Diet-induced chemical phytomimesis by twig-like caterpillarsof Biston robustum Butler (Lepidoptera: Geometridae)

Summary. Polyphagous caterpillars of the giant geometerBiston robustum resemble the twigs of their respective foodsources in color and shape. Common predatory ants, includingLasius and Formica, were often observed to freely prowl directly on caterpillars bodies, even after antennal contact.This suggests that the cuticular chemicals of the caterpillarsresemble those of the twigs of the foodplants, so we analyzedboth by GC and GC-MS. The chemical compositionsdiffered among caterpillars fed on a cherry, Prunus yedoensis,a chinquapin Castanopsis cuspidata, and a camellia Camellia japonica. The cuticular chemicals of the caterpillarsresembled those of their corresponding food sources.When the caterpillar diets were switched from the cherry tocamellia or chinquapin at the 4^th instars, the caterpillarscuticular chemicals changed after molting to resemble thoseof their respective foods. Caterpillars also changed theircuticular chemicals when they perched on cherry twigs andfed on camellia or chinquapin leaves, but not when theyperched on camellia or chinquapin twigs and fed on cherryleaves. The chemical similarities between the caterpillarsand the twigs were due to the digestion of host leaves, whichindicates that this is a diet-induced adaptation.