iridoids and iridomyrmecin

According to current evolutionary theory, insect pheromones can originate from extant precursor compounds being selected for information transfer. This is exemplified by females of the parasitoid wasp Leptopilina heterotoma whose defensive secretion consisting mainly of (-)-iridomyrmecin has evolved secondary functions as cue to avoid other females during host search and as female sex pheromone. To promote our understanding of pheromone evolution from defensive secretions we studied the chemical ecology of Leptopilina clavipes. We show here that L. clavipes also produces a defensive secretion that contains (-)-iridomyrmecin as major component and that females use it to detect and avoid host patches occupied by other females. However, the female sex pheromone of L. clavipes consists solely of cuticular hydrocarbons (CHCs) and males did not respond to female CHCs if presented in combination with the defensive secretion containing (-)-iridomyrmecin. This is in contrast to other species of Leptopilina, in which the iridoid compounds have no inhibiting effect or even function as sex pheromone triggering courtship behaviour. This indicates that Leptopilina species differ in the cost-benefit ratio for males searching for females, which might explain the strong divergence in the composition of the sex pheromone in the genus.

Topics: Animals; Evolution, Molecular; Female; Iridoids; Male; Sex Attractants; Sexual Behavior, Animal; Wasps

Improved syntheses'of iridomyrmecin and isoiridomyrmecin, major components of matatabilactone, are described. The synthesis features a direct transformation of nepetalactol into key intermediates by DIBAL-H reduction and provides an expeditious and straightforward production of iridoid lactones for biological investigations of the Matatabi phenomenon.

Topics: Actinidia; Animals; Behavior, Animal; Cats; Iridoids; Lactones; Molecular Structure

Detecting danger is one of the foremost tasks for a neural system. Larval parasitoids constitute clear danger to Drosophila, as up to 80% of fly larvae become parasitized in nature. We show that Drosophila melanogaster larvae and adults avoid sites smelling of the main parasitoid enemies, Leptopilina wasps. This avoidance is mediated via a highly specific olfactory sensory neuron (OSN) type. While the larval OSN expresses the olfactory receptor Or49a and is tuned to the Leptopilina odor iridomyrmecin, the adult expresses both Or49a and Or85f and in addition detects the wasp odors actinidine and nepetalactol. The information is transferred via projection neurons to a specific part of the lateral horn known to be involved in mediating avoidance. Drosophila has thus developed a dedicated circuit to detect a life-threatening enemy based on the smell of its semiochemicals. Such an enemy-detecting olfactory circuit has earlier only been characterized in mice and nematodes.

Topics: Alkaloids; Animals; Animals, Genetically Modified; Behavior, Animal; Bridged Bicyclo Compounds, Heterocyclic; Drosophila melanogaster; Drosophila Proteins; Female; Iridoids; Larva; Mutant Proteins; Nerve Tissue Proteins; Odorants; Olfactory Bulb; Oviposition; Protein Isoforms; Pyridines; Receptors, Odorant; Sensory Receptor Cells; Signal Transduction; Terpenes; Wasps

The iridoid natural products iridomyrmecin, isoiridomyrmecin, teucriumlactone, and dolicholactone were prepared from citronellol using a divergent diastereoselective approach. Key steps include a highly diastereoselective enamine/enal cycloaddition and the selective reduction of masked aldehyde functionalities by ionic hydrogenation.

Topics: Acyclic Monoterpenes; Iridoids; Molecular Conformation; Monoterpenes; Stereoisomerism

Chemical defense mechanisms are widespread among insects but have rarely been demonstrated in parasitoid wasps. Here, we show that the Drosophila parasitoid Leptopilina heterotoma (Hymenoptera, Figitidae) produces (-)-iridomyrmecin and (+)-isoiridomyrmecin in a cephalic gland, and that these chemicals have a highly repellent effect on ants. Stereoselective synthesis of 4 stereoisomers of iridomyrmecin allowed us to demonstrate that the repellent effect of iridomyrmecins depends on the stereochemistry. Potential food items impregnated with natural doses of (-)-iridomyrmecin were avoided by ants much longer than those impregnated with (+)-iridomyrmecin, (+)-isoiridomyrmecin, or (-)-isoiridomyrmecin, respectively. Quantitative headspace analyses revealed furthermore that females and males of L. heterotoma released iridomyrmecins in higher amounts when confronted with ants. This is the first time, that (-)-iridomyrmecin and (+)-isoiridomyrmecin are reported as natural products. Females synthesize more iridomyrmecins than males, and the most active (-)-iridomyrmecin is produced by females only. We, therefore, hypothesize that this defense mechanism is used mainly by female wasps when foraging for Drosophila larvae on rotten fruits, but also may protect male wasps during dispersal.

Topics: Animals; Ants; Behavior, Animal; Drosophila melanogaster; Female; Hymenoptera; Insect Repellents; Iridoids; Male; Stereoisomerism

The Argentine ant (Linepithema humile) is recognized as one of the world's most damaging invasive species. One reason for the ecological dominance of introduced Argentine ant populations is their ability to dominate food and habitat resources through the rapid mobilization and recruitment of thousands of workers. More than 30 years ago, studies showed that (Z)-9-hexadecenal strongly attracted Argentine ant workers in a multi-choice olfactometer, suggesting that (Z)-9-hexadecenal might be the trail pheromone, or a component of a trail pheromone mixture. Since then, numerous studies have considered (Z)-9-hexadecenal as the key component of the Argentine ant trails. Here, we report the first chemical analyses of the trails laid by living Argentine ants and find that (Z)-9-hexadecenal is not present in a detectible quantity. Instead, two iridoids, dolichodial and iridomyrmecin, appear to be the primary chemical constituents of the trails. Laboratory choice tests confirmed that Argentine ants were attracted to artificial trails comprised of these two chemicals significantly more often than control trails. Although (Z)-9-hexadecenal was not detected in natural trails, supplementation of artificial dolichodial+iridomyrmecin trails with an extremely low concentraion of (Z)-9-hexadecenal did increase the efficacy of the trail-following behavior. In stark contrast with previous dogma, our study suggests that dolichodial and iridomyrmecin are major components of the Argentine ant trail pheromone. (Z)-9-hexadecenal may act in an additive manner with these iridoids, but it does not occur in detectable quantities in Argentine ant recruitment trails.

Topics: Animals; Ants; Feeding Behavior; Iridoids; Monoterpenes; Nesting Behavior; Pheromones

Topics: Anti-Bacterial Agents; Antibiotics, Antitubercular; Dermatologic Agents; Iridoids

Topics: Anti-Bacterial Agents; Antibiotics, Antitubercular; Chloramphenicol; Chlortetracycline; Dermatologic Agents; Iridoids