insects make smart, instinctive dietary choices

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From today's WP Science section:

New evidence suggests that insects make smart, instinctive dietary choices

that strengthen their immune systems when they are battling infections.

Previous studies have shown that some leaf-eating insects alter their daily

choices of leaf types to ensure they get a balance of nutrients. But what

about when insects are sick? Do they make chicken soup? Although researchers

have shown that some insects infected with parasites feed specifically on

plants loaded with medicinal chemicals, it remained unknown if insects could

do something more subtle: alter their protein and carbohydrate intake to

maximize the general potency of their immune systems.

Kwang Pum Lee of the University of Oxford and his colleagues tested that

possibility in experiments with Spodoptera littoralis , a caterpillar known

to dine on a variety of leaf types. The scientists infected scores of the

caterpillars with a virus that is often fatal within a week and tallied the

death rates in those fed diets with varying protein-to-carbohydrate ratios.

Tests showed that the immune systems of the caterpillars that were fed lots

of protein functioned better than those of the caterpillars that were fed

lots of carbohydrates. The caterpillars with protein-rich diets also had

significantly higher survival rates.

The team then offered a variety of foods to sick and healthy caterpillars.

The healthy ones selected diets that were about evenly balanced with protein

and carbohydrates. But the infected ones went for the high-protein, immune

system-boosting meals.

" Our study provides the first experimental evidence that pathogen infection

induces a compensatory shift in diet selection to supplement the specific

nutrients required to fight infection, " Lee and his colleagues reported last

month in the Proceedings of the Royal Society B.

-- Rick Weiss