Pheromones as general modulators of insect behaviour – PHEROMOD

Testing our hypotheses requires a combination of pheromone exposure and conditioning protocols in both modalities, appetitive and aversive.
For honeybees, we will use two aversive (alarm) pheromones and two appetitive pheromones. In ants, we will use two alarm pheromones as aversive, and a trail pheromones/queen pheromone as appetitive. In the moths we will use the species sex pheromone as appetitive and the sex pheromone of a related species as aversive (deterrent).
We will use exposure to both kinds of pheromones before appetitive and aversive conditioning and will have groups of non-exposed insects as control.

Conditioning protocols are available for honeybees in the two modalities; for ants and moths only in the appetitive modality but will be developed in the aversive modality. The effect of pheromone exposure on learning will be studied in harnessed and semi-free individuals (with locomotion compensator).

We will use pharmacological experiments aimed at blocking/boosting aminergic systems potentially involved in pheromone modulation and associative learning. We will use agonists and antagonists of the octopaminergic system (signalling appetitive reinforcements), the dopaminergic system (signalling mainly aversive reinforcements) and the serotoninergic system (involved in modulation of olfactory learning).

We will compare in vivo calcium imaging recordings at the level of the antennal lobe before and after pheromone exposure, for a set of neutral odorants. This will allow detecting potential changes induced by this treatment in the intensity of calcium activation patterns, or in their temporal dynamics.

Our results are in accordance with the hypotheses and suggest that appetitive pheromones (pheromones signalling valuable resources) exert an incremental effect on appetitive learning (association with reward) and a decremental effect on aversive learning (association with punishment). By contrast, aversive pheromones (pheromones signalling potentially noxious situations) exert
an incremental effect on aversive learning and a decremental effect on appetitive learning. This effect is specific to pheromones.

This research project will produce results allowing to achieve a comprehensive knowledge on how pheromones influence learning performances in three paradigmatic insect taxa that are models for fundamental and applied biological research.

PEREZ M., GIURFA M., D’ETTORRE P., 2015. The scent of mixtures: rules of odour processing in ants. Scientific Reports Vol.: 5, Pages: 8659

www.nature.com/articles/srep08659

David BARACCHI, Patrizia D’ETTORRE, Jean-Marc DEVAUD, Martin GIURFA (2015). Appetitive and aversive pheromones modulate sucrose response thresholds in honey bees. IFE-GDR meeting, 12-14 Oct, Paris, France (Talk)

David BARACCHI, Jean-Marc DEVAUD, Patrizia D’ETTORRE, Martin GIURFA (2016). Appetitive and aversive pheromones induce opposed modulation of appetitive sucrose responsiveness and learning and memory performances on honey bees. XII Congress, International Society of Neuroethology, 30 march-03 April, Montevideo, Uruguay (Poster)

Matthieu DACHER, Meena MURMU, Camille HOSTACHY, Guillaume PORTEMER, Mélissa HANAFI, Michel RENOU, Nina DEISIG (2016). La réponse au sucre du papillon Agrotis ipsilon (Lépidoptères, Noctuidés) est-elle modulée par la phéromone sexuelle? Colloque SFECA, 22-24 mars 2016, Caen, France (poster)

Matthieu DACHER, Philippe COUZI, Camille HOSTACHY (2016). L’habituation gustative chez la noctuelle Agrotis ipsilon et sa modulation par les phéromones sexuelles. 18ème Colloque Biologie de l’Insecte, 27-29 juin 2016, Tours, France (talk)

Matthieu DACHER, Meena MURMU, Camille HOSTACHY, Guillaume PORTEMER, Mélissa HANAFI, Michel RENOU, Nina DEISIG (2016). Modulation of sucrose perception, sucrose habituation and olfactory learning by sex pheromone and biogenic amines in the moth Agrotis ipsilon 10th FENS forum of Neuroscience, 2-6 July 2016, Copenhagen, Denmark (poster)

Nina DEISIG (2016) Pheromones as modulators of insect behaviour. XII Congress, International Society of Neuroethology, 30 march-03 April, Montevideo, Uruguay (talk)

Pheromones are chemical messengers that elicit stereotyped behavioural or physiological responses in another organism of the same species. They are responsible for triggering immediate or delayed innate responses to relevant stimuli, and are thus crucial for the regulation of social or sexual interactions. In addition to their well-documented function as communication signals, some pheromones have been recently shown to play a role as “modulators” of cognitive phenomena, facilitating or inhibiting associative learning and memory both in vertebrates and invertebrates. This modulation corresponds to a previously unknown effect of pheromones as it targets behaviours that are different from the innate responses typically controlled by a given pheromone. In this context, a pheromone, as modulator, affects the intensity or the probability of experience-dependent behaviour.
We propose to study the modulator effect of pheromones on experience-dependent behaviour of three species, the honeybee Apis mellifera, the ant Lasius niger and the moth Agrotis ipsilon, in order to determine the mechanisms that are either conserved across species or species-specific and associable with particular life-styles. Thesespecies differ in their evolutionary history and ecological environments. Bees and ants are social insects, living in large colonies with enhanced division of labour, while the moth is a solitary insect. They have different food habits as honeybees forage on nectar and pollen, ants on dead insects, nectar and honeydew, while moths are herbivorous at the larval stage and nectivorous as adults. Since pheromones are used as alternative to pesticides, controlling experience-dependent behaviours via pheromone modulation has a strong economic potential in all three species.
Our working hypothesis is that appetitive pheromones (pheromones signalling valuable resources) exert an incremental effect on appetitive learning (association with reward) and a decremental effect on aversive learning (association with punishment). By contrast, we posit that aversive pheromones (pheromones signalling potentially noxious situations) exert an incremental effect on aversive learning and a decremental effect on appetitive learning. Pheromones would thus provide contextual information rendering subsequent learning relevant or irrelevant for the context signalled. Testing this hypothesis requires a combination of pheromone exposure and conditioning protocols in both modalities, appetitive and aversive.
The next question is whether the modulatory effect of pheromones on learning is pheromone-specific or can be induced by any odour that has acquired a given valence (appetitive, aversive) through previous learning. We will thus determine whether odours that are initially neutral, and become appetitive or aversive through learning, modulate further learning similarly to pheromones.
We will then study the mechanisms of pheromone modulation by focusing on octopaminergic and dopaminergic circuits, which in many insects signal appetitive and aversive situations, respectively. We hypothesize that appetitive pheromones will mainly activate octopaminergic circuits that may prone insects to learn about reward whilst aversive pheromones will mainly activate dopaminergic circuits that may prone animals to learn about punishment. This hypothesis will be tested using a combination of behavioural and pharmacological methods.
As odour coding changes after appetitive learning in olfactory centers of the insect brain, we will analyse if pheromone exposure modifies per se the odour code in the antennal lobe of the three species considered. A combination of pheromone/neutral odour exposure and calcium imaging recordings of antennal lobe activity will be used to this end.
This research project will thus achieve a comprehensive knowledge on how pheromones influence learning performances in three paradigmatic insect taxa that are models for fundamental and applied biological research.