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 limited neural ability to e¤ciently process large amounts of information in short periods of time. This neural-constraints hypothesis predicts that generalist herbivores should make slower or poorer decisions than specialists when 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 versus generalist populations of the aphid Uroleucon ambrosiae. Populations of U. ambrosiae from eastern North America are highly speci¢c to the host plant Ambrosia tri¢da (Asteraceae), whereas those from the American south-west also feed on a variety of other taxa from the Asteraceae. Experiments with winged (alate) and wingless (apterous) individuals showed that host-¢nding, host-selection, host-acceptance, host-sampling and hostsettling were more e¤ciently performed by the eastern specialists. These very consistent results provide evidence that strongly supports the neural-constraints hypothesis.