Bugs within bugs, part 2

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by Patrick
Publish date
7 May 2014
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Like any group of animals (or people), populations of bugs are susceptible to disease, pathogens and parasites. At Live Exhibits we keep our populations free from parasites, but sometimes new bugs from the wild turn out to be Trojan horses filled with unwanted guests.

Tachinid fly pupae Tachinid fly pupae, newly emerged from the abdomen of a Rainforest Mantid (Heirodula majuscula), collected from Cairns, North Queensland. These flies are always fatal to the mantid.
Image: Patrick Honan
Source: Museum Victoria
 

The parasites not only kill the bugs themselves, but could get into captive populations and cause havoc. Most of them are easily controlled once identified, and occasionally we can even operate to remove the parasite and allow the host to lead a long and fruitful life.

parasitic wasp larva A parasitic wasp larva being successfully removed from the abdomen of a living Olive-green Katydid (Austrosalomona falcata) collected from the wild.
Image: Alan Henderson
Source: Museum Victoria
 

But often this is not so successful and the first sign of something wrong is the presence of two different species within an enclosure rather than just one. When you get to recognise the signs of parasitism, it’s often difficult to find individual insects in the wild that are not parasitised.

tachinid fly larva A tachinid fly larva emerges from a wild-caught Robust Fan-winged Katydid (Psacadonotus robustus). The only indication of infection was the abnormally large abdomen of the male katydid.
Image: Melvin Patinathan
Source: Museum Victoria
 

One of the most insidious is the Gordian worm, named after the Gordian knot of mythology. These are long, hair-like worms up to half a metre long which begin their lives in freshwater streams attacking aquatic insects. When the aquatic host, such as a dragonfly or mayfly nymph emerges into adulthood, it leaves the stream and is caught and eaten by a spider, cricket or beetle. The worm grows within its new host, filling up the entire body cavity until the host is 95 per cent Gordian worm.

Gordian worm emerging A Gordian worm emerging from an Olive-green Katydid (Austrosalomona falcata).
Image: Alan Henderson
Source: Minibeast Wildlife
 

When fully fed, the worm causes its host to become thirsty to encourage it to seek out water where the worm emerges and continues its life cycle, laying more than 10 million eggs. Earlier this year Live Exhibits staff collected eight huntsmans near Cape Tribulation, North Queensland, five of which produced Gordian worms over the next few weeks.

 

Video: A newly emerged Gordian worm and its host, Beregama cordata, from the #liveexhibits takeover of the Museum Victoria Instagram account.
Source: Patrick Honan/Museum Victoria

The relationship between parasites and their hosts is an evolutionary arms race – as hosts come up with more effective defences, the parasites evolve techniques such as behavioural modification to overcome them. This fascinatingly gruesome relationship can be the stuff of nightmares; inspiration for everything from zombies to the film Alien, proving that science is stranger than science fiction.

This is the second in pair of posts about parasites. Don't miss Bugs within bugs, part 1

References:

Askew, R.R., 1971, Parasitic Insects, American Elsevier, USA, 316pp

CSIRO, 1990, Insects of Australia, Volume 1 & 2, Melbourne University Press, Melbourne, 1137pp

Gauld, I.D., 1984, An Introduction to the Ichneumonidae of Australia, British Museum (Natural History), UK, 413pp

Matthews, E.G. & Kitching, R.L., 1984, Insect Ecology (second edition), University of Queensland Press, Brisbane, 211pp

Comments (5)

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Rod 8 May, 2014 09:50
Delightfully gross. Thanks for this fascinating series of posts.
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Rodney 9 May, 2014 15:19
These are a great series of photos that has now made me think twice about going into fresh water up North.
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Simon 10 May, 2014 10:18
As always Patrick, a great read coupled with amazing photos.
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brian anderson 9 August, 2014 07:56
could anyone identify this caterpiller /larve/..?
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Discovery Centre 11 August, 2014 09:44
Hi Brian, if you have an image of something you would like identified please feel free to email it to discoverycentre@museum.vic.gov.au and we'll do our best.
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