Natures wonders: wasps and zombie caterpillars (Introduction)

by David Turell @, Wednesday, January 06, 2016, 15:17 (1112 days ago) @ dhw

In this setup wasps infect caterpillars with their larvae who tells their hosts to eat more carbs, resulting in bigger larvae:

"Bernardo has been examining host diet manipulation to determine if any empirical evidence can back up what has largely been just a hypothesis. She's found support that diet manipulation might be possible for one special parasitoid wasp, considered a "master manipulator." About 14 days after laying eggs inside its host (the wooly bear caterpillar), the larvae of this wasp emerge, killing the caterpillar in the process. Bernardo has turned to this system because, unlike most caterpillars, the wooly bear caterpillar grazes on over 80 different plant species, meaning the parasitoid could have a veritable smorgasbord of diets to choose from. If diet manipulation exists, this would be a good place to look for it.

"In a series of experiments, Bernardo found that when caterpillars were allowed to choose between a protein- or carbohydrate-rich diet, unparasitised caterpillars chose a protein diet, whereas parasitized caterpillars preferred a carbohydrate diet. In effect, Bernardo says, "The wasps are making their hosts carb-load."

"But why? It turns out that when caterpillars eat more carbs, the wasp larvae that chew their way out of the caterpillar's carcass are bigger. Bernardo explains, "when these parasitoids are older larvae living in the host, they switch from feeding on host blood to feeding on specific host tissue." This tissue is rich in lipids, which wasps can't make, so they get the lipids from their hosts when they are larvae. By making the caterpillars eat more carbs, the wasps cause more lipids to accumulate in the caterpillars, leading to bigger wasps."

Comment: Like all the other examples, I wonder how this arrangement evolved. This is a complex lifestyle. I don't see this is set up by trial and error. the wasp must pick out the perfect food source or the wasp species doesn't survive.

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