Chem. Senses doi:10.1093/chemse/bjn034 Functional Characteristics of a Tiny but Specialized Olfactory System: Olfactory Receptor Neurons of Carrot Psyllids (Homoptera: Triozidae)

With only;50 olfactory receptor neurons (ORNs), the carrot psyllid Trioza apicalis (Homoptera: Psylloidea) may have the smallest olfactory system described in adult Neopteran insects. Using single sensillum recordings (SSR) and gas chromatograph–linked SSR, we characterized 4 olfactory sensilla forming a distinct morphological type, which together house;25 % of all ORNs. We recorded responses to extracts and single constituents from Daucus carota ssp. sativus, from the conifers Picea abies, Pinus sylvestris, and Juniperus communis, as well as frommale and female T. apicalis. Receptor neurons were highly selective; only 9 compounds in total elicited repeatable responses, and each neuron responded to at most 3 individual compounds. Chemical profiles of carrot and conifers showed significant overlap, with 4 out of 9 electrophysiologically active compounds occurring in more than one type of extract, but a carrot-specific compound elicited themost repeated responses. We identified 4 tentative neuron classes and found a rather high degree of neuronal redundancy, with 1 neuron class present in 3 and another present in all 4 of the sensilla, respectively. Key words: GC-SSR, host plant, olfaction, sensillum, single sensillum recording, Trioza apicali