Metamorphosed with memory
A CHILD in the museum asked whether a butterfly remembers its previous existence as a caterpillar — a good question.
Insects like butterflies and moths undergo complete metamorphosis, changing through the egg, caterpillar (larva), pupa and adult stages. The caterpillar (a stage for feeding and growth) and the adult (a stage for mating and dispersal) have totally disparate ways of life that require completely different body forms. The larval and adult stages are separated by a quiescent baglike pupal stage, in which the enclosed body liquefies and then reforms as an adult. One would think it impossible that memories of so different a creature as a caterpillar could survive the process of its body breaking down as it changed from pupa into a butterfly. Yet a paper published in 2008 found that behaviour learned as a caterpillar in the laboratory was retained when it had metamorphosed into an adult moth.
Tobacco hornworm Manduca
sexta caterpillars were trained to avoid the odour of ethyl acetate by combining it with a mild electric shock using a standard Ytube used for choice tests. The caterpillars learned to avoid the arm through which the smell of weak ethyl acetate, together with an electric shock, was delivered, and retained this learned behaviour as adult moths when they were again tested in the Ytube.
The insects were placed in a box to which three tubes were connected. Air was drawn into the box through two inclined tubes and passed out through a third (exhaust) tube. When air with no ethyl acetate, or air with ethyl acetate, was passed through one tube, but no electric shock was administered, or with an electric shock only, caterpillars entered either tube with equal frequency. But when finalstage caterpillars were given an electric shock on entry into a tube with air and ethyl acetate odour, this was subsequently remembered both by the same caterpillars and by the same individuals after they had moulted into adult moths.
The results of this experiment have surprised many entomologists.
See: Blackiston, DJ; Silva Casey, E; Weiss, MR. 2008. Retention of memory through metamorphosis: can a moth remember what it learned as a caterpillar? PLoS One 3(3): e1736. Doi: 10.1371/journal.pone.0001736 http://www.plosone.org/doi/ pone.0001736