Press Info item. 21/07/2011

When a moth meets a bat, or how its olfactory system adjusts to different sensory signals

INRA researchers and their Scandinavian colleagues have demonstrated the ability of the insect olfactory nervous system to adapt to environmental changes. Their original findings reveal that this adaptation by insects operates at two levels. At a physiological level, the scientists noted an increase in the sensitivity of certain neurons, while in behavioural terms, an insect subjected to an initial stimulus became more sensitive to a different chemical message. Thus, having heard the attack sounds emitted by a bat, it was more sensitive to the chemical message emitted by the female. This adaptive ability could be exploited in the context of integrated control strategies to control insects in a farming context.

Communication is vital to the survival and reproduction of insects, which use these senses to perceive their environment.   Although insects can communicate via auditory and visual signals, chemical communication predominates during their lives.  Although they live in a changing environment (global warming, increasing actions of humans on the environment), they must be able to adapt their behaviour to different sensory signals.  Humans can also deviate the behaviour of insects by exploiting this capacity, in order to protect crops, forests, foods, etc., against insect pests.

How to study the response of insects to varied sensory stimuli

The INRA scientists, working in collaboration with Scandinavian colleagues, focused on the ability of the olfactory system of a moth, Spodoptera littoralis, to adapt to changing environmental conditions.  To achieve this, they measured the displacement of these young male moths in respect to odours within a closed space called a "olfactometric arena".  The insects had, or had not, previously been exposed to an initial sensory stimulus before being subjected to a second signal.  These observations were supplemented by electrophysiological measurements.  The resulting data enabled study of the effects of pre-exposure to different sensory stimuli – auditory or olfactory – at two levels; behaviour and the central nervous system.

The sound emitted by a bat increases the sensitivity of a male moth to the sexual pheromone of female moths of the same species

The researchers thus demonstrated that young male Spodoptera littoralis moths exposed briefly to an auditory stimulus imitating the attack sounds emitted by a bat – an insectivorous predator – were subsequently more sensitive to the chemical message produced by their female fellows.  
This message, or sexual pheromone, triggered a physiological and behavioural response in the male.  The latter moved closer to the point of emission of the pheromone when compared with a male that had not been exposed beforehand to an auditory stimulus.
At the level of the insect's brain, the scientists demonstrated an increase in the sensitivity of the olfactory neurons implicated in processing information relative to the pheromone.  

The behaviour and central nervous system of insects can adapt to environmental changes.  

Although sensitisation and adaptation to signals of the same type have been described in many cases, as have some of the neurobiological mechanisms underlying these processes, these findings are original in that they demonstrate how these effects are not limited to the same sensory modality (in this case, the initial stimulus was auditory and the second was chemical).  
These data also provide proof that the insect olfactory system is capable of adapting to environmental changes, not only at a behavioural level but also in terms of the central nervous system.  The mechanisms underlying this reorganisation of the neuronal network, and the  effects of neuromodulators that might be responsible for this plasticity, are currently under study.

The fact that olfactory systems function in the same way in both insects and vertebrates, including humans, suggests possible applications in the fields of human medicine or environmental psychology, or in farmed livestock.
Furthermore, these findings open new perspectives with respect to integrated control* in agriculture; for example, by exploiting the effects of stimuli of one modality on the perception of stimuli for another modality related to behaviour.

*Integrated protection was defined by the International Organisation for Biological Control (IOBC) in 1973 as a system to control harmful organisms that uses a series of methods which comply with economic, ecological and toxicological requirements, priority being given to the deliberate implementation of natural limiting elements and respect for tolerance thresholds.

Spodoptera littoralis, both a crop pest and a study model

Spodoptera littoralis, adult moth © Inra, M. Renou

Spodoptera littoralis is a noctuid moth whose caterpillars are a major crop pest.  
In its region of origin, Egypt, it is one of the most dangerous pests that affect cotton.
In the southern Mediterranean basin, this moth notably attacks industrial crops (tomato, bell peppers, cotton, maize) and legumes.      
It has also been found in several European countries, including France, where it does not yet appear to have a fixed habitat.  In Italy, the species mainly affects greenhouses where it damages horticultural and floral production, being recognisable for the large bite marks it makes to leaves.  Vegetable crops and forage legumes are also victims of this moth.  
It is one of the species most frequently intercepted on ornamental plants imported into Europe and constitutes a major threat to greenhouse crops in northern Europe.

• it is a species of agronomic interest in the context of contributing to the development of integrated crop protection methods,  
• its sensory apparatus and nervous system are relatively simple and accessible, and the genes involved in olfaction are well understood,
• its behaviour has been widely studied and described,
• it is an insect that can easily be bred.

For more information

Sylvia Anton^a, K. Evengaard^b, R. B. Barrozo^a,c, P. Anderson^b, and N. Skals^d. 2011.
Brief predator sound exposure elicits behavioral and neuronal long-term sensitization in the olfactory system of an insect.  Proceedings of the National Academy of Science of the United States of America, 108, 340.

^a Institut National de la Recherche Agronomique (INRA), Unité mixte de recherche 1272, Centre de Recherches de Versailles, 78026 Versailles Cedex, France
^b Chemical Ecology, Department of Plant Protection Biology, Swedish University of Agricultural Sciences, 230 53 Alnarp, Sweden
^c Department of Biodiversity and Experimental Biology, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, C1428EHA Buenos Aires, Argentina
^d Institute of Biology, University of Southern Denmark, DK-5230 Odense, Denmark.

Browse by subject :

Browse by type of document :

Browse by year :

Search :