First Sex Pheromone of the Order Strepsiptera: (3R,5R,9R)-3,5,9-Trimethyldodecanal in Stylops melittae Kirby, 1802

Abstract

The twisted-wing parasites (Strepsiptera) are an unusual and small order of insects with about 600 known species. As obligate endoparasitoids, they develop and spend most of their lives living in other insects. Adults show an extreme sexual dimorphism: The free-living males have large eyes, branched antennae, reduced forewings, and well developed hind wings, while the neotenic females of most species lack all external characters that normally define an insect, remain endoparasitic, and only extrude the cephalothorax from the host. Due to the males' short life span of only a few hours, there must be an efficient means of mate finding. This is believed to be mediated by chemical cues released by virgin females. Here, we report the first identification and synthesis of a female-produced strepsipteran sex pheromone, (3R,5R,9R)-3,5,9-trimethyldodecanal, from Stylops melittae, a species parasitizing andrenid bees. We found this highly EAD-active compound to be present in cephalothoraxes of and released from unmated females, and synthetic samples proved to be extremely attractive when offered in the field during the swarming period of the males. The structural features of this new natural compound may further support the re-establishment of the Strepsiptera as the closest living relatives of the Coleoptera.

We do not select, nor are we choosy: reproductive biology of Strepsiptera (Insecta)

“…Immediately upon emergence, he is ready to fly and must find a conspecific female that is often scarce. Thus, one would predict that he cannot afford to be choosy, even though he may prefer females that produce a lot of pheromone, as shown in or implied for S. melittae (Tolasch et al ., ). If males are numerous, it might be advantageous for a male to deliver multiple ejaculates, as has been reported previously (Silvestri, ); however, male combat over mating has not been observed in Strepsiptera (Linsley & MacSwain, ).…”

“…At the species level, the antennae can be obviously or subtly species‐specific. The flabellate antennae have numerous chemoreceptors that are presumably capable of detecting the sex pheromone emitted by conspecific females (Figs , A), as has been demonstrated in Stylops melittae Kirby (Tolasch, Kehl & Dötterl, ) and X. peckii (M. Hrabar, A. Danci, S. McCann, P.W. Schaefer, & G. Gries, unpubl.…”

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

“…Comparison of spectral data derived from these materials to those of the natural pheromone, along with results from a field trapping experiment, unambiguously demonstrate that (3 R ,5 S ,9 R ,7 E ,11 E )‐3,5,9,11‐tetramethyl‐7,11‐tridecadienal is the X. peckii sex pheromone. The pheromone differs both in its unsaturation and termination of the polyketide chain from the recently reported ( R , R , R )‐3,5,9‐trimethyldodecanal ( 2 ) pheromone of the bee parasitoids S. mellittae and S. muelleri . Despite these differences, the two strepsipteran pheromones still bear an astounding resemblance not only in their molecular structure and functional group but also in their stereochemistry, suggesting similar pathways for their biosyntheses.…”

“…She emits a long‐range, male‐attractant sex pheromone, which we recently identified as (7 E ,11 E )‐3,5,9,11‐tetramethyl‐7,11‐tridecadienal ( 1 ) (Figure ) . While this structurally unusual pheromone resembles that of the bee parasitoids S. mellittae and S. muelleri (Strepsiptera: Stylopidae) [(3 R ,5 R ,9 R )‐trimethyldodecanal ( 2 )], these two aldehydes (i.e., 1 and 2 ) are the only pheromones known in the entire order Strepsiptera.…”

The unusual eyes of Xenos peckii (Strepsiptera: Xenidae) have green- and UV­-sensitive photoreceptors

“…Males pupate without exiting their hosts, and only later eclose, becoming airborne immediately. Mature, unmated females emit a sex pheromone (Cva cka et al, 2012;Tolasch et al, 2012), which attracts adult males ( Fig. 1A) through olfaction, while females also protrude their cephalothorax out of the wasp, potentially providing an additional visual signal.…”