Pyrethroid resistance of thrips has been reported in many countries, and knockdown resistance (kdr) has been identified as a main mechanism against pyrethroids in many insects. To characterize pyrethroid resistance in Megalurothrips usitatus from the Hainan Province of China, we conducted a biological assay and sequenced the voltage-gated sodium channel gene domain II from M. usitatus field populations. It showed high resistance to the pyrethroids for 2019 and 2020, in which LC₅₀ to lambda-cyhalothrin of M. usitatus was 1683.521 mg/L from Sanya in 2020. The LC₅₀ value of deltamethrin was lower in Haikou than in other locations, which mean the south of Hainan has higher resistance than the north of Hainan. Two mutations of I873S and V1015M were detected in the domain II region of the sodium channel in M. usitatus; however, the mutation frequency of V1015M was only 3.33% and that of I873S was 100%. One is homozygous and the other is a heterozygous mutant type. The three thrips-sensitive strains of sodium channel 873 are highly conserved in amino acids (isoleucine), while the M. usitatus pyrethroid-resistant strains are all serine, so I873S may be related to the resistance of M. usitatus to pyrethroids. The present study will contribute to the understanding of the evolution of pyrethroids resistance and contribute to the development of resistance management of M. usitatus in Hainan.

Megalurothrips usitatus is a major pest of cowpea in tropical regions, where frequent insecticide use has promoted the development of resistance. In this study, field populations of M. usitatus were collected from five major cowpea-producing areas in Hainan from 2023 to 2025, and their susceptibility to five commonly used insecticides was evaluated using a modified leaf-tube residual film method. Resistance levels varied among regions and insecticides, with southern populations generally showing higher LC₅₀ values than central and northern populations. The tested neonicotinoid insecticide, acetamiprid, showed the highest resistance levels. By 2025, the resistance ratios of the Ledong, Sanya, and Lingshui populations to acetamiprid reached 298.48-, 139.60-, and 130.25-fold, respectively. Spinosyn resistance also increased rapidly, particularly in southern Hainan. The resistance ratio to spinetoram reached 110.78-fold in the Ledong population, while resistance to spinosad reached 37.06-fold in the Lingshui population. However, the absolute LC₅₀ values of spinosad and spinetoram remained relatively low compared with those of acetamiprid and chlorfenapyr, indicating that these two spinosyn insecticides retained relatively high bioassay activity in laboratory bioassays. A significant positive correlation was detected between the LC₅₀ values of spinosad and spinetoram across field populations (r = 0.8972, p < 0.0001), suggesting cross-resistance within the spinosyn class. These results indicate that resistance management for M. usitatus in Hainan should prioritize reducing the use of high-resistance-risk insecticides, avoiding consecutive applications of spinosyns, and designing region-specific rotation programs based on local resistance monitoring.

Background: The bean flower thrips, Megalurothrips usitatus, is a destructive agricultural pest with increasing resistance to pyrethroid insecticides. Most mechanistic studies emphasize mutations in the pore-forming voltage-gated sodium channels α-subunit, whereas the contribution of insect-specific sodium-channel auxiliary subunits remains unclear. Methods: We used dsRNA feeding, pyrethroid bioassays, RNA sequencing, and RT-qPCR validation to evaluate the role of temperature-induced paralytic E (TipE) in M. usitatus. Results: The optimized RNAi condition was 400 μg/mL of dsTipE for 48 h, which reduced TipE expression by 32.55%. TipE knockdown increased adult mortality after exposure to λ-cyhalothrin and permethrin, indicating increased pyrethroid-associated susceptibility under laboratory conditions. Transcriptome sequencing identified 205 differentially expressed genes, with enrichment in metabolism-related pathways. RT-qPCR confirmed reduced expression of CYP307a1, an ecdysteroid-biosynthesis-related P450 gene, and SCD, a lipid-metabolism gene, while Na_v α-subunit transcript abundance did not change significantly. Conclusions: These results identify TipE as an auxiliary-subunit factor associated with pyrethroid susceptibility in M. usitatus and provide a transcriptome-based working model linking sodium-channel auxiliary regulation with endocrine- and lipid-metabolism-related responses. This study expands the candidate space for pyrethroid resistance research beyond Na_v α-subunit mutations, although the causal roles of CYP307a1 and SCD require further validation.

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.