Visual and olfactory evidence of host plant recognition by Cacopsylla pruni

The plum psyllid, Cacopsylla pruni (Hemiptera: Psyllidae), is the primary vector of 'Candidatus Phytoplasma prunorum', the causal agent of European Stone Fruit Yellows (ESFY). Its seasonal host alternation - from conifers in winter to Prunus species in spring - requires precise host recognition, yet the underlying sensory mechanisms remain poorly understood. We investigated the visual and olfactory responses of overwintered C. pruni during remigration. Electroretinographic recordings revealed a visual system comprising UV-, blue-, and green-sensitive photoreceptors, potentially allowing trichromatic colour vision. Colour vision modelling indicated that white Prunus flowers and white sticky traps provide nearly identical chromatic and achromatic signals, likely accounting for the pronounced attraction of remigrants to white traps in early spring. Complementary electroantennographic analyses demonstrated robust antennal responses to key Prunus floral volatiles, including benzaldehyde, benzyl alcohol, phenylacetaldehyde, linalool, 2-phenylethanol, 4-oxoisophorone, and methyl salicylate. Together, our results provide the first electrophysiological evidence that C. pruni has the potential to integrate both visual and olfactory cues during host location. These findings are consistent with the broader understanding of psyllid host finding, in which long-distance orientation is primarily mediated by visual cues, whereas olfactory inputs likely facilitate short-range host assessment. This multimodal recognition strategy likely enhances foraging efficiency during seasonal migration and has important implications for monitoring and management of this economically significant vector.