Cost efficient foraging is of especial importance for animals like hawkmoths or hummingbirds that are feeding ‘on the wing', making their foraging energetically demanding. The economic decisions made by these animals have a strong influence on the plants they pollinate and floral volatiles are often guiding these decisions. Here we show that the hawkmoth Manduca sexta exhibits an innate preference for volatiles of those Nicotiana flowers, which match the length of the moth's proboscis. This preference becomes apparent already at the initial inflight encounter, with the odour plume. Free-flight respiration analyses combined with nectar calorimetry revealed a significant caloric gain per invested flight energy only for preferred—matching—flowers. Our data therefore support Darwin's initial hypothesis on the coevolution of flower length and moth proboscis. We demonstrate that this interaction is mediated by an adaptive and hardwired olfactory preference of the moth for flowers offering the highest net-energy reward.

Finding a partner is an essential task for members of all species. Like many insects, females of the noctuid moth Heliothis virescens release chemical cues consisting of a species-specific pheromone blend to attract conspecific males. While tracking these blends, male moths are also continuously confronted with a wide range of other odor molecules, many of which are plant volatiles. Therefore, we analyzed how background plant odors influence the degree of male moth attraction to pheromones. In order to mimic a natural situation, we tracked pheromone-guided behavior when males were presented with the headspaces of each of two host plants in addition to the female pheromone blend. Since volatile emissions are also dependent on the physiological state of the plant, we compared pheromone attraction in the background of both damaged and intact plants. Surprisingly, our results show that a natural odor bouquet does not influence flight behavior at all, although previous studies had shown a suppressive effect at the sensory level. We also chose different concentrations of single plant-emitted volatiles, which have previously been shown to be neurophysiologically relevant, and compared their influence on pheromone attraction. We observed that pheromone attraction in male moths was significantly impaired in a concentration-dependent manner when single plant volatiles were added. Finally, we quantified the amounts of volatile emission in our experiments using gas chromatography. Notably, when the natural emissions of host plants were compared with those of the tested single plant compounds, we found that host plants do not release volatiles at concentrations that impact pheromone-guided flight behavior of the moth. Hence, our results lead to the conclusion that pheromone-plant interactions in Heliothis virescens might be an effect of stimulation with supra-natural plant odor concentrations, whereas under more natural conditions the olfactory system of the male moth appears to be well adapted to follow the female pheromone plume without interference from plant-emitted odors.

Female-released sex pheromones orchestrate the mating behaviour of moths. Recent studies have shown that sex pheromones not only attract adult males but also caterpillars. Single sensillum recordings revealed that larval antennal sensilla of the moth Heliothis virescens respond to specific sex pheromone components. In search for the molecular basis of pheromone detection in larvae, we found that olfactory sensilla on the larval antennae are equipped with the same molecular elements that mediate sex pheromone detection in adult male moths, including the Heliothis virescens receptors 6 (HR6) and HR13, as well as sensory neurone membrane protein 1 (SNMP1). Thirty-eight olfactory sensory neurones were identified in three large sensilla basiconica; six of these are considered as candidate pheromone responsive cells based on the expression of SNMP1. The pheromone receptor HR6 was found to be expressed in two cells and the receptor HR13 in three cells. These putative pheromone responsive neurones were accompanied by cells expressing pheromone-binding protein 1 (PBP1) and PBP2. The results indicate that the responsiveness of larval sensilla to female-emitted sex pheromones is based on the same molecular machinery as in the antennae of adult males.

Insects are exposed to a complex environment consisting of a wide range of different odors. The information content of a certain odor bouquet, which is perceived by an insect, is essential for preventing predators, finding oviposition sites, navigation, foraging and mating. In the latter case, pheromone detection and processing is crucial for an insect to find its conspecific sexual partner. Because of their extremely specialized pheromone detection appendages, the antennae, moths are the most used model organisms to investigate the function of the pheromone system. In the noctoid moth, Heliothis virescens, we could demonstrate that plant volatiles interfere with pheromone responses at the level of the olfactory sensory neurons (OSN). By in vivo calcium imaging we stimulated simultaneously with the major sex pheromone component of H. virescens, Z11-16:Ald, and plant-related odorants. The results show that plant odorants significantly suppress Z11-16:Ald-evoked activity in the magroglomerular complex, where Z11-16:Ald-tuned OSNs terminate. These findings indicate that the effect of an odor background is important for the complex mechanism of pheromone detection and coding.Furthermore, we aim to decipher how a plant odor background influences pheromone-guided flight behavior. We are in the process of performing wind tunnel experiments to analyze the interaction of pheromone components and plant volatiles at the behavioral level in order to mimic the natural situation.