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Absence of food-aversion learning by a polyphagous scarab, Popillia japonica, following intoxication by geranium, Pelargonium x hortorum

Potter, D.A., Held, D.W.
Entomologia experimentalis et applicata 1999 v.91 no.1 pp. 83-88
Tilia cordata, food plants, mortality, fecundity, Popillia japonica, feeding behavior, food choices, Pelargonium hortorum, poisonous plants, learning
It is commonly held that food-aversion learning should be more prevalent in polyphagous herbivores than in specialists. We tested the ability of Popillia japonica, a polyphagous scarab, to learn avoidance of a palatable but illness-inducing plant. Beetles that feed on flowers of geranium, Pelargonium x hortorum, became paralyzed, although most recovered within 24 h. In choice tests, naive beetles strongly preferred geranium petals over leaves of linden, Tilia cordata, a highly suitable host. Experienced beetles maintained this preference although it resulted in repeated bouts of paralysis. Fecundity was > 10 times higher for beetles fed linden foliage for 2 wk than for those fed only geranium. Nevertheless, when a surplus of both foods was provided, the beetles fed mainly on geranium, resulting in greatly reduced fecundity. These results contradict the view that generalists should show propensity for food-aversion learning. Indeed, in this case, P. japonica continued to prefer the toxic plant, compromising its fitness.