What's learning to a grasshopper?

Grasshoppers may not be all that much brighter than the grass they hop, but a new test demonstrates that even for them, learning pays.

Hard-wired preferences and patterns seem to dominate insect behavior, explains Reuven Dukas of Simon Fraser University in Burnaby, British Columbia. Yet many insects can learn at least to associate two stimuli, like a color and a taste. Demonstrating such a feat's benefits to insect fitness, however, hasn't been easy.

To look for a fitness payoff, Dukas and Elizabeth A. Bernays of the University of Arizona in Tucson observed grasshoppers in cages with two dishes of food. One offered a nutritionally balanced mix and the other, a carbohydrate-deficient diet. Both foods attracted insects at first, but as in previous research, grasshoppers, unlike supposedly smarter people, came to prefer nutritious food.

Researchers made life predictable for 12 grasshoppers so even a bug brain could learn where to find the good food. The nutritious fare always had the same flavoring, position in the cage, and color of its marker card. Another group of grasshoppers contended with a mad world of food clues randomly reassigned to the diets at each feeding.

After 6 days, the grasshoppers in the predictable world scarcely bothered to visit the junk food. The others showed no pattern in which dish they sampled first.

The learners' rate of body growth topped the nonlearners' by 18 percent, the researchers report in the March 14 PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES. Increased growth translates into more eggs and perhaps more generations a year, a clear benefit of education.