Specialists make faster decisions than generalists: experiments with aphids

Theoretical studies and a few recent experimental reports suggest that the evolution of diet breadth in herbivorous insects is constrained by a limite d neural ability to efficiently process large amounts of information in sho rt periods of time. This neural-constraints hypothesis predicts that genera list herbivores should make slower or poorer decisions than specialists whe n selecting plants, because generalists must discriminate and decide among stimuli from a wider variety of potential hosts. The present study compares the speed with which host-associated decisions are made in specialist vers us generalist populations of the aphid Uroleucon ambrosiae. Populations of U. ambrosiae from eastern North America are highly specific to the host pla nt Ambrosia trifida (Asteraceae), whereas those from the American south-wes t also feed on a variety of other taxa from the Asteraceae. Experiments wit h winged (alate) and wingless (apterous) individuals showed that host-findi ng, host-selection, host-acceptance, host-sampling and host-settling were m ore efficiently performed by the eastern specialists. These very consistent results provide evidence that strongly supports the neural-constraints hyp othesis.