a b s t r a c t

Olfaction is crucial for short distance host location and pheromone detection by insects. Complexes of
olfactory receptors (ORs) are composed of odor-specific ORs and OR co-receptors (Orco). Orcos are widely
co-expressed with odor-specific ORs and are conserved across insect taxa. A number of Orco orthologs
have been studied to date, although none has been identified in cereal aphids. In this study, an Orco gene
ortholog was cloned from the grain aphid, Sitobion avenae, and named “SaveOrco”; RNA interference
(RNAi) reduced the expression of SaveOrco to 34.11% in aphids, resulting in weaker EAG (electroantennogram)
responses to plant volatiles (Z-3-hexene-1-ol; methyl salicylate, MeSA) and aphid alarm
pheromone (E-b-farnesene, EBF). Aphid wing differentiation induced by EBF was investigated in both
RNAi treated and untreated aphids. EBF induced production of winged aphids in both pre-natal and postnatal
periods in untreated aphids, but no such induction was observed in the RNAi-treated aphids. We
conclude that SaveOrco is crucial for the aphid's response to pheromones and other volatiles, and is
involved in wing differentiation triggered by EBF.