Grubs fight parasites with food-OT

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Grubs fight parasites with food

 

The caterpillars develop a fondness for certain plants

to fight a parasite infection

Tiger moth caterpillars have been seen medicating

themselves to treat a nasty influx of parasites.

 

Scientists found the caterpillars' sense of taste

actually changed when they became infected with

parasites.

 

Instead of avoiding certain alkaloid plants, the

caterpillars actually developed a fondness for them.

 

This change in diet helps to beat the creatures'

parasite infection, the researchers report in Nature.

 

The finding is slightly unusual because often when

animals change their behaviour following a parasitic

infection, it is to the invaders' benefit.

 

" It is a new and surprising kind of interaction

between organisms, " said Elizabeth Bernays, of the

University of Arizona, US.

 

" When parasites change the behaviour of their hosts,

it's usually to their own advantage. "

 

Race to live

 

Caterpillars of the tiger moths Grammia geneura and

Estigmene acrea , which live in the grasslands of

southern Arizona, US, are susceptible to a range of

insect parasites.

 

The parasitic flies lay eggs on the surface of the

caterpillars' skin which, on hatching, bore into the

larvae's flesh.

 

 

They can survive because they find the protective

plants more tasty

Elizabeth Bernays, University of Arizona

It is here that the struggle for life between host and

parasite really begins.

 

The parasite's objective is to feast on the generous

supply of live tissue, before it pupates and bursts

out of the dead caterpillar.

 

If the caterpillar is to survive such an onslaught, it

must develop an effective defence strategy.

 

Instead of eating a wide range of plants, which the

tiger moth lava usually does, the caterpillar becomes

much more specific: it homes in on plants that are

particularly toxic to its parasites.

 

Chemical war

 

These plants, such as woolly plantain, produce

chemicals known as pyrrolizidine alkaloids and iridoid

glycosides.

 

Not only do these chemicals wash through the

caterpillar's body, making it an unattractive meal,

they also collect in its skin, deterring future

invaders.

 

Dr Bernays and her colleagues found that, when a

caterpillar acquires a parasite infection, its taste

cells react differently to the chemicals in food.

 

These cells become more responsive to the protective

chemicals and less sensitive to other chemicals, which

are usually distasteful to the caterpillars.

 

Just how this change occurs in the caterpillars is not

known yet.

 

" It's still a mystery how they do it, " Dr Bernays

said. " But the result for the caterpillars is the

same: they can survive because they find the

protective plants more tasty. "

 

 

 

" Do not be afraid of enemies; the worst they can do is to kill you. Do

not be afraid of friends; the worst they can do is betray you. Be afraid of the

indifferent; they do not kill or betray. But only because of their silent

agreement, betrayal and murder exist on earth. "

- - -- Bruno Yasienski - " The Plot of the Indifferent " (1937)