Male moths locate females by navigating along her pheromone plume, often flying hundreds of meters en route. As the first male to find a calling female is most apt to be her mate, this can be termed “a race to find the female” and it is assumed to be under strong selective pressure for efficiency and rapidity. Locating a distant, odor-linked resource involves two strategies. The first is to contact the outer envelope of the odor plume. When wind direction is relatively invariant, the plume stretches and then crosswind flights may be favored, although when wind direction shifts over 60°, upwind and downwind paths may be optimal. Alternatively, the path may be random with respect to the direction of wind flow, with periodic changes in direction, as in either Lévy or Random Walks. After first detecting the pheromone, a second strategy follows: moths navigate along the plume by heading upwind when the pheromone is detected, with crosswind casting to re-establish contact if the plume is lost. This orientation path is not straightforward in nature, however, because atmospheric turbulence fragments the plume, thereby creating large odor gaps. Furthermore, a shifting wind direction can lead the responder out of the plume. One way to explore which strategies are optimal for enabling initial contact with the plume and subsequent navigation is through modeling of plumes’ dispersal and of insects’ flight strategies. Our simulations using the flight characteristics of the male gypsy moth (Lymantria dispar) suggest that search strategies similar to Lévy Walks are most apt to result in a high probability of contact with plumes. Although a searching trajectory aimed predominately crosswind performed almost as well as those with a random orientation when wind direction was relatively stable, downwind biased trajectories were least successful. A random orientation with respect to immediate wind flow, as used in our simulations of Lévy and Random Walks, seems optimal both for initial discovery of the plume and likelihood of locating an odor source. In the two available direct field observations, moths adopted a random orientation with respect to concurrent wind direction.

In a wind tunnel trifluoromethyl ketones (TFMKs) have been found to disrupt the orientation flight of male moths to pheromone sources (virgin females or synthetic pheromone). This is demonstrated by comparison of the flight parameters of the Egyptian armyworm Spodoptera littoralis and the Mediterranean corn borer Sesamia nonagrioides, which had been topically treated with TFMKs, with those calculated for untreated insects. Inhibition occurred in all types of behavior and that of the source contact has been quantified and found to be dose-dependent. The same effect has also been noticed in Mediterranean corn borer males flying to an attraction source consisting of mixtures of (Z)-11-hexadecenyl trifluoromethyl ketone ( 8), a closely related analogue of the major component of the pheromone, and the natural pheromone blend. The most active TFMKs are those closest in structure to the natural pheromone, along with those chemicals which easily hydrate in solution, such as theβ -thiosubstituted derivatives. Along with the previously reported reduction of catches in the field, our results suggest the possible application of these chemicals in future new pest control strategies.

Trains of 20-ms-duration pulses of pheromone were delivered at rates of 1–33 Hz to antennal preparations of males of Bombyx mori and Lymantria dispar, two moth species with bipectinate antennae. Resolution of rapidly pulsed plumes of pheromone was not compromised by a complex antennal morphology or by moderate changes in wind speed (25–50 cm/s). Fourier analysis of the electroantennograms resolved the temporal structure of the signal at frequencies up to 25 Hz for B. mori and up to 5 Hz for L. dispar. The ability of these sensory structures to identify the original (unchanged) frequency of the pulse train is particularly noteworthy because air is slowed by about an order of magnitude as it passes through bipectinate antennae. Although an unchanging frequency in slowed airflow may be counterintuitive, this flow pattern, and its effects on odorant patch shape and spacing, is explained from fluid mechanical principles (i.e., the principle of continuity). An unchanging frequency suggests that as decelerating air passes through a bipectinate antenna, the slowed patches of odorant are stretched, thinned, and brought closer together by the same factor with which they are slowed.

Delta- and bucket-style (Universal or Unitrap) traps baited with 1 standard survey lure and 1/3 and 3 lures were compared for their attractiveness and trapping efficiencies for gypsy moth, Lymantria dispar L. (Lepidoptera: Erebidae), males. With bucket traps, the numbers of males attracted to within 2 m of traps and the proportion of these actually captured were identical among the three doses although the percentage of attracted males actually captured in bucket traps was low, less than 15%. A three-lure delta trap attracted about 70% more males than traps with the two lower doses. Capture efficiencies were above 80% for 1/3- and one-lure traps and about 60% for traps baited with three lures. The number of males captured in delta traps was equivalent for the three doses although our observations also suggest that a delta trap baited with three lures drew males from a wider range than lower dose lures and therefore would be a more sensitive trap for detecting incipient populations. We also noted that males tended to arrive in clusters, suggesting that attraction over moderate distances requires periods when the wind direction is fairly constant. This observation coupled with the great variability in the direction of male arrival to the traps also suggests that important changes in the area of influence of the plume are driven in such forested areas by slower but greater changes in wind direction compared with open habitats.