With few exceptions, the sensory receptors involved in taste mediation by polyphagous insects are poorly known. We studied the role of olfactory and gustatory organs in close-range dietary discrimination by the Japanese beetle, Popillia japonica, which as an adult feeds on >300 plant species in > 80 families. Scanning electron microscopy revealed clusters of sensilla basiconica at the tips of the labial and maxillary palps, sensilla coeloconica and placodea on antennal lamellae, and patches of small coeloconic pits on the labium and labrum. Unilateral or bilateral ablation of lamellae, tips of palps, or tarsi in various combinations did not impair beetles' ability to discriminate between host and non-host plants. Such ablations also did not impair normal discrimination among acceptable hosts of varying palatability, or beetles' response to a phagostimulant (sucrose) or a deterrent substance (azadirachtin). Remarkably, even six-way amputees (bilateral ablation of all palps and antennal lamellae) displayed normal dietary acuity. Biting and consumption rates were similar for ablated and normal beetles, ruling out food-aversion learning as the compensatory mechanism. Remaining epipharyngial or labial sensilla evidently provide sufficient sensory input for dietary discrimination, demonstrating redundancy of gustatory receptors in normal beetles. This study also provided the first detailed description of mouthpart morphology of P. japonica. The mandibles, in particular, are noteworthy, each having a greatly expanded, grate-like basal molar lobe. These lobes appear to "mash" bits of excised plant material before their passage to the foregut.
Species 1: Coleoptera Scarabaeidae Popillia japonica (Japanese beetle)
Keywords: Insect-Plant Interactions, Host Plant Resistance
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