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Venomous, Bloodsucking Parasite Is Doting Mother

By Ross Pomeroy

If the larvae of the parasitoid wasp Sclerodermus harmandi could speak, they might say, "Gee, mom, thanks for ripping open the flesh of that other bug so we can drink it's blood!"

Most parasitic wasps do not spend a lot of time on maternal care, they simply lay their eggs on or inside a host and hightail it out of there. But the adult females of S. harmandi are different. After stinging and paralyzing a woe begotten insect host -- often the wood-boring bug Monochamus alternatus -- the mother cleans the surface of the host to make sure everything is sterile for her offspring. She then lays a clutch of eggs.

Over the next couple weeks, the young graduate from eggs, to larvae, and then to cocoons, until they finally emerge as functional adult wasps. During this time, the doting mother wasp will visit each of her eggs and pat them gently with her antennae. If an egg becomes detached from the host, the mother will quickly cradle it in her mandibles and move it back to its original position.

When the larval stage begins, the watchful mother will tear epidermal chunks out of the still alive, yet paralyzed host so the vulnerable larvae can poke their heads in and drink the host's nutritious hemolymph, the insect equivalent of blood. While the larvae gorge themselves, the mother parasite will continue to visit each of them and provide gentle antennae massages.

Occasionally, despite the mother's nurturing love, a larvae dies. When this happens, she removes the dead juvenile and places it away from the rest of the healthy brood. That way, there's no chance for potential infection.

Does all of this doting pay off? Reporting in PLoS ONE, a team of Chinese researchers compared two groups of S. harmandi young: one with mothers, one with mothers removed. Over many trials, they found that survival rate for those with mothers was substantially higher than the group without. The researchers also ran a few trials where they removed mother wasps after a certain number of days. They found that the more days that the mother spent watching over the offspring, the higher the offspring's survival rate (see above).

In the wild, S. harmandi female wasps remain with their brood from egg to adult. Their stoic maternal behavior is something we non-parasites should aspire to!

Source: Hu Z, Zhao X, Li Y, Liu X, Zhang Q (2012) Maternal Care in the Parasitoid Sclerodermus harmandi (Hymenoptera: Bethylidae). PLoS ONE 7(12): e51246. doi:10.1371/journal.pone.0051246

Ross Pomeroy is the assistant editor for RCScience. Follow him on Twitter @SteRoPo.

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