How flies are flirting on the fly.

BACKGROUND: Flies have some of the most elaborate visual systems in the Insecta, often featuring large, sexually dimorphic eyes with specialized "bright zones" that may have a functional role during mate-seeking behavior. The fast visual system of flies is considered to be an adaptation in support of their advanced flight abilities. Here, we show that the immense processing speed of the flies' photoreceptors plays a crucial role in mate recognition. RESULTS: Video-recording wing movements of abdomen-mounted common green bottle flies, Lucilia sericata, under direct light at 15,000 frames per second revealed that wing movements produce a single, reflected light flash per wing beat. Such light flashes were not evident when we video-recorded wing movements under diffuse light. Males of L. sericata are strongly attracted to wing flash frequencies of 178 Hz, which are characteristic of free-flying young females (prospective mates), significantly more than to 212, 235, or 266 Hz, characteristic of young males, old females, and old males, respectively. In the absence of phenotypic traits of female flies, and when given a choice between light emitting diodes that emitted either constant light or light pulsed at a frequency of 110, 178, 250, or 290 Hz, males show a strong preference for the 178-Hz pulsed light, which most closely approximates the wing beat frequency of prospective mates. CONCLUSIONS: We describe a previously unrecognized visual mate recognition system in L. sericata. The system depends upon the sex- and age-specific frequencies of light flashes reflecting off moving wings, and the ability of male flies to distinguish between the frequency of light flashes produced by rival males and prospective mates. Our findings imply that insect photoreceptors with fast processing speed may not only support agile flight with advanced maneuverability but may also play a supreme role in mate recognition. The low mating propensity of L. sericata males on cloudy days, when light flashes from the wings of flying females are absent, seems to indicate that these flies synchronize sexual communication with environmental conditions that optimize the conspicuousness of their communication signals, as predicted by sensory drive theory.

Total Synthesis, Stereochemical Assignment, and Field-Testing of the Sex Pheromone of the Strepsipteran Xenos peckii.

The sex pheromone of the endoparasitoid insect Xenos peckii (Strepsiptera: Xenidae) was recently identified as (7E,11E)-3,5,9,11-tetramethyl-7,11-tridecadienal. Herein we report the asymmetric synthesis of three candidate stereostructures for this pheromone using a synthetic strategy that relies on an sp(3) -sp(2) Suzuki-Miyaura coupling to construct the correctly configured C7-alkene function. Comparison of (1) H NMR spectra derived from the candidate stereostructures to that of the natural sex pheromone indicated a relative configuration of (3R*,5S*,9R*). Chiral gas chromatographic (GC) analyses of these compounds supported an assignment of (3R,5S,9R) for the natural product. Furthermore, in a 16-replicate field experiment, traps baited with the synthetic (3R,5S,9R)-enantiomer alone or in combination with the (3S,5R,9S)-enantiomer captured 23 and 18 X. peckii males, respectively (mean±SE: 1.4±0.33 and 1.1±0.39), whereas traps baited with the synthetic (3S,5R,9S)-enantiomer or a solvent control yielded no captures of males. These strong field trapping data, in combination with spectroscopic and chiral GC data, unambiguously demonstrate that (3R,5S,9R,7E,11E)-3,5,9,11-tetramethyl-7,11-tridecadienal is the X. peckii sex pheromone.

(7E,11E)-3,5,9,11-Tetramethyltridecadienal: Sex Pheromone of the Strepsipteran Xenos peckii.

Xenos peckii is a strepsipteran parasitoid of the common North American paper wasp, Polistes fuscatus. Mate-seeking X. peckii males respond to a long-range sex pheromone emitted by the female, which remains permanently embedded within the abdomen of a mobile host wasp. During peak pheromone signalling, we excised the female from her host, severed the cephalothorax containing the pheromone gland, extracted it in hexane, and analyzed aliquots of combined extracts by coupled gas chromatographic-electroantennographic detection (GC-EAD). These analyses revealed a candidate pheromone component (CPC) that consistently elicited strong responses from male antennae. We identified the CPC as (7E,11E)-3,5,9,11-tetramethyltridecadienal based on its retention indices (RI) on three GC-columns, RI inter-column differentials, mass and NMR spectra, and synthesis of an authentic standard that matched the GC-retention and spectrometric characteristics of the CPC. For a field experiment, we prepared (7E,11E)-3,5,9R,11-tetramethyltridecadienal and (7E,11E)-3,5,9S,11-tetramethyltridecadienal. Xenos peckii males were caught in traps baited with either compound singly or a 1:1 mixture of the two but not in unbaited control traps. The sex pheromone of X. peckii resembles that reported for the strepsipterans Stylops mellittae and S. muelleri, (R,R,R)-3,5,9-trimethyldodecanal, suggesting a common biosynthetic pathway across taxonomic genera.

In the nick of time: males of the parasitoid wasp Pimpla disparis respond to semiochemicals from emerging mates.

Males of the parasitoid wasp Pimpla disparis Viereck (Hymenoptera: Ichneumonidae) aggregate on parasitized gypsy moth, Lymantria dispar, host pupae when the emergence of a prospective mate is imminent or under way. We tested the hypotheses that the developing parasitoid ("DePa") inside the host pupal case produces a pheromone that attracts and arrests mate-seeking males, and that the pheromone is most effective during the emergence of the parasitoid from the host. Results obtained in two-choice laboratory experiments, with 4-7-d-old virgin males, indicate that (1) DePa-derived semiochemicals arrest males, (2) the opening of a host pupal case strongly arrests males, and (3) the arrestment cue emanates from oral fluid secreted by both female and male parasitoids while they chew their way out of a host pupal case. This phenomenon implies that emerging females, which are haplodiploid and can reproduce without mating, do not engage in active pheromone signaling to attract males, and that mate-seeking males co-opt chemicals involved in eclosion as a mate-finding cue, taking a 50% chance that the prospective mate is a female.