One of the many problems farmers of various kinds of legumes need to deal with is the
pea aphid. They reproduce incredibly fast and live by sucking the sap out of the plants,
an electron micrograph of one in action. However, while they are terrifying parasites of legumes, they have their own yet more horrific parasites, a
parasitoid wasp.
Here is a really nice close up picture of one doing its thing,
a video of the act, and
here is a brain meltingly horrific video of a dissection of the mummified aftermath 8 days later. Essentially,
these wasps deposit their eggs in a pea aphid and the growing larva feeds on it, developing there for about a week, and then consuming the host from the inside out like a
Xenomorph. When it’s done, the wasp larva dries the aphid’s cuticle into a papery brittle shell and an adult wasp emerges from the aphid mummy. Legume farmers love them,
and you can even order their mummies online these days. However, farmers noticed that the wasps didn't work as effectively on all of the aphids, and so researchers went to work figuring out why. It turns out that all aphids have a
primary bacterial endosymbiont living inside their cells, in addition to and just like a mitochondria, and that many have some combination of five other secondary endosymbionts. Interestingly, two of those other five,
Hamiltonella defensa and
Serratia symbiotica have been shown to confer varying levels of resistance to the parasitoid wasp, allowing the aphid to survive infection. However, it turns out that there is yet one more layer to this story,
[more inside]
posted by Blasdelb
on Oct 22, 2012 -
50 comments
"Why do parasites harm their hosts? Conventional wisdom holds that because parasites depend on their hosts for survival and transmission, they should evolve to become benign, yet many parasites cause harm. Theory predicts that parasites could evolve virulence (i.e., parasite-induced reductions in host fitness) by balancing the transmission benefits of parasite replication with the costs of host death. This idea has led researchers to predict how human interventions—such as vaccines—may alter virulence evolution, yet empirical support is critically lacking."
Two papers demonstrate empirical evidence for related models predicting the origin of virulence:
[more inside]
posted by Blasdelb
on Oct 21, 2012 -
23 comments
