Spectral composition differentially drives host location, plant residency, and feeding states in the pea aphid, <i>Acyrthosiphon pisum</i>

Visual cues strongly influence aphid host location; however, whether spectral composition differentially affects the transition from searching to settling and to feeding is unclear. Here, we investigated how narrow-band spectral illumination differentially impacts these stages in wingless adult pea aphids (Acyrthosiphon pisum). Results indicated that green and yellow wavelengths elicited the highest host-finding success and shortest contact latencies. While green-yellow wavelengths elicited the highest host-finding efficiency, short-wavelength radiation (UVA/violet) triggered a distinct "sheltering" response characterized by high plant occupancy but minimal feeding activity. Strikingly, while short-wave light (UVA/blue-violet) induced high rates of retention on plants, particularly on shaded leaf surfaces, it coincided with markedly reduced honeydew secretion. These data are consistent with a shelter-seeking residency under short-wavelength illumination rather than normal feeding-motivated settling, although alternative explanations cannot be excluded. Six-hour tracking further suggested high locomotor activity under UVA. Furthermore, light treatments altered the expression of genes encoding enzymes for monoamine synthesis, suggesting an upregulation of tyrosine metabolic pathways, potentially linked to stress responses or cuticle melanization. Collectively, the results highlight that spectral composition can differentially influence host location versus plant occupancy in pea aphids, a distinction that may be useful for optical pest-management strategies. Future work should integrate aphid-weighted spectral measures and direct feeding endpoints to refine these inferences.