How dangerous is the enemy coming your way? Some animals warn each other so that they can flee.
Thrips warn each other of danger
Recent research has shown that Western Flower Thrips (Franklinella occidentalis) can encrypt information about danger in a chemical alarm signal.
Animals need to stay alert for predators. With warning signals, animals don’t have to use so much time staying alert for danger.
It's been recognised that some mammals alter their alert signal depending on the type of danger.
Blue monkeys for example, have three different alarm sounds for different predators: leopard, eagle or snake. Blue monkeys that hear these sounds adjust their defensive behaviour depending on which sound they hear.
Are chemicals as effective as sound?
An alarm can take many forms such as vocal, chemical, visual and mechanical.
Vocal communication was previously thought to be the only way in which the level and nature of the danger could be communicated. But lots of insects use a chemical alarm signal (alarm pheromone).
Ecologist Paulien de Bruijn researched whether this pheromone release could be changed depending on the situation, by changing the component elements.
De Bruijn used thrips in her study and exposed the larvae to a relatively safe enemy (predatory mites) or a dangerous enemy (predatory bugs).
The thrips seemed to change their alarm signal depending on the type of danger.
Thrips produce alarm pheromone in dangerous situations. This is a mix of two materials: decyl acetate and dodecyl acetate.
With an increasing level of danger, the amount of pheromone increased and the mix was changed. The thrips can change their alarm signal to match the kind of danger that they encounter.
The variable alarm signal of thrips is far more complex and detailed than previously thought.
Presumably such alarm signalling can take place in other insects. The research from de Bruijn asks new questions about the existence and evolution of alarm signals in insects.
See this article in Tree Fruit April 2017