TO CATCH an aphid, you've got to think like one. Seven-spotted ladybirds gauge which plants their aphid prey covet and then set up camp there to increase the chances of grabbing a juicy meal.
Amanda Williams and Samuel Flaxman of the University of Colorado in Boulder treated broad bean plants with a non-toxic chemical to toughen up plant tissue, making them harder for pea aphids (Acyrthosiphon pisum) to feed on. Unsurprisingly, aphids spent more time on more edible, untreated plants. But so did the ladybirds (Coccinella septempunctata), even when there were no aphids for them to eat (Animal Behaviour, DOI: 10.1016/j.anbehav.2012.01.008).
It's the first evidence, says Flaxman, that predators not only go where their prey's food is plentiful but also where its quality is high. How the ladybirds judge plant quality is unclear.
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