Dual-Polarizer Linearly Polarized Light Alters Wavelength- and E-Vector-Dependent Aggregation Responses in Locusta...

Light-based trapping is a promising non-chemical approach for sustainable locust management in protected agriculture. However, how polarized light properties influence locust aggregation behavior under shed conditions remains insufficiently characterized. To clarify how polarized spectral properties and polarized light configurations, namely linearly polarized light (LPL) and linear detection-polarized light (LDPL), modulate polarotactic aggregation sensitivity, and to support the development of polarized spectral trapping devices for locust control, this study systematically evaluated the responses of Locusta migratoria manilensis to violet light (405 nm) and orange light (610 nm) based on prior laboratory findings. Locusts were exposed to LPL and LDPL with different E-vector orientations (0-330° at 30° intervals) under different nocturnal illumination durations. The results showed that differences in aggregation sensitivity between the two polarized light configurations were wavelength-dependent. Under violet light, the largest sensitivity differences occurred at the 150° E-vector orientation for LPL and the 240° E-vector orientation for LDPL, whereas under orange light, the largest differences were observed at the 270° E-vector orientation for LPL and the 240° E-vector orientation for LDPL. The duration-dependent enhancement of aggregation sensitivity also exhibited wavelength-dependent temporal threshold characteristics. After 10 h of illumination, LPL induced the highest mean aggregation sensitivity at the 270° E-vector orientation under both violet and orange light, whereas LDPL produced the highest mean aggregation sensitivity at the 240° E-vector orientation under violet light and at the 30° E-vector orientation under orange light. The spectral properties of LPL did not alter the cosine-periodic response of locusts to the E-vector, with sensitivity-associated E-vector orientations occurring at 270°, 180°, 0°, and 90°. In contrast, the spectral properties of LDPL reshaped the wavelength-dependent sine- and cosine-like tuning patterns and markedly shifted the sensitivity-associated E-vector orientations, with prominent orientations of 240° and 270° under violet light and 30° and 240° under orange light. Notably, under violet light, LDPL elicited significantly stronger light-induced aggregation sensitivity than LPL, with the highest observed response occurring at the 240° E-vector orientation after 10 h of illumination. Moreover, the polarized light configuration modulated the combined effects of polarized spectral properties and illumination duration: the duration-dependent enhancement was more pronounced under orange light, whereas the overall light-induced aggregation response was stronger under violet light. Collectively, these findings demonstrate that polarized spectral properties and polarized light configurations jointly determine locust polarotactic aggregation sensitivity, with linear detection polarized violet light producing the highest induction effect under specific E-vector and temporal conditions. This study reveals the sine- and cosine-like tuning characteristics of locust responses to different polarized light configurations, together with their wavelength dependence and temporal threshold effects, thereby providing a theoretical basis and behavioral evidence for the development of efficient polarized spectral trapping devices.