How do sex attractants work? A butterfly should provide information

The tobacco hawk moth, Latin Manduca sexta, is an inconspicuous representative of the butterfly family. As a moth, it does not require conspicuous markings - but it does have an extremely good sense of smell. "Swarmers can apparently detect individual molecules with their olfactory antennae," says Prof. Dr. Monika Stengl, head of the Department of Animal Physiology at the University of Kassel, describing the animals' abilities. She has been researching Manduca sexta's sense of smell for more than 20 years and has developed a primary cell culture procedure for it that is unique worldwide. The procedure makes olfactory cells available "in culture", i.e. in the Petri dish; this is the basis of the tandem project of the priority program "Olfactory Transduction" at the University of Kassel, which the German Research Foundation has now extended by three years and supported with 331,188 euros. The project partner is the Max Planck Institute in Jena.

Female butterflies attract their males across kilometers by releasing species-specific scents (pheromones). When a male smells these pheromones, it instantly changes its behavior: It begins to search for the female against the wind and in zigzag flight. The research group led by Stengl is investigating how the receptors of tobacco hawkmoth males perceive the pheromones and translate them into electrical potential changes that can then be further analyzed by the brain. Tobacco hawkmoths are common in North and South America. The moths are considered pests because the voracious caterpillars feed on crops such as tomatoes and tobacco.

For the studies, the Kassel scientists cultivate cell cultures of the animals' olfactory receptor neurons - because the cells are able to smell in vitro, i.e. even when they are separated from the organism in a Petri dish. To do this, the researchers take cells from the Manduca pupae, which have already developed the anlagen for the olfactory antennae but have not yet formed the antenna. "The process of growing these sensory insect olfactory cells in long-term cultures is something that only we in Kassel have mastered worldwide in this form," explains Prof. Dr. Stengl.

The cells removed from the pupa continue to develop in the dish and remain alive there for months. If scent molecules are applied to the cells, ion channels open in the membrane through which ion currents flow - the cells smell. Stengl's group is now using various methods (patch clamp technique, pharmacological methods, etc.) to investigate how the pheromones and other scents are translated into electrical impulses via intracellular signal cascades. In brief, two pathways are conceivable: via an ion channel receptor, which is effectively a "fast track to the brain"; transmission here is in the microsecond range, but this pathway is less sensitive in detecting the scents. Or via a so-called metabotropic receptor, which triggers a downstream, stimulus-amplifying cascade. This works more slowly, within the millisecond range; however, the sensitivity of this receptor is higher and its operating range is larger. "We assume that Manduca sexta uses this second pathway," explains Prof. Dr. Stengl. "This is because the butterfly has an evolutionary advantage not through fast smelling in the microsecond range, but through more sensitive smelling over a large concentration range."

The results of the project, like the primary olfactory cell cultures, may be useful in the future for the development of artificial noses, among other things. But they also provide very fundamental information about how smelling and the processing of sex attractants work. "The general logic of chemosensory signal transduction is transferable and also finds application in olfactory systems of other animals and also in the nose of humans," says Prof. Dr. Stengl, "even if individual details of this general logic may be somewhat different in each species."

Image by Prof. Dr. Monika Stengl at:
www.uni-kassel.de/uni/fileadmin/datas/uni/presse/anhaenge/2013/stengl1.jpg  
(Image: Stengl)

Enlargement of the cell cultures used:
www.uni-kassel.de/uni/fileadmin/datas/uni/presse/anhaenge/2013/Zellkulturen.jpg
(Image: Stengl)

Image of Manduca Sexta (unable to determine if male or female):
www.uni-kassel.de/uni/fileadmin/datas/uni/presse/anhaenge/2013/Manduca_Sexta.JPG
(Image: Uni Kassel)

Contact:

Prof. Dr. Monika Stengl
University of Kassel
FB 10 - Mathematics and Natural Sciences
Department of Animal Physiology
Tel.: +49 561 804-4564
E-Mail: stengl[at]uni-kassel[dot]de