a situation where a trap outcompetes a female simply by loading the trap dispenser with additional pheromone, thereby increasing the active space of the trap over and above that generated by pheromone emission of the female. In fact, artificially high rates of emission may not provide increased trap catch because the optimum rate needed for close-range orientation may be exceeded.