Parasite turns host into bodyguard

08 June 2008
Posted by Chris Smith.

Scientists in the Netherlands and Brazil have discovered a parasite that turns its caterpillar host first into an egg incubator and then into a bodyguard!

A caterpillar of the geometrid moth with pupae of the Braconid parasitoid waspWriting in the journal PLoS one, University of Amsterdam researcher Amir Grosman and his colleages studied how a species of parasitic wasp called Glyptapanteles takes control of the caterpillars of the geometrid moth Thyrinteina leucocerae.  The team exposed caterpillars in the laboratory to the adult wasps, which immediately laid clutches of 80 eggs inside the caterpillars bodies.  The caterpillars showed no ill effects and continued to move and eat normally for the next 11-16 days. But then things changed dramatically.

During this time the eggs had hatched inside the caterpillars and turned into larvae, which then made holes in the sides of the caterpillar and crawled out onto the nearby leaf surface where they formed a pile of pupae.  At this point the previously-parasitised caterpillar stopped moving around and also ceased eating.  Instead it took on the role of a minder and for the next 6-7 days before the adult wasps emerged it defended the pile of pupae, lashing out aggressively with head-rearing movements whenever a potential predator approached.  50% of the time at least this was sufficient to dislodge or disuade the approaching predator from lunching locally.

Unfortunately there was no reward for the hard work done by the caterpillar, which died once the adult wasps emerged from their pupae.  The team aren't sure how the wasp larvae achieve this feat of behavioural manipulation of their host, but one theory is that not all the wasp larvae vacate the caterpillar to pupate.  One or two sacrifice themselves by remaining behind, suggest the researchers, to cause the caterpillar to defend their kin, although exactly how, at this stage, remains a mystery.

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