Dishabituating long-term memory for gustatory habituation in the cabbage looper, Trichoplusia ni

The gustatory rejection response of the cabbage looper, Trichoplusia ni (Lepidoptera: Noctuidae), habituates to antifeedant compounds, allowing for the consumption of deterrent yet nontoxic plant materials. In the present study, we demonstrate that habituation to an antifeedant compound (quinine) persists through the moult between larval instars. As an indirect test of whether the memory was protein synthesis-dependent, we tested whether disrupting protein synthesis would block memory reconsolidation after a reminder. The results indicated that disrupting protein synthesis in habituated larvae following a reminder treatment (reexposure to quinine) eliminated the memory for habituation and restored the antifeedant properties of the quinine. We then examined whether the learned memory could be dishabituated and whether this would disrupt or eliminate long-term memory. We show that 6 hr after exposure to a novel/noxious stimulus (a second antifeedent, xanthotoxin) habituated larvae showed a transient dishabituation-like effect in which the quinine deterred feeding again. However, this effect did not permanently eliminate the habituation produced by the extended exposure as larvae tested 72 hr after xanthotoxin exposure again showed a willingness to consume the quinine treated leaves, indicating that the earlier habituation was still present.