Insect sensors in "Chemistry World"

Chemistry World
Vol.3, No.7
July 2006 pp.26-30
(c) Royal Society of Chemistry

Insect detectives
John Bonner

"The powerful sense of smell that insects possess is being put to use in applications from detecting rotten tomatoes to controlling one of the deadliest of diseases in Africa"

http://www.rsc.org/chemistryworld/Issues/2006/July/InsectDetectives.asp

"‘Biological systems have sensitivities several orders of magnitude higher than the best artificial noses that we have developed. A gas chromatograph/mass spectrometer (GC–MS) will be able to detect compounds at the nanomolar or picomolar level but an organism may respond to some compounds found at femtomolar concentrations. It all depends on how important that compound is to the animal,’ explains John Pickett, head of the [Rothamsted] lab’s biological chemistry division.

"The odorant molecule passes through pores in the outer cuticle of the sensillum and becomes attached to an odorant binding protein (OBP). This protein carries the hydrophobic ligand through the lymph fluid found inside the cell and attaches it to a receptor on the dendritic projections of a sensory nerve cell. The initial signal from this receptor to the central nervous system is amplified by the activation of the G protein pathway that is a common feature of signal transduction systems in all living organisms.

"However, the position of the insect olfactory organs on the surface of its body allows them to be investigated using methods which would be ethically unacceptable in vertebrates.

"A technique developed by German biologist Dietrich Schneider in the 1950s enables researchers to make direct recordings of activity in insect olfactory nerves and identify the specific plant or animal-derived compounds that trigger a behavioural response. "

Read more ....

www.chemistryworld.org
Previously known as "Chemistry in Britain"
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Pyrazine(s) in "Behavioral Ecology" OxfordUP

Warning signals made by unpalatable insects to potential predators commonly target more than one sense: such signals are "multimodal."

Pyrazines are odors produced by warningly colored insects when attacked, and have been shown to interact with food coloration, biasing avian predators against novel and typically aposematic food. However, at present it is not known whether this is an adaptation by prey to exploit a general feature of avian psychology, or an evolutionary response by birds to enhance their avoidance of unpalatable prey. Here we investigate the effect of other odors on the innate responses of naive domestic chicks (Gallus gallus domesticus) to food that is of novel color, or of a color that is associated with warning coloration, yellow. In the first experiment, we demonstrate that natural and artificial odors that have no association with aposematism in the wild can produce biases against both novel colored foods and yellow colored foods.

In a second experiment, we also show that odor novelty is vital for eliciting such effects. These results support the idea that warning odors have evolved in response to preexisting psychological biases against novel odors in predators, rather than predators evolving specific responses against odors associated with unpalatable prey.
http://beheco.oxfordjournals.org/cgi/content/full/12/2/134
Behavioral Ecology Vol. 12 No. 2: 134-139

© 2001 International Society for Behavioral Ecology


Non-warning odors trigger innate color aversions—as long as they are novel

Walter Jetz, Candy Rowe and Tim Guilford

These findings have considerable significance for the functional understanding of warning signals. Without the necessity to invoke aversion learning, multimodal warning signals can apparently exploit innate predispositions, similar to the way that startle displays are proposed to function (Sargent, 1990; Schlenoff, 1985). To date, the facilitation of avoidance learning has been the favored explanation of the adaptive significance of aposematic displays. Our findings advocate the additional prominent role of innate aversions.

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